Effects of Biochar Amendment on CO₂ Emissions from Paddy Fields under Water-Saving Irrigation

The role of carbon pool of biochar as a method of long-term C sequestration in global warming mitigation is unclear. A two-year field study was conducted to investigate the seasonal variations of CO₂ emissions from water-saving irrigation paddy fields in response to biochar amendment and irrigation patterns. Three biochar treatments under water-saving irrigation and one biochar treatment under flooding irrigation were studied, and the application rates were 0, 20, 40, and 40 t ha^-1 and labeled as CI + NB (controlled irrigation and none biochar added), CI + MB (controlled irrigation and medium biochar added), CI + HB (controlled irrigation and high biochar added), and FI + HB (flood irrigation and high biochar added), respectively. Results showed that biochar application at medium rates (20 t ha^-1) decreased CO₂ emissions by 1.64⁻8.83% in rice paddy fields under water-saving irrigation, compared with the non-amendment treatment. However, the CO₂ emissions from paddy fields increased by 4.39⁻5.43% in the CI + HB treatment, compared with CI + NB. Furthermore, the mean CO₂ emissions from paddy fields under water-saving irrigation decreased by 2.22% compared with flood irrigation under the same amount of biochar application (40 t ha^-1). Biochar amendment increased rice yield and water use efficiency by 9.35⁻36.30% and 15.1⁻42.5%, respectively, when combined with water-saving irrigation. The CO₂ emissions were reduced in the CI + MB treatment, which then increased rice yield. The CO₂ emissions from paddy fields were positively correlated with temperature. The highest value of the temperature sensitivity coefficient (Q₁₀) was derived for the CI + MB treatment. The Q₁₀ was higher under water-saving irrigation compared with flooding irrigation.