Fertilizer Management and Environmental Factors Drive N 2 O and NO 3 Losses in Corn: A Meta‐Analysis

Core Ideas Systematic review and meta‐analysis demonstrate key factors for reducing agricultural N losses. Nitrification inhibitors and side‐dress fertilizer N each reduce N 2 O losses by ∼30%. Temperature controls N 2 O emissions and precipitation controls NO 3 leaching losses. Higher levels of soil carbon reduce NO 3 losses, but increase N 2 O emissions. Lack of simultaneous data for N 2 Oand NO 3 impedes understanding of tradeoffs and synergies. Effective management of nitrogen (N) in agricultural landscapes must account for how nitrate (NO 3 ) leaching and nitrous oxide (N 2 O) 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 N 2 O (417 observations, 27 studies) and NO 3 (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 N 2 O and NO 3 differed by location, time period, and management practices. Meta‐analysis of side‐by‐side comparisons found significant yield‐scaled N 2 O emission reductions when SUPERU replaced urea or UAN, and when urea replaced anhydrous ammonia. Hierarchical regression models found near‐equivalent magnitude effects on N 2 O 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 NO 3 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 N 2 O and NO 3 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.