Improving Nutrient Management

Transcription

1 Improving Nutrient Management Using Methods Taken From Ecological Agriculture A case study on a conventional Danish dairy farm Project in the Theme Course Ecological Agriculture (SOCRATES Curriculum) Birge Ude ED5310 Camilla Ruø Rasmussen L10629 Peter Thomas Fitzgerald ED5292 Philson Philip Parekalam ED5293 Supervisor: Jesper Luxhøi

2 Preface This report is the product of project work for the thematic course: Ecological agriculture I (SOCRATES European Curriculum). The report deals with nutrient management by use of organic farming tools. A specific farm in Denmark, Højtofte, has been the basis of the study. General aspects related to nutrient management under Danish conditions are discussed as well as specific conditions at the farm. The report is intended for people require need ground knowledge concerning nutrient management, especially under Danish conditions. Hopefully the report can also function as inspiration for the owner of the farm, Kim Ellebæk Hansen. We would like to thank Kim Ellebæk Hansen for showing us the farm and spending some of his precious time with us to pass on his knowledge. We would also like to thank our supervisor Jesper Luxhøi, KVL for good advice, and Bente Broeng, KVL for help in the laboratory. Thanks also to Andreas de Neergaard and Anders Petersen for their advice. KVL, May

3 Summary The aim of this project was to investigate current nutrient management practices of a conventional dairy farm in Denmark with particular focus on crop rotation, and manure storage and utilisation. A detailed analysis of the current management practices including a literature review, farm visit, soil analysis and theoretical modelling were carried out to determine whether the system could be improved using organic management principles. As it now stands, the current crop rotation, manure handling and utilisation of the farm is below optimal. The study revealed that nutrient surpluses are present and that high amounts of nutrients are being lost from the system through inappropriate crop rotations and manure handling facilities. A further investigation into the variability of soil nutrients at the farm showed that there is sufficient variability in the fertility of the soil within the same field to warrant further investigation into the adoption of precision farming technology. The adoption of variable rate nutrient applicators can be used as an additional tool for minimising nutrient losses that occur due to current application methods. It was shown that if we are able to change the crop rotation, we are able to make better use of nutrients in the soil; and decrease the proportion of uncovered soil over winter; thus decreasing nutrient losses through leaching and volatilisation and hence improving nutrient use efficiency. The manure storage facilities need to be upgraded in-order to minimise nutrient losses through N volatilization and also to enable better utilization of plant available N at the time of manure application. In short, better managerial practices in the area of crop rotation, manure storage, handling and application and the adoption of advanced technology can improve the nutrient management of the farm. Thus, adding to the overall profitability and productivity of the farm whilst minimising the effects on the environment

4 Table of contents 1 Introduction Introduction to nutrient management problems Introduction to the project Introduction to the farm Soil and landscape properties Crop Types Manure handling and storage Nutrient Composition of Fertilization Products Literature review Nutrient description Nitrogen Phosphorus Potassium Sulphur Crop description Maize Cereals - Spring Barley and Winter Wheat Seed Grass Sugarbeet Rape Manure description The formation of animal manures: Nutrient value of manures N losses in the stable Collection, storage and processing of different types of manures Manure Types Application of manures Rates of Manure Application Manure handling as a nutrient management tool Composting Anaerobic Digestion Nitrogen Utilisation and Mineralization of Compost, Slurry and Digestate Precision Farming and crop production Crop rotation as a nutrient management tool Cover Crops in general The use of cover crops before and after spring barley Maize in a crop rotation Management of grass leys Materials and Methods The farm report The interview with Kim Ellebæk Hansen The SUNDIAL model Pools and flow diagrams Inputs Output Adapting to local conditions Limitations

5 3.3.6 Modelled sequences Methods for the precision farming experiment Discussion of Materials and Methods The Farm report The SUNDIAL model Analysis of soil samples Results and Analysis Nutrient account for the farm Nutrient management in relation to manure handling The Stable The Slurry Tank Deep litter manure Manure Supply to Crops Sulphur Application Nutrient management in relation to crop rotation Precision Farming Results ph Soil Carbon Phosphorous Discussion of the recommendations for an improvement of the nutrient management Improvements for the Manure Handling Slurry tank Deep litter application Slurry application Soil testing Alternative manure management strategies Sulphur management Precision Farming Improvements for the crop rotation Maize Seed grass production Spring barley Introduction of rape The interaction between the ideas of improvement The surplus at farm level Conclusion Perspectives...99 Appendices Appendix

6 1 Introduction 1.1 Introduction to nutrient management problems The nutrient situation on farms in Denmark has developed from systems with a nutrient deficit to nutrient surplus. The reason for this has been the rising stoking rate at the farms and the increasing accessibility of artificial fertilizers. As a result of the nutrient surplus at the farm level nutrients losses from the farming system are occurring. Nutrients may be lost to the environment or bound within the soil. Nitrogen surplus from the farms has become a problem for the Danish environment. Increasing N-values in the ground- and seawater, due to leaching from fields has increased aquatic biomass production and caused deoxygenation in many Danish coastal waters. Moreover ammonia volatilization has caused huge nitrogen depositions especially near big farms, which has become inconvenient for people living nearby, and has caused changes in the Danish flora. The reaction on these problems was the development of the NPo Action plan in 1986 and one year later the Action plan on the aquatic environment I with the objective to lower the nitrogen losses to the environment. The contents of these action plans were several regulations that placed restrictions on manure storage capacity, application-time and technique; a requirement of green cover of 65% in wintertime; as well as regulation concerning livestock density. The plan has been followed by Action plan on the aquatic environment II and the third edition is in preparation The N-surplus on arable land in 1980 was about 175 kgn/ha/year (Jensen and Eriksen, 2003, Chapter 18), and as a result of the action plans the nitrogen surplus in Denmark has decreased by about 20% over the period 1986 to the present. Interestingly this is mainly due to a reduction of mineral fertilizer, because the nitrogen input from animal manure has not changed. The reduction of the N-surplus has increased the N-use efficiency at the farms without decreasing the yields. (The State of Environment in Denmark, 2001). In the last few years the phosphorus surplus has become an issue due to the fact that the phosphorus binding capacity in many Danish agricultural soils has reached capacity, which has lead to the leaching of phosphorus. For that reason the next action plan will also focus on phosphorus

7 If we take a look at the nitrogen surplus on Danish farms in relation to the animal density of the farms, it is seen that the N-surplus is dependent on the stocking rate. Sillebak Kristensen (2001) showed the nitrogen surplus as a function of the stocking rate, expressed in kg N/ha from animal manure. The data are derived from Danish pilot farms over the period Figur 1: N-surplus per ha as a function of the animal density (expressed as N/ha in animal manure). Data from Danish pilot farms (Sillebæk Kristensen 2001) At each stocking rate there can be seen a variation of approximately 100kg/N ha, which indicate that certain improvements in the management system are possible. However, in the figure it can also be seen, that in many cases the nitrogen applied in manure is as high as the nitrogen surplus. This indicates that other sources of nitrogen like the mineralization of soil organic matter or inorganic fertilizer must be used for the plant nutrition. The graph shows that manure is not used efficiently at Danish farms. Another study indicates that there is an over fertilization on Danish farms of 20-30% (Grant et al., 1996 in Jensen and Eriksen 2003, Chapter 18) Eighteen years after the first action plan the question of whether it is possible to lower the nutrient surplus on Danish farms further. The graph above shows that it is possible due to the inefficient use of manure and fertilizer. But how and with what tools can an improvement of nutrient management be achieved? The main nitrogen inputs in Danish agriculture are artificial fertilizer (46%) and imported fodder (38%), while the output are mainly products (32%), leaching (38%) and volatilization (17%). It is within these areas that improvements can be made

8 As we see it there are two main tools that can help to lower these losses by preventing leaching and volatilization. That is manure handling and crop rotation. To add further difficulty to the case, the question about the level of improvements arises. In other words, how low should the N-surplus be? Organic agriculture is usually seen to be the more environmental friendly way of agriculture so that suggestions about the possibility of a reduction can be derived from there. Dalgaard et al. (1998) made a study about the differences of N-surplus in conventional and organic mixed farms. He showed that on organic dairy farms the N-surplus per ha is 50% lower than on conventional dairy farms. This shows that it is difficult to define the lowest possible surplus because it depends on the intensity of the farming system, and furthermore on many practical factors which differ in between the farms. The focus of this report will therefore be on nutrient management practises, which correspond to organic agriculture and in particular, concerning manure utilization and crop rotation. Manure utilization and crop rotation are two tools that can help to lower leaching and volatilisation. When the losses are lowered the import of nutrients through fodder and artificial fertilizer can also be lowered due to a more efficient nutrient management. 1.2 Introduction to the project The task of this project is to investigate how a conventional farmer can improve his nutrient management by the use of organic farming tools, that makes it possible to maintain and enhance soil fertility without using inorganic fertilizers whilst minimising nutrient losses, particularly N. The focus will be on manure utilisation and crop rotation as tools to optimise the nutrient management We would like to investigate this topic by carrying out a literature review to develop background knowledge on the two topics, manure utilisation and crop rotation in order to make a case study on a conventional Danish dairy farm. Within the case study we would like to analyse the current nutrient management system and identify possibilities for its enhancement using organic alternatives i.e. use of cover crops, eliminate inorganic fertilisers and attempt to improve sustainability. Methods for improvement will focus on croprotation and manure utilisation including the opportunity for adoption of precision farming techniques and crop rotation

9 The case study will be based on calculations from the dataset given on A small experiment about precision farming as well as a visit to the farm and an interview with the farmer will be also an integral part of this project. All methods are used in order to gain a better understanding of the practical problems that may be encountered while attempting to modify the current nutrient management system. For the precision farming experiments soil samplings will be carried out in order to determine heterogeneity of soil chemical properties. We will take soil samples across 1 paddock and analyse them individually for ph, P, K and soil organic matter, to determine whether or not the adoption of precision farming techniques is possible. Our expectations from the project are that the information on webcase including the Gårdrapport will enable us to assess the nutrient management at the farm level and the field level. The use of the SUNDIAL model will be a tool to identify weak points in the crop rotation. The Farm visit will deliver us additional information needed for the two points above and give us a practical view for problems and possible improvements on the farm. The analysis of the soil samples will enable us to determine if precision farming or management practices related to this could be a method for the improvement of the nutrient management. The results of the four points above and the literature will enable us to determine the problems of nutrient management on this farm and identify the areas were improvements are needed. According to the literature we will make suggestions for improvements concerning manure utilization and crop rotation, including a discussion of the improvements. 1.3 Introduction to the farm The farm, which is the focus for our case study is named Højtofte. It is described in a case study available at the Internet at the page An introduction to the page can be found in appendix 1. Højtofte is owned and operated by Kim Ellebæk Hansen who purchased the farm in August Højtofte is situated in the village of Kustrup, in the Local Authority of Middelfart, County of Funen. The farm consists of 81.7ha and the main enterprise is milk production from a herd of 125 RDM (Red Danish Dairy Breed) dairy cows. The entire 81.7ha is cultivated; silage maize produced for livestock feed accounts for the majority of crop production with seed grass and cereal production acting as secondary cash crops

10 1.3.1 Soil and landscape properties The farm covers a variety of soil types. 62% of the land is fine sandy clay loam (JB6), 31% sandy clay/sandy clay loam (JB8) and 7% fine sand (JB2) and some humus soil (JB11). No irrigation facilities are established within the farm area. Silage Maize tends to be grown on the clayey soils as well as on the more sandy lowland soils (JB6 and JB8). Wheat is grown on the clayey soils; with barley being produced on the sandy clay/sandy clay loam soils; and the seed grass is generally grown on either of the 3 soil types found on the farm depending on the timing of the crop rotation Crop Types As previously mentioned, silage maize produced for livestock feed accounts for the majority of crop production with seed grass and cereal production acting as secondary cash crops. Several different seed grass species, namely Perennial Ryegrass (Lolium perenne L.), Reed Fescue (Festuca giganta), and Red Fescue (Festuca rubra L.) are also cultivated. Spring barley at the farm is grown primarily as a cover crop for seed grass outlay and it is sown at double row distance in order to ensure light to the outlay. Winter wheat has a high yield potential on the clayey soils of the farm Manure handling and storage There are two stable systems at the farm, loose housing for the heifers, and deep litter for the calves. All livestock remain inside all year round in order to avoid soil degradation and because the farmer does not regard grazing to be profitable at his farm. Authorities have approved the farm for 191 livestock units (LU). A scraper system that scrapes down the dung from the slotted flooring has been installed. The slot scraper, which is passed over twice a day, is expected to help reduce the ammonia volatilisation from the stable and to help obtain better udder hygiene, as dragging of dung to the cows bed boxes will be reduced. The manure storage room beneath the slotted flooring has capacity for one weeks manure production. It is emptied twice a week and the manure is pumped through buried pipes across the road to the slurry tank. The deep bedding from calf boxes is mucked out once a year and is spread within about two weeks by a dung spreader

11 The farm has at its disposal a 1,530m 3 slurry tank from The manure storage capacity of the farm is therefore limited, which makes autumn spreading of slurry a necessity. Two types of animal manure are produced at the farm: straw-based deep litter bedding and cattle slurry. Approximately 204 tonnes of Deep litter manure is produced on Højtofte. The deep litter consists of a mixture of manure, and straw and is removed from the stables in April and applied directly to the fields. In addition approximately 3300 tonnes of slurry is produced on the farm annually Most of this is used on farm, although some is also sold to neighbouring farms. Højtofte currently has a total slurry storage capacity of 1,850 tonnes, with the highest and the lowest stocks occurring respectively in March and April, which is the main period of distribution Nutrient Composition of Fertilization Products The farmer uses a combination of fertiliser sources on the farm. The mineral fertiliser NS 25-5 is used and contain 24,5 kg N/100 kg, and 5 kg S/100kg. The cattle slurry from the loose housing contain 5 kg N/t and the straw deep litter bedding manure contain 9 kg N/t

12 2 Literature review 2.1 Nutrient description In this nutrient description we will concentrate on the four macronutrients, nitrogen, phosphorus, potassium and sulphur. The reason for choosing these nutrients is that they are most often the limiting nutrient for the crop growth, and for that reason they are also important nutrients that are applied to the soil. Nitrogen is most important because of its high leaching potential that can lead to environmental problems. Sulphur is interesting in this case because it is applied as artificial fertilizer. The nutrient description, where no sources are adduced, is based on information from Petersen (1994) and Mengel et al. (2001) Nitrogen Nitrogen (N) in the soil occurs mainly as organic N, because the minerals only contain nitrogen in infinitesimal amounts. The organic matter can be divided into a humus fraction, meaning more or less decomposed organic matter, and microbial biomass. The organic N is not accessible for the plants, first the organic material has to be decomposed, and thereby release N as ammonia (NH 3 ). This process is called ort he zation. The opposite process is called immobilisation. NH 3 reacts with water and gives the ammonium ion (NH 4 + ). NH 4 + is generally not leached because it is a positive ion and most of the soil particles are negative, and can thereby adsorb the NH 4 +. But NH 4 + can be converted into nitrate (NO 3 - ) by a process called nitrification, and NO 3 - is easily leached, because it is a negative ion. Both mineralization and immobilisation of N occur in the soil depending on the C/N ratio of the organic matter. The lower the C/N ratio the higher the proportion of N mineralised. The C/N ratio in Danish soils, in which there are good growth conditions for the soil organisms, especially the bacteria, is about 10. The C/N ratio of organic matter added to fields is also important, because it determines if N will be released to the crops or if mineralised N is immobilised. Nitrogen is not only applied to the soil by application of manure or fertilizer. Legumes have the ability to take N from the atmosphere in a process called N fixation; if legumes are present to a large extent then they can fully or partly replace the need of manure or fertilizer additions

13 One of the biggest tasks in nutrient management in Danish agriculture is to prevent N from leaching from the soil profile. This is of particular concern in the autumn and winter where there is a net downwards movement of water and no growing plants to take up the mineralised N. It is even more difficult to manage if manure is applied instead of artificial N-fertilizer, because the N has to be plant available exactly when the plants need it, which is impossible as the N is released in time with decomposition. The speed of the ort he zation of organic matter is less dependent on the temperature than immobilisation. That means ort he zation can occur during the winter to a higher extent than immobilisation. Plants take up N as both NH + 4 and NO - 3, but mostly NO - 3. In farming systems N is normally the limiting factor (Franco and de Faria, 1997). If plants suffer from N deficiency, they will mature earlier, and the vegetative growth stage is often shortened, which results in lower yields Phosphorus Phosphorus (P) in the soil can be divided into three pools according to varying accessibility for the plants. The completely plant accessible P pool makes up only a minute fraction of the total P in the soil, this is P in solution, that means HPO 4 2- and H 2 PO 4 - ions. The reason for that is that they form more or less insoluble compounds with normally occurring cations, and these compounds make up the two other pools: labile and non-labile P, depending on the grade of insolubility, thus the three pools are connected by equilibriums. More than 90% of the total P is non-labile, that is P fixed in primary minerals, humus, Ca, Fe and Al compounds, hydrous oxides and silicate minerals. The labile pool contains more accessible P that means solid phosphate from precipitation or adsorbed on the soil surface. There is no clear limit between labile and non-labile P-compounds; it depends on how soluble they are. The labile P is in rapid equilibrium with P in solution, but can also be fixed in the non-labile fraction, from where it is slowly released. The quantity of P present in the soil solution is normally about 0,3 3 kg P/ha, but rapidly growing crops take up 1 kg P/ha/day which means that P from the labile pool must be continuously released to the soil solution. The quantity of P present in the labile fraction is about kg P/ha. The labile and the non-labile P is bound either in organic or non-organic compounds. The organic P makes up 20-80% of the total P in the soil, and the availability depends on the

14 degradability of the soil organic matter. The availability of the non-organic P is determined by ph and the ability of the soil to adsorb P. The availability of P is highest at ph values about neutral or a bit below, because sparingly soluble calcium-phosphates are formed at ph values above 7, and reactions between P and Fe(III)- or Al-compounds mainly occur at ph values below 6. The adsorption capacity of the soil, meaning the ability to make insoluble compounds with P, depends on the type of minerals and their surface, and differs considerably. If large amounts of P are supplied for many years the adsorption capacity can be used up and leaching will occur. Experiments have shown that in some places in Denmark P- leaching has already started. The plants take up P as H 2 PO - 4 and HPO 2-4 from the soil solution. Organic bound P can be mineralised by phosphatase, an enzyme that is produced by plant roots, numerous microorganisms and mycorrhiza. Furthermore there is an influence of plant roots and microorganisms on the availability of both organic and inorganic P by producing acids and chelating agents. P deficiency depresses the formation of fruits and seeds, and gives not only poor yields, but also bad quality of fruits and seeds. In contrast the shoot and root growth is less inhibited, but the dry matter content of the shoot goes down, because the carbohydrates are concentrated in the root, to give energy to an extension of the absorption area. The concentrations of P deficient plants are generally low with about 1 to 2 mg P/g dry matter. In compare Cereals and Herbages supplied with sufficient phosphate will have P concentrations of about 3 to 4 mg P/g dry matter Potassium Potassium (K) in the soil originates from K containing primary and secondary clay minerals, from where it is released by weathering, and is made plant available. The amount of released K depends on the K content of the minerals, and the speed of weathering, which differs between minerals. On a soil with 20% clay, a weathering of 100kg K/ha/year is possible but it can differ greatly; sandy soils in general have a low K release (Wild, 1988). Potassium is released as K +, which is a cation that can be adsorbed on the surface of the negatively charged soil particles, and is thus only leached on sandy and high organic matter soils, with low cation adsorption. Free K can also be fixed in the clay particles in between the layers of the minerals, and is again made inaccessible to the plants

