Scientific registration n : 1754 Symposium n : 14 Presentation : poster. ERIKSEN Jørgen, ASKEGAARD Margrethe

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1 Scientific registration n : 754 Symposium n : 4 Presentation : poster Nitrate leaching in a dairy crop rotation as affected by organic manure type and livestock density Lixiviation des nitrates dans une rotation herbagère en fonction du type de fumure organique et du chargement ERIKSEN Jørgen, ASKEGAARD Margrethe Danish Institute of Agricultural Sciences, P.O. Box 50, 8830 Tjele, Denmark INTRODUCTION In Danish aquifers nitrate concentrations commonly exceeds the EC Drinking Water Directive upper limit of 50 mg/l (Duus Børgesen et al., 997). Reduction of nitrate concentrations requires decreased nitrate concentrations in water draining from the root zone into the aquifers. The source of leaching nitrate from the agricultural land is excess fertilizer N or mineralization of crop residues and soil organic matter. In order to achieve optimal yields and reduce the risk of nitrate leaching in the arable crops it is important that nitrogen added to the soil in plant residues and animal manure is available at the time of plant growth. Preferably, N mineralization in the soil should be synchronized with the consumption of N by plant uptake. Farms with dairy production usually have mixed cropping systems (pasture/arable) and during the pasture phase of the rotation, symbiotic N -fixation by clover can import large amounts of N. In the first year following ploughing-in of the pasture, N-fertilizer is not required but in the following years gradually more and more fertilizer N is required to achieve reasonable yields (Francis et al., 995). Thus, the mixed rotation can be divided into three phases with different specific objectives regarding nutrient management: i) the pasture phase where N -fixation is maximized to make nitrogen available in the system, ii) the years immediately after ploughing-in of the pasture, where nitrogen consumption by crops are optimized to maximize fodder production and to minimize nitrate leaching and iii) the following years where utilization of nitrogen in organic manures are optimized for the same reasons. The objective of this work was to investigate the effect of four types of organic husbandries with different livestock densities and different types of organic manure (slurry and deep litter) on crop yields and nitrate leaching in a typical dairy crop rotation.

2 MATERIALS AND METHODS Site The dairy crop rotation is located at Research Centre Foulum, in the central part of Jutland (9 34 E, 56 9 N). The soil is classified as a Typic Hapludult with 7.7% clay and.6% carbon. The fields were converted to organic farming in 987, where a six-year rotation was introduced as replacement of a conventional cereal rotation (Table ). Table: History of the dairy crop rotation at Research Centre Foulum Period Agricultural management system Mostly cereals; straw removal; inorganic fertilizer Organic dairy crop rotation; cattle slurry (-.3 LU/ha) undersown with grass-clover st year grass-clover nd year grass-clover /pea/ryegrass (wholecrop) Oats or winter wheat Fodder beets Organic dairy crop rotation continued with different fertilizer treatments ) Slurry (0.9 LU/ha) ) Slurry (.4 LU/ha) 3) + slurry (0.9 LU/ha) 4) + slurry (.4 LU/ha) Field trail In autumn 993 and spring 994 four organic fertilizer treatments in four replicates were established (Table ), replacing the previous slurry application equivalent to.3 livestock units (LU) ha -. The treatments represent two systems of cattle housing based on either slurry alone or a combination of slurry and deep litter at two livestock densities. Organic fertilizer was applied in spring and ploughed into the soil immediately after application, or by using trail hose application to growing plants. The difference between the 0.9 and.4 LU ha - systems were in average 40 kg of total-n (Table ). In the deep litter systems the major part of total-n was organic bonded and therefore not immediately plant-available. Each of the six fields in the rotation were divided into four blocks, where the four organic fertilizer treatments were present in plots of 5x8m. After one cut, the fields were grazed by cattle.

