Enhