Strategies for Site Specific Fertilization in a Highly Productive Agricultural Region

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1 Strategies for Site Specific Fertilization in a Highly Productive Agricultural Region H.-W. Griepentrog M. Kyhn The Royal Veterinary and Agricultural University Dept. Agricultural Sciences / AgroTechnology Agrovej 10, DK - Taastrup Denmark hwg@kvl.dk Presented at the 5th International Conference on Precision Agriculture Minneapolis, USA, July 2000 Keywords: Precision farming, site-specific nitrogen fertilization, management strategies 1

2 STRATEGIES FOR SITE SPECIFIC FERTILIZATION IN A HIGHLY PRODUCTIVE AGRICULTURAL REGION H.-W. Griepentrog and M. Kyhn Department of Agricultural Sciences The Royal Veterinary and Agricultural University Copenhagen, Denmark ABSTRACT The eastern part of the county Schleswig-Holstein in northern Germany is region with high productive agricultural land use. Yields of 11 t ha -1 for winter wheat and 10 t ha -1 for winter barley are quite frequently achieved. The input of fertilizers and pesticides is high, e.g. total nitrogen applications of more then 200 kg ha -1 are common. The mostly hilly county is a landscape of terminal moraines. Extreme changes of soil properties and conditions within small areas are typical, and there is a strong correlation between soil properties and topography. Yield maps of fields show fluctuation between 5 and 16 t ha -1 for winter wheat and 5 to 14 t ha -1 for winter barley. Due to the heterogeneity of soils in this region there is potential to increase efficiency in crop production by using precision farming methods. We investigated different strategies to increase yield and/or decrease fertilizer inputs. Our results suggest that an increase in the already high yields by using site-specific fertilization is not possible. But that these yields can be maintained with a 36 % reduction in nitrogen inputs using precision methods. Obtaining high seed protein content with reduced nitrogen input seems to be problematic. Site-specific fertilization can increase efficiency and reduce environmental impacts in this region. Keywords: Precision farming, site-specific nitrogen fertilization, management strategies INTRODUCTION The objective of precision farming is to adjust agricultural operations to the varying yield potentials of sub-areas of fields. Variation in fertilizer dose rate according to local conditions can lead to an optimization of nutrient utilization. The site-specific yield potential is mostly determined by the attributes of the field but also by unpredictable weather conditions (Blackmore, 1994; Blackmore, 2000). Homogeneous soil conditions do not provide any optimization potentials 2

3 except plant protection and thus spatial optimization is not appropriate. Distinct heterogeneity implies there is potential for optimization and increased efficiency with precision farming. The improved spatial distribution of nitrogen is specially important because nitrogen has the strongest influence on yield, has a higher temporal and spatial dynamics, and can contribute to environmental pollution due to leaching. The eastern part of the county Schleswig-Holstein in northern Germany is a mostly hilly landscape comprised of terminal moraines. Large changes in soil properties and conditions within small areas are typical for this region. For example soil substrates are predominantly sandy loam to loam on cupolas whereas in depressions the substrates can have high organic matter content. This is a landscape with highly productive agriculture; 10 to 11 t ha -1 yields for winter wheat and winter barley are common. The input of pesticides and fertilizers is high and total nitrogen applications of more then 200 kg ha -1 are not unusual. High soil relief is characteristic for this landscape and most soil properties are strongly correlated with it (Basten and Lamp, 1989; Haneklaus et al., 1996). Such correlations have also been found in North America (Brubaker et al., 1993; Moore et al., 1993, Fiez et al., 1994; Bell et al., 1995). Yield variation within one field are recognized by farmers of this region. This variation arises due to the reaction of plants to different local resources such as the supply of water, nutrients and light. Crop plants respond to these varying conditions with different growth and development behavior. The heterogeneity of soils in this region suggests that there is potential for achieving improved economic results and reduced environmental impacts with precision farming methods. One of the perceived constraints on the adoption of precision farming techniques by farmers is the lack of readily available recommendations for management strategies for variable rate nitrogen fertilization. The objective of this study was to investigate different strategies by performing large scale field trials with site-specific nitrogen application. A second aim was to build these strategies on information systems applicable to farmers. METHODS AND MATERIALS The most important key variables for fertilizer recommendations for the considered region are the geomorphology and soil type characterized by texture, soil depth and organic matter content. These three parameters show the strongest influence on the nitrogen dynamic of soils (Basten and Lamp, 1989; Haneklaus et al., 1996). The slope and aspect in the terrain are important parameters for lateral and vertical water and, thus, nutrient fluxes. More than 95 % of nitrogen is bound in the organic matter which is therefore an important nitrogen pool. The clay fraction is the most important parameter of soil texture and is closely related to the water balance and potential vertical nitrogen movement.

