Improving fertilizer management in the US and Canada for N2O mitigation: Understanding potential positive and negative side-effects on corn yields

The potential for mitigation of N2O emissions arising from fertilizer management practices in corn systems has been scientifically assessed in recent decades. Given the strong association between fertilizer management and crop productivity, which to a large extent determines farmers' willingness to adopt such practices, it is essential to incorporate the impacts on yields before any mitigation practice can be recommended. Here, we address this issue by integrating available results via meta-analysis to quantitatively evaluate the effect of fertilizer management practices on N2O emissions and corn yields in the U.S. and Canada. The combined application of nitrification and urease inhibitors represented the best N2O mitigation option of the practices tested, and their use tended to lead to concurrent increases in crop yields. In comparison, polymer-coated urea was less effective at both reducing N2O emissions and increasing corn yields. Substitution of synthetic fertilizers by organic sources served to reduce N2O emissions but at the cost of significant yield penalties. Sidedress fertilizer applications rather than applying all the fertilizer at planting consistently increased crop productivity. No significant effects were found for the use of urea vs. ammonium nitrate or urea ammonium nitrate, nor for fall vs. spring fertilizer application. However, further research is needed to confirm these observations due to the highly variable nature of the data. Two key soil parameters were identified: 1) Soil texture; N2O and crop yield are highly responsive to fertilizer management in fine-texture soils; and 2) C/N ratio; mitigation of N2O emissions without concurrent yield reductions is most frequently achieved in soils with a low C/N ratio (i.e. <12.5). Our study provides a step forward in achieving an integrated understanding of the positive and negative side-effects of fertilizer management practices for N2O mitigation in agriculture. (C) 2016 Elsevier B.V. All rights reserved.