Nutrient Management Research Database

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.

• Urban greenwaste compost was applied along with mineral N fertilizers to four different soil collected from across California
• The soils studied were of sandy or clay loam textures.
• Soil N2O emissions were measured along with ammonium and nitrate concentrations over the course of the 14 day laboratory experiment

• Compost applied to sandy soils increased N2O emissions from the applied mineral fertilizer
• N2O emissions from soil N, as opposed to the supplemental fertilizer N, was suppressed by compost application.
• Rates of N mineralization (organic N being broken down into plant available forms) and nitrification were increased by compost addition in the sandy soils but not in the clay loams.