The cycling and volatile loss of N derived from cattle urine at upland and lowland sites, within the shortgrass steppe of eastern Colorado was studied, using 15N-labelled urea as an N source. Losses were higher from coarse than from fine textured soils. Immobilization and plant uptake of N accounted for significant amounts of added N. Extrapolating the plot measurements to a typical pasture, using spatially and temporally stratified urine deposition data, losses from upland sites were calculated to be 0.016 g N.m-2 .y-1, while losses from lowland sites were negligible. This resulted in an average loss of 0.011 g N.m-2 .y-1 for a pasture divided 70:30 between uplands and lowlands. The loss of urine N calculated, assuming no spatial stratification, would be sevenfold higher. The authors calculated a potential loss of NH30 from senescing vegetation of 0.26 g N.m-2 .y-1, an order of magnitude larger than all other losses combined.
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