Plane (Platanus orientalis L.) leaf biochar improves wettability of a silty clay soil irrigated with saline water

The wettability of coarse-grained soils has been studied previously. However, soil drying in arid regions due to limited precipitation or irrigation has resulted in soil water repellency to some extent in fine-grained soils. In this study, laboratory experiments were conducted to investigate the effects of plane (Platanus orientalis L.) leaf biochar with fine (< 0.1 mm) and coarse grains (0.1–0.5 mm) on the wettability of a silty clay soil irrigated with saline and non-saline water. Eleven rates of each biochar, ranging from 0 to 10% with 1% intervals, were investigated along with five ionic strengths of water, including 0, 0.2, 0.4, 0.6, and 0.8 mol L^-1, prepared using sodium and calcium chloride, which are two dominant salts in arid regions. The results showed that application of 5%–10% fine-grained biochar changed the soil hydrophobicity class from strongly to slightly water-repellent, while only 4% coarse-grained biochar was sufficient for the same change in soil wettability. Furthermore, the use of 10% coarse-grained biochar made the soil hydrophilic. The positive effect of plane leaf biochar on soil water repellency reduction was limited by water salinity. The sodium chloride solution was more effective in decreasing the soil wettability than calcium chloride solution and increased the demand for biochar for soil water repellency reduction. In conclusion, plane leaf biochar could be beneficial in managing the hydrophobicity of fine-grained soils. However, water quality as well as biochar particle size determined the quantity of biochar required for improving soil wettability.