Abstract
High nitrogen (N) input is typical of irrigated intensively managed dairy pasture systems, but the plant uptake of the applied N is often low. This leads to high nitrate (NO 3 − ) accumulation in the soil which, under wet conditions, can trigger significant loss of N as nitrous oxide (N 2 O) and dinitrogen (N 2 ). We investigated the effect of soil moisture [60, 80 and 100% water filled pore space (WFPS)] and NO 3 − concentrations (45 mg and 80 mg NO 3 − -N kg − 1 soil) on emissions of N 2 O and N 2 by applying 15 NO 3 − -N as a tracer in laboratory conditions using soil from an intensive dairy pasture. The flux of N 2 dominated N loss at 80% and 100% WFPS and N 2 O emissions were more strongly affected by NO 3 − concentrations compared to N 2 emissions. N 2 O emissions responded more strongly to NO 3 − concentrations at 100% WFPS than at 80% WFPS. The flux of N 2 O was significantly lower at 60% WFPS compared to the other WFPS levels, with no detectable N 2 emission. Denitrification dominated N 2 O emissions at 100% WFPS, whereas at 80% WFPS, contributions from denitrification and other sources were similar. These results demonstrate that while managing soil moisture and NO 3 − availability can reduce N 2 O emissions in intensive dairy pastures, substantial fertiliser N losses as N 2 are likely to persist, limiting improvements in overall N use efficiency.