An agronomic assessment of greenhouse gas emissions from major cereal crops

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.