Publication

Abstract : Field trials were conducted to study the emission of nitrous oxide during the summers of 2012 and 2013 from fields with harvested field pea, harvested wheat and winter fallow at Merredin and Cunderdin respectively, two wheat growing regions of Western Australia. The nitrous oxide emission fluxes from these treatments were regularly monitored during the postharvest summer period using a closed chamber technique, before and after wetting the soil. Very low nitrous oxide flux occurred in the dry soil conditions prior to wetting. However, significantly increased nitrous oxide flux was observed at both the sites after wetting, with emissions from a harvested field pea plots being 55–86 fold higher than prior to wetting at the two sites. After wetting, the field pea plots also had significantly higher emissions (3.47–3.87 g N2O–N ha−1 h−1) than those following winter fallow (1.17–1.95 g N2O–N ha−1 h−1), although no nitrogen fertiliser was applied to either during the crop growing period. The harvested wheat plots had emissions that were similar (1.18–3.15 g N2O–N ha−1 h−1) or higher than the winter fallow treatment. The sudden increase in nitrous oxide was observed 3 h after wetting, with a significant reduction in nitrous oxide flux occurring approximately 20 h after wetting. This indicates the need for regular monitoring of nitrous oxide flux to capture the emission pulses that occur under favourable conditions. Nitrous oxide flux was positively correlated with soil nitrate-N, water filled pore space and soil temperature at both the sites. The study shows that the use of winter fallow does not result in high soil nitrous oxide emissions over the following summer, compared with harvested wheat or field peas. The studies are important because more frequent summer rains are predicted in the region, and as shown in this study, high summer temperature together with rainfall could lead to nitrous oxide emission peaks.