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Nitrous oxide emissions and dynamics of soil nitrogen under 15N‐labeled cow urine and dung patches on a sandy grassland soil
Authors:Christine Wachendorf  Carola Lampe  Friedhelm Taube  Klaus Dittert
Institution:1. Institute of Soil Science, Hamburg University, 20146 Hamburg, Germany;2. Institute of Crop Science and Plant Breeding, Christian‐Albrechts‐University, 24098 Kiel, Germany;3. Institute of Plant Nutrition and Soil Science, Christian‐Albrechts‐University, 24098 Kiel, Germany
Abstract:Grazing animals highly influence the nutrient cycle by a direct return of 80% of the consumed N in form of dung and urine. In the autumn‐winter period, N uptake by the sward is low and rates of seepage water in sandy soils are high, hence high mineral‐N contents in soil and in seepage water as well as large losses of N2O are expected after cattle grazing in autumn. The objective of this study was the quanitfication of N loss deriving from urine and dung leaching and by N2O emission. Therefore the deposition of urine and dung patches was simulated in maximum rates excreted by cows by application of 15N‐labeled cow urine and dung (equivalent to 1030 kg N ha–1 and 1052 kg N ha–1, respectively) on a sandy pasture soil in N Germany. Leachate was collected in weekly intervals from free‐draining lysimeters, and 15N‐NOequation image , 15N‐NHequation image , and 15N‐DON (dissolved organic N) were monitored over 171 d. Furthermore, the 15N‐N2O emission rates and the dynamics of inorganic 15N in the upper soil layer were monitored in a field trial, adjacent to the lysimeters. After 10 d following the urine application, the urea was completely hydrolyzed, shown by a 100% recovery of urine‐N in the soil NHequation image . The following decrease of 15N‐NHequation image in the soil was higher than the increase of 15N‐NOequation image , and some N loss was explained by leaching. Amounts of 51% and 2.5% of the applied 15N were found in leachate as inorganic N, 2.4% and 0.7% as DON derived from urine and dung, respectively. Release of N2O from urine and dung patches applied to the pasture was low, with losses of 0.05% and 0.33% of the applied 15N, respectively. Overall loss of dung‐derived N was very low, but as the bulk dung N remained in the soil, N loss after mineralization of the dung needs to be investigated.
Keywords:ammonium  dissolved organic nitrogen  nitrate  nitrous oxide
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