15 The plants take up K as K + from the soil solution, which under natural conditions comes from the release of K from the minerals and adsorbed K. the K ions can be replaced by other ions, mostly H +, produced by the plants, which can then take up the K + instead Sulphur Sulphur (S) in the soil occurs mainly in organic compounds. The organic S content can vary between 0,8 100% of the total S, depending on the soil organic matter content. The plants take up S as sulphate (SO 4 2- ), and the main source of sulphate in the soil is decomposed organic S. SO 4 2- is a negatively charged ion, which does not form insoluble compounds like HPO 4 2- and H 2 PO 4 -, and which is only weakly adsorbed by the soil minerals, as a result S is easily leached. The amount of adsorbed S depends on the ph-value and the clay content. Low ph and high clay concentration enlarge the adsorption capacity, but the sensitivity is lower than for P. Earlier S was normally not a limiting factor for the plants in Denmark, because of industrial areas near the arable land, that supplied the soil with SO 2 from the burning of S-containing fuels. But now filters have been installed on many chimneys and S is again a limiting factor some places. 2.2 Crop description The following chapter contains a description of the main crops that are grown at Højtofte; that is silage maize; the two cereals winter wheat and spring barley; and seed grass. Furthermore sugar beet and rape are described. The farmer told us in the interview that he is not growing sugar beet any more, but as we want to investigate sugar beet in relation to the crop rotation we will describe it here. Rape is not grown at Højtofte but as the farmer told us that he would like to grow it in the future, we found it relevant to describe this crop too Maize Maize (Zea) belongs to the grass family Gramineae. After intensive breeding maize has adapted to the climate conditions in Europe and is mainly grown as a hybrid cultivar. In the northwestern part of Europe maize is mainly grown for fodder production as Silage maize, Corn maize or as Corn Cob Mix

16 Typical yields for silage maize are over 10t dry matter/ha. The growing period is from the beginning of April to the middle of October. Maize is a C4 crop and for that reason has a high CO 2 efficiency, which results in a high quantity of dry matter production in combination with low water requirements per unit of production (Mengel et al. 2001).The usual cultivation practice is sowing in bare soil and fertilization with slurry. Ploughing in autumn or spring, or no ploughing at all are all common cultivation practices (Zscheischler et al. 1990) Nutrient requirements The N uptake for silage maize is about 14 kg N/tonne (dry matter) plus 20 kg N/tonne stubble. The root dry matter is approximately 2-2,5tonne per ha, and with a slightly lower N content it can be assumed that the roots contain about 30kg N/ha (Oehmichen 1986). The following table shows the nutrient uptake by silage maize, and the Danish nutrient application norms for some selected nutrients. The norms are different depending on the previous crop

17 Table 2.1: Plant uptake and nutrient norms for silage maize. 1) The uptake is per 12 tonne dry matter (8000 FU), which ort h average yield per ha (Webcase ). 2) For yields about 8000 FU (Webcase), (Oehmichen, 1986). 3) The uptake given by Kali und Salz GmbH (2004) has together with the average yields given in the webcase been used for calculation of the uptake per ha. 4) Maximum legal N application rate (MLNA) ort he growing season 2001/2002 on loam and clay soils (Webcase). 5) Suggested application ort he growing season 2001/2002 on loam and clay soils (Webcase). N P K S kg/ha kg/ha kg/ha kg/ha Uptake by silage maize Nutrient norms Silage maize after cereals Silage maize after maize The highest nutrient amount is needed from the 8-leafstadium to the end of the flowering stadium, where approximately 80% of the total nutrient uptake occurs in 5-6 weeks. The growth, nutrient uptake, and competition ability is very low in the juvenile phase. Especially phosphorus nutrition is characterized by a high need and a low uptake ability, this makes the time of manure or fertilizer application important to avoid defficiencies (Oehmichen 1986). Maize has a high N utilization rate for organic fertilizers like slurry because the time of available N correspondent with the growth time. Also the utilization rate is dependent on the amount of N-supplied and differs between 50-70% (Schröder et al. 1998). The use of slurry, which is very common, can deliver the nutrients in the same ratios as they are needed and ensure the supply of micronutrients too (Zscheischler et al. 1990). Maize has shallow roots as well as deep roots, especially on sandy soils, so the nutrient uptake can occur at different depths (Oehmichen 1986) Climate requirements Maize is very sensitive to frost, as a result sowing and harvesting must occur in a certain time without frost. For maturing a high temperature sum (2000 ) and a high radiation (900 hours) are required for growth. In parts temperature can be replaced by radiation. The amount of water needed depends on the growth stadium and has a high influence on the yield. Most importantly maize requires mm of moisture in both July and August for the development of cobs (Oehmichen 1986)

18 Plant soil interactions Although maize leaves a lot of nutrients in the residues, which can become a source of leaching, the plant is described as humus reducing, but it depends on the amount of applied organic fertilizer. Maize production induces high potential for water and wind erosion after sowing and soil compaction at harvest under wet conditions, for this reason maize should not be grown on clay soils (Grass 2003) Maize in crop rotation Maize is described as suitable for monoculture. There are no diseases known which are promoted by monoculture, but the soil characteristics limit the ratio of maize in the rotation. Also problems of N leaching can occur due to a lack of plant cover in the wintertime. If maize is in a rotation it is often the previous crop for winter wheat and winter rye because these species can be sown late (Oehmichen 1986). Maize has no diseases, which are common for cereals, so it is also possible to break pathogen cycles of cereals with maize cultivation. Legumes, Grass leys or green manures as previous crops increase the yield of maize (Zscheischler et al. 1990) Cereals - Spring Barley and Winter Wheat Cereals belong to the grass family, Gramineae. At Højtofte two types of cereals are grown; that is spring barley (Hordeum vulgare) and winter wheat (Triticum aestivum). Both cereals can be grown for silage and fodder; in addition barley and wheat are often grown for malt and bread respectively. Winter wheat can be sown from mid September to mid December, and is harvested in late august or early September if it is for grain production; if the grains are doughy it can be used for silage instead. Winter wheat prefers a humid clay soil, with high soil organic matter content and sufficient lime supply. It demands mild winters, and warm and wet summers (Larsen and Mølgaard, 1986; Oehmichen, 1883; Bachthaler et al., 1987; Landbrugets rådgivningscenter, 2000). The Danish yield norms are lowest on sandy soils without irrigation, where they are about 5,5 tonne grain/ha, and highest on clay soils, where they are about 9 tonne grain/ha

19 Spring barley is sown as soon as the soil is cultivable in the spring, and harvested mid August if it is for grain production and like winter wheat when the grains are doughy it can be used for silage. Spring barley gives the highest yields on a well-drained loamy soil, but can be grown on all soil types if there is good drainage and relatively high chalk levels. It prefers a proportional dry soil at germination in March, but is often limited by water availability in June and July, especially on sandy soils without irrigation (Larsen, 1986; Larsen and Mølgaard, 1986; Oehmichen 1883; Bjergmark, 2000). The Danish yield norms are about 6,5 tonne grain/ha on clay soils, and about 4,5 tonne grain/ha on non-irrigated sandy soils. Irrigated sandy soils and sandy clay loam soils give about 6 tonne grain/ha (Plantedirektoratet, 2003) Nutrient requirements The following table shows the nutrient uptake by winter wheat and spring barley, and the Danish nutrient application norms for some selected nutrients. The norms differ depending on the previous crop. Table 2.2: Plant uptake and nutrient norms for winter wheat and spring barley. 1) The uptake is per 8,7 and 5,9 tonne yield respectively, which are the average yields per ha (Webcase). 2) The uptake given by LAP and ALLB (1987) has together with the average yields given in the Webcase been used for calculation of the uptake per ha. 3) For yields about 8,7 tonnes per ha (Oehmichen, 1986). 4) The uptake given by Kali und Salz GmbH (2004) has together with the average yields given in the webcase been used for calculation of the uptake per ha. 5) Maximum legal N application rate (MLNA) for the growing season 2001/2002 on loam and clay soils (Webcase). 6) Suggested application for the growing season 2001/2002 on loam and clay soils (Webcase). N kg/ha P kg/ha Uptake by winter wheat 1 Uptake by spring barley Nutrient norms Winter wheat after cereals Winter wheat after seed grass Winter wheat for bread grain Spring barley in rotation Spring barley after beet add K S kg/ha kg/ha To understand the optimal time of application of manure or fertilizer, it is necessary to identify the different growth stages. The common method for identifying growth stages for cereals is to divide the growth period into 10 principal stages and then subdivide each principal stage into secondary growth stages. Henceforward we will use the designations of secondary growth stages. A detailed description of the principal and secondary growth stages can be found in Fagaria (1997) p

20 Depending on the reason for growing cereals the farmer is interested in one or more of the following factors: The grain yield, the protein content of the grains and the amount of straw. His reasons determine his fertilizing practice, because wheat and barley divert photosynthetic products to vegetative growth early in the season and to grain later (Fagaria, 1997). Winter wheat N uptake is most rapid from the tillering to booting, that means from growth stage 20 to % of the total N accumulation occurs before grainfilling (growth stage 70). Landsførsøgene (2003) recommend the following fertilizing strategies for winter wheat for grain production: If the farmer wants grain production for fodder i.e. no extra charge for protein content, kg N/ha should be applied mid March, (about growth stage 25), and the rest in late April (about growth stage 30), or all the N once in mid April (about growth stage 28). If the grain production is for bread then extra N is require, kg N/ha should be applied in March (between growth stage 23 and 26) and the rest in the early May (at growth stage 32). If the farmer has permission to use extra N, a third application is recommended in early June (about growth stage 55-59), where kg N/ha can be applied. The best way to fertilize winter wheat for silage, is to apply N in two turns to discourage lodging, and to attain a good straw to grain ratio. First application should be in late March (about growth stage 26), and the second around the 1 st of May (about growth stage 32) (Bjergmark, 2000). Barley has a high N uptake from short after sowing (Briggs, 1978), and as the growth period for spring barley is short too, it is important that the needed nutrients are available as the growth start in early spring independent of the kind of production. That means that the best time of application of manure or fertilizer is about sowing time (Larsen 1986) Winter wheat and spring barley in crop rotation It is common in Denmark to grow winter wheat in monoculture, because it is easy to manage, the price does not depend on the market because most of the earnings come from EUsubsidies, and spring seeds on clay soils are difficult to establish (Andersen 2002), furthermore the areas are covered in the wintertime, and thereby prevent leaching of N. However, crop rotation experiments show that the yields are about 10-15% lower in a monoculture of winter wheat than in winter wheat grown in rotation with rape or pea, because of reduced root diseases. Moreover winter wheat in monoculture can lead to grass-weed problems (Andersen 2002)

21 Spring barley is the most suited to crop rotations with many cereals, especially when double nematode resistant varieties are used. Barley gives the highest yields after a previous crop, of beet, rape or clover grass (Larsen 1986). In relation to other crops it is also important to identify the rooting depth. Both cereals have a rooting depth of more than 1m, though wheat is tends to go a bit deeper than barley. The rooting intensity is high, as much twice that of maize for example (Wild, 1988) Seed Grass At Højtofte several seed grass species are grown including: perennial Ryegrass (Lolium perenne L.) Reed fescue (Festuca giganta), Red fescue (Festuca rubra L.) All of them belong to the grass family, Gramineae. The production of seed grass has the aim to deliver seeds for sowing and maintenance of grass leys as well as for sale for gardening and landscape opportunities. Two different cultivation practices common. One is sowing in bare soil; the other is undersowing in a crop, usually a cereal. The production of seeds starts one year after the harvest of the cereal crop or in the second year after sowing in bare soil. The sowing time can be either autumn or spring depending on the requirements of the grass variety. The grass is usually trimmed once in autumn or in spring and the seeds are harvested in late August. Usually a seed grass culture is used for approximately 3 years. The avoidance of losses due to weeds is the main challenge in seed grass production (Fairey and Hampton, 1998) Plant requirements The plant requirements are highly dependent on the species. Of great importance is the supply of nutrients in different growth-stages. N fertilization should promote the production of fertile tillers, therefore an application in autumn and spring is common. Hebblethwait and Ivins (1977) found maximum yields for perennial Ryegrass occurred if between kgN/ha was applied in spring. The amount of fertilizer after harvest of the crop in which the grass is undersown was 60 kg with low fertilization levels of the harvested crop. Higher amounts (Hebblethwait and Ivins 1977) or late application in different species (Nordestgaard 1989) decrease the seed yield and increase the amount of second tillers thus increasing competition

22 between the tillers and plant susceptibility to lodging. Although there was no increase in seed yield due to split application in spring, the use of fertilizers with slow N release is recommended (Hebblethwait and Ivins 1977). The best timing and amount for the application was found for red fescue with no difference between 50 and 100kg N/ha in the beginning of March and an autumn fertilization of 50kg (Nordestgaard 1989). Italian ryegrass showed no response to an autumn fertilization. The best yields (2180kg) where received with a spring application of 100 kg N/ha in the beginning of April (Nordestgaard 1989), the total amount of N supply may also be valid for perennial ryegrass. A response to the amount of autumn fertilization was found for perennial Ryegrass and red fescues with an optimal amount of 30-60kg N/ha. The spring application for perennial Ryegrass was 100kg N/ha and for red fescue 50kg/ha. The seed grass in all field trials was under sown in barley. Better seed yields where found with winter rape and winter wheat; particularly for red fescue the increase of seed yield was highest (+240kg) in winter rape (Boelt 1997). For reed fescue there was no recommendation found. Due to the use for fodder in autumn a higher amount of N supply after cover crop harvest is needed. The total amount of applied N should be calculated from the expected yield: 3-5% of the plant dry matter is N. An overview of the research mentioned above can be seen in following table

23 Table 2.3.1: Overview over different recommended N application rates in kg N per ha. for different grass species. Recommended N application Autumn Spring Red fescue [Nordestgaard 1989] Red fescue [Boelt 1997] Perennial Ryegrass [Boelt 1997] Perennial Ryegrass [Hebblethwait and Ivins 1977] In the table below the average yields for some of the grass species is given together with the Danish nutrient norms. Fig 2.3.2: Yields and Danish nutrient norms for some grass species. 1) Webcase 2) Maximum legal N application rate (MLNA) for the growing season 2001/2002 on loam and clay soils (Webcase). 3) Suggested application rates for the growing season 2001/2002 on loam and clay soils (Webcase). Yield 1 N 2 P 3 K 3 kg/ha kg/ha kg/ha Perennial Ryegrass 1,2 t year old Ryegrass 1,2 t Red Fescue 1,1 t Undersown pure grass after cereals 1000FU Climate requirements Seed grass production needs long and warm summers to ensure the harvest of mature seeds. The precipitation shouldn t be too high, particularly between flowering and maturing, dry conditions are needed Plant soil interaction Seed grass as a permanent crop over a few years increases the soil organic matter content and maintain the soil fertility properties. Due to the plant cover over the whole year, less leaching and soil erosion occurs. One reason for this is may be the intensive root system, which reaches to approximately 1m. (Oehmichen, 1986) Seed grass in crop rotation For the reasons mentioned above seed grass is a very good previous crop for crops with high requirements for the nutrient supply and the soil properties (Oehmichen, 1986)

24 2.2.4 Sugarbeet Beet (Beta vulgaris) belongs to the family Chenopodiaceae. Beet can be grown on all mineral soils, with good soil properties, but sandy soils with sufficient water supply give the highest yields (Bjergmark, 2000).Beet can be sown after the 1 st of April. Earlier there were problems with bolters if the spring was cold, but this tendency is gone after many years of breeding, which make it possible to sow earlier, and thereby extend the growing season, which gives higher yields. The optimal harvest time is late October or early November. The risk of late harvest is that frost makes the harvest impossible (Bjergmark, 2000). Beet has a low N uptake in the time after sowing, and after some week s large amounts of N are taken up. But as the beet still need available nutrients from the beginning, manure or fertilizer is often applied at or prior to sowing. There should be about 40kg N/ha in the upper 5-10 cm soil. The needs of P and K will be covered if about 60 tonne cattle slurry per ha is applied (Bjergmark, 2000). That means about 54kg P/ha and 342 kg K/ha, and spring application gives the best effect (Bjergmark, 2000). The Danish norms for application of N, P and K are given in the table below together with the standard yields

25 Table 2.4.1: Plant uptake and nutrient norms for sugarbeet. 1) The uptake is per 50 tonne, which is the average yield per ha (Webcase). 2) The uptake given by (LAP and ALLB, 1997) has together with the average yields given in the webcase been used for calculation of the uptake per ha. 3) The uptake given by Kali und Salz GmbH (2004) has together with the average yields given in the webcase been used for calculation of the uptake per ha. 4) Maximum legal N application rate (MLNA) for the growing season 2001/2002 on loam and clay soils (Webcase). 5) Suggested application for the growing season 2001/2002 on loam and clay soils (Webcase). N kg/ha P kg N/ha K kg N/ha S kg N/ha Uptake by sugarbeet Nutrient norms Sugarbeet (beets only) Sugar beet (incl. Top harvest) add Climate requirements Beet has high water requirements from mid June, but as July, August and September are normally rainy months, the Danish climate is good for beet production (Bjergmark 2000) Sugarbeet in rotation Beet in rotation should be grown with an interval of at least three years in between crops, otherwise problems with diseases, pests and weed will occur. When beets are grown continuously, one year with bad weed control can give intense weed problems in the following years. Rape and beet in the same rotation can give weed problems in the beet, because rape can occur as a weed in beet. Furthermore both rape and beet is attacked by beetnematodes. Grass and old grass leys can also gives problems as previous crops for beet because of crane fly grubs (Bjergmark 2000) Rape Rape (Brassica napus) is a member of the Brassicaceae family. Mostly it is used for oil production, but also for fodder in wintertime. A high N uptake occurs in autumn, approximately 70kg/ha and the total uptake rises at flowering to 180kg. The requirements per tonne seed are kg N. For a normal yield of 3,2 tonnes the nutrient requirements are given in the table below (Oemichen 1986). Nearly half of the uptaken P, K, and S is left on the fields with the non-harvested parts (Kali und Salz GmbH 2004). A factor which distinguishes rape from the other named species is the deep rooting system and the fast root development in combination with a high nitrogen uptake capacity (Thorup-Kristensen, 2001)