4 Subdivision of fields To achieve an adapted treatment to varying conditions of a field it is necessary to achieve a subdivision of fields into homogenous or near-homogenous subareas. Because of the strong correlation between soil properties and soil relief a determination of sub-areas were based on relief categories. The sub-areas were categorized as plain, slope, cupola or depression areas. Furthermore, we distinguished between sub-areas of different clay content - heavy or light soil conditions - and different soil organic matter content. By using the relief categories and the estimate of soil type and organic matter content the farmer can easily do the subdivision by himself, thus minimizing the cost in money and time. Thus, the information utilized was mainly based on selfsurveys and existing data about field property variations. Field trials were carried out on a 36 ha field called Viehkoppel in 1996 and 1997 and on a 34 ha field called Achterkoppel in The relief elevations of both investigated fields show a high variation on short distances (Fig. 1, 2). It is obvious that soil development in this landscape occurs in response to the water movement through and over the soil surface. Therefore relief categories are a convenient parameter to characterize soil attributes. Fig. 1. Relief contour map of field Viehkoppel 4

5 Fig. 2. Relief contour map of field Achterkoppel Assessment of crop growth and nitrogen need The determination of the nitrogen requirement was based on plant growth and development and on yield potential, depending on regional historic and predicted weather conditions. The crop assessments on the fields were performed shortly before each fertilization application. Tiller rate and density were determined for the sub-areas. In order to rationalize this procedure, only some typical places per field were investigated. These data were then applied to the entire field. The objective was to achieve a particular tiller density depending on variety and weather, but especially relative to plant density, soil type and yield potential. The local commercial agricultural advisory service called HanseAgro assisted in the plant analysis of the sub-areas. This ensured the utilization of latest knowledge and experience about variety behavior and fungicide and herbicide applications. Pesticide applications were performed with constant dose rate. Yield mapping is an effective tool to monitor the efficiency of variable rate fertilization and also shows the heterogeneity of growth. It is therefore a useful tool to identify and optimize spatial varying growth conditions in a historical analysis. Spatial variation in yield potential can be estimated from perennial yield maps. These maps are an effective instrument to gather information about the annual removal of plant nutrients which is essential for P and K fertilizer recommendations. But this information is not the most appropriate for determination of the nitrogen need. Actual crop growth and development is more useful than mapped yield potential. For example the yearly influence of the variation in weather condition has more influence on crop growth than historic mean yield potential 5

