Core Ideas Systematic review and meta‐analysis demonstrate key factors for reducing agricultural N losses. Nitrification inhibitors and side‐dress fertilizer N each reduce N2O losses by ∼30%. Temperature controls N2O emissions and precipitation controls NO3 leaching losses. Higher levels of soil carbon reduce NO3 losses, but increase N2O emissions. Lack of simultaneous data for N2Oand NO3 impedes understanding of tradeoffs and synergies. Effective management of nitrogen (N) in agricultural landscapes must account for how nitrate (NO3) leaching and nitrous oxide (N2O) emissions respond to local field‐scale management and to broader environmental drivers such as climate and soil. We assembled a comprehensive database of fertilizer management studies with data on N2O (417 observations, 27 studies) and NO3 (388 observations, 25 studies) losses associated with 4R fertilizer N management in North American corn‐cropping systems. Only one study measured both losses, and studies of N2O and NO3 differed by location, time period, and management practices. Meta‐analysis of side‐by‐side comparisons found significant yield‐scaled N2O emission reductions when SUPERU replaced urea or UAN, and when urea replaced anhydrous ammonia. Hierarchical regression models found near‐equivalent magnitude effects on N2O emissions of 1°C rise in average July temperature (+), increase in soil C by 10 g kg–1 (+), nitrification inhibitors (–), side‐dressed fertilizer timing (–), broadcast fertilizer (–), and 100 kg N ha–1 decrease in fertilizer rate (–). Average NO3 leaching response to 100 kg N ha–1 reduction in fertilizer rate (–) were comparable to effects of 100 mm less annual precipitation (–), 10 g kg–1 more soil C (–), or replacing continuous corn with corn‐soybean rotations (–). The large effects of climate and soil, and the potential for opposite reactions to some management changes, indicate that more simultaneous measurements of N2O and NO3 losses are needed to understand their joint responses to management and environmental factors, and how these shape tradeoffs or synergies in pathways of N loss.

No abstract