26 Table 2.5.1: Plant uptake and nutrient norms for rape. 1) The uptake is per 3,2 tonne, which is the average yield per ha (Webcase). 2) (Oehmichen, 1986). 3) The uptake given by Kali und Salz GmbH (2004) has together with the average yields given in the webcase been used for calculation of the uptake per ha. 4) Maximum legal N application rate (MLNA) for the growing season 2001/2002 on loam and clay soils (Webcase). 5) Suggested application for the growing season 2001/2002 on loam and clay soils (Webcase). N kg/ha P kg N/ha K kg N/ha S kg N/ha Uptake by rape Nutrient norms Winter rape Spring rape Slurry fertilization is possible in autumn and spring. The application rate and time is crucial. A too high or too early autumn application can increase the growth above the level that is needed to overwinter without losses. The spring application should occur early, in February or March, and a second application during shooting. Rape needs a deep soil with good structure and is very sensitive to soil compaction and water logged soils. Winter wheat is often the subsequent crop. In a crop rotation rape has shown good results after seed grass and barley. The most important aspect is the early harvest of the previous crop, to ensure a sowing between 5-20 th of August. Rape shouldn t be grown with less than 3-4 years in between crops. The main reason for this is due to disease problems (Oemichen 1986). 2.3 Manure description Manure is a valuable resource on any farm. Livestock are inefficient in extracting nutrients from feedstuffs; typically, per cent of the major nutrients that are fed to livestock pass directly through the animal into the manure (Tamminga, 2003). In many production systems, these animal excreta are collected as manures consisting of mixtures different proportions of faeces, urine and straw (Thomsen, 2000). Manures can be defined as plant wastes and animal products which are being reused by incorporating them to the soil and which have amendable or fertilizing effect on the soil and the plants growing in the soil. This can occur directly in the form of excreta from grazing animals, but in the case of housed or confined animals the excreta may need to be processed and stored before they are retuned to the soil (Jensen, 2002). The value of manure varies considerably depending on the age, feed and productivity of the animal. With nitrogen losses taken into account most manures are well-balanced fertilizers

27 Nitrogen losses occur due to leaching, volatilization of ammonia, or denitrification of nitrates. Nitrogen losses are the most difficult to control but composting, rotting, adding chemicals and having proper infrastructure and better management can prevent their occurrence. Animal manure is the oldest of the known fertilizers that is available to the farmer. They are cheap, readily available and the benefits to the soil and to the plant growth are well recognised. Animal manures are a valuable source of both macro and micronutrients The formation of animal manures: The conversion of fodder in livestock provides energy and nutrients for to the growth and maintenance of the animal and results in the production of products such as milk, meat, wool and other goods, but also leads to the production of faeces and urine. All animal manure is produced in the form of dung and urine, and can be stored as such. Faeces are a mixture of undigested feed and microbes and microbial residues from the digestive system. The manorial value of the faeces is therefore dependent on the digestibility of the feed. Figure 2.3.1: Shows amount of excreta produced by livestock

28 2.3.2 Nutrient value of manures Various factors determine the nutrient value of manures. In common, the richer the feed that is fed to the animal, the richer the manure. Feeding animals with fodder that is rich in proteins like grains produces a richer manure. The nutrient value of manure is inversely related to the weight gain and productivity of the animal. Young animals produce poorer manure than mature animals, and milk-producers generate poorer manures than non- milk producers. Draught animals require high amounts of carbohydrates, and as a result most of the nutrients in the feed pass through them. Animals which do not gain weight or produce a product only require nutrients for maintenance; old, dead tissue is sloughed off, and so the nutrient value of their manure is similar to the value of the feed. (Parnes 1990) Another important factor is the form or structure of feed, a high roughage diet produces more faeces while on the other hand highly succulent feeds with high nitrogen content results in more urine. Urine contains soluble metabolic products excreted from the tissues, and generally the nutrient content in the urine has a high bioavailability, most of the N in the urine being urea. However, the nitrogen in faeces is more stable, and can be composted, while nitrogen in the urine although its more readily available, can be hard to utilize as a greater part of it is lost through volatilization. Poultry manure is very rich in nitrogen, phosphorous and calcium due to highly concentrated feed mixed with lime. Cage layer manure collected from the trays below the birds are very strong and wet, and hence difficult to handle. But there are variations in poultry manure too, for instance, broiler manures are drier and easy to handle but it is very hard to predict the nutrient content. The main reason being broiler hens are allowed less movement and the number of times the manure is collected and piled is unknown. Other manures are better balanced than poultry manures, but their nutrient content is hard to predict without the information on feeding pattern and the purpose of the animal. Horse manure seems to be least variable because their diet is more predictable. Sheep manure is the strongest of the non-poultry manures, and indeed sheep manure is often sold dried and bagged

29 The moisture content of the manure is another very important factor that helps to determine nutrient availability. Horse manure is very dry and it heats up very fast while pig and cattle manures are wet and they rot very easily with less nitrogen loss. Sheep manure can be classified in between horse manure and cattle manure; it is moderately coarse and dry. Animal digestive system is another important factor that determines the value of manure. Estimation of nutrient excretion by ruminants is much more complex than for monogastric animals, e.g. pigs and poultry, due to both greater variability in the amount and the quality of the feed and to greater variability in the production level (Jongbloed and Lenis, 1993) The excretion of undigested feed N is very small in ruminants (10-20%), but due to the ruminant digestive system, the content of microbially derived N is very high. According to Kristensen (1997), the microbial N excreted in the faeces increases strongly with high carbohydrate content in the feed at high feeding levels, and N excretion in the urine is high when the protein content of the feed is increased (Kristensen and Ohlsson, 1996) In ruminant animals most of the K in the feed is excreted from the animal except for 2-8% that is retained in the body. But in the case of monogastric animals almost all the K is excreted in the urine (Jongbloed and Denis, 1993). P is present in the form of phytate in the feed and ruminant animals are capable of digesting feed P due to their ruminal microflora, but on the other hand monogastric animals are incapable of digesting feed P. A very small fraction of P is excreted in the urine but more of the P is excreted through the faeces of ruminant animals. As a result, when more quantities of soluble feed P are fed to the animals during the productive stage, the excreted faeces contains a lot of P and which can be a problem when applied to the soil. It is well known that nutrient content in cattle manures vary from farm to farm due to different feeding practises, in general cows excrete 98kg of urinary N/year without feeding concentrates but if they are fed with feeding concentrates the figure can go as high as 191Kg N per cow per year. Monogastric animals are generally fed a uniform diet that varies little from farm to farm and the variability in the feed is minimal except for the protein content of the feed, which is fed

30 only once. Most of the feed N is being utilised by the animal and hence less N is excreted. However, as mentioned earlier monogastric animals are not capable of digesting P in the form of phytate and this results in high excretion of P in the faeces and this can be a great problem to the agricultural land that uses a lot of pig manures. Table 2.3.2: Typical total nutrient content of livestock manures (adapted from Chambers et al. 2001). Manure Type DM % Nitrogen Phosphate Potassium Sulphur Magnesium Solid Manures Amount of Nutrient (Kg/t) Cattle FYM Pig FYM Dairy Slurry Beef Slurry Pig Slurry N losses in the stable Design of the stable systems often contribute to N losses, most often it is dependent on whether the dung and urine is collected separately, mixed as slurry or in a deep litter system. Generally loss of excreted N is higher in deep litter system than in slurry systems. Stables: Nearly 42% of N is lost in animal stables through ammonia volatilization (Tybirk & Jorgensen, 1999). As soon as urine is excreted the hydrolysis of urea N will be initiated by the urease enzyme, producing ammonia and bicarbonate, the former being highly susceptible to volatilization

31 Figure 2.3.3: Loss of Ammonia-N from varying surfaces (Sommer 1997) N losses in the stables are higher in pig production system. In poultry production a large part of manure N is in the form of uric acid, which is quickly converted to ammonium after excretion, the loss of N is even higher.. Other factors that determine the loss of N are type and rate of ventilation (Aarnink et al., 1993), floor type (Elzing and Swierstra. 1993), temperature (Andersson, 1998) and the frequency and method of slurry removal (Hoeksma et al., 1993) Collection, storage and processing of different types of manures The processing and storage of animal manures before application to the soil affects the quality as well as quantity of available nutrients. Transformation of organic and inorganic forms of nutrient takes place depending on the method of storage and manure quality. Collection method also has an impact on the nutrient composition Overcash et al. (1983 in Eghball, 2000) showed that N contents of beef cattle manure were 31, 42, 27, and 19 g N kg -1 (dry weight basis) when collected from scraping under slotted floors, in pits or tanks, bedded units, and feedlots, respectively

32 2.3.5 Manure Types Solid Manures Farmyard manure is the most common manure that is easily and readily available to a farmer, especially to a diary farmer. It is a decomposed mixture of animal excreta and urine with straw and litter used as bedding material and residues from fodder. The manure is removed daily from the stable and in straw yard systems the manure is allowed to build up without being replaced. The main disadvantage in this system is the slow mineralization due to less soluble nitrogen. The total loss of N amounted to ca. 20% for cattle manure due to denitrification of manorial N under aerobic conditions in the heap (Petersen et al, 1998) Deep litter manure systems offer a more natural and adequate housing environment for animals, promoting their welfare by allowing them to walk and live on fresh straw defecating onto the straw before it is replaced again on the next day. The straw and faeces are mixed by the animal themselves by their movement in the shed and thus reducing human labor. The upper layers are aerobic while the bottom layers are anaerobic. This system produces relatively large ammonia losses through volatilization and induces nitrogen loss through denitrification. Due to use of cereal straw in cattle sheds, deep litter has a high C/N ratio and low content of inorganic N, so the N contained in this manure is available very slowly Liquid Manures In Denmark about 60% of the nitrogen excreted from housed cattle and pigs is collected and transported in the form of slurry, equivalent to a yearly production of ton N (Kofoed and Hansen, 1990). Slurry is a combination of faeces, urine, straw and water that can provide a quick release of organic fertilizer. Handling of slurry is very easy but managing slurry is one of the most expensive among all other manures available to farmer except for deep litter manure. About 50% of nitrogen in the slurry is present in the form of ammonium nitrate or urea due to the urine content. The rest is present in the form of undigested protein. Considerable amount of ammonia may be lost from slurry tanks if there is no barrier between the fresh slurry and the air; hence it s always good to have a surface crust, which can prevent ammonia losses considerably. The surface crust created a stagnant air layer above the liquid slurry and increased the surface roughness, creating a higher surface resistance and reducing the

33 ammonia loss. The losses occurring during the application of slurry from the tanker, while in the air ranges around 3-4% (Sommer and Christensen 1990) As mentioned earlier urine is the soluble metabolic product excreted from the tissues and hence the nutrient content in the urine is of high bio-available value. Most of the nitrogen is present in the form of urea and can be readily used by plants and the uptake is easier. But it is essential to store urine in well-sealed tanks otherwise even a small leakage may result in the loss of more than 50% of the total N. Figure 3.5.1: Shows Nitrogen losses during storage Application of manures There are many different types of machines and methods available for manure application depending on the type of manure used (liquid or solid). The main mechanized methods can be described as either slurry injection systems or solid manure spreaders. A number of different methods for the application of slurry into the soil or spraying it on the soil are described below

34 Slurry Application Systems Band Application Systems: Slurry can be placed in narrow bands with the use of a band spreader fitted with a rotary distributor. Slurry can be placed under the crop canopy with the help of trailing shoe spreader or placed in shallow open slots with the help of an open slot shallow injector. Figure 3.6.1: Above shows a picture of tanker with band spreader with rotary distributor and below shows a tanker with trailing shoe spreader

35 Figure 3.6.2: Shallow injector system Open Slot Shallow Injectors: These inject slurry under the soil surface with different types of injectors depending on the soil type and the requirement. The different type of

36 injectors fit into either one of two categories: open slot shallow injection that injects slurry up to 50mm deep; or deep injectors that inject slurry to a depth of up to 150mm. Direct Injection Umbilical Systems: these systems use a series of umbilical pipes to feed the slurry to the injection machine, which injects the slurry into the ground via modified cultivator tines. Shallow Slurry Injection System: These systems have been designed specifically for increased grass yield with the use of natural fertilizers Irrigation system for manure application: In this system the manure is pumped out through drag hoses from the tanker and manure is sprayed onto the soil from less than 1.2m above the soil surface. Broadcast Spreader: A broadcast spreader pumps out slurry under pressure from a tanker with the help of splash plates or nozzles Solid manure spreaders Figure 3.6.3: Side discharge manure spreader There are 3 types of solid manure spreaders available

37 Side Discharge Spreaders: these are capable of handling both slurry and solid manures (see figure above). Rota-spreader: this is a type of side discharge spreader which is capable of spreading slurry and finer particle solid manures. Rear discharge spreader: Very similar to the side discharge spreader except the delivery of slurry or manure is from the rear. Figure 3.6.4: N loss as NH 3 % of applied total N depending on application technique Alternative Slurry Transport A Continuos Flow system The concept of a continuous flow of transport and application of slurry using umbilical transportation systems rather than traditional tanker transport may reduce labour requirements, increase capacity, and open up new ways for reducing ammonia emissions Animal slurry is transported from storage units to the field in tankers, which is both laborious and technically demanding. For all countries within the European Union, manure transport incurs considerable operating costs (Huijsmans et al., 2001). Heavy slurry tankers may cause considerable yield losses in the range of 7 32% of the initial slurry value due to compaction (Arvidsson, 1998). The combination of pipeline transport and lightweight in-field spreading units equipped with trailing hoses can reduce ammonia losses by around 30%, and nitrogen utilisation will be

38 increased significantly by the dilution of the slurry prior to application in the field (Sørensen et al. 2003). In the case of unmanned spreading units, application may take place at night, which will reduce ammonia loss by around 50% (Sommer & Olesen, 2000 in Sørensen et al. 2003). Sørensen et al. (2003) undertook an analysis of the handling of manure from a cattle farm of 125 cows and determined that the labour requirement for a self propelled in-field spreading unit with trailing hoses coupled to in-field hydrants is 39 41% lower than that using a conventional tanker with trailing hoses. At the same time the system capacity was 74 80% higher. The costs of handling manure using a conventional tanker with trailing hose s varies from 2.2 to 2.7/t; while the costs of using a self-propelled spreading unit with trailing hoses and a mobile transfer hose or coupled to in-field hydrants varies from 15.3 to 21.5/t. As such, the umbilical system is not feasible as an on-farm investment for a dairy with 125 cows. An economically feasible on-farm operation of an umbilical system will require an annual distributed amount above t. In its most efficient configuration, the use of umbilical systems may reduce the labour requirement by about 40% and increase capacity by 80%. However, these systems are costly and will only be profitable for annual applications above t Rates of Manure Application The amount of manure that is needed by the crop and the soil depends on the soil nutrient level at the time of application, the nutrient requirement of the crop and the actual nutrient value of the crop. The farmer is very often tempted to get rid of the manure from his storage area due to surplus amount and this often leads to loss of nutrient through emissions and leaching causing serious environment problems. It is therefore essential for farmers to understand the real value of manure and to manage it efficiently so that no excess amount is added to the soil and no nutrient deficiencies are felt by the crop. In order to determine the rate of application the following factors need to be thoroughly understood by the farmer

39 The variability of nutrient content in manures before application include: Manure source The volume of manure Type of on-farm bedding used Wash water volumes Yard areas contributing drainage to the slurry system Local rainfall Ammonium volatilisation Generally drainage and wash water collected in the slurry systems can cause substantial slurry dilution and increase excreta volume. The moisture content and analysis of solid manures will be affected by rainfall and the degree of composting that occurs, which can reduce both the weight and volume of the manure produced Guidelines to estimate the nutrient content in manures: For reliable rate of application it is essential to understand the nutrient content of the applied manures. Nutrient content is given as the element for nitrogen (N), and as the oxide for phosphate (P 2 O), potash (K 2 O 5 ), sulphur (SO 3 ) and magnesium (MgO), because this is the convention for expressing their content in the fertilizers. It is always advisable to measure nutrient contents of manures due to the variability in nutrient content that can occur depending on feed and productivity. A laboratory analysis should be carried out for dry matter content (DM), total N, P, K, S and Mg, and ammonium-n (crop available N) and for well composted FYM nitrate-n should also be measured. For slurry analysis laboratory results can be supplemented by on farm rapid N meter measurements of ammonium-n. A slurry hydrometer can be used to estimate DM, total N and total P contents Significance of controlled application and machinery calibration To ensure that the estimated amount of nutrients in slurry and solid manure has been applied to the crop, it is essential that the machinery used is chosen, calibrated and operated to ensure exact application. It should be capable of being set up to apply the intended rate in m 3 /ha or tones/ha, and to produce an acceptably even spread pattern

40 To reduce the risk of pollution by the excessive incorporation of manures, the DEFRA Water Code advises limits for nutrient loading and amount of manures applied. The total N applied should not be more 250kg per ha per year. Once the desired application rate is known it is very important to apply slurry or solid manures as accurately and evenly possible Estimation of application rate for slurries and solid manures To estimate the application rate there are international standards for calibrating slurry and solid manure spreading systems. The full calibration procedure determines the application rates achievable by the spreader and how evenly slurry or solid manure is spread. This is expressed in terms of C of V. The equipment used to measure this is large and expensive, but for farmers other options are available which are simple and less expensive and can be carried out in the farms. The rate of application of slurry and solid manure is dependent on three major factors: Bout Width Discharge rate Forward speed Once the target application rate is finalized based on the crop requirements and the nutrients in the slurry, forward speed to achieve target application rate can be calculated by the formulae: Forward speed (km/hour) = Discharge rate (m3/second x 36000) Bout width (m) x Application rate (m3/ha) Time of application of manures In order to minimize the loss of nutrients the farmer needs to take care of the time of application and mostly incorporation of manure should be done a day before tillage operations. Appropriate timing will result in better plant uptake and thus increasing the yield and reducing the losses due to leaching and volatilization. The Action plan for aquatic environments says 12h before incorporation as a maximum

41 Normally the farmer applies manure in the autumn to grow winter crop and apply manure in the spring if he wants to grow a spring crop. But most of the time, farmers bring out manure in the autumn even if they want to grow a spring crop, the main reason being there is no storage area left to store the manures and also the farmer is very busy in the next season to dedicate time for manure spreading. This normally results in great nutrient losses as there are no crops on the field for nutrient uptake during the subsequent winter and hence cause serious leaching into the ground water. Generally the conditions for uptake of nutrients from manure will be best for spring crops. (Jorgensen, 2000) Application of manure in relation to ploughing techniques For many years, farmers have been applying manure before any kind of tilling and then plough the manure down to soil with the stubbles and dead plants after harvest. Most farmers plough the soil to a depth of cm and then spread manure. But this practice is rather inefficient due to the fact that a lot of the nutrients are being lost before the crop establishes the root system to this depth. (Hansen et al. 2003) So it s becoming a normal practice to incorporate manure after ploughing however, very little research has been done in this field. Conservation tillage is one option. The main idea behind conservation tillage or reduced tillage is to keep the nutrients from manures and other organic residues at the top surface of the soil. This enables the plant to maximise nutrient uptake, till the crops has established and the roots start to grow down to the subsoil where nutrient availability is reduced. (Sorensen et al.2003) The main advantage of this system is that the loss of nutrients is kept to a minimum and also the roots are able to capture the nutrients that are moving downwards from the topsoil to subsoil. Application after drilling is normally carried out after the crop has established and the roots have grown to lower depths. This system is successful with slurry where slurry is applied in tubes after drilling and the roots are able to take up the nutrients in time without much loss and this system reduces ammonia emission to the atmosphere. (Jorgensen et al. 2000) Application during drilling enables the farmer to apply fertilizer or slurry during sowing. In case of synthetic fertilizer, fertilizer can be placed at the same drill with the seed and the fertilizer is drilled in together with the seed. This technology has helped the farmers in increasing yield and the machinery has been a great success. However when using slurry, the

