Impact of biochar amendment on soil hydrological properties and crop water use efficiency: A global meta‐analysis and structural equation model

The regulation of soil water retention by biochar amendment has been concerned especially in cropland ecosystem. However, the quantification of biochar's effects on soil hydrological properties and crop water use efficiency (WUE) is still limited, and the factors driving the biochar effect need to be investigated. Based on a database with 681 observations, meta‐analysis and structural equation model (SEM) were employed to reveal how biochar amendment affects water supply capacity and WUE. The results showed that biochar application increased available water content (AWC) and WUE by 26.8% and 4.7% on average, respectively. According to the SEM of AWC (R2 = 0.70–0.96), the increase of soil organic carbon (+36.1%) by biochar application can not only directly improve AWC but also indirectly improve AWC by affecting permanent wilting point (−1.0%) and mean weight diameter (+11.1%). The SEM of WUE (R2 = 0.74) indicated that soil moisture and porosity were increased by 10.8% and 7.0% under biochar amendment, which was the reason why biochar improved WUE. This study emphasized that biochar can improve soil hydrology and crop yield by increasing soil water supply conditions. And a rational rate of biochar is the precondition to obtaining the benefits of soil hydrology, otherwise, the excessive use of biochar may lead to the decline of WUE. According to a meta‐analysis, this study indicated that biochar amendment had a positive effect on soil hydraulic properties, and this effect could be influenced by soil conditions and biochar's properties. Moreover, structural equation models explained that biochar not only directly improved soil water supply, but also indirectly affected soil hydrology and crop productivity by increasing soil organic carbon, soil porosity, and promoting the formation of soil aggregation. Thus, biochar was a hopeful measure to improve soil hydrology and crop water use efficiency.