6 maps can describe. Furthermore, for varying crop rotations it is difficult to determine yield potential variation for a specific crop. We based our nitrogen fertilizer recommendation on the key variables soil relief, organic matter and clay content (light vs. heavy soil type) in combination with the long-term experience of the farmer. Our hypothesis is that these more qualitative assessments and determinations can provide sufficient field information for introduction of site specific fertilization procedures. Without expensive soil-testing this strategy can be described as a soil relief oriented strategy (Lamp, 1987; Haneklaus et al., 1996). Tested fertilization strategies The following nitrogen application strategies were tested: (i) a variable high dose rate with a mean close to normal levels to ask if a variable rate can increase the crop yield, (ii) a variable low input application to try to minimize fertilizer input and keep crop yields high. To make the results comparable a conventional uniform application as the farmer usually performs was added. We also investigated the effect of how a variable dose rate application influences grain protein content of winter wheat. The crop rotation for the two fields was winter wheat, winter barley and winter rape or sugar beets, which is typical for this region. All crops are sown in autumn and harvested in July (barley) and August (winter wheat). Soil types were predominantly sandy loam to loam and the substrates change from normal to strongly high organic matter contents in depressions. Nitrogen was applied three or four times. Only two tramlines in each field were used for the variable low treatment. All the remaining tramlines were divided between the conventional and variable high treatments in an alternating pattern of two tracks for each treatment. Although the variable low treatment was limited to a smaller area than the other two treatments it was still 3.6 and 3.2 ha in Viehkoppel and Achterkoppel respectively. The working width of used implements and therefore the transverse distance between tramlines was 24 m. The data collected near where treatments overlapped were not used in the analysis. Equipment For the control and measurement tasks tractor, combine harvester and spreader was equipped with the necessary measurement technology. The fertilizer application was achieved by using a centrifugal twin disc spreader B2 from company Bredal, Denmark, with a working width of 24 m. The electromechanical dosage system of the spreader obtained the correct dose rate dependent on the position on the field. Tests have shown that spreading with triangular transverse distribution pattern, as found with centrifugal fertilizer spreaders, showed the least application errors, because the gradual increase or decline created by spread and overlapping corresponds with the wanted gradual transitions between parallel tramlines (Persson and Bangsgaard, 1999; Griepentrog, 1998). 6

7 The fields were yield mapped at harvest. Yield was measured in the combine harvester 4075 HTS from company Deutz-Fahr, Germany, with a cutting width of 5.3 m and a yield logging equipment LH 565 from company LH-Agro, Denmark. Positioning of the harvester during harvest is required and a DGPS system was used. The tractor was additionally equipped with special software to measure positions of tramlines and soil relief category demarcations. To achieve a high accuracy for elevation measurements on cm levels a Kinematic GPS, better known as RTK GPS, was used. RESULTS At the starting point in 1996 a conventional even distributed nitrogen fertilizer amount of 201 kg ha -1 was performed in Viehkoppel (Table 1). The variable high application had a mean of 183 kg ha -1 and the variable low application had a mean of 149 kg ha -1. From the entire yield data set the relevant data regarding to the strategies were extracted and analyzed. The results show that the yields of 11 t ha -1 were the same for all three treatments. Due to the different input of fertilizer the nitrogen productivity rate increased from 54 with a constant application to 74 with the low variable dose rate (Table 1). In 1997 the trials were continued. Based on the results from 1996 it was concluded that an increase of these already high yield levels due to variable nitrogen applications is not achievable. Therefore the aim was to keep the yield at high levels and to reduce nitrogen fertilizer inputs. In 1997 the trials were extended to the second field, Achterkoppel. The results show the same pattern as A reduction of nitrogen input by 23 % for barley and 20 % for wheat had no influence on mean yield levels (Table 2, 3). The variable low strategy achieved the same yield with the reduction of 30 % and 36 % in the two fields. Consequently, yield per unit nitrogen applied increased. Yield varied from 5 up to 16 t ha -1 for wheat and from 5 up to 14 t ha -1 for barley (Fig. 3). An important objective for wheat production in this region is to achieve a high content of protein, when special quality varieties are used. A conflict of aims emerged when considering strategies to decrease nitrogen inputs, because the last application is used to ensure high protein contents in grains. In 1997 the results for winter wheat were not satisfactory, because the mean protein content was too low. There was a relationship between last applied N amount and grain protein content (Fig. 4). 7

8 Table 1. Nitrogen fertilization strategies and yield for winter wheat Ritmo, Quarnbek, Viehkoppel, 1996 Strategies Conventional constant high low Applied nitrogen amount (kg ha -1 ) 201 (100 %) 183 (91 %) 149 (74 %) Yield (t ha -1 ) Nitrogen productivity * * kg grain per kg N Table 2. Nitrogen fertilization strategies and yield for winter barley Theresa, Quarnbek, Viehkoppel, 1997 Strategies Conventional constant high low Applied nitrogen amount (kg ha -1 ) 191 (100 %) 147 (77 %) 133 (70 %) Yield (t ha -1 ) Nitrogen productivity * * kg grain per kg N Table 3. Nitrogen fertilization strategies and yield of winter wheat Bandit, Quarnbek, Achterkoppel, 1997 Strategies Conventional constant high low Applied nitrogen amount (kg ha -1 ) 206 (100 %) 164 (80 %) 131 (64 %) Yield (t ha -1 ) Nitrogen productivity * * kg grain per kg N 8