42 slurry needs to be drilled into the soil through a different drill fitted to the same machine at a depth of 12 cm. (Birkmose 2001) The main advantage of this system is that sowing of seed and slurry application can be done at the same time which saves time and money, but the main disadvantage is the machinery used needs high tractor power and can create greater soil compaction. (Birkmose 2001) Timing of application of manure The amount of manure added during the seedbed preparation and during the growing stage of the crop should be carried out carefully and in planning depending on the demand of the crops. If proper planning and care is not taken it might result in adverse growth conditions to the crops thus reducing yield and developing diseases. But it should be noted that timing of application of manure is different for each crop and the above-mentioned timing is meant only for wheat and barley, and can vary with other crops. During application of manure with irrigation systems, the wind direction and the speed of wind should be noted. Strong wind can carry the droplets to other direction thus creating nonuniformity in application. High wind speed decreases the boundary resistance at the surface of the slurry and the transfer of ammonia from the slurry to the atmosphere increases. Strong wind can carry the droplets to other direction thus creating non-uniformity in application Availability of nutrients When we talk about the nutrient supply of manure in general to a crop, the availability of nutrients in the manure is more important than the total nutrient value. In the case of N, plants may utilise N in the form of nitrate or ammonium, both of which are found in manure (Dahlberg et al. 1986). A large proportion of the N in manure is normally in the organic form. Organic N must be mineralised before being utilised by plants Dahlberg et al. 1986). A general rule of thumb for determining the amount of nitrogen available in manure is to add 100% of the ammonia to 30% of the organic nitrogen. In the case of Phosphorous it is 50% of the P available to the crop in the year of manure application. Manure analysis data from Manitoba Agriculture and Food (1997) shows that liquid manures have an available phosphate ratio of 2.6:1. Whereas solid manures have an available N ratio of 1.7:1 and P 2 O 5 has an availablity ratio of 1.5:1-42 -

43 The nutritional value of phosphate, potassium and micronutrients is generally higher than that in mineral fertilizers. But the main problem with this nutrient availability to the plant is; these nutrients are slow and are not readily available to the crops at the early stage and hence the crop might suffer from nutrient deficiency. Manure availability of S is low when compared to P and K. (Eriksen et al.1995). The reason is due to the turn over of slurry in the storage causing conversion of sulphate to organically bound S, but the actual mechanism is not yet understood properly. Phosphorous is mainly found in inorganic forms (80-90%) and become soluble in soils, which are mostly neutral or acidic in reaction. In general animal manures can supply enough P and K to the crop throughout the growing period, but most of the time the amount is so high that they get leached to the waters or subsoil and are lost. Figure 3.7.1: Shows available nitrogen effective for spring growth 2.4 Manure handling as a nutrient management tool As already mentioned, manure is a valuable resource on any farm. Livestock are inefficient in extracting nutrients from feedstuffs; typically, per cent of the major nutrients that are fed to livestock pass directly through the animal into the manure (Tamminga, 2003). In many production systems, these animal excreta are collected as solid manures consisting of mixtures of faeces, urine and straw in different proportions (Thomsen, 2000). As previously mentioned, the extent to which these nutrients can be returned to the soil and made available to subsequent crops will depend on the way the manure is collected, stored and handled. A typical animal production system may produce either slurry, FYM or both. When removed from the houses, solid manure is generally stored in the open for varying

44 periods of time before being applied to soil (Thomsen, 2000). Slurry, on the other hand may be collected and stored in large tanks on farm, and stored prior to disposal at appropriate times. During the storage period manure may undergo different decomposition processes depending on its character and composition. This usually results in the production and loss of the greenhouse gases and their constituent nutrients, CO2, CH4, NH3 and N2O, the magnitude of which depends on the origin of the manure and the storage conditions (Petersen et al., 1998). If the manure is slurry, and stored in tanks then it may begin to degrade anaerobically. However, if the manure is porous and sufficient oxygen supply is present, a composting process may start (Thomsen, 2000) Composting A broad definition of composting may be taken as the controlled biological decomposition of organic material that has been sanitised through the generation of heat and converted into relatively stable humus-like substances the successive action of bacteria, fungi and actinomycetes in a warm, moist aerobic environment (Anonymous 1993; Jeong and Kim, 2001; Szmidt and Dickson, 2001). Composting has been recommended as a method that may further improve manure quality for reuse in agricultural plant production (Tamminga, 2003). Compost itself can be described as any product of a composting process that is effectively free from pathogens, weed seeds and inert contaminants that is fit for an intended purpose (Szmidt and Dickson, 2001). Compost bears little physical resemblance to the raw material from which it originated; contains plant nutrients; and has the ability to improve the chemical, physical, and biological characteristics of soils (Szmidt and Dickson, 2001). Compost maturity is one of the most important aspects of compost quality (Wang et al in press). Compost maturity relates to the degree to which the organic matter has been stabilised during the composting process. Young compost that has not reached the stable humus stage, will be high in effective humus and available nutrients but low in stable, colloidal humus. Mature compost, which is close to the final decomposition stage, will have a higher proportion of stable humus, and will be considerably reduced in bulk. Compost at

45 various stages, from young to fully-aged, may be used according to the needs of the soil and the crop (Szmidt and Dickson, 2001). The nutritive and other benefits of the material will depend very much on the source materials, the conditions under which it was made and the maturity of the compost when it is applied. Young or medium compost will encourage biological activity in the soil. Mature compost will make a greater contribution to soil organic matter levels and soil structure. In general, however, the addition of compost to a soil results in a net improvement to soil fertility, compared to an application of manure. As a general rule of thumb, 1 ton of field applied FYM will supply 100kg of stable humus after a 4-5 year breakdown period. In comparison, a ton of medium compost supplies about 180kg and mature compost supplies 330kg of stable humus after the same period Advantages and Disadvantages of composting The additional storage and handling requirements involved in the production of compost can be offset by the advantages of compost to the organic farmer. Composts have been successfully used as fertiliser for a range of agricultural crops ranging from grass to maize, grains and horticultural crops such as broccoli (Rodrigues 2000: Szmidt, 1997). Compost can have primary value as a fertiliser but at the same time will secondarily provide benefits of improving physical and microbial soil characteristics (Szmidt and Dickson, 2001). Substantial amounts of C held in manure may be lost during composting. It seems, however, that despite high C losses during storage, maximum C stabilisation in soil is obtained by using composted organic wastes rather than less decomposed wastes thus reducing the potential immobilization of soil mineral N (Thomsen, 2000). Although composting may be advantageous in achieving a homogeneous product that can be spread more uniformly, there are some drawbacks (Thomsen, 2000). Large proportions of N may be lost through gaseous emissions (Karlsson and Jeppsson, 1995; Kirchmann, 1985; Martins and Dewes, 1992; Petersen et al., 1998) which may reduce both the total amount of N available and the proportion of total N in inorganic form (Kirchmann and Witter, 1989). The fertiliser value of composted manure for crop production may therefore be reduced compared to non-composted manure (Thomsen and Kjellerup, 1997)

46 For a manure with a C:N ratio of 14:1, Thomsen (2000) found that 46% of the initial amount of N was lost during composting after 86 days of storage compared with only 18% for anaerobically stored manure. Similar N losses have been found for composting manure having the same initial C:N ratio as in the present experiment (Kirchmann and Witter, 1989; Martins and Dewes, 1992 in Thomsen 2000) whereas manures having higher C:N ratios have shown lower losses (Thomsen, 2000). According to Poincelot (1975), a C:N ratio of 30 will yield the most efficient composting process, whereas a higher ratio would lead to a longer composting phase and a lower ratio will cause increasing N loss. A high C:N ratio may be obtained by using large amounts of e.g. straw. However, manures with high C:N ratios do not necessarily prevent large losses from easily decomposable parts in the manure, but losses may seem lower when expressed relatively to the background of large amounts of slowly decomposable N (Thomsen, 2000). However, as a result of lower microbial activity after the application of composted manure to the soil, less N may become immobilised compared to non-composted manures. This may influence the availability of N applied with the manures. Also, the availability of N in the various manure components may be changed when exposed to different decomposition processes during storage. Thus although large amounts of N may be lost during composting, the fertiliser N value may not be lowered correspondingly. (Thomsen, 2000) Composted manure slowly releases its nutrients into the soil, enhancing the soil microbiological life, whereas the highly-soluble nutrients in raw manure are quickly leached away and can damage both the soil biology and the crop (Szmidt and Dickson, 2001). However, this slow release may not be optimal for plant growth as plants require higher nutrient supply at critical growth stages this may in fact lead to nutrient deficiencies and subsequent yield reductions. Furthermore, composting reduces the 1st year fertilizer value of the manure due to losses of N during storage (Sommer 2001). Compost supports and encourages the growth of earthworms, bacteria, fungi and other microorganisms and adds organic matter to the soil. In this way, compost improves the biological, physical and chemical properties of the soil. In comparison, raw manure also adds organic matter but can cause a period of disruption to the soil life by creating an imbalance of nutrients

47 The application of compost has also been shown to increase ph, soluble salts and cation exchange capacity. These increases would appear to be due to an increase in soil organic matter and available plant nutrients. Soil fertility therefore will increase with the application of suitable compost, at an appropriate level (Stratton et al. 2000). Compost returns nitrogen, phosphorous, potassium, calcium, magnesium and the micronutrients back to the soil. Amounts vary, but a well-prepared mature compost may contain kg/t N, kg/t P 2 O 5 and 15kg/t K 2 O (Szmidt and Dickson, 2001). The nature of the material and the fungal/actinomycete mycelia contained in the compost and stimulated in the soil by its application help to bind the soil particles into aggregates, greatly increasing the stability of the soil to wind and water erosion. Compost has a lower density, kg/m3 compared with typical manure that may be kg/m3. Handling is easier and fewer trips are made to the field. Weed seeds are reduced by a combination of factors including the heat of the compost pile, rotting and premature germination. (Any weeds found growing on the pile should be destroyed before they go to seed.) Composting Methods Making good compost depends on having the proper sources of nutrients with a balance of carbon and nitrogen, keeping the pile of compost moist and making sure that there is adequate aeration. The compost pile can heat up to C due to the microbial activity. However, high temperatures will result in substantial losses of nitrogen in the form of ammonia gas. The most commonly used materials for the compost pile are manure mixed with livestock bedding. When the bedding (which is predominantly carbon) is mixed with the raw manure (which is an excellent source of nitrogen), an optimal C:N ratio of between 25-35:1 can be achieved thus providing good conditions for the composting process to begin. Bedding materials vary in their carbon: nitrogen (C:N) ratio from about 80:1 in straw to 200:1 or more in sawdust or shavings. Bedding with a high content of wasted hay will have a lower C:N ratio. If the bedding: manure ratio is high, and the manure is very dry, it might be beneficial to water the material with a high N additive such as liquid manure imported from a hog operation. In practice, this is difficult to do Anaerobic Digestion Anaerobic Digestion is a possible alternative treatment method for the slurry produced on Højtofte. Anaerobic digesters produce conditions that encourage the natural breakdown of

48 organic matter by bacteria in the absence of air. Anaerobic digestion (AD) provides an effective method for turning residues from livestock farming and food processing industries into: Biogas (rich in methane) which can be used to generate heat and/or electricity Fibre which can be used as a nutrient-rich soil conditioner, and Liquor which can be used as liquid fertiliser How does Anaerobic Digestion work? The digestion process takes place in a warmed, sealed airless container (the digester) which creates the ideal conditions for the bacteria to ferment the organic material in oxygen-free conditions. The digestion tank needs to be warmed and mixed thoroughly to create the ideal conditions for the bacteria to convert organic matter into biogas (a mixture of carbon dioxide, methane and small amounts of other gases). There are two types of AD process. Mesophilic digestion - The digester is heated to o C and the feedstock remains in the digester typically for days. Mesophilic digestion tends to be more robust and tolerant than the thermophilic process, but gas production is less, larger digestion tanks are required and sanitisation, if required, is a separate process stage. Thermophilic digestion - The digester is heated to 55 o C and the residence time is typically days. Thermophilic digestion systems offer higher methane production, faster throughput, better pathogen and virus kill, but require more expensive technology, greater energy input and a higher degree of operation and monitoring. During the digestion process 30-60% of the digestible solids are converted into biogas. This gas must be burned, and can be used to generate heat or electricity or both. It can be used as heat for nearby buildings including farmhouses, and to heat the digester. It can be used to power associated machinery or vehicles. Alternatively, it can be burned in a gas engine to generate electricity. If generating electricity, it is usual to use a more efficient combined heat and power (CHP) system. A larger scale CHP plant can supply electricity to larger housing or industrial developments, or supply electricity to the grid (Anaerobic Digestion of Farm and Food Processing Residues Good Practice Guidelines). After digestion the residual digestate can be stored and then applied to the land at an appropriate time without further treatment, or it can be separated to produce fibre and liquor. The fibre can be used as a soil conditioner or composted prior to use or sale. The liquor contains a range of nutrients and can be used as a liquid fertiliser which can be sold or used

49 on-site as part of a crop nutrient management plan. There is also the potential for the liquor to be utilised within a precision agriculture variable rate nutrient management system (see section on Precision Farming below) if it has a high degree of uniformity Improving farm waste management Establishing an AD project does not eliminate wastes, but it can make them easier to manage. The AD process stabilises slurries (so they do not putrefy or create odour), which allows them to be stored more easily and for longer. Slurry handling costs are reduced because the digestate liquor is easier to pump than slurry due to the fact that it is less viscous. Traditionally, slurry has to be tankered on to the land which can incur contracting costs. A further advantage of the AD process is that digestion at high temps destroys virtually all weed seeds (Anaerobic Digestion of Farm and Food Processing Residues Good Practice Guidelines). There are also two aspects of financial incentives for developing an AD project: firstly in saving costs, and, secondly, by converting residues into potentially saleable products including biogas, soil conditioner, and liquid fertiliser. It can also contribute to the economic viability of farms, by keeping costs and benefits within the farm if the products are used on site. AD can also provide an on-site energy source, displacing their existing bought-in electricity (Anaerobic Digestion of Farm and Food Processing Residues Good Practice Guidelines) Nutrient Quality of the Digestate During AD, the more readily biodegradable materials found in the manure are broken down and immobilised by bacteria. As a result of this, digestate from an Aerobic digester has been found to be more stable than fresh manure and similar to humus in its organic-n makeup (Dahlberg et al. 1986). AD is effective at both preserving the N content of the manure and retaining it in forms useful to plants. On a total solids basis, digester effluent contains more N and a greater percentage of ammonium than undigested manure (Dahlberg et al. 1986). This increased concentration of ammonia N, which is readily available to plants, would seem to make effluent at least as effective as fresh manure in supplying N for crop growth. Pigg and Vetter (in Dahlberg et al. 1986), found that 93%of the nitrogen present in the manure added to a digester was still

50 contained in the digestate at the time of application to the soil. It has also been shown that AD results in less N loss than aerobic digestion. Dahlberg et al. (1986) showed that there was no yield difference in wheat when the crop was fertilised with anaerobically digested manure, compared to wheat yields from crops that were treated with either fresh or stored manure. The Organic-N levels for each of the manure types used were almost identical, however the digestate had a higher NH 4 -N fraction (3.8%) compared to the stored manure (2.1%) and fresh manure (1.6%). This increase in NH 4 -N can be attributed to the fact that when the solid portion of the digested slurry was reduced, the organic N contained within was converted to NH 4 -N. The table below summarises the benefits and disadvantages of a number of the manure management options described above

51 Table 4.2.1: Comparison of management options for farm residues. Derived from Department of Trade and Industry, Agriculture and Forestry Fact Sheet 2. November Option Merits Problems Anaerobic Digestion Good odour control. Energy production. Valuable digestate: fibre (soil conditioner), and liquor (liquid fertiliser). Continuous flow process. Improves storability. Ease of handling. Reduces spreading costs & methane emissions. High capital costs for full system. Operational costs. Needs to be integrated into whole business. Requires daily management. Composting of manures Alleviates nuisance odours if properly managed. Markets already in existence. Many organic wastes can be composted. Manure/solid residue storage Liquid residue storage Allows for better timing of applications to land, as the residues are stored and then spread when required. Convenient at cleaning out times. Low capital costs. Allows for better timing of applications to land, as the residues are stored and then spread when required. Convenient at cleaning out times. Bad management = odour problems and emissions. High marketing cost. Medium/high capital costs associated with requirement for covered yards and concreted areas. Management and operational costs. Rainfall causes effluent run-off and nutrient loss. Potential risk of pollution. Problems can occur with the capping of stores. Requires a powerful mixing system. Energy costs associated with mixing. Medium capital cost. Potential odour problems Nitrogen Utilisation and Mineralization of Compost, Slurry and Digestate The amount of nitrogen in animal manure is influenced by N mineralisation-immobilisation processes in the soil after manure application, and by losses of N due to NH 3 volatilisation and NO 3 - leaching and denitrification (Sørensen and Jensen, 1995)

52 It is difficult to predict the availability to plants of manure N since both N turnover processes and losses of manure N influence the availability. The net mineralisation of manure N is variable and there may be net immobilisation of N during a period following manure application, especially after application of anaerobically stored manures such as slurry (Kirchmann and Lundvall, 1993, in Sørensen, 2001). The N efficiency of slurry injected into soil has been reported to be higher than that of surface applied slurry. Sørensen and Jensen, (1995) found that incorporation of slurry N by simulated injection increased the plant uptake of total N compared to mixing the slurry into the soil. This difference in N efficiency is mainly due to a reduction in the volatilization of NH 3 from injected slurry (Thompson et al. 1987, in Sørensen and Jensen, 1995). However soil injection of slurry may increase the potential for denitrification Nitrogen mineralization needs to be considered when manure or compost are used as an N fertiliser source in a crop production system (Eghball, 2000). The amount of manure to be applied to a particular soil will depend on the nutrient composition of manure, the crop grown, and environmental conditions. Nitrogen pools in composted manure differ from those in noncomposted manure. In composted manure, most of the easily mineralizable N has already been converted to inorganic forms and may be lost, and the remaining organic N is in more stable N pools (Eghball et al. 2000). Furthermore, after the application of dry manure such as compost, the manure will be moistened by water transported from the soil, and initially there may be little transport of soluble compounds from the compost into the soil matrix (Sørensen and Jensen, 1998). By contrast, after application of slurry, soluble compounds in the slurry are quickly dispersed into the soil matrix, resulting in greater contact between decomposable organic material and the soil matrix. Hence, after application of compost the turnover of compost N is less influenced by the soil (Sørensen and Jensen, 1998). Sørensen, (2001).determined that soil effects on the net mineralization of manure N are mainly caused by different immobilisation/ remineralisation rates, i.e. different opportunities for the survival and turnover of soil microbial biomass and their metabolites, while the primary decomposition of the organic nitrogen compounds in manure is not significantly influenced by the soil type

