Meta-analysis of yield and nitrous oxide outcomes for nitrogen management in agriculture.

Improved nitrogen (N) use is key to future food security and environmental sustainability. While many regions still experience N shortages, agriculture is the leading global emitter of N2 O due to losses exacerbated by N surpluses in other regions. In order to sustainably maintain or increase food production, farmers and their advisors need a comprehensive and actionable understanding of how nutrient management affects both yield and N2 O emissions, particularly in tropical and subtropical agroecosystems. We performed a meta-analysis to determine the effect of N management and other factors on N2 O emissions, plant N uptake, and yield. Our analysis demonstrates that performance indicators-partial N balance and partial factor productivity-predicted N2 O emissions as well as or better than N rate. While we observed consistent production and environmental benefits with enhanced-efficiency fertilizers, we noted potential trade-offs between yield and N2 O emissions for fertilizer placement. Furthermore, we observed confounding effects due to management dynamics that co-vary with nutrient application practices, thus challenging the interpretation of the effect of specific practices such as fertilization frequency. Therefore, rather than providing universally prescriptive management for N2 O emission reduction, our evidence supports mitigation strategies based upon tailored nutrient management approaches that keep N balances within safe limits, so as to minimize N2 O emissions while still achieving high crop yields. The limited evidence available suggests that these relationships hold for temperate, tropical, and subtropical regions, but given the potential for expansion of N use in crop production, further N2 O data collection should be prioritized in under-represented regions such as Sub-Saharan Africa.

Water and Temperature Stresses Impact Canola (Brassica napus L.) Fatty Acid, Protein, and Yield over Nitrogen and Sulfur.

Interactive effects of weather and soil nutrient status often control crop productivity. An experiment was conducted to determine effects of nitrogen (N) and sulfur (S) fertilizer rate, soil water, and atmospheric temperature on canola (Brassica napus L.) fatty acid (FA), total oil, protein, and grain yield. Nitrogen and sulfur were assessed in a 4-yr study with two locations, five N rates (0, 45, 90, 135, and 180 kg ha-1), and two S rates (0 and 17 kg ha-1). Water and temperature were assessed using variability across 12 site-years of dryland canola production. Effects of N and S were inconsistent. Unsaturated FA, oleic acid, grain oil, protein, and theoretical maximum grain yield were highly related to water and temperature variability across the site-years. A nonlinear model identified water and temperature conditions that enabled production of maximum unsaturated FA content, oleic acid content, total oil, protein, and theoretical maximum grain yield. Water and temperature variability played a larger role than soil nutrient status on canola grain constituents and yield.