3 Table : Organic fertilizer application to the dairy crop rotation Slurry Slurry + deep litter 0.9 LU ha -.4 LU ha LU ha -.4 LU ha - kg total-n ha (50) 75 (90)., grass-clover undersown Slurry (80) 75 (90). st year grass-clover Slurry 3. nd year grass-clover Slurry /pea wholecrop Slurry Winter wheat Slurry (80) 70 (40) (90) (90) 6. Fodder beets Slurry Average ( ) Fertilizer application in 994. In the following years it was changed to avoid deep litter application to winter wheat in the autumn. Nitrate leaching In each of the 6 plots in each field three ceramic suction cups were installed before experiment start in a depth of m. Every or weeks, depending on precipitation, a suction of approximately 80 kpa was applied 3 days prior to sampling. During this period, the suction decreased as a result of water sampling. The samples were either analyzed separately or bulked for the three replicates per plot before analysis for nitrate concentrations. The water balance was calculated using the model Evacrop (Olesen and Heidmann, 990) where inputs were daily measurements of meteorological data (precipition, temperature and evaporation) and type of crop, time of sowing, cutting and irrigation and soil physical parameters. Nitrate leaching was estimated using the trapezoidal rule (Lord and Shepherd, 993), assuming that nitrate concentrations in the extracted soil water represented average flux concentrations. The accumulated leaching was calculated from April to 3 March. Climate In the three years climatic conditions were very different. In the period from April to 3 March of precipitation were above normal, and in below normal, resulting in a difference in drainage of approximately 500 mm (Table 3). 3

4 Table 3: Precipitation and drainage (mm) in the experimental years. Drainage was calculated as average of all crops. Year Precipitation Calculated drainage at m s depth April to Sept. Oct. to March April to 3 March Normal RESULTS AND DISCUSSION Yields Dry matter yields as average of the three experimental years are shown in Table 4. Table 4: Yields (t DM ha - ) as average of 994, 95 and 96. Treatments were: ) Slurry (0.9 LU/ha), ) Slurry (.4 LU/ha), 3) + slurry (0.9 LU/ha) and 4) + slurry (.4 LU/ha) according to Table. Yields in grass-clover are from the first cut, after which the plots were grazed by cattle. Treatment Grass-clover Winter wheat Fodder beets Grain Straw st yr nd yr /pea Grain Straw roots tops LSD Increasing the livestock density from 0.9 to.4 LU ha - increased yields in grain of barley and wheat, in the barley/pea wholecrop and in wheat straw. In contrast no significant yield differences were observed between slurry application alone and a combination of slurry and deep litter application. Nitrate leaching In Fig. is shown nitrate concentrations, calculated drainage volume and estimated accumulated nitrate leaching in one of the six fields in the rotation for the system with slurry application equivalent to.4 LU ha -. 4

5 40 Grass-clover /pea Winter wheat Bare soil NO 3 -N (mg l - ) Drainage (mm) Nitrate leaching (kg N ha - ) The example illustrates how nitrate leaching losses depend not only on soil nitrate concentrations, but also on the drainage volume, which was subject to considerable year to year variations. Thus, the estimated accumulated nitrate leaching from the in reached around 50 kg N ha - because of high drainage volumes with only moderate nitrate concentrations. In the extremely dry winter of nitrate concentrations under winter wheat was similar to the previous year, but due to low drainage volumes the estimated accumulated leaching losses was only a few kg ha -. After winter wheat in the winter , where the soil was kept bare, nitrate concentrations in soil water sampled at m depth increased to 33 mg NO 3 -N l -. Although the drainage volume was lower than that in the high nitrate concentrations caused leaching losses of around 50 kg N ha -. The estimated accumulated nitrate leaching losses was significantly (P<0.05) affected by the fertilizer treatments (Table 5). Thus, nitrate leaching was higher in the system with.4 LU ha - based on slurry than from both systems with 0.9 LU ha -. No significant differences were found between the combined slurry and deep litter system with.4 LU ha -, and any of the other treatments. In contrast to the small differences 5

