Gaseous nitrogen losses from a grassland area used for overwintering cattle

Abstract

The grassland area where cattle overwinter was identified as an important point source of N 2O due to soil compaction and excrement deposition. The rates of N 2O emission were mostly directly related to the intensity of animal impact. However, laboratory measurements had shown a much greater potential for N 2O production from soil in a severely impacted site than indicated by field measurements, possibly due to factors affecting the mole fraction of N 2O. The 15N gas-flux method was used to measure the emissions of N 2O and N 2 at three sites along a gradient of animal impact. Over the experimental period (72 h), the loss of NO 3 −-N as N gases was 60%, 12% and 3%, and the mole fraction of N 2O was 0.04, 0.15 and 0.75 for the severe, moderate and control treatments, respectively. We hypothesize that soil pH, which is enhanced in impacted sites (from 5.7 up to 7.8), may control mole fraction of N 2O in such a way that under alkaline conditions most of the nitrogen escapes as N 2.