Can biochar change the effect of soil hydrophobicity on soil pores distribution and soil water characteristic curve?

Soil hydrophobicity is a limiting factor in agricultural systems with limited water resources. Biochar is a wetting agent that influences the water behavior in hydrophobic soil. This study was conducted to investigate the effect of different amounts of sugarcane biochar (0, 2 and 5% w/w) on soil pore size distribution (PSD) and soil water retention curve (SWRC) in soils with strong and extreme water repellency with the water penetration time of 150 and 1230 s respectively. A non-hydrophobic soil was also considered as a control. Results showed that at strong and extreme soil hydrophobicity levels the volume of soil macropores decreased by 11.7% and 41%, respectively, compared to non-hydrophobic soil. While this decrease was 11% and 30% for mesopores and only 3.2% and 9.5% for micropores. Increasing the amount of biochar increased the volume of macro, meso and micropores in the soil with the greatest impact on macropores. In addition, the impact of hydrophobicity on the reduction of soil effective porosity decreased with increasing biochar application rate. Increasing biochar increased the volumetric water content of the soil especially at matric suctions of 0 to 100 hPa. Increasing hydrophobicity generally decreased the water held in the soil at all three biochar levels. increasing hydrophobicity to strong and extremely hydrophobic levels caused a decrease of 4.5% and 14% in soil available water compared to non-hydrophobic soil, respectively. These results showed that increasing the amount of biochar reduced the negative effect of hydrophobicity on water retention in the soil.