Nitrous oxide (N2O) is a potent greenhouse gas and a strong ozone-depletion substance. There is an urgent need to improve management of agricultural nitrogen to reduce N2O emissions from agricultural soils. A vast body of scientific research has investigated the impact of fertilizer-based management strategies, while fewer studies have examined the ecologically-based nutrition management practices (ENM) that manage carbon and nitrogen additions simultaneously and target multiple processes of the nitrogen cycle (e.g. the use of diversified rotations and cover crops). The objective of this work was to better understand the impacts of ENM practices and its interaction with environmental variables on N2O emissions through a meta-analysis, an on-farm experiment, and a 15N tracer experiment. I performed a meta-analysis on 596 pairwise comparisons (129 papers) to compare the efficacy of a wide range of management strategies. ENM practices generally had N2O emissions that were not significantly different from conventional fertilizer-based practices, however this outcome is based on a small number of studies and N was frequently over-applied in the ENM systems.
I also conducted an on-farm experiment to assess the interactive effects of landscape characteristics and management regimes. I monitored N2O emissions in two adjacent grain farms in upstate New York that have both undergone the same management for 20 years. I found comparable N2O emissions from winter bare fallow- maize phase in the fertilizer-based field and the legume cover crop (red clover)- maize phase of the cover crop-based rotation. The lowest emissions were found in the winter grain (spelt)- legume cover crop growth period of the organic rotation. The impact of landscape position on N2O emissions was only significant in the fertilizer-based field but not in the cover crop-based field. I conducted a 15N crop residue exchange experiment to measure the contribution of nitrogen from a clover cover crop to N2O emissions. The study found that the dominant source of N2O fluxes shifted from aboveground biomass to belowground sources (root-derived N and soils) around 7 weeks after incorporation. This study provided quantitative evidence that the belowground nitrogen was a significant source of N2O emissions after incorporating legume cover crops.