Responses of nitrous oxide emissions and nitrate leaching to farm field management, climate, and soil characteristics: a meta-analysis

Abstract:

Agriculture is a major source of both nitrous oxide (N₂O) to the atmosphere and nitrate (NO₃^-) to surface and groundwaters, but synergies and tradeoffs between these nitrogen (N) loss pathways in response to agricultural practices are not well understood. We conducted a meta-analysis of both N₂O emissions and NO₃^- leaching losses to quantify their individual responses to fertilization rate, tillage, and other practices. Overall, we assembled over 40 studies that reported fertilization rate, yield, and either N₂O emissions or NO₃^- leaching losses over the growing season from North American corn fields. Our complete database ultimately included over 600 observations of N₂O emissions or NO₃^- leaching. Notably, we found no individual studies that reported both NO₃^- leaching and N₂O emissions. We used multiple regression to quantify the response of N loss pathways to fertilization rate; rotation crop and tillage practice; and climate and soil type. We also included yield as a predictor to better account for the magnitude of surplus N. We found insufficient data to address effects of fertilizer placement, timing and source. On a mass basis, NO₃^- losses were far greater than N₂O emissions. Both NO₃^- leaching and N₂O emissions exhibited positive relationships with fertilizer rate and surplus N, but the responses of N loss pathways to environmental conditions and to various management practices varied considerably. These results suggest that minimizing excess fertilizer application will both improve water quality and reduce greenhouse gas emissions, but that other practices such as tillage induce tradeoffs between these N loss pathways.