The Effect of a Superabsorbent and Biochar on Some Physical and Hydraulic Properties of Two Arable Sandy Loam and Clay Loam Soils

Biochar and superabsorbents are used to improve a wide range of soil properties, including water holding capacity and nutrient retention. In this research, the effect of adding biochar and a superabsorbent on some of the physical properties of two arable soil types (a sandy loam and a clay loam soil) was studied. A greenhouse experiment was performed as a completely randomized design with three replications. Three levels of AquaSorb superabsorbent including zero (control), 5, and 10 g kg(-1) soil, and three levels of walnut shell biochar including zero (control), 10, and 20 g kg(-1) soil were used. The AquaSorb and biochar treatments were applied independently. Soil properties that included bulk density (rho(b)), particle density (rho(s)), porosity (f), saturated hydraulic conductivity (K-s), residual moisture (theta(r)), saturated moisture (theta(s)), moisture curve coefficient (alpha), moisture curve slope (n), field capacity (theta(fc)), permanent wilting point (theta(pwp)), and total available water (TAW) were measured after one and six irrigations. The use of 10 g of superabsorbent and 20 g of biochar per kilogram of soil had the greatest effect on the physical properties of both tested soils. Addition of 10 g of superabsorbent per kilogram of sandy loam soil decreased rho(b) by 22.7% and increased f, K-s, theta(s), theta(fc), and theta(pwp) parameters by 28.9, 533.3, 16.3, 30.43, and 50.0%, respectively, and in clay loam soil, decreased rho(b) by 25.9% and increased the other parameters mentioned by 22.6, 155.6, 26.1, 44.8, and 46.2%, respectively. Addition of 20 g of biochar per kilogram of clay loam soil increased K-s, theta(s), and theta(pwp) parameters by 33.3, 10.9, and 23.1%, respectively, and had no significant effect on other properties of this soil and sandy loam soil. The application of the superabsorbent and biochar in the studied soils had the greatest effect on K-s and theta(pwp).