53 In the case of field applied slurry, part of the organic N in manure may be lost shortly after application in the field if there are favourable conditions for ammonia volatilisation or leaching, or it may be used by plants or immobilised by microorganisms (Sørensen, 2001). However, there is often no net mineralisation of N due to the manure within the first weeks after application in spite of an intense turnover of manure N. Immobilisation and remineralisation of N are decisive for the net release of manure N during the first weeks of decomposition (Sørensen, 2001). Crop N use efficiency has been estimated in a number of studies. N use efficiency is greater for manure than compost application (Sørensen, 2001). Eghball (2000) showed that the percentage of N mineralized during the summer growing season following autumn application of composted beef cattle feedlot manure was about half that of non-composted feedlot manure - 21% of organic N in manure and 11% of organic N in compost. The lower N availability from compost reflects the loss of easily convertible N compounds during composting and presence of stable N compounds ( Westerman et al. (1985, in Dahlberg et al. 1986) noted that mineralization of organic nitrogen in the year of application may vary from 10 50%. The mineralisation rate is higher with higher temperatures. Further estimates of N use efficiency have been made by Gilbertson et al. (1979, in Eghball, 2000) who estimated that 40, 20, 10, and 5% of the applied N in FYM would be plant available in the first, second, third, and fourth years after application, respectively. However, Eghball (2000) found this assumption to be an overestimation of N availability from compost. N availability from compost was estimated at approximately 20%, based on plant N uptake in the first year of the experiment. Eghball (2000) determined that N availability from compost was in fact 20, 20, 10, and 5% for compost applied to the soil over a 4 year period. The utilization of slurry N can be increased in the 1st year by minimizing the contact between slurry and soil, provided that losses of N by ammonia volatilization and denitrification are also minimized (Sørensen and Jensen, 1998; Sørensen and Jensen 1995). Increased contact between slurry and soil results in increased immobilization of ammonium N (Sørensen and Jensen 1995) and faecal N in slurry, especially in fine-textured soils. The effects are probably due to an increased microbial assimilation of C and N when the contact between the manure and the soil is increased (Sørensen and Jensen, 1998)

54 2.4.4 Precision Farming and crop production Figure 4.4.1: Shows how precision farming works The picture above illustrates how modern technology is now integrated into a generalised farming system. In precision farming real-time or previously collected information about soil nutrient status can be sent to machinery involved in cropping operations from a satellite, thus allowing more precise operations, with minimal human intervention. Precision Farming is a management strategy that uses information technology to bring data from multiple sources to bear on decisions associated with crop production. The new agricultural system called site specific management (SSM), now more generally named precision agriculture (PA) is the start of a revolution in natural resource management based on information technology; it is bringing agriculture into the digital and information age. But it can also be seen as an evolution: more precise management (control) of soils and crops made possible by more precise information and new technologies. The basic principal of adapting soil and crop management to specific within-field conditions is certainly not new. But the continuous increase in field and farm size and bigger machinery in developed countries moved producers away from small-scale field variability. (Robert, 1999) Agricultural managers have for decades taken advantage of new technologies, including information technologies, that enabled better management decision making and improved economic efficiency of operations. The concept that is linked with precision farming is that it offers the promise of increasing productivity while decreasing production costs and

55 minimizing environmental impacts. The technologies and practices of precision agriculture offer the potential to fundamentally alter agricultural decision-making. Even though farmers know from experience that yields are higher in some parts of the field than in others, conventional management practices have focused on applying inputs at a uniform rate to an entire field. Precision farming may improve the farm profitability and reduce environmental spill over from agriculture. Potential improvements in environmental quality and reducing input cost to run a farm without sacrificing the yield or productivity may be an important reason for using precision farming technology. This view is due to strong belief that most of the environmental pollution occurs due to over use of synthetic fertilizers and manures. Calibrating input usage more precisely should increase the percentage of applied inputs taken up by the crop, therefore simultaneously reducing economic waste and emissions into the environment. Field level agronomic studies show that precision agriculture may permit large reductions in fertilizer and pesticide application rates without sacrificing crop yields Spatial and Temporal Variability The most significant impact that precision agriculture is likely to have on crop production systems is that it will aid management decisions based on time and space scales, rather than on actual production practices. Precision farming techniques have the potential to increase the efficiency of input use by allowing the producer to mange the crop on both a spatial and temporal basis with prescriptive rather than prophylactic treatments. The management of a crop production system involves many decisions, which are most of the time interrelated and in the end affect profit. Crop production is subject to uncertainty due to both stochastic processes (weather, external factors) and to unmeasured variability in agronomic conditions like soil fertility and structure due to percentage of soil organic matter. Soils vary significantly as a result of regional geological origin and past and present cultural practices. At the highest level of resolution, soil physical, biological and chemical properties vary vertically; horizontally; with treatment; and with time. For example, variable distributions of soil nutrients in the field may result from improperly adjusted mechanical application equipment (Bashford et al., 1996; Olieslagers et al., 1995)

56 In other cases, past practices such as an old feedlot or storage yard can generate local pockets of higher organic matter producing healthier plants than surrounding areas. This can also happen due to the slope of the field where lot of SOM is washed down due to erosion and the crops growing in that particular area of the slope suffer from nutrient deficiency whereas down the slope the crops yield better and are healthier. Thus natural variability pattern and management practices need to be considered in assessments of soil spatial variability Variable Rate Tecnology Variable rate technologies were introduced during the mid 1980 s. Dry nitrogen, phosphorus and potassium fertilizer application rates were simultaneously varied on commercial spreader applicators based on predetermined map strategy (developed from earlier data collection such as photographically derived soil maps or lab analysis of soil samples or grid sampling). The main advantage this system of precision farming is that an application plan for each location of the field can be achieved due to the variability of soil fertility for each location within the field. Variable rate technology can be used in slurry and manure application and the technology is developed for the advantage of application of manures at different rates for each location of the field. The main benefit of using this system is that the amount of manure that is added to the field can be controlled on a much finer scale. The manure is not added uniformly to the same filed but added at different rates depending on the need of the crop and the fertility of the soil. This way wastage of inputs such as manures, are kept to a minimum and the environmental effects caused by leaching can be decreased. However, this kind of technology can be time consuming and expensive in the initial stages but can deliver outstanding results when the system is up and running. The most widely used precision farming technique is probably the management of soil nutrients and ph. Precision management of soil nutrients can increase profit in two ways. The first is improved crediting of residual nutrients remaining in the soil after a crop is harvested. This works best for less mobile soil chemical properties such as phosphorous and potassium or ph. Nitrogen is more mobile and requires more frequent sampling to assess the appropriate credit levels. Nitrogen remaining in the soil after the harvest may be available to the next crop, unless temperature and rainfall conditions results in leaching or volatilization. More accurate crediting of residuals can reduce cost and environmental load where over

57 applications would have occurred, and can improve yields for locations that would have been under treated. Secondly, precision management of soil nutrients allows the producer to set variable yield goals for fields that do not have a uniform productive potential. With variable yield goals, inputs for a specific area of the field can be matched with the expected yield, and supplied at a more economically optimal level (Hergert et al., 1997). The evaluation of soil nutrient level across the field is performed by taking soil samples, analyzing them in the laboratory for their nutrient content, and interpolating values between the sampling points (Wollenhaupt et al., 1997) Sampling for soil characteristics has inherent problems with resolution and accuracy at non sampled location. With appropriate sensors available, real time technique can give data on a much finer scale, eliminating the need to estimate values and contribute to enhanced variable rate technology methods. Although few sensors are available, more capability, including fine scale resolution, for sensing important crop and soil parameters are needed (Hergert et al., 1997)

58 2.5 Crop rotation as a nutrient management tool Concerning nutrient management, leaching under uncovered soil with water surplus, is one of the processes, which can be influenced by the crop rotation, together with an appropriate nutrient supply for each crop. The possibilities to avoid uncovered soil in the wintertime are the growing of winter crops and cover crops. The latter term is used for catch crops as well as for green manures. These two possibilities of nutrient management are investigated in this chapter. The first part about cover crops is more general to enhance understanding of the interaction processes. Afterwards there are several systems described with the focus on the crops grown on the case farm Cover Crops in general Cover crops are non-commercial crops grown between the main crops; they are usually not harvested, but incorporated in the soil. Other reasons, to grow cover crops, than the prevention of leaching, are weed and pest control and the additional nutrient supply from green manures (Thorup-Kristensen et al., 2003). The main influence of the cover crops on the nutrient management are prevention of leaching and the Pre-emptive competition for the subsequent crop. Pre-emptive competition takes place when the supply of nitrogen from the cover crop to the subsequent crop is lower than the amount of non-leached nitrogen, which occurs without the use of a cover crop (Thorup- Kristensen et al., 2003). How intensive the prevention of leaching is and if pre-emptive competition takes place or not, is determined by similar factors. The abiotic factors are mainly the precipitation surplus during the winter, the soil type and the temperature. Precipitation and N-Leaching are positively correlated. With less precipitation the possibility of pre-emptive competition increases. The influence of soil type is mainly due to its effect on water and nutrient holding capacity (Burns, 1984 in Thorup-Kristensen et al., 2003). The temperature has an influence on microbial processes. Therefore it is important to know that the temperature influence on immobilisation is much higher than on mineralisation, which can result in high net mineralization at cool temperatures (Andersen and Jensen, 2001; Magid et al., 2001, Nicolardo et al., 1994 in Thorup-Kristensen et al., 2003)

59 The cover crops properties, which influence the nutrient management system directly, are mainly the N- uptake capacity, the N-release to the subsequent crop and the influence on other nutrients. The rooting depth and the cover crop establishment and growing period determine the N- uptake capacity. The rooting depth was found to be more important for the N-uptake than the rooting intensity. (Thorup-Kristensen, 2001 in Thorup-Kristensen et al., 2003). The rooting depth also determines the depth distribution of Nitrogen for the subsequent crop. The quality of the plant material and the kill date determine the Nitrogen release. The C:N ratio is the factor that determines if mineralisation or immobilisation takes place. The discussed balance point between a C:N ratio of 10 and 20. But other parameters like the lignin content, water solubility and the degradability of non-water soluble compounds have also an influence on the Nitrogen release. Also important is the distribution of the matter where mineralisation and immobilization take place and the possibility for the plant to interrupt the N transportation between these places with N-uptake from the root (concluded after Thorup-Kristensen et al., 2003). The kill date has an influence on the time of N-uptake before and the N-mineralisation after killing. There are two types of catch crops: winter hardy; and winter killed catch crops, the latter has a high variability of viability among the species (Thorup-Kristensen 1994b in Thorup-Kristensen et al., 2003). Cover, like every other crop, crops also have an influence on other nutrients. The influence of catch crops on Phosphorus can be, except the uptake before and the release after the kill date, to increase the availability due to root exudations of legumes (Jones 1998 in Thorup-Kristensen et al., 2003). Another advantage is the non-homogenous distribution after incorporation, which increases unavailability (Wang and Bakken 1997 in Thorup-Kristensen et al. 2003). The crucial aspects of the availability of phosphorus are already mentioned in the nutrient description. For potassium, calcium and magnesium it is possible to reduce the leaching by catch crops (Yanai et al. 1996, Jäggli 1978, Scott et al in Thorup-Kristensen et al. 2003). The release of these cations from the decomposing plant material is fast so that there is no fear of competition (Lupwayi and Haque 1998 in Thorup-Kristensen et al. 2003)

60 Sulphur has a similar behaviour in the soil to Nitrogen, so that catch crops can be a good method against leaching. The S uptake can vary a lot between the plant species, with the cruciferous plants having the highest uptake (Thorup-Kristensen et al., 2003). The biotic factors, can be influenced by the farmer with the choice of the plant species and the management system. For the plant species the focus here is on grass species and non-legume dicotyledonous plants, because the farm already has a nitrogen surplus and no need for additional nitrogen supply. There will be only a legume used for fodder production in the maize system. The way of establishment can be distinguished between sowing after the harvest of the main crop and undersowing. For cover crops, which are sown after the crop, there is the ability for a fast establishment and a certain growing period to ensure a certain N-uptake (Thorup- Kristensen et al., 2003). Typical catch crops that exhibit this behaviour include. grass and non-legume dicotyl species. For catch crops, which are undersown other properties are desirable including, slow juvenile development, low competition with the main crop and vigorous plant growth after harvest of the main crop (Karlsson-Strese et al., 1996). Plants with these properties where identified in Graminieae, Fabacea and other plant families. Another aspect for the decision is, how related the cover crop is to the main crop and if the pressure of certain diseases or weeds can increase due to their use. (Karlsson-Strese et al., 1996) The non-legumes have a higher N-uptake from the soil, but this also differs between grass and the non-legume dicotyl species, for several reasons. (Thorup-Kristensen et al., 2003). The main differences are the rooting depth and the nitrogen uptake capacity. The root development of dicotyl species is with 1,5-2.3 mm/day/ C while monocot species reach only 1,0-1,2 mm/day/ C. Also the maximal rooting depth, the rooting intensity and speed is higher for dicotyledonous species, for example, is the root development for dicotyledonous species are less dependent on temperature than monocot species. The nitrogen uptake capacity is also higher for the dicotyledonous species. Fodder radish can reduce a nitrogen concentration in soil water from 119µg/l to 1,5µg/l while ryegrass reduced it only to 61 µg/l (Thorup- Kristensen, 2001)

61 The influence that the monocotyl and dicotyl catch crops have on the main crop is now examined with a focus on barley The use of cover crops before and after spring barley Spring barley in rotation as well as in monoculture has the typical problem of uncovered soil during the winter season. Also there exists a lot of experience with undersowing because spring barley is often used as a main crop for the establishment of seed grass. The two aspects concerned here, include the establishment of catch crops after barley and the behaviour of barley after a catch crop. In a species screening for catch crops undersown in spring barley, there were species identified which increase the yield and also have a satisfying green matter production. These species were Red fescue (festuca rubra), Birdsfood Trefoil (Lotus corniculatus), White clover (Trifolium repens) and Chicory (Chicorium intybus). Some other legume species and a few very uncommon plants species also showed positive results (Karlsson-Strese et al. 1998). Even if the research above, found species which show good properties as a catch crop undersown in barley, the use of grass as a catch crop in farming and research is very common. The yield reduction for barley, due to undersown grass is estimated to be approximately 5-10% (Boelt 1997) Also much research has been done on the behaviour of barley after the incorporation of a grass catch crop. Until now, the focus on other catch crops has been minimal. Different results were found for the yield response of barley after an incorporation of a ryegrass catch crop. A good reduction of leaching, in this study 39kg, can be received with incorporation in spring, in combination with a slight decrease of yield (Hansen and Djurhus 1997). Other studies also showed decreasing soil mineral N contents, but only a slight response to leaching, after a ryegrass catch crop and spring incorporation. The highest yields were received after removal of the residues and ploughing in late autumn, but differences between an incorporation of the residues in autumn or spring was small. Barley was the only crop in relation to oats and spring wheat, which showed a positive response to a delay of the soil cultivation and a catch crop in combination (Stenberg et al. 1999). Higher yields and the reduction of leaching in the same cropping system where also found by (Thomson and Christensen 1998), but they also measured an increased leaching in the second winter after ryegrass incorporation

62 The differing results show the sensitivity interaction between the catch crop and the main crop. Grass species in general have a high Nitrogen uptake potential and a low decomposition rate, which makes the occurrence of pre-emptive competition likely. Another effect, which corresponds with these properties is the increase of leaching in the second winter after incorporation of a ryegrass catch crop (Thomsen and Christensen 1998). Even if the properties of brassicaceas as dicotyl plants differ a lot from grass species there where only slight differences in the yield response. Bodner and Liebhard (2002) found a yield reduction of 6% on average for mustard, phacelia and a cross breeding of brassica rapa (Perko). There were also no differences observed between winter killed and non winter killed species. The different properties of the species, like high and low nitrogen uptake capacity, for dicotyl and monocotyl plants, respectively, may be compensated by the differences in decomposability of the plant residues. This could be a reason for the similar results in relation to the yield. Another concern is the use of the cover crop for fodder production. Several brassica species, grass species, cereals, legumes and mixtures with different species, allow a cutting approximately 2-3 month after sowing in late summer. For all of them the time of sowing, usually at the end of July, determine the yield which differ between 3-4t dry matter. Most of the brassica species are less sensitive for sowing time, with sowing possible until the end of August (Oemichen 1986) Maize in a crop rotation The sowing and satisfactory establishment of a catch crop is more likely to occur when a cereal, rape or other early harvested crop is the previous crop for maize. While the influence on the yield was found to be very different, the reduction of leaching due to catch crops showed higher agreement within the studies. The yield response seemed to be strongly influenced by the area, the catch crop used and the cultivation system.results of Ruegg et al. (1997), show decreasing yields with phacelia and rye as catch a crop in

63 combination with minimum-tillage, in relation to ploughing without a catch crop. The difference between phacelia as a winter killed catch crop and the traditional ploughing systems was low, while the rye showed a strong decrease in yield, because the residues were removed and used for fodder. The addition of the rye and maize yield shows the highest total yield, which could be even better if the amount of nitrogen taken away with the rye, is taken into account with a higher fertilization of the maize (Ruegg et al. 1997). The research was made under wet conditions with 1000mm precipitation and the effect of the catch crop on its own can not be separated from the influence of the minimum tillage. The nitrogen leaching was significantly reduced under the catch crops, where rye was more successful than the phacelia. (Ruegg et al. 1997) The use of mustard (Sinapis alba) and Birdsrape mustard (Brassica rapa var. silvestris) between wheat and maize showed good results in the reduction of leaching. The N-uptake was nearly equal but had another time flow. Mustard has a very fast uptake in autumn which stops after the first frost, while Birdsrape mustard shows a N-uptake over the whole period. Under cold winter conditions there is almost no difference between the two crops and the inbetween incorporation in late autumn and spring in relation to mineralization. Under more temperate conditions Birdsrape mustard as well as the incorporation in spring reduce the mineralisation as potential of leaching more intensive. The response to yield had a high fluctuation, but there was a tendency to get lower yields in the system with catch crops and spring incorporation. The relative yield decrease with catch crops showed a response to an increase of the amount of manure applied in autumn. No soil cultivation showed low N mineral values of 15kg N/ha, even in May, that successful nutrition of the maize is not ensured (Burtin et al. 1998). The influence which was shown from the weather conditions, kill-off date, incorporation and N-supply from the soil corresponds with the general behaviour of catch crops described in the beginning of this chapter. Positive results were found by Weise et al. (1994) in Bodner and Liebhard (2002). Dicotyl catch crops shows 7% yield increase, particularly on sandy soils. Another approach to prevent leaching and soil erosion is the seeding with a rotary- cultivatordrilling combination in strips of living mulch, which is killed or reduced after maize emergence.the use of grass species required a high level of nitrogen supply (250kg inc. soil

