Biochar and Soil Physical Properties

Biochar is considered to be a potential soil amendment. However, its implications for soil physical and hydraulic properties have not been widely discussed. Changes in the soil physical environment influence the numerous services that soils provide. This paper (i) reviewed the impacts of biochar on soil compaction, mechanical, structural, hydraulic, and thermal properties; (ii) discussed factors affecting biochar performance; and (iii) identified research areas. Biochar generally reduces soil bulk density by 3 to 31%, increases porosity by 14 to 64%, and has limited or no effects on penetration resistance. Biochar increases wet aggregate stability by 3 to 226%, improves soil consistency, and has mixed effects on dry soil aggregate stability. It increases available water by 4 to 130%. Saturated hydraulic conductivity decreases in coarse-textured soils, and increases in fine-textured soils following biochar application. Studies on other properties are few but suggest that biochar reduces tensile strength and particle density, alters water infiltration, moderates soil thermal properties, and has minimal effect on soil water repellency. Sandy soils appear to respond more to biochar than clayey soils. Biochar effectiveness increases as the amount of biochar applied increases. A decrease in biochar particle size can increase water retention but may reduce saturated flow. Field-scale and long-term studies assessing all soil physical properties under different scenarios of biochar management are needed. Overall, biochar generally improves the soil physical environment, but long-term field studies are lacking to conclusively ascertain the extent of biochar effects.