Abstract
AbstractReducing nitrous oxide (N2O) emissions from agriculture is critical to limiting future global warming. In response, a growing number of food retailers and manufacturers have committed to reducing N2O emissions from their vast networks of farmer suppliers by providing technical assistance and financial incentives. A key challenge for such companies is demonstrating that their efforts are leading to meaningful progress toward their climate mitigation commitments. We show that a simplified version of soil surface nitrogen (N) balance—or partial N balance—the difference between N inputs to and outputs from a farm field (fertilizer N minus crop N), is a robust indicator of direct N2O emissions from fields with maize and other major rainfed temperate‐region crops. Furthermore, we present a generalized environmental model that will allow food‐supply‐chain companies to translate aggregated and anonymized changes in average N balance across their supplying farms into aggregated changes in N2O emissions. This research is an important first step, based on currently available science, in helping companies demonstrate the impact of their sustainability efforts.
Highlights
Agriculture is the dominant anthropogenic global source of nitrous oxide (N2O) emissions (Tian et al, 2019), a long‐lived greenhouse gas 265 times more powerful than carbon dioxide
With multiple N fertilizer rates, treatments at this site provided a large range in measured N balance and allowed us to explore the impact of changes in N balance under otherwise constant conditions
We emphasize N balance over N fertilizer rate because it (i) better conforms to theoretical relationships between N application, crop growth, and N losses, (ii) has been shown by others to outperform N fertilizer rate as a predictor of N2O emissions, and (iii) is more acceptable to farmers, whose business and stewardship interests tend to be aligned with improving N balance
Summary
Agriculture is the dominant anthropogenic global source of nitrous oxide (N2O) emissions (Tian et al, 2019), a long‐lived greenhouse gas 265 times more powerful than carbon dioxide. As companies seek to reduce their overall GHG emissions (Krabbe et al, 2015), food suppliers using sustainability platforms such as Walmart's Project Gigaton look to translate improvements in agricultural management on their sourcing farms to changes (reductions) in N2O emissions. Nitrous oxide is most commonly produced in agricultural soils through the microbial processes of nitrification and denitrification (Butterbach‐Bahl et al, 2013) Rapid response of these microbial processes to variations in the environmental factors governing N2O emissions
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