Drivers of biochar-mediated improvement of soil water retention capacity based on soil texture: A meta-analysis

Biochar has been widely applied as a soil modifier to improve the physical properties and increase the water content of the soil. Although the response of soil hydrological properties to biochar has been extensively studied, the effect of biochar on soil hydrological properties in different soil textures has not been comprehensively quantified. Here, we performed a meta-analysis of 939 observations to quantify the effects of biochar on the water retention capacity of soil with different textures. The effect of biochar on field capacity (FC) and available water capacity (AWC) of the soil was greater in coarse-textured soils (23.8%, 25.6%) than those in medium- (5.0%, 20.9%) and fine-textured soils (7.2%, 11.5%). The permanent wilting point increased in coarse-textured soils (19.9%), decreased in medium-textured soils (−4.2%), and did not change considerably in fine-textured soils as affected by biochar. We demonstrated that FC is not always the main driver of increased AWC. In coarse-textured soils, there is a high correlation between hydrological properties. In addition, the specific surface area, surface functional groups, and cation exchange capacity of biochar are important factors affecting the water retention of soils with different textures. Our study establishes that the differences in soil texture cause heterogeneity in the mechanisms by which biochar improves soil water retention.