Synthesizing the evidence of nitrous oxide mitigation practices in agroecosystems

Abstract

Nitrous oxide (N2O) emissions from agricultural soils are the main source of atmospheric N2O, a potent greenhouse gas, and key ozone-depleting substance. Several agricultural practices with potential to mitigate N2O emissions have been tested worldwide. However, to guide policymaking for reducing N2O emissions from agricultural soils, it is necessary to better understand the overall performance and variability of mitigation practices and identify those requiring further investigation. We performed a systematic review and a second-order meta-analysis to assess the abatement efficiency of N2O mitigation practices from agricultural soils. We used 27 meta-analyses including 41 effect sizes based on 1119 primary studies. Technology-driven solutions (e.g., enhanced-efficiency fertilizers, drip irrigation, and biochar) and optimization of fertilizer rate have considerable mitigation potential. Agroecological mitigation practices (e.g., organic fertilizer and reduced tillage), while potentially contributing to soil quality and carbon storage, may enhance N2O emissions and only lead to reductions under certain pedoclimatic and farming conditions. Other mitigation practices (e.g., lime amendment or crop residue removal) led to marginal N2O decreases. Despite the variable mitigation potential, evidencing the context-dependency of N2O reductions and tradeoffs, several mitigation practices may maintain or increase crop production, representing relevant alternatives for policymaking to reduce greenhouse gas emissions and safeguard food security.

4R Research With Impact

“…In 44 site‐years of measurements on the Canadian Prairies, the use of such double inhibitors reduced emissions by 40% (M. Tenuta, personal communication), even without counting the rate adjustments possible from reduced total losses and higher N use efficiency with these products. This reduction figure roughly agrees with a recent global “meta‐analysis of meta‐analyses” (Grados et al., 2022), which found an average reduction of 49% for the same comparison. The use of a nitrification inhibitor on its own produces a similar reduction, but caution is encouraged when applied to urea because of the risk of increasing ammonia volatilization in some situations (Fan et al., 2022).…”

“…The use of a nitrification inhibitor on its own produces a similar reduction, but caution is encouraged when applied to urea because of the risk of increasing ammonia volatilization in some situations (Fan et al., 2022). For slow‐ and controlled‐release fertilizers, the reduction found was 33%, and for urease inhibitors, 23% (Grados et al., 2022). Thus, clearly it is possible through choices of “right source” to substantially mitigate nitrous oxide emissions, providing large value in the effort to move society to “net zero” in terms of emissions that affect the climate.…”

Literature Review, Meta-Analysis, and Mega-Analysis in Ecological and Agricultural Sciences

“…Biochar enhanced crop yield, reduced N 2 O and NH 3 emissions, but increased CO 2 emissions. Grados et al [35] conducted a systematic review to assess the N 2 O emission mitigation practices in agricultural soils using 27 meta-analyses from 1119 primary studies and found that technology-driven solutions such as enhanced-efficiency fertilizers, drip irrigation, and biochar and optimization of fertilizer rate have considerable mitigation potential. Agroecological mitigation practices such as organic fertilizer and reduced tillage may enhance N 2 O emissions.…”

Investigating tradeoffs in nitrogen loss pathways using an environmental damage cost framework

“…(Christianson et al, 2018;IEPA et al, 2015; Iowa impacts such as increased N 2 O emissions. Several synthesis studies have documented higher N 2 O emissions with cover crops as a potential tradeoff, up to 37% in a recent secondorder meta-analysis (Basche et al, 2014;Grados et al, 2022).…”

“…Given the lack of studies evaluating multiple N loss pathways in the same site‐year (Eagle et al., 2017), it remains unknown whether efforts to reduce NO 3 ‐N losses will have unintended environmental impacts such as increased N 2 O emissions. Several synthesis studies have documented higher N 2 O emissions with cover crops as a potential tradeoff, up to 37% in a recent second‐order meta‐analysis (Basche et al., 2014; Grados et al., 2022).…”