Controls of nitrous oxide emission after simulated cattle urine deposition

Urine deposited during grazing is a significant source of atmospheric nitrous oxide (N2O). The potential for N2O emissions from urine patches is high, and a better understanding of controls is needed. This study investigated soil nitrogen (N) dynamics and N2O emissions from cattle urine, and effects of increasing urinary N to 1000 kg N ha−1 or delaying nitrification by amendment of the nitrification inhibitor dicyandiamide (DCD). Soil N2O concentration profiles and mineral N dynamics were monitored. The study was a randomized block experiment initiated in May 2012, in which urine deposition was simulated in paired field plots to accommodate all measurements. One plot had a pre-installed chamber support for N2O flux measurements. Volumetric water content (VWC) was determined in the same position in both sub-plots, i.e., with and without chamber supports. Plant growth was monitored using ratio vegetation index (RVI). Compared to unamended urine, emissions of N2O were significantly higher with urea-amendment, and lower with DCD amendment, also when expressed as proportions of N applied. Soil mineral N dynamics showed that N2O emissions were closely linked to nitrification activity. There was no close relationship between N2O emissions and concentration profiles of N2O in the soil; instead, emissions were significantly (p < 0.05) related to N2O concentrations at 5 cm depth. Chamber supports increased water retention in urine-amended soil, but not in reference soil. Based on patterns of mineral N and VWC it is proposed that nutrient retention and higher salinity in the presence of chamber supports increased water retention. This may have implications for the quantification of N2O emissions from urine patches.