9 Fig. 3. Frequency distribution of yield for fields and crops Fig. 4. Protein content of seeds versus last nitrogen application 9

10 DISCUSSION The smaller total dose rate of 183 kg ha -1 a reduction of 9 % - for the variable high application occurs mainly due to the fact that there was no or almost no nitrogen fertilizer given to the relief category depression with strongly high organic matter content. This category had a mean share varying from 10 to 15 % of total area of all fields. From long term experience it is known that nitrogen bound in soil organic matter is a high nitrogen pool which releases nitrogen latter during the vegetation and often leads to logging problems. Therefore a reduction of applied N at these locations ensures a reduction of nitrogen over-supply and its negative consequences. These sub-areas received nitrogen fertilizer only if any in the 1 st application within the variable high and low strategy at the beginning of the growth period in early spring. Thus, the nitrogen supply of the crop for the conventional constant and the variable high treatments are similar. For the agricultural region considered the yield levels achieved with conventional constant dose rate of fertilizer can not be increased by introducing variable rate nitrogen applications. rate application can reduce nitrogen input by up to 36 % while maintaining the high yields. The developed information system mainly based on soil relief categories and self-surveyed soil type classification combined with crop growth assessment procedures provides sufficient data to introduce variable rate fertilization in this highly productive agricultural region. Reduced nitrogen fertilizer application does lead to reduced seed protein content. So consistent reduced fertilizer input may be incompatible with high seed protein. Future crop management decisions regarding nitrogen fertilization need reliable actual information support about crop development and spatial crop property distribution. These are the most interesting challenges to achieving optimized nitrogen application. Improved and verified remote control sensing operations are promising tools today and will perhaps in future be able to provide the necessary information about plant growth. ACKNOWLEDGEMENT We would like to acknowledge Bredal, Denmark (disc spreader); John-Deere- Werke-Mannheim, Germany (tractor); Deutz-Fahr Erntesysteme, Germany (combine harvester); LH-Agro, Denmark (GPS and electronic components) and HanseAgro, Germany (advisory service) for support and assistance of the project. REFERENCES Basten M. and J. Lamp Zur Erfassung lokaler Stickstoffbilanzen am Beispiel eines ostholsteinischen Ackerbaubetriebes. Mitteilungen Deutsche Bodenkundliche Gesellschaft 59, p

11 Bell, J.C.; Butler, C.A.; Thompson, J.A Soil-terrain modeling for sitespecific agricultural management. p In: Site-specific Management for Agricultural Systems, ASA-CSSA-SSSA, Madison, WI, USA Blackmore, S Precision Farming - an introduction. Outlook on Agriculture 23 (4), p Blackmore, S The interpretation of trends from multiple yield maps. Computers and Electronics in Agriculture 26, p Brubaker, S.C.; Jones, A.J.; Lewis, D.T.; Frank, K Soil properties associated with landscape position. Soil Science Society of America Journal 57, p Fiez, T.E.; Miller, B.C.; Pan, W.L Winter wheat yield and grain protein across varied landscape positions. Agronomy Journal 86 (6), p Griepentrog, H.-W Overall fertilizer distribution. p In: Proc. Int. Conference on Agricultural Engineering, August 1998, Oslo, Norway Haneklaus, S.; Schroeder, D. and Schnug, E Strategies for fertilizer recommendations based on digital Agro Resource Maps. In: Proc. 3 rd International Conference on Precision Agriculture, Minneapolis, Minnesota, p Lamp J Prospects of soil information systems. In: Quantified land evaluation procedures, ITC, Publ. no. 6, Enschede, NL Moore, I.D.; Gessler, P.E.; Nielsen, G.A.; Peterson, G.A Soil attribute prediction using terrain analysis. Soil Science Society of America Journal 57, p Persson, K.; Bangsgaard, J Accuracy of fertiliser distribution for site specific fertilisation. p In: Proc. Precision Agriculture 99, 2 nd European Conference on Precision Agriculture, July Odense 1999, SCI, Oxford 11