Role of green waste compost in the production of N2O from agricultural soils

The increasing use of green waste compost as an agricultural soil amendment requires an understanding of its role in influencing nitrous oxide (N2O) emission, particularly in managing these amendments on different soil types and cropping systems. We conducted a set of experiments to determine the influence of compost application on the pathways and sources of N2O production. 15N-labeled soil nitrogen (N) and fertilizer N were used separately in different soil types to differentiate the sources of N2O from compost, fertilizer and soil N and the different pathways of heterotrophic denitrification and ammonia oxidation. In sandy soils amended with N fertilizer + compost, total N2O emissions and nitrification rates, respectively, ranged from 1.4 to 2.9 and 0.2 to 16 times greater than soils amended solely with N fertilizer. In contrast, no significant difference in N2O emissions was found between compost and non-compost treatments in clay loam soils, likely due to the high capacity of these soils to buffer changes in biochemical properties such as nitrifier activity or pH. Compost application in sandy soils increased N2O emitted from both heterotrophic denitrification and ammonia oxidation by a factor of 1.2 and 2, respectively. In these soils, compost not only acted as a source of N for N2O, but also increased N2O produced from fertilizer (NH4)2SO4. However, N2O derived from soil N was suppressed by compost application, indicating that the overall N2O emissions could be decreased by compost application when applied to soil with high N2O production potential. Therefore, strategies to reduce the environmental impact of green waste compost and mitigate N2O emission from agricultural soil should potentially be aware that green waste compost application to sandy soils could increase N2O production, though further study is needed to predict a generalized response in coarser-textured soils.