Short-term measurement of N2O emissions from sheep-grazed pasture receiving increasing rates of fertiliser nitrogen in Otago, New Zealand

Abstract

The purpose of this short-term study was to investigate the effect of increasing fertiliser nitrogen (N) application rates on nitrous oxide (N2O) emissions over the late winter/early spring period from sheep-grazed pasture in Otago rolling hill country. We measured N2O gas emissions from plots on a mottled Fragic Pallic hill soil receiving 0, 100 and 500 kg N/ha.year for 2 years. Plots were sampled weekly for 10 weeks over the 2006 winter/spring period using a static chamber method. Increased N fertiliser rate and the attendant increase in stocking rate significantly increased total N2O emissions (P < 0.05). Total N2O emissions for the measurement period were estimated to be 0.08, 0.13 and 1.36 kg N2O-N/ha (s.e.m, 0.1, 0.18 and 0.45) for the 0, 100 and 500 N treatments, respectively. Our results suggest that high application rates of fertiliser N (i.e. 500 kg N/ha.year) and attendant increased stocking rates may significantly increase emissions of N2O even in dry winter/spring conditions in Otago rolling hill country. These results will assist in the development of best management guidelines for reducing N2O emissions from fertiliser N in hill country.