64 N mineral) and herbicides to lower the competition to a level where 95% of the yield of the conventional system was obtained. With lower N supply and/or mechanical control of the grass, yield losses were higher than 15%- 30%. (Feil et al., 1997) Anken (2002) shows comparable results, but also found a lower utilization rate of slurry and only a slight difference in leaching in relation to the use of a plough. The use of legumes for this system seemed to be more successful, concerning the yield as well as the control of the mulch by herbicides. (Ammon and Scherer, 1996) Due to the lower nitrogen uptake capacity of legumes, the prevention of leaching could be less successful in the system. Independent from the soil cultivation, the combination of legumes and non legumes is seen as a possibility to reach both aims, prevention of leaching and the N-supply for the maize (Rannels et al., 1997). The importance of the water supply for the pre-emtive competition (Thorup Kristensen, 2003) makes the use of numerous studies from dry climate regions obsolete. As shown above several disadvantages are associated with the environmental improvement of maize cultivation systems. The biculture system combines several aspects to overcome these disadvantages. The system developed by Grass (2003) includes a previous crop in combination with directand late-sowing of maize. The growing conditions were in a climate with 8,7 C and 8,5 C mean temperature and 620 and 698 mm Precipitation on different loamy soils. The cropping system starts with the sowing of winter peas or a winter pea/rye mixture at the end of September/beginning of October. This crop is harvested between the second and fourth week of May. The direct seeding of the maize occurs immediately after the harvest. A total N- supply of 0, 40 and 80 kg was given 4 weeks later with slurry. Maize harvest occurs in the 1st-2nd week of October which is 2 weeks later than maize in a traditional system. The yield of the winter pea was around 5,7t/ha dry matter and for winter pea/rye mixture 6,4 t/ha dry matter. The maize yield was dependent on the N-supply and as the previous crop. The highest yields were shown at 80kgN/ha with winter peas as previous crop with a difference of 2t compare to the pea/rye mixture. Yields and the fodder qualities were comparable to the level of the yield in the traditional cultivation system (12t/ha dm)

65 Further differences between the previous crops are in the use and the behaviour after the harvest. Winter peas need to be mixed with grass to ensure quality silage production, while the pea/rye mixture can be fermented without additions. In the pea/rye mixture more weed control was necessary because the weed depression ability is lower and the rye can start shooting after harvest. But with both crops the need for weed control was reduced in relation to the traditional cultivation system. Nitrogen leaching over the whole cropping method and in the winter after harvest was lower in all cropping systems in relation to the traditional cultivation system. Factors contributing to the success of this system are the use of a winter hard, broad leaved pea variety e.g. the variety EFB 33; and a maize variety which is feasible for late sowing and have a short maturing process e.g. the variety Probat (Grass 2003) Management of grass leys The nutrient requirements and the positive effects of grass leys on the crop rotation due to an increase of Soil organic matter content and soil properties are already mentioned in the crop overview. Now, the focus is more on certain management of the grass leys in the rotation, particularly the time of break in and the N-release afterwards. Nevens and Reheul (2002) found a N release after the incorporation of o 3 year grass ley in spring, which was high enough to achieve optimal silage maize yields without additional fertilizer supply. In the second and third year after the ley a supply of 139kg and 154 kg N/ha necessary to obtain optimal yields, while the required fertilizer supply without a grass ley in the rotation was 20-30kg higher in maize monoculture. This considerable N-supply is probably not fully applicable for the conditions of the case farm, because the N fertilization of the ley in the trial was 240kg N/ha, which is more than 100kg higher than the MLNA-values for Denmark, and also there was additional grazing on the leys which reduced the nutrient export. However, there is an additional N-supply after ley ploughing which should be considered for the fertilization of the subsequent crop

66 Spring barley also shows satisfying yields after leys (Djurhus and Olsen, 1997; Linden and Wallgren, 1993). But the early nitrogen need of barley in relation to maize need to be taken into account. Another factor of concern is the mineralisation in the winter periods after the ley. A substantial risk of leaching was identified particularly after a high level of fertilization and in the first year. However, even with a low supply of 0 and 75 kg N/ha and in the second and third year, the mineralization was always higher than in the arable rotation (Nevens and Reheul, 2002). The differences between the leaching in the first and the second winter were found to be only kg after incorporation of a 3-year old grass ley followed by winter wheat (Cameron and Wild, 1984). Djurhus and Olsen (1997) showed that the leaching in the second year is dependent from the time of ploughing. The first winter leaching was higher after ploughing in early autumn, while the second winter leaching was higher after ploughing in late autumn. The lowest total amount of leaching over two years was identified with spring incorporation and spring barley followed by winter rye. Fyrthermore, yield was independent of time of ploughing. In a Swedish study, the mineral nitrogen corresponds better with the need of spring cereals after spring incorporation of the ley than after autumn incorporation (Linden and Wallgren 1993). The study also showed a low yield response and high response of leaching to the incorporation time. Incorporation in autumn followed by wheat showed lower fertilizer replacement values than after spring ploughing and maize. This was due to the low uptake of the wheat in autumn and a high mineralisation, which results in leaching (Johnson et al.1994 in Nevens and Reheul, 2002). N-leaching under winter wheat after autumn incorporation reached values of kgn/ha in the research by Cameron and Wild (1984). The studies which compare grass leys with clover grass leys, found higher yields after clover grass incorporation, which was mainly explained by a lower C:N ratio and a higher N supply (Linden and Wallgren, 1993; Djurhus and Olsen, 1997). This research indicates that maize and barley may be a good crop after ley ploughing in spring but these crops shouldn t be grown in monoculture afterwards, as the need of a plant cover in autumn is evident. Winter wheat and other winter cereals seemed to be unsuitable crops for the prevention of leaching in the first winter, but they can ensure plant cover in the second

67 winter. Also a small addition of fertilizer in spring could help to increase the initial decomposition resulting in a higher N-supply for the first crop, particularly for barley. 3 Materials and Methods 3.1The farm report Some data about Højtofte that is not given in the webcase can be found in the farm report, which is composed by studielandbrug (study-farms), which is a co-operation between the Danish research institute of food economics, the Danish institute of agricultural science and the Danish agricultural advisory service. The farm report contains information about the production system, economy, nutrient account and the crop and animal production etc. The farm report that is used in this project is from 2002 as is the data from the webcase. In 2002, 44 farmers participated and delivered information about their farms to studielandbrug, and from that data farm reports were made. 14 conventional and 12 organic dairy farms participate. The farm reports are mainly made for researchers and advisers, but the farmers can use the information to compare themselves to other farmers (Driftskontoret for studielandbrug 2003). Only the nutrient account for Højtofte and a comparison of the N- account of the 26 dairy farms will be used in this project. 3.2 The interview with Kim Ellebæk Hansen At a farm visit we asked our open questions to gain additional knowledge, which was not mentioned in the webcase. There was no particular method used and the results are used as additional information to the webcase. 3.3 The SUNDIAL model SUNDIAL (SimUlation of Nitrogen Dynamics In Arable Soils) was developed in It is a menu driven Version of the Rothamsted Nitrogen Turnover Model, which is based on the long-term field trials in Rothamstedt (Smith et al. 1996). In 1996 there where several additions planned, which are now included in the model (e.g. the choice of irrigation and soil cultivation parameters). For this project the version FRS-2.2 from July 30 th 2001 is used

68 3.3.1 Pools and flow diagrams The structure of the SUNDAIL model can be described with the following figure. Figure 3.3.1: Flow diagramm of SUNDIAL (Wu, McGechan; 1997). The two organic soil N- Pools are Humus and Soil microbial biomass. They are identified by a certain rate of decomposition, and a C:N-ratio of 8,5 as the turning point between mineralisation and immobilisation (Smith et al. 1996). The main influence factor for the flows between the pools is the climate, which is given as weekly values for Temperature, Precipitation and potential Evaporation. The Precipitation and the Evaporation is used in relation to the soil type to estimate the soil water content. Mineralization and immobilization are simulated with the C:N-ratio of each pool and a decomposition rate, which is influenced by the temperature and the soil water content. All flows between the pools are calculated as first order kinetics (dq/dt = -Kq). A further correction of the decomposition rate is done for the clay content (Wu, McGechan; 1997) Inputs The inputs in the N-simulation are the manure, fertilizer and deposition. Also the residues of the subsequent crop and the N-fixation of legumes are included. The crops are listed and can be chosen from a list. The manure type can be chosen from a list, but the nutrient content of the manures is given and cannot be described. The values for the different kinds of fertilizers

69 can be identified with the total amount of N-application. The user can also choose the deposition (Handbook SUNDIAL-FRS V2.1). Other information s for the model, which can be chosen by the user, include the soil properties, the soil cultivation and timing, additional weather data, atmospheric inputs, time under grass in the last 10 years and the expected yields (Handbook SUNDIAL-FRS V2.1) Output The outputs of the N-simulation are the N-output in yield, leaching and denitrification, volatilisation and gaseous losses. (Wu, McGechan; 1997) Leaching and denitrification are given together in one value, but is mentioned later in the project only as leaching, because this is the main part of the value under the present soil conditions. For the leaching and gaseous losses it is interesting to know that the SUNDAIL model uses only vertical transport processes and no horizontal movement. The soil profile is divided into four layers, of thickness 250 mm for the upper two and 500 mm for the lower two; the upper two layers are then subdivided into five slices each 50 mm thick. The water filling occurs in each layer until the water-holding capacity is reached before draining to the layer below. The same process in the opposite direction takes place during evaporation. The layer principle is also used for the calculation of the denitrification which can only occur in 0-250mm layer and has no influence on the nitrate content in the layer below. Volatilisation is identified by a certain percentage, which is volatilisated from the total N-application if ammonium sulphate or urea is applied with rainfall less than 5mm in the first week after application. The crop growth and N-uptake is simulated as a time flow without moisture and temperature (Wu, McGechan; 1997) Adapting to local conditions To ensure the model fitted to the local conditions, we used climate data from Funen in exchange of the data of one of the regions in the UK. We used corrected climate data for a particular year, which means that the distribution corresponds to a particular year, but the absolute values are adapted to the long-term average. The long long-term average values, were not chosen because they imply a more even climate than reality

70 3.3.5 Limitations The SUNDIAL model influences our observations and also has a few limitations. Firstly it is not possible to work in the model with undersowing and the crops seed grass do not exist. For this reason it was not possible to include the sequence with seed grass undersown in barley. However, the impact of the 3-year grass ley on subsequent crops could be included by choosing the number of the years under grass cover in the last ten years. Secondly it is not possible to identify the management practices of the previous crop (before the first crop). Problems also occur with the definition of the soil cultivation before the first crop, because each modelling starts with the sowing of the crop, and the soil cultivation of the subsequent crop refers to the crop before. Sometimes it was necessary to make a few changes in the cultivation dates, because the model does not allow the next cultivation until two weeks after harvest. The Nitrogen content of the dairy slurry and of the manure is lower in the standard tables for the model, than on the case farm. For that reason all application rates of slurry were multiplied with the factor 1,3 and for solid manure 1,5 to correct the differences in the content Modelled sequences As a first step we have modelled most frequently used sequences without seed grass. These can be seen in the table below. As a second step we have determined the areas of problems and put them in repeating sequences to reduce the influence from previous crops. Field Soil Previous crop 1. Year 2. Year 3. Year 4. Year 9-1 JB 2 maize Maize maize 11-0 JB 8 winter wheat winter wheat winter wheat winter wheat winter wheat 13-1 JB 8 sugar beet winter wheat maize winter wheat maize 13-2/3 JB 8 maize winter wheat sugar beet winter wheat maize 16-0 JB 6 maize winter wheat sugar beet spring barley 16-1 JB 6 maize winter wheat maize spring barley 19-0 JB 6 sugar beet winter wheat maize spring barley The cultivation practices for each crop where taken from the cultivation practices from 2002 given in the webcase. A detailed description of the inputs can be seen in the Appendix X

71 3.4 Methods for the precision farming experiment Eighteen soil samples were taken from field 13, at 9 separate locations, with 2 samples being taken at each location. There are 75 m between each sampling location and 1 m between the samples taken at the same location. The samples are distributed as shown on the map. The two samples at location one are named 1-1 and 1-2 etc. The samples have been taken to a depth of 25 cm depth. The field has a slope, which is situated so that plots 1,2 and 3 are at the top, plot 6,5 and 4 are directly on the slope and plots 7,8 and 9 are below the slope. N W E S Figure 3.4.1: Map of field 13, showing the distribution of the spots where the samples have been taken ph was been measured in a suspension of soil in 0.01 M CaCl 2 -solution, with a soil/solution proportion of 1 to 2,5. The Danish standard unit for ph is the Reaction number (Rt), which is defined as ph(cacl 2 ) + 0.5, and is the unit that we use (Plantedirektoratet, 1994). The C content was measured by burning the organic matter in an oven while oxygen is passed through, and the formed carbon dioxide is measured by an infra-red detector. The C, from which the carbon dioxide is formed, comes not only from organic matter but also from

72 carbonate. But as carbonate C is released later as the organic bounded C, it is possible to make a approximate distinction. The plant available phosphorus has been measured by use of the generally accepted sodium bicarbonate procedure for soils with ph > 5. In the procedure a single solution reagent, containing ammonium molybdate, asorbic acid and small amounts of antimony to react with P to develop blue colour was used. By using this method the phosphorus number (Pt), which is a Danish standard unit for plant available phosphorus, can be calculated. Pt is defined as exchangeable mg phosphorus per 100g soil (Plantedirektoratet, 1994). The exchangeable Potassium in the soil is released by extraction with ammoniumacetatosolution, and the potassium content is determined by flame-photometry. By using this method the potassium number (Kt), which is a Danish standard unit for plant available potassium, can be calculated. Kt is defined as exchangeable mg potassium per 100g soil (Plantedirektoratet, 1994). Double determinations for each sample for all four investigations were carried out. To analyse the differences between the samples at the same plot, the standard deviation between the plots have been compared to the standard deviation between the double determinations. Comparisons of ph, Carbon content and Phosphorous content were made in two directions: Treatments were compared down the gradient and across the gradient that naturally occurred within the sampled paddock (see figure below). For the treatments across the gradient, sampling sites 1, 2, and 3 were combined (A) and compared against the grouped data from sampling sites 6, 5, and 4 (B); sampling sites 7,8 and 9 were also combined into a single group (C) and compared against the previously mentioned groups (A and B). The data was also combined such that the sampling sites were combined and compared across the gradient. Group (D) consisted of the combined data from sampling sites 1, 6, and 7; group (E) consisted of data from sampling sites 2, 5, and 8; and group (F) was formed by combining the data from sampling sites 3, 4, and

73 A D Slope B E C F Figure. Grouping of Sampling sites for ANOVA across and down the slope 4. Discussion of Materials and Methods 4.1 The Farm report The Gårdrapport made the nutrient account of the farm, on basis of the farm and field level. According to Sveinsson et al., (1998) there are many different ways in to carry out nutrient accounting. But this point is less important for our project, because no comparison takes place with different studies. However, two tradeoffs were found during the project. Firstly there was a nitrogen loss for NH 3 treatment for straw of 888 kg N taken into account. In the interview with the farmer he gives us the information that he stopped the NH 3 treatment of straw one year before, but he wasn t sure. We leave this value in the calculation, because it influences the farm balance by only about 10kg N/ha. Secondly the values for the total N supply for the crop is higher than the values we calculated from the slurry amount given in the webcase. This may be due to the use of 5kg N/t slurry in the Gårdrapport and 4 kg N/t slurry measured by the farmer and reported in the webcase. The difference in the N-concentration reflect exactly the difference between the calculated values and the given in those Gårdrapport. To have a satisfying response to reality we used the concentration of 4kg N/t slurry for every calculation. 4.2 The SUNDIAL model SUNDIAL was used for the Analysis in order to find the weak points in the crop rotation, rather than estimate the absolute value. For that reason it seemed feasible for us to use weather data and cultivation practice from one year. The use of solid manure in the model results in a higher mineralisation and leaching, than was to expect from the literature. For that reason no interpretation about the use of solid manure on the basis of the SUNDIAL model

74 was done. Also we have taken the decision to model some of the sequences in repetition to reduce the influence of the previous crops for that the management practices cannot be defined. That this was necessary can be seen in the table where the real crop rotations were modelled. The reasons for the decision to use SUNDAIL only to identity the weak points instead of absolute values are discussed in the text below. For the response to the reality of a model, there not only is the correctness of each process important, but also the interaction between this processes. To prove this, the validation against real data from long-term field experiments is an appropriate way of testing. In such a validation in relation to three other models (CERES, NCSOIL, STICS) and real data, SUNDIAL was described to have a number of strengths and weaknesses The main weakness of SUNDIAL was found in an overestimation of the decomposition rate. Particularly the decomposition rate of the slow turnover pools were overestimated, which has a high impact on predicting the validity of long-term experiments as it can be seen in the top right of the figure (Gabrielle et al. 2002). In short term, SUNDIAL (and another model) was identified to give more realistic predictions than the other models, however it also produces an overestimation of nitrogen mineralisation in autumn. This was highly dependent on the soil type; SUNDIAL is able to include the influence of the clay content but fails in the estimation of the protective effects of high CaCO 3 contents. This can be seen in the differences between the pictures in top left and below, showing soil types with high and lower CaCO 3 content (Gabrielle et al. 2002). The problem with the overestimation of decomposition is that it has a higher influence on Carbon than on Nitrogen. The problem that it is not possible to simulate realistic dynamics for Carbon and Nitrogen, simultaneously occurs also in the three other models. Other problems were found by Rodrigo et al. (1997), where SUNDIAL was identified as having high and stable decomposition rates under changing soil moisture conditions and high values for the corresponding microbial activity in relation to the temperature. Another factor of impact could be the use of weekly averages for the climate data. Because it implies a more even climate, i.e. more even conditions for the microbes, than in reality

75 Due to the information above and the fact that the observed farm has no soils with a high Ca CO3 content (Halpic Calcisol) it is expected that the timing of the fluxes in nitrogen will correspond with reality. Simuleated (lines) and observed (symbols) time course of net mineralization in a long term trail in Rafidin (A) and surface (0-20cm) soil nitrate content in three different locations near Beauce. (Gabrielle et al. 2002) 4.3 Analysis of soil samples The analysis was made according to the standard methods mentioned in the Method description. The Potassium values are not used because many of the results show abnormally high K content in the soil, and furthermore they differ by a factor of 100. After finishing the analysis in the laboratory, we were informed that a lot of work with strong concentrations of potassium had been carried out prior to our use of the laboratory. The possibility that the samples were polluted was so high that we had to discard our results

