A global synthesis of nitrous oxide emissions across cotton-planted soils

Globally, acquiring information on region- and crop-specific nitrous oxide (N₂O) emissions is vital for establishing effective N₂O mitigation strategies. Soil cultivated with cotton (Gossypium hirsutum L.) is an important source of N₂O in agricultural production. However, little is known about the magnitudes and main drivers of soil N₂O emissions from cotton fields worldwide. In this meta-analysis, we were the first to synthesize 34 peer-reviewed papers (298 observational datasets) to quantify the magnitudes and controlling factors of area-scaled N₂O emissions (N₂O_area), direct N₂O emission factors (EF_d), and yield-scaled N₂O emissions (N₂O_yield) from the soils of cotton fields and to explore associated potential mitigation strategies. On average, the N₂O_area from global cotton-planted soils was 2.10 kg N ha⁻¹, with a mean EF_d of 0.92 %, which is comparable to those reported for cereal crops (e.g., maize, 1.02 %) and the Intergovernmental Panel on Climate Change default value of 1 % for global croplands. The global mean N₂O_yield estimated here was 622 g N Mg⁻¹. At the global scale, the variations in all N₂O-related indices in the soils of cotton fields were demonstrated to be primarily controlled by climatic conditions (e.g. climate type) and soil properties (e.g., bulk density, pH, C/N or soil texture) rather than by well-recognized management practices (e.g., N fertilization rate). Furthermore, our analysis showed that the application of urease and/or nitrification inhibitors significantly reduced soil N₂O emissions while maintaining seed cotton yields. These findings emphasize that cotton production has an obvious climate footprint and provide potential N₂O mitigation options for the sustainable intensification of cotton production.