6 between fertilizer treatments, large differences were found between crops. As average of the three experimental years, the highest nitrate leaching losses of 45 kg NO 3 -N ha - was found in the two crops following ploughing in of the grass-clover pasture. The lowest leaching losses (8 kg NO 3 -N ha - ) was found in the first year of grass-clover. Table 5: Estimated leaching losses as average of the three experimental years (kg NO 3 -N ha - ). Treatments were: ) Slurry (0.9 LU/ha), ) Slurry (.4 LU/ha), 3) + slurry (0.9 LU/ha) and 4) + slurry (.4 LU/ha) according to Table. Treatment a b 4 ac bc st yr 7 a 8 a a 8 a nd yr 47 ab 8 a 5 b 35 ab /pea 37 ab 54 a 40 b 5 ab Winter wheat 4 a 47 a 43 a 47 a Fodder beets 7 ac 34 b 7 c 8 bc Average Average Values with the same letter are not significantly different within the column 9 ab 3 b 5 c 3 bc As shown in the example in Fig. large differences in estimated nitrate leaching losses existed between years. Nitrate leaching, as average of the four treatments, and all crops, varied from 57 kg NO 3 -N ha - in to only 5 kg ha - in followed by 7 kg ha - in Table 6: Variations between years in estimated leaching losses as average of treatments (kg NO 3 -N ha - ). Coefficient of variation (CV%) in italics. Year st yr nd yr /pea Winter wheat Fodder beets (33) () () 3 0 (6) (68) (8) 79 3 (57) (63) (8) (8) () (30) (8) (0) () Average (6) (3) (0) Nitrate leaching from nd year grass-clover was high in the winter of , probably due to grazing of cattle after the first cut of grass. The random urination by cattle in patches with deposition of between 400 and 00 kg N ha - (Hack-ten Broeke et al., 996) may have been the cause of some very high nitrate concentrations measured in soil water sampled at m depth. For instance concentrations of 00 mg NO 3 -N l - were observed in one of four replicates in a short period, while at the same time concentrations in the remaining replicates were around 0 mg NO 3 -N l -. The large variations in nitrate concentrations caused the coefficient of variation on estimated accumulated nitrate leaching to be highest in the grazed grass-clover fields (Table 6). Nitrate leaching was only weakly affected by livestock density or type of organic fertilizer. Probably, this is the effect of the protective agronomic practices used, such as 6

7 spring application of slurry and deep litter, incorporation immediately after application and use of trail hoses when applying slurry to growing plants. The results are comparable to those of Johnson et al. (997), who in a five course crop rotation (barley-oilseed rapewheat-pea-wheat) found only limited effects of reducing the N application rate 50% in a system aimed at decreasing nitrate loss as much as possible. Leaching losses of nitrate were related to the ploughing in of the grass-clover pasture, and the largest leaching losses were observed in the two years following ploughing in of the pasture. It has been demonstrated that early autumn ploughing of grass-clover increases leaching losses compared to delayed ploughing in winter or spring (Francis et al., 99; Djurhuus and Olsen, 997). Our results showed that even when the grass-clover sward was spring ploughed there was a high risk of nitrate leaching in the following years in a typical dairy crop rotation. Future research will concentrate on the beneficial effect of catch crop strategies in such rotations. REFERENCES Djurhuus J. & Olsen P. (997): Nitrate leaching after cut grass/clover leys as affected by time of ploughing. Soil Use and Management 3: Duus Børgesen C., Kyllingsbæk A. & Djurhuus J. (997): Model simulations of nitrogen leaching from Danish agriculture (in Danish with English abstract). SPreport no. 9 from The Danish Institute of Agricultural Sciences. 66 pp. Francis G.S., Haynes R.J., Sparling G.P., Ross D.J. & Williams P.H. (99): Nitrogen mineralization, nitrate leaching and crop growth following cultivation of a temporary leguminous pasture in autumn and winter. Fertilizer Research 33: Francis G.S., Haynes R.J. & Williams P.H. (995): Effects of the timing of ploughing-in temporary leguminous pasture and two winter cover crops on nitrogen mineralization, nitrate leaching and spring wheat growth. Journal of Agricultural Sciences, Cambridge 4: -9. Hack-ten Broeke M.J.D., De Groot W.J.M. & Dijkstra J.P. (996): Impact of excreted nitrogen by grazing cattle on nitrate leaching. Soil Use and Management : Johnson P.A., Shephard M.A. & Smith P.N. (997): The effect of crop husbandry and nitrogen leaching from a shallow limestone soil growing a five course combinable crop rotation. Soil Use and Management 3: 7-3. Lord E.I. & Shepherd M.A. (993): Developments in use of porous ceramic cups for measuring nitrate leaching. Journal of Soil Science 44: Olesen J.E. & Heidmann T. (990): EVACROP. A program for calculating actual evaporation and drainage from the root zone. Version.0. Research note no. 9, Dept. of Agrometeorology, Danish Institute of Agricultural Sciences. 65 pp. Keywords : Nitrate leaching, organic manure, nutrient cycling Mots clés : lixiviation des nitrates, fumure organique, cycle, éléments nutritifs 7