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.

Luck versus Skill: Is Nitrogen Balance in Irrigated Maize Fields Driven by Persistent or Random Factors?

The nitrogen (N) balance (i.e., the difference between N inputs and grain N removal) provides an indication of potential N losses to the environment. The magnitude of the N balance in a given year reflects the influence of random (e.g., climate, pest outbreak) and/or persistent (e.g., producer skills, soil type) factors over time. We assessed here the degree to which variation in magnitude of N balance across irrigated maize fields in the US Corn Belt was explained by persistent factors and identified the underlying drivers. Fields with large N balance were identified in specific ("ranking") years, and these same fields were assessed in other ("nonranking") years. Persistent factors explained up to half of the variation in N balance, with 70% of fields with N surplus in a given year also exhibiting surplus in other years. Persistence in large N balance was associated with fields growing maize continuously and applying higher N inputs without any yield advantage compared with other fields. There was also a relationship between N balance and mismatch between producer actual and recommended N rate. These findings highlight available room to reduce N excess in producer fields via improved management, providing a starting point to set priorities and inform policy.

The Nitrogen Balancing Act: Tracking the Environmental Performance of Food Production.

Farmers, food supply-chain entities, and policymakers need a simple but robust indicator to demonstrate progress toward reducing nitrogen pollution associated with food production. We show that nitrogen balance-the difference between nitrogen inputs and nitrogen outputs in an agricultural production system-is a robust measure of nitrogen losses that is simple to calculate, easily understood, and based on readily available farm data. Nitrogen balance provides farmers with a means of demonstrating to an increasingly concerned public that they are succeeding in reducing nitrogen losses while also improving the overall sustainability of their farming operation. Likewise, supply-chain companies and policymakers can use nitrogen balance to track progress toward sustainability goals. We describe the value of nitrogen balance in translating environmental targets into actionable goals for farmers and illustrate the potential roles of science, policy, and agricultural support networks in helping farmers achieve them.

Crediting agricultural soil carbon sequestration.

Regional consistency is necessary for carbon credit integrity.