76 5. Results and Analysis To analyse the nutrient management at Højtofte we will start at the farm level and take the nutrient account for 2002 (Driftskontoret for studielandbrug 2003), as a starting point because it gives an overview of the nutrient fluxes at the farm. To investigate where the losses actually occur the nutrient management in relation to crop rotation and manure handling respectively will be analysed. Also the result from the precision farming experiment will be analysed. 5.1 Nutrient account for the farm The nutrient account shows that the farm has a surplus of N, P and a deficit of K. The surplus of N can be interpreted as losses in the form of volatilisation, leaching, or as an increase of soil organic matter. The content of soil organic matter is highly correlated with management practices. There is a tendency for soil organic matter to decrease on arable soils as a result of intensive agriculture, as observed on the farm. However, a number of fields that make up the farm used to be managed without animal manure, but we don t know for how long. The intensive use of slurry and the seed grass leys in the rotation are would help to increase soil organic matter. However, as we have no measurements it is not possible to conclude if the amount of soil organic matter is changing. But as the N-surplus is high there is no doubt that most of the surplus may result in losses to the environment. The surplus of P is as described in the nutrient description, is most likely bound in the soil (unless the P binding capacity is used up, which we don t know). The P surplus is at a low level of 28 kg/ha, and cannot be seen as a problem, because some surplus is required to ensure available P for the plants. The K deficit at 29 kg/ha as seen in the short term is also no problem, because K is released from the soil minerals. But the weathering on sandy soils is much lower than on clay soils. At this stage it is impossible to determine whether the levels of P and K loss will become a problem inn the long term, because it depends on many factors that can be changed in the future. The farmer should be aware of the availability for the plants of both nutrients. Surplus or deficits in this dimension of P and K are not an environmental nor plant nutrition problem. The N surplus on the other hand is a problem. The N surplus at farm level is 186 kg/ha. To compare the average N surplus of the 14 conventional dairy farms participating in studielandbrugsbedrifter 2002 (Driftskontoret for studielandbrug 2003), is 175 kg N/ha, and

77 the 75% fractal is 189kg N/ha. So the farm does not have an alarmingly high surplus in relation to other farms. Also the 13 organic dairy farms that participated had an average surplus of 142 kg N/ha, and the 75% fractal is 150 kg N/ha. From these results it can be seen that it is possible to lower the surplus, but if we look at the yields at the conventional and the organic farms respectively, it is seen that the yields are lower at the organic farms. At the conventional farms 134 kg N/ha is removed on average by the crops, while only 112,5 kg N/ha is removed at the organic farms. The question is, is it possible to lower the N surplus without lowering of the yields. First it is needed to understand where the losses occur. The N surplus at farm level is as mentioned 186 kg N/ha, and at field level the surplus is 150 kg N/ha. The difference between farm level and field level is what is lost from the stable and by storage. This tells us that most of the losses are occurring at the field. 5.2 Nutrient management in relation to manure handling The Stable The stable being the initial stage of manure production was functional and adapted to the condition of reducing nutrient losses. The slotted floors were scraped 3 times a day and the faeces and urine were collected in the slurry tank. The practices the farmer followed within the boundaries of the stable could be recognized as good managerial practice to reduce any nutrient loss from the produced manure. The transportation of slurry from the stable to the slurry tank was through pipes. It is very common to have concrete or PVC pipes running under the stables to the tank and there is nothing of concern in this aspect of the manure handling process The Slurry Tank The slurry tank is quite old and rather outdated. The inlet pipe was fitted at the base of the slurry tank. However, the outlet pipe was fitted at the top, and as a result it protrudes through the surface crust. Researchers have shown that any disturbance to the crust can result in great loss of nutrient into the atmosphere through volatilization. The surface crust was very thin and at some places cracked which permitted a lot of gaseous loss of ammonia especially in the summer. This may be one reason why the farmer was complaining about N-reduction in the

78 soil in the last 3-4 years as he is actually losing a lot of N from the slurry during the storage (Kim Ellebæk Hansen, pers comm. 26 th April, 2004) Deep litter manure The farm used a relatively small amount of deep litter manure to supply the nutrient required of the crops. Spreading of deep litter manure was carried out once in 9 months, till then it was stockpiled. One reason was to reduce cost on hiring labour and other was to accumulate enough to spread the whole field Manure Supply to Crops Nutrient supply to the crops; the farmer supplied FYM during February for barley and supplied slurry for maize in spring which was ploughed in to reduce ammonia loss. Maize requires a high amount of nitrogen. However, slurry was applied only once and the main reason was due to limitations of application machinery, which might destroy the existing crops. The farmer expected to have achieved P and K from FYM and slurry for his crop while N and S were applied additionally in the form of synthetic fertilizer Sulphur Application To investigate if the amount of sulphur applied to the fields is sufficient, following calculations have been done. We have chosen to do the calculations on a maize paddock. Total S applied to a Maize field, where the previous crop was also Maize can be calculated by determining the amount of S contained in the applied synthetic fertiliser and slurry. S applied in fertiliser (NS 25-5) is 5kg/S per 100kg. S applied in Slurry can be calculated this way: For S content of slurry we will assume 10% DM slurry which gives an N:S ratio of 4.0:1.1 (Chambers et al. 2001). The slurry applied on Højtofte has an N content of 4kg/t. Taking the simple N:S ratio from above we see that for every 1kg of N present in dairy slurry, there is 0.275kg of S present. Therefore on Højtofte for every kg of N in slurry, 0.275kg of S is available. By a typical silage maize crop where the previous crop was silage maize 45t of slurry is applied plus 75kg of NS 25-5 at sowing time. That gives following calculations. S in NS 25-5 = 0.75 x

79 = 3.75kg S 4kg N/t slurry = 1.1kg S/t slurry 45t slurry x 1.1 = 49.5kg Total S applied = 49.5kg kg 53.25kg/ha Maize requires 24kg/ha as described in the from crop description. From this calculation it can be seen that the sulphur application is approximately 2.2 times greater than is required. However, this is only a rough estimation ; from these results it would appear that synthetic sulphur application in a back to back maize rotation is unnecessary, as there is more than sufficient S applied in the slurry. 5.3 Nutrient management in relation to crop rotation Nutrient losses in relation to crop rotation occur as leaching. The following is an analysis of the timing of, and with which crops the leaching at the fields occurs. As there is no general rotation plan at the farm the analysis will concentrate on frequently used sequences. In the interview the farmer only mentioned that he likes to grow winter wheat after maize and that he always use spring barley to establish the seed grass. On the sandy soils he prefers maize, because it shows the highest yields there. The SUNDIAL model will be used to indicate where the main problems are, but will be supported by knowledge from the literature review. The table below shows the modelled sequences, and the leaching that SUNDIAL calculated from the harvest of one crop to the harvest of the next. However in reality the main leaching occur from the harvest of one crop to the sowing of the next

80 Table 5.3.1: Modelled sequences and the leaching in kg N/ha. from the harvest of one crop to the harvest of the next. 1) Sugarbeet fertilised with solid manure. 2) Sugarbeet fertilized with slurry. Field Soil Previous crop 1. Year 2. Year 3. Year 4. Year 9-1 JB 2 Maize maize maize JB 8 winter wheat winter wheat winter wheat winter wheat winter wheat JB 8 Maize winter wheat maize winter wheat maize /3 JB 8 Maize winter wheat sugarbeet winter wheat maize JB 6 Maize winter wheat sugarbeet spring barley JB 6 Maize winter wheat maize spring barley JB 6 sugarbeet winter wheat maize spring barley The results shown in the table show no clear pattern, but the tendency for leaching is higher in spring crops. This corresponds with the literature, which says that leaching occurs when the soil is uncovered. The variation in this tendency is very high. For instance the leaching that occurs from the harvest of sugarbeet to the sowing of barley in field 16-0 is lower than for fields, which are covered with wheat in the wintertime, such as field If the same sequences are modelled for more years, on the other hand results show a lower variation and correspond with the literature. The reason for this may be that we remove the impact of previous crops and cultivation practises that Sundial does not allow us to change. For that reason we have picked out some interesting sequences that we have modelled for more years. Maize is one of the main crops at Højtofte, and for that reason it is important to analyse. Maize is both grown in rotation with other crops and in monoculture, but only for 3 years in succession. The following graph shows silage maize grown in monoculture for seven years on sandy soil. It is seen that after 4 years the curve for leached N has stabilized, and shows the same levels year after year. If we look at the stabilized part it is seen that about 90 kg N/ha is leached every winter between the harvest one year and short after sowing the following year. 90 kg N/ha is quite a lot. This is because maize residues contain a high concentration of N,

81 and when this N is mineralised, especially in the early spring, there are no crops to take up the N, as it is seen at the graph, and the soil Mineral N rises. Figure 5.3.1: Silage maize grown in monoculture for seven years What the graph shows corresponds with the literature, described in the maize description. For a comparison of two different crops grown in monoculture, we have modelled winter wheat grown in monoculture. The farmer grows winter wheat for up to five years in succession, but we have modelled for seven years as for maize. The modelling is done on a clay loam soil. The results corresponded with the table above. The leaching that occurs from the harvest one year until the following crop starts growing in the spring is about 40 kg N/ha. This is much less than for maize, and that is because the winter wheat plants have the capacity to take up the mineralised N during the winter and especially in early spring. We have tried to calculate both maize and winter wheat monoculture on both sandy and clay loam soil, to see if the soil type has a big influence, and it doesn t seem to, The leached N was approximately the same in both cases, so that is not the reason for the difference. The modelling for seven years clearly shows that the main leaching occurs in the wintertime, which correspondent with the common knowledge The crop sequence for field is: Silage maize winter wheat silage maize winter wheat silage maize. In this sequence uncovered soil occurs only every second year. The results from modelling of the sequence for 7 years on clay loam, is showed below

82 Figure 5.3.2: Winter wheat and silage maize grown alternately It is seen that high leaching occurs after winter wheat, about 100 kg N/ha and lower leaching occurs after silage maize, about 30kg N/ha. The low leaching after silage maize is because of the winter wheat which can take up the mineralised N. As wheat and seed grass are the only winter-crops grown at the farm, and as they are all together grown on only about 30 ha on average it is necessary to grow spring crops after each other. Table X gives an overview of sowing and harvesting dates for the crops Kim has. Table 5.3.2: Approximately sowing and harvest dates for crops grown at Højtofte Crop Sowing Harvest Winter wheat Early October Late August Spring barley Early April Mid August Sugarbeet Early April Early October Silage maize Late April Early October Sugarbeet and spring barley are the two other crops, which are sown in spring, and we have modelled the sequences in which they occur. The first is wheat sugarbeet maize and the other is wheat barley maize. The farmer has two different cultivation practises for sugarbeet, one where farmyard manure is used and another where slurry is used. It appears that the way SUNDAIL deals with farmyard manure does not correspond with reality so we have chosen the slurry cultivation. The results from the modelling of the two sequences is shown below

83 Figure 5.3.3: Crop sequence of winter wheat, sugarbeet and silage maize Figure 5.3.4: Crop sequence of winter wheat, spring barley and silage maize It is seen that to replace sugarbeet with spring barley shows good results. The reason for that is the late uptake of N by sugarbeet. This shows that not only the sowing time but also the time of uptake is important. As mentioned earlier, many combinations of crops are possible, but the factors, which determine how much N is leached, are the same as explained for the simulated crop sequences. The SUNDIAL analysis shows an agreement with the literature that N leaches when there are no plants to take up mineralised N. It can be concluded that the main problem at the farm is that only one of the grown crops is a winter crop

84 For the grass leys there is no modelling possible, for that reason, the analysis derives only from the literature. The detailed management of the crops is only available for 2002 in webcase, where no ley was ploughed in this year. In general, a ley accumulates soil organic matter and has for that reason a high mineralisation after ploughing. Ploughing in early autumn without a plant cover or only winter wheat, results in high leaching, which is already described in the literature review. As mentioned the different soil types don t seem to have a big influence on leaching if we believe SUNDIAL. But the fact is that there is a big difference, and there is a perceptibly higher leaching on sandy soils. This makes it even more important to have the soil covered in the wintertime. But as sandy soils are also poor soils very few crops produce satisfying yields. Maize is the only crop grown at Højtofte that shows satisfying yields, but as maize in monoculture leaves a long period with bare soil it is a problem on sandy soils, On the other hand maize has relative deep roots which decreases the problem somewhat. Another concern is, if the crop sequences are suitable, concerning the influence of rooting depth. As for cover crops, the influence of rooting depth is important for the crop rotation. For example if a shallow rooted crop is grown and the nitrogen is transported in deeper soil layers, a subsequent crop can take up the nitrogen if the rooting system is deep enough, but the speed of the root growth is also very important (Thorup-Kristensen, 1999). The crops which are grown now by the farmer only have a low variation in the rooting depth. However, maize with a less intensive rooting system, related to the other crops, makes the situation of an extended period of uncovered soil in the rotation even worse. In general the problem is more that there are no plants with a very deep rooting system in the rotation, however, the length of time the soil remains uncovered has a considerably higher influence. 5.4 Precision Farming Results An analysis of variance (ANOVA) was carried out on the data collected from the soil samples from Højtofte. No significant differences in ph, Carbon content, and Phosphorous were observed between the 2 soil samples taken at each of the sampling sites as was witnessed by

85 the very small S.D. values i.e. sample 1-1 was not significantly different to sample 1-2; sample 2-1 was not significantly different to sample 2-2; etc ph The greatest variation in ph was found to occur down the gradient. Group A had a significantly lower ph of 6.6 (p<0.001) compared to both group B (ph = 7.5) and group C (ph = 7.1). The values obtained for group B and C were also significantly different (p<0.001) to each other. This result is quite normal considering the positions of each of the treatments across the slope. Soils at the top of a slope are generally more highly leached due to rainfall infiltration and runoff and therefore have a lower or more acid ph value, as was observed. Soils situated further down the and at the base of a slope tend to be deeper and have a higher more alkaline ph values. However, in this case, the ph was actually more alkaline at the mid slope, rather than at the base. This may be due to the way that the farmer applied synthetic fertilisers over the area he preferentially applies more fertiliser over the slope than the rest of the paddock in order to improve the nutrient status of the soil in this area as I believe that it is lacking in certain nutrients (Kim Ellebæk Hansen, pers comm. 26 th April, 2004). The values obtained for ph across the slope i.e. for the comparison of groups D, E, and F were 6.9, 7.2 and 7.1 respectively. D had a significantly lower (p<0.001) ph value compared to F. However, a comparison of the ph values for E and F; and for D and E showed that no significant differences occurred between each of the two soil sampling groups. No significant differences in ph were expected to occur across the slope. However, the reason D had a significantly lower ph value compared to F may be due to the fact that the gradient down the hill where the samples from group D were taken was much steeper than the gradient for group F Soil Carbon Soil Carbon (SC) levels were determined to be the highest for group C which had a value of 1.6%C per weight, and occurred at the bottom of the gradient. The lowest value for SC was found within group B which had a value of 1.2%C per weight and was located at the mid point of the gradient. Soil Carbon levels were significantly different at each of the three levels

86 of the gradient i.e. Group C had a significantly higher SC value than both groups A and B; and group A had a significantly higher SC value when compared to group B. The distributions of SC levels down the soil slope are a little surprising, as it was anticipated that SC would increase from the top of the slope to the bottom. This was expected due to removal and re-deposition of the easily eroded SC from the upper slope down to the lower levels. However, our results indicated that SC was actually lowest at the middle of the gradient. The reason for this may again be attributed to the fact that this section of the paddock had a much steeper gradient compared to samples taken for groups A and C. No significant differences in Soil Carbon levels were found to occur across the gradient, with values obtained being 1.4, 1.4, and 1.5%C per weight for groups D, E and F respectively. This result was as anticipated prior to testing Phosphorous The highest Phosphorous (P) level of 5.7mg/100g soil was found to occur within group A at the top of the slope. The result for A was significantly different (p<0.003) to both groups B and C which had P levels of 3.2mg/100g soil and 3.5mg/100g soil respectively. There were no significant differences in P levels between groups B and C. The higher P levels at the top of the slope (group A) may be a result of the preferential nutrient applications carried out by the farmer, rather than soil formation processes. In the comparison of P levels across the gradient it was determined that group D had a P value of 4.5 mg/100g soil; group E a value of 4.0 mg P/100g soil and group F had a value of 4.0mg/100g soil. These results indicated that there were no significant differences in P levels when they were compared across the gradient. 6. Discussion of the recommendations for an improvement of the nutrient management One of the reasons why we conducted the farm visit and why we undertook the case study was to understand what is actually happening in the farm situation and whether the management practices are suitable to obtain optimal yields and also environmentally friendly

87 After a detailed study of the farm a number of areas where nutrient management practices could be improved were identified. The structure is according to the following system: At first the improvements are discussed which are feasible in the short term and require no fundamental changes or economical disadvantages in the farm system. They are briefly called Step 1 improvements. Secondly there are further improvements, which require more changes in the farming system e.g. ecological agriculture or have economical disadvantages to reach a further improvement. They are called Step 2 improvements. 6.1 Improvements for the Manure Handling Slurry tank The farmer needs to seriously consider building a new slurry tank with a cover and with an outlet valve at the bottom of the slurry tank. As noted, the outlet valve of the existing tank is situated at the top and penetrates through the crust. If the surface crust is not disturbed and the slurry is pumped out from the bottom, ammonia volatilization may be reduced by up to 20%. A cheaper alternative would be to install a proper roof- top according to the study conducted by Bode (1991). The farmer could use rapeseed oil surfaces, lids or PVC-foils to reduce transfer of ammonia from the slurry to the air. A layer of surface crust reduced ammonia loss rates with 80% compared to poor surface crust or no surface crust. This reduction was attributed to the development of a stagnant liquid and air layer in the surface crust Deep litter application The farmer uses deep litter manure to supply nutrients to his crop. The current practice is to apply the manure once in nine months and plough it directly into the soil. This system produces relatively large ammonia losses through volatilization and induces nitrogen loss through denitrification. Due to the use of cereal straw and sawdust in cattle sheds, the deep litter has a high C/N ratio and low content of inorganic N, so the N contained in this manure is available very slowly. The farmer has been complaining about low N content in the soil for in the last 3-4 years. This system of manure application might be one of the contributing factors leading to the loss of Nitrogen. The farmer needs to apply the deep litter manure at least twice

88 a year once in autumn and again in the spring so that nutrient losses from the manure during storage are minimized Slurry application Another important area where change is required is the pattern of slurry application in silage maize. The farmer applies slurry to his crop only once and applies the rest in the form of synthetic fertilizer. The farmer should inject the slurry using a direct injector systems to a depth of 10cm in the beginning of crop production (during sowing or seed bed preparation). A second application of slurry could be carried out directly onto the soil between the rows of the plants with hoses trailed on the surface of the soil. This system provides three benefits, the farmer can stop using synthetic fertilizer (both economic and environment benefit). Secondly, the maize is not damaged by application machinery because the drag hose lies on the surface of the soil and can be easily installed and removed the slurry can be pumped onto the field from a high pressure tanker that is outside the cropping area. And thirdly, the application timing of the N in the slurry can be better matched to the growing plants needs. This system of application of slurry between the rows of plants with hoses can reduce ammonia losses (Bless et al., 1991) and allow better timing of N supply to the growing plant. Furthermore, the efficiency of use of the N applied in the slurry is higher due to a reduction of wind speed due to the canopy of plants. The reduced wind speed with in the crop canopy will increase the gaseous ammonia concentration, by which leaf absorption of ammonia can be increased Soil testing The farmer does the soil test only once in 5 years but studies and observations prove that soil testing should be done, at least for residual nitrogen, after every crop. This practice can help the farmer to determine the amount of Nitrogen left in the soil after the harvested crop and work out the amount of nitrogen to be supplied to the next crop. Thus, over application of fertilizer can be eliminated, leading to a decrease in the input costs as well as improved environmental effects. Frequent sampling is not necessary for less mobile soil chemical properties such as phosphorous and potassium concentrations or ph. Nitrogen is more mobile and requires more frequent sampling to assess the appropriate credit levels

