An agronomic assessment of greenhouse gas emissions from major cereal crops

TLDR

Agricultural greenhouse gas emissions account for about 12 % of global anthropogenic GHGs, and cereals—rice, wheat, and maize—provide the largest share of human calories, requiring a 1.3 % annual production increase to 2025 while also demanding consideration of cultural, ecosystem, and health factors. The study aims to identify how sustainable intensification of cereal production can maintain high yields while reducing environmental costs. A meta‑analysis of 57 published studies (62 sites, 328 observations) tested whether the global warming potential of CH₄ and N₂O emissions per ton of grain is similar across rice, wheat, and maize, and whether the lowest values occur near optimal yields. Rice exhibited the highest GWP for CH₄ and N₂O (3757 kg CO₂‑eq ha⁻¹ season⁻¹) and a yield‑scaled GWP about four times that of wheat and maize, with the lowest yield‑scaled GWP occurring at 92 % of maximal yield—approximately twice as high for rice—indicating greater mitigation potential in rice systems, while N₂O emissions represented 0.68 %, 1.21 %, and 1.06 % of applied N in rice, wheat, and maize, respectively, and no correlation between CH₄ emissions and N rate was observed in rice.

Abstract

Abstract Agricultural greenhouse gas ( GHG ) emissions contribute approximately 12% to total global anthropogenic GHG emissions. Cereals (rice, wheat, and maize) are the largest source of human calories, and it is estimated that world cereal production must increase by 1.3% annually to 2025 to meet growing demand. Sustainable intensification of cereal production systems will require maintaining high yields while reducing environmental costs. We conducted a meta‐analysis (57 published studies consisting of 62 study sites and 328 observations) to test the hypothesis that the global warming potential ( GWP ) of CH 4 and N 2 O emissions from rice, wheat, and maize, when expressed per ton of grain (yield‐scaled GWP ), is similar, and that the lowest value for each cereal is achieved at near optimal yields. Results show that the GWP of CH 4 and N 2 O emissions from rice (3757 kg CO 2 eq ha −1 season −1 ) was higher than wheat (662 kg CO 2 eq ha −1 season −1 ) and maize (1399 kg CO 2 eq ha −1 season −1 ). The yield‐scaled GWP of rice was about four times higher (657 kg CO 2 eq Mg −1 ) than wheat (166 kg CO 2 eq Mg −1 ) and maize (185 kg CO 2 eq Mg −1 ). Across cereals, the lowest yield‐scaled GWP values were achieved at 92% of maximal yield and were about twice as high for rice (279 kg CO 2 eq Mg −1 ) than wheat (102 kg CO 2 eq Mg −1 ) or maize (140 kg CO 2 eq Mg −1 ), suggesting greater mitigation opportunities for rice systems. In rice, wheat and maize, 0.68%, 1.21%, and 1.06% of N applied was emitted as N 2 O , respectively. In rice systems, there was no correlation between CH 4 emissions and N rate. In addition, when evaluating issues related to food security and environmental sustainability, other factors including cultural significance, the provisioning of ecosystem services, and human health and well‐being must also be considered.