Effect of biochar, lime, and compost application on phosphorus adsorption in a Ferralsol

Use of biochar has multiple benefits like C, soil organic matter stabilization, and agricultural productivity. However, there is limited information about the effect of biochar on P dynamics in acidic soils. Hence, we investigated the effects of fresh and aged hydrothermal coal produced from bark (HTC) and low temperature coal synthesized from sewage sludge (LTC) on the kinetics of P adsorption in a Ferralsol. The treatments comprised of a control, compost [7.7 g (kg soil)⁻¹], hydrothermal carbonization coal [HTC, 2 g (kg soil)⁻¹], low temperature conversion coal [LTC, 3.8 g (kg soil)⁻¹], lime [0.3 g CaO (kg soil)⁻¹], compost + HTC [3.8 + 1.0 g (kg soil)⁻¹], compost + LTC [3.8 + 1.9 g (kg soil)⁻¹, respectively], compost + lime [7.6 and 0.4 g (kg soil)⁻¹, respectively]. The soil samples were incubated for a period of 3 months at 60% of the maximum water holding capacity. After 5 d and 3 months of the incubation period soil pH, Ca‐acetate lactate (CAL) extractable soil‐P, and P‐adsorption isotherms were determined. The results show a significant effect of treatments on soil pH just after 5 d, which remained consistent after three months of incubation. All treatments, except HTC increased the soil pH compared with the control treatment. The maximum increase in soil pH was observed with compost + lime (from 4.5 to 6.1). The CAL‐extractable P was significantly increased with application of LTC, compost + LTC, and compost + lime. The sorption parameters were not affected after 5 d of incubation. Due to residence effects, the P sorption capacity (Sₘ) was significantly reduced in the LTC treatment [from 1182 to 1099 mg (kg soil)⁻¹], and in the combination treatments compost + HTC [from 1182 to1078 mg (kg soil)⁻¹], and compost + LTC [from 1182 to 1099 mg (kg soil)⁻¹] treatments. The P binding energy (K) was significantly increased by the addition of LTC (from 2.18 to 4.26 mg L⁻¹), lime (from 2.18 to 4.53 mg L⁻¹), compost + HTC (from 2.18 to 7.03 mg L⁻¹) and compost + LTC (from 2.18 to 4.68 mg L⁻¹). Based on the results of the present study it is concluded that alone application of biochars do not alter the P bioavailability and sorption in a Ferralsol. However, combined application of biochars along with compost significantly decreases P sorption and increases bioavailability.