Quantification of biochar effects on soil hydrological properties using meta-analysis of literature data

The use of biochar as a soil amendment had been increasingly advocated for its effects on carbon sequestration and greenhouse gas emission mitigation as well as on improvement of soil fertility. However, lack of a general assessment of biochar effects on soil physical properties made it difficult for the recommendations for its practical use for soil quality improvement in global agriculture. In this study, we performed a meta-analysis of literature data published by October 2015 and quantified biochar effects on selected soil physical properties. The literature data covered a range of feedstocks, pyrolysis temperature, soil and experimental conditions. Results showed that biochar amendment significantly improved all the soil physical properties tested. On average, soil bulk density was significantly reduced by 7.6% whereas soil porosity significantly increased by 8.4%, aggregate stability by 8.2%, available water holding capacity (AWC) by 15.1% and saturated hydraulic conductivity by 25.2%. Furthermore, the changes in soil bulk density were negatively correlated to porosity and AWC. In addition, these effects were greater in coarse textured soils than in fine textured soils. While the size of biochar effect on soil physical properties varied with the amount of biochar added, changes in bulk density only was correlated to application rates of crop residue and wood biochar. Overall, biochar amendments could likely improve soil hydrological properties though varying with biochar and soil conditions. Use of biochar thus could offer a viable option to improve moisture storage and water use efficiency for soils poor in organic carbon in arid/semiarid zones. More studies on dynamics of soil hydrological behaviors following biochar amendment should be deserved in field conditions for a sound understanding of biochar's potential in world agriculture.