89 6.1.5 Alternative manure management strategies A number of different strategies for the treatment of the dairy slurry were put forward in the literature review above e.g. composting, anaerobic digestion, umbilical application etc. After considering the pros and cons of each of these methods it would appear that the current manure treatment of slurry anaerobic storage is probably still the best option for slurry management. Overall, more N can be directly applied using anaerobic storage conditions rather than composting (Thomsen, 2000). It has been shown that supplying N in non-composted anaerobically stored manure at a rate of two thirds of the N in composted manure to maize, resulted in similar yield levels. Similarly, Thomsen (2000), determined that applying N in anaerobically stored manure at a rate of 75% of the N level in composted manure to crops also resulted in similar yield levels. Consequently, compost may not be the best option for direct plant nutrition. However, the addition of compost every few years may help to further enhance soil structure and other soil physical, chemical and biological properties. Aerobic digestion was also put forward as an option, however insufficient quantities of manure are produced on the farm and the costs of implementing such a system may be inhibitive Sulphur management As can be seen in the results of the simple field balance above, Sulphur application in the form of Slurry is more than sufficient to meet the needs of maize production. As a consequence, there is no need for the farmer to be applying the extra S in the form of synthetic NS 25-5 fertiliser. This would mean a slight reduction in fertiliser costs as a straight N based fertiliser could be applied instead. In the case of Spring Barley, which requires (38)kg S per ha, the addition of synthetic S may still be required as only 30-40t/ha of Slurry is applied (i.e kg S/ha). This means that there may be a deficiency in S levels at the lower slurry application rate. Wheat does not receive any slurry treatment so synthetic S application is the only source of S for the crop

90 6.1.7 Precision Farming The results above show that there is sufficient variability in the soil chemical properties within the paddock that gives rise to the potential for the adoption of precision farming technology, namely Variable rate technology. The farmer is already aware that there are differences in the soil chemical properties of this paddock due to the gradient that occurs within. Currently, He applies the slurry and manure at a slightly lower rate across the paddock and then applies an extra sweep through the middle where the slope is most pronounced. This is a very imprecise method and may in fact be contributing to additional nutrient loss/wastage. If time and monetary constraints persist, it may be a worthwhile venture to further investigate the possibility of adopting precision farming technology such as variable rate nutrient management. This could be done with the use of a simple grain yield mapping device attached to a header at harvest in order to determine yield variability and hence, plant nutrient uptake. This information could be analysed and subsequently used to help determine nutrient requirements and management for future crops. The most common strategy in soil fertility management is to match fertilizer inputs with crop needs. The goals of this mass balance approach are to increase nutrient uptake efficiency and minimize fertilizer losses. However, the farmer could adopt variable rate technology techniques in the application of synthetic fertilizer instead of the current method of broadcasting. Synthetic fertilizers are mostly granular and dry and the nutrient content is very uniform, which makes it ideal for use in nutrient management as a part of a precision agricultural package. Fertilizer can be applied with site specific requirement of the field rather than applying a uniform rate throughout the field, thus saving on input costs. The soil analysis of the farm showed quite a lot of variability in nutrient status from location to location. This fact gives concrete conclusion that precision farming technology may effectively be adopted for the application of synthetic fertilizer. Since the farm is of medium sized, precision farming has the potential to reduce labour costs and improve productivity. Current, variable rate application technology for manures has not been very successful for a number of reasons including lack of homogeneity of nutrients within the manure; lack of appropriate technology; and economic reasons. At this stage variable rate application of manure appears to be unfeasible, however, research is being carried out in this field and results are looking promising

91 6.2 Improvements for the crop rotation As the problem analysis indicates that the biggest nutrient management problems, concerning crop rotation, are related to the bare soil in winter time the improvements are based on the prevention of bare soil in winter time. All recommended amounts of slurry are based on 4 kg N/t slurry and 0,7 utilisation rate, according to the method to calculate the MLNA values Maize One of the systems, which shows reasonable advantages for the environment and for the yield, was the biculture system with rye or pea/rye mixture as the previous crop for late and direct seeded maize. The fact that the climate conditions under that the research was made are comparable to the conditions on the case farm and that radiation and temperature are compensating factors are two reasons more to choose this system. Under the present conditions the use of the pea rye mixture seems to be more feasible, because there is no grass available for a mixture with pea to ensure a satisfying fermentation. The pea/rye mixture shows a 2t lower maize yield than the pea as a previous crop. If this difference is seen as a result of the lower nitrogen supply, an addition of ca kg Nitrogen could compensate this. This system require a seeding time between mid to late of September, therefore winter wheat, rape, spring barley and seed grass are suitable previous crops. For the same reason this system is not possible in a maize monoculture. The harvest of the late sown maize is approximately 1-2 weeks later than usual. For the reason of soil destruction under wet conditions it may be not possible to use the biculture system on the heavy JB8 soils. Another aspect is the time after harvest. The later the harvest, the more difficult it is to establish a catch crop (Burtin et al. 1998). Undersowing is probably not possible in this system because of water competition, due to the fact that the pea/rye mixture has already reduced the water supply for the maize. On the other hand, the residue N mineral values after harvest were lower than in the traditional system, because of the higher N uptake of the late sown maize later in the season. (Grass 2003)

92 However, the only suitable plant for growth after maize harvest, within the present farming system is winter wheat. Another possibility could be winter rye or triticale. The area of grown winter wheat is 15ha smaller than the maize area. With no changes in this, there is still an area with bare soil in the wintertime. A reduction of the maize area may be possible, due to the additional fodder production from the pea/rye mixture. Another crucial aspect is the nitrogen fixation of the peas, which could be between 40-60kgN/ha (Grass 2003). On the present maize growing area of 30 ha, this would produce an additional nitrogen supply of kg. When taken into account this can result in the reduction of mineral fertilizer use, fodder import or an increase of the saleable crops. Otherwise the N-surplus will increase and the system makes no improvement for the environment. Another possibility to have a covered soil in the winter time is the growing of maize after late autumn or spring incorporation of the ley. However, this system has no protection from soil erosion and leaching after the maize sowing. According to Nevens and Reheul (2002) maize yields are satisfactory after grass leys. The detailed management is discussed in the grass ley management below. The use of undersown grass in a maize monoculture and the use of catch crops like mustard, phacelia or brassica rapa in a wheat-maize rotation show no positive yield response Burtin et al. (1998), Büchter et al. (2001), Schröder et al. (1996). But the prevention of leaching was satisfying in these studies. Due to the extra costs for seed and cultivation, these methods are Step 2 improvements. Under conditions of ecological agriculture the Biculture system should be used with only pea as a previous crop because of the better weed control. This requires additional areas with grass to mix with the pea for silage production. Also it could be possible to make cops from the pea, but the farmer has indicated that this method which he already uses for the after growth cut of seed grass is too expensive. To leave the grass ley in stripes between the maize, like in the system developed by Feil et al. (1997), Ammon and Scherer (1996) results in lower yields and a higher herbicide use. For that reason it doesn t seemed to be a feasible method, even if the prevention of leaching and soil erosion is high in this system

93 6.2.2 Seed grass production In the seed grass production there are two parts for possible improvements. One is fertilization during the production; the other is the management of the ley breakdown. For an optimal seed production the application of slurry in autumn need to be reduced. The red fescue and the perennial ryegrass shouldn t receive more then 60kg N total/ha in autumn (ca. 20t slurry). The spring application can still remain in the beginning of March for the red fescue and in April for the perennial ryegrass. The application rate should be reduced to 50kgN/ha (18t slurry) for red fescue and 100kgN/ha (35t slurry) for perennial ryegrass. For the reed fescue there were no recommendations found. Due to the use of the seed grass for fodder with an after growth cut a higher amount of slurry seems to be appropriate. A yield of 1300 FU corresponds to 1,6t dm with an N-content of 3% (Foddermiddeltabel 1997). With these values there is at most 50kg N needed for the yield. An additional amount of 50kgN/ha can be given, which is recommended for the other grasses. The applied amount of ca. 163kgN/ha (40t slurry) can be so reduced to 100kgN/ha. If barley is used as a main crop to establish the seed grass, there is still the problem with uncovered soil. Good results where found by Boelt (1997) with the establishment in winter rape or winter wheat. The ley incorporation in late autumn or spring showed definite reductions of leaching in combination with spring crops in comparison to an autumn incorporation with fallow or winter wheat (Djurhus and Olsen (1997), Nevens and Reheul, (2002) Linden and Wallgren (1993)). For practical farming it is important which incorporation time is possible in relation to the soil conditions and a satisfying incorporation of the root mass. A late autumn ploughing was the usual practice for the cultivation for spring barley and seemed to be possible on the case farm. The possibility for spring ploughing unknown. Maize and Barley are suitable crops after ley incorporation; they show a positive or at least no negative yield response (Nevens and Reheul, (2002), Djurhus and Olsen (1997)). In the study of Nevens and Reheul, (2002) Maize showed high yields without any fertilizer supply. In our case a little supply of fertilizer seems to be necessary, because the seed grass receive lower amounts of nitrogen than the ley in the study mentioned above. Also important is the growing of winter crops or catch crops after the first spring crop, because the mineralization in the second winter is still on a high level (Djurhus and Olsen (1997)

94 6.2.3 Spring barley The growing of spring barley without undersown grass is possible after a ley, established 3 years before in spring barley, rape or winter wheat, is already mentioned above. If spring barley is used to establish the seed grass it s not recommendable to do so that directly after a seed grass period, due to weed problems (Fairey and Hampton 1998). Other possibilities are the use of catch crops, concerning the yield, the differences between the catch crops are very low, so that no one crop in particular can be chosen. The focus should then be on the crop rotation in general, as well as the possibility for establishment and the nitrogen uptake ability of the catch crop. For the former aspect the use of grass and cereal species is not the best choice because these species are already in the rotation to an extent of one quarter each. With the view on the establishment after or in the previous crop the options for maize are winter rye or undersown grass. If wheat or other cereals are grown the establishment of many species possible. Here a non-legume dicotyledonae would be most beneficial, because they have a higher N uptake capacity. Also it needs to be decided if the crop will be used for fodder or not. Due to the nitrogen surplus at the farm level it is recommended that additional fodder is produced instead of fodder import, if it is possible. Trafficability of the fields without soil destruction and the workload in relation to the output are probably the crucial factors for the decision. Rape (Brassica napus) Birdsrape mustard (Brassica rapa var. silvestris) and Fodder radish (Brassica oeleracea var. medullosa) can be used for fodder, where the former two are harvested in October, the latter can be cut in winter. Mustard, (Sinapis alba) Raphanus sativus oleiformis and Phacelia are only possible as a catch crop Introduction of rape In the interview at the farm visit, the farmer mentioned that he would like to grow oil seed rape in the future. The introduction of rape in the crop rotation has several advantages. Rape has a long growing season and covers the soil over winter. Rape also shows a positive response to slurry fertilization in autumn and spring (Oemichen 1986). To have one winter crop more in the rotation, reduces the periods of uncovered soil if rape is grown instead of spring barley. The

95 deep rooting system and the high N-uptake capacity also have a positive influence in the crop rotation, because N from deeper soil layers can be transported to the surface again. For seed grass, particularly red fescue, rape was seen as a better cover crop than spring barley (Boelt 1997). The optimal slurry application for rape is described in the crop description part The interaction between the ideas of improvement The improvements should be seen in relation to the other crops and the influence on the whole system. With the introduction of rape and the Biculture system for maize the areas for autumn spreading of slurry increase. This is the basis for a slurry application in low amounts to decrease the potential for leaching in wintertime. Also it enables lower fertilization rates to be used on the seed grass, which increases the potential for obtaining higher seed yields. The growing of winter wheat after every maize crop doesn t fit the ratios in which both crops are grown now as a part of the area will still remain uncovered. To grow winter wheat after maize, is more important when the maize is grown after the seed grass, because in the former the mineralization was with kgn/ha higher (Cameron and Wild 1984), than in the Biculture system with under 20kgN/ha in all years (Grass 2003). The surplus at farm level To make an overview about useful crop sequences and catch crops the following table is given

96 Table 6.2.1: Useful crop sequences without catch crops Suitable previous crops main crop useful subsequent crops comments spring barley, winter wheat, winter rape w.o. seed grass, seed grass winter pea/rye mixture + maize (biculture system) winter wheat (spring barley) spring barley is not the best choice, but better than for the sequence below seed grass, incorporated in late autumn or spring maize, normal system winter wheat spring crops shouldn t be used, because they result in high leaching winter rape seed grass 3 years, late autumn or spring incorporation spring barley w.o. undersown seed grass, maize late autumn or spring incorporation for the spring crops spring barley seed grass 3 years, incorporation after harvest winter rape w.o. undersown seed grass other winter crops with lower N-uptake cause N-losses (e.g. wheat) winter rape, spring barley seed grass 3 years, incorporation after harvest winter pea/rye mixture + maize (biculture system) there could be too much accumulation of SOM in this rotation, which can result in higher mineralization and leaching in the subsequent winters seed grass spring barley w.o. seed grass maize in the biculture system, rape, winter wheat maize in the biculture system spring barley with or w.o. seed grass maize in the biculture system, rape, winter wheat the sequence maize- spring barley still has uncovered soil in wintertime

97 Table 6.2.2: Useful catch crops for the spring crops in the rotation previous crops possible catch crops subsequent crops maize (normal system) rye sown after harvest, grass undersown in maize maize (normal system), spring barley winter wheat, spring barley Dicotyle catch crop species e.g. brassicaceas or Phacelia maize (normal system), spring barley The surplus at farm level In general there is not only the problem of preventing losses as the surplus on the farm is high in general. The improvements reduce the losses in the farming system, but they don t change the surplus at the farm level. All improvements in the storage and handling of the manure which increase the nitrogen content of the slurry, must result in a lower use of mineral fertilizer or a higher export of manure. Otherwise the source of losses is only shift from the storage to the fields. The reduction of leaching in the winter time does not result in a reduction of leaching in general, when the amount of applied nitrogen increases due to a higher N concentration in the slurry. The prevention of losses enables the farmer to reduce the N-surplus without yield losses, because the amount which was lost to the environment before can be now used for plant nutrition. The possibilities for a reduction of the farm surplus are the reduction of N-input or the increase of N-output in the farming system. The output can be increased with higher plant or animal production and is a very limited factor. The yields for each crop are already high, so the possibility to produce higher yields is very low. The only way for a higher plant production is a more efficient use of the whole growing period with cash and or fodder crops, as mentioned in the improvement part. Also the animal production is already at a high level. The inputs can be reduced with a lower import of mineral fertilizer combined with a higher export of manure. Both methods can be achieved relatively easily. Concerning the farm

98 balance, it would be better to reduce the import of mineral fertilizer, because the slurry contains other Nutrients which are needed for plant nutrition. A further option is to reduce fodder import and instead, increase fodder production in the farm system. This method only reduces the surplus if the amount of cash crops is not reduced. This is possible with the use of the whole growing period as mentioned above. 7. Conclusion After the careful investigation of the nutrient management at Højtofte, the following aspects were identified as the main problems: Firstly the nitrogen surplus at field and farm level is high, but typical for the stocking rate at the farm. The sources where the main losses occur are the storage of the slurry and the crop rotation. The slurry is stored in an open tank and shows a very weak and in parts even non-existent crust. This allows a lot of volatilisation of NH 3. The application rates of the slurry are generally high, because split applications are not used. Especially in autumn the application rates are higher than the plant needs. In relation to this it can be said that the area suitable for autumn spreading is too small, and/or the storage capacity for slurry is to low. Concerning the crop rotation there are possibilities for leaching due to uncovered soil in wintertime for the main crop maize and also barley. For the other nutrients there were no crucial problems observed, but the application of sulphur was identified to be unnecessary for most crops as adequate plant nutrition occurred from slurry application. The analysis of the soil samples showed a reasonable heterogeneity, which can result in over fertilization and deficiency in the same field. After investigating several systems used for the reduction of N losses, we identified the following improvements. The choice of the improvements was based on the following characteristics: The improvements needed to be feasible and useful for the farmer and the reduction of N-losses must be efficient and found to be significant in the research. To prevent the losses from the slurry storage it is necessary to close the surface of the old tank or build a new and closed slurry tank. A higher storage capacity is also needed to adapt the autumn spreading to the plant needs

99 The distribution of the slurry can be more even in autumn with the biculture system for maize and the use of catch crops. Also the fodder production can be increased within this system. The reduction of the application rate for maize and seed grass makes slurry supply for other crops possible and can result in a reduction of mineral fertilizer applications. Also split applications need to be considered. With the use of the suggested methods to reduce the losses, a reduction of the N-surplus becomes possible without a decrease of yield. The surplus on farm level can be reduced with a reduction or a stop of the use of mineral fertilizer, or the increase of the manure export. For future development, precision farming could be an option for the farm. However, as slurry is currently the main source of nutrients; a more precise application technique is required. Suitable technology does not exist at the present time; however the farmer can still pay more attention to the variability in his fields. 8. Perspectives As concluded, a reduction of nutrient losses from the farm is possible, indicating that there are still possibilities to improve the quality of ground and seawater. However, for these effects to be realised it is important that the farmer is motivated, whether economically or idealistically, to implement the changes. Generally speaking, idealistic motivation will not be enough as the changes would probably already be in place, as a result economic motivation is required. Some improvements at the farm will be readily implemented without incurring any economic disadvantages, some may even result in better returns than at present, for example improved manure utilization will mean that lower imports of nutrients will be required. However, some improvements may require large amounts of investment in both time and money; other improvements may in fact have a detrimental effect on farm income. If all the improvements suggested are to be implemented, then both idealistic and economic motivations need to balance each other out. If this is not possible and in this case it probably isn t, then changes in legislation may be required to ensure that the improvements and their associated benefits are adopted by the wider farming community. Perhaps the Action plan on

100 the aquatic environment III that is currently being developed could be a vehicle to drive the motivation for changes for the better

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107 Appendices Appendix 1 The webcase The case study is based on a webcase to be found at the Internet address To find the specific webcase, go to the front page and click WebCase Study Modules. Now six cases are lined up. Pick the case called Case Study of the Environmental Impact on a Danish Dairy Farm (The name of the cases appears when you hold the mouse at them) Click at the big yellow text and a short summary of the case study will show up. Different possibilities are now available (see the bar on top). In the project we have been using the information given in the Case description and Region and background. The Case description contain information about the farm itself, and Region and background describes the area, in which the farm is located, and informs about climate, soils, agriculture and environmental regulation in Denmark. A click at Case description brings you to the page partly shown below