Effects of gypsum application on grain yield and methane emissions in rice paddies: a global meta-analysis

Gypsum is a widely recommended soil amendment for rice paddies, but a meta-analysis of the responses of rice yield and greenhouse gas emissions to gypsum application has less been reported. In this study, a global meta-analysis was conducted to quantify the effects of gypsum application on rice yield and greenhouse gas emissions. The dataset was collected from 74 studies involving 382 pairs of rice yield observations, 39 pairs of methane emission observations, 10 pairs of nitrous oxide emission observations, 10 pairs of area-scaled global warming potential (GWP) observations, and 10 pairs of yield-scaled global warming potential (GHGI) observations, where the absence of gypsum acted as the control and the application of gypsum acted as the treatment. Based on a meta-analysis, the effects of gypsum application on rice yield and paddy CH₄ emissions were examined under different gypsum application measures (type and application rate), soil properties (pH, organic carbon content, and texture), and field management methods (N rate, irrigation regime, rice type, and experiment type). Overall, gypsum application significantly increased rice yield (+58%) and reduced CH₄ emissions (−47%), GWP (−22%), and GHGI (−31%), but did not affect N₂O emissions relative to those without gypsum application. The magnitude of the increase in rice yield and reduction in CH₄ emissions of desulfurization gypsum was significantly higher than that of gypsum and phosphogypsum. Applying gypsum increased rice yield at gypsum rates ≥ 2 t·hm⁻², while no significant effects were observed at gypsum rates < 2 t·hm⁻². The magnitude of the increase in gypsum application-induced rice yield increased with increasing soil pH. The gypsum rate and soil pH showed a positive interactive effect, whereby the increase in rice yield increased with the gypsum rate in the initial soils with pH ≥ 8.5 but remained stable at soil pH < 8.5. Gypsum application induced a reduction in CH₄ emissions with increasing gypsum application rate. Our results indicate that gypsum application could increase rice yield and reduce greenhouse gas emissions, providing a theoretical basis for evaluating the effects of gypsum application on high rice yield and mitigating global warming.