Biochar Effects on Rice Paddy: Meta-analysis

Rice is staple for nearly half of the world population. Biochar (BC) improves crop yields, reduces greenhouse gas (GHG) emissions, and immobilizes heavy metals in the soil. This study was aimed to meta-analyze the data from the published articles focused on the various BCs’ effects on rice yield, soil acidity, GHG emissions, and bioavailability of Cd and Pb. The data of pyrolysis temperature, application rate, and feedstock of BCs were categorized by using the MetaWin software for calculating the mean effect sizes (E) with 95% confidence intervals (CI). Compared to the control, the BCs increased soil pH and rice yield by 11.8% (medium E +: 0.436 to 0.439) and 16% (large E +: 0.790 to 0.883), respectively. Applying BCs derived from different feedstocks and pyrolysis temperatures reduced N2O emissions from rice paddies (large E −: − 0.692 to − 0.863). The BCs produced at 550–600°C reduced the GHG emission with medium to large negative effects (E −: − 1.571 to − 0.413). Applications of BCs at a range of 41–50 t ha− 1 were the best for rice productivity. Applications of all types and rates of BCs showed the significant decrease of available Cd by 35.4%–38.0% in a soil and led to the Cd reduction by an average of 43.6% in rice grains compared to the untreated soils. Applying BC is a promising approach to meet the challenges of sustainable global rice production, and the properties of BCs should be fully characterized and designed depending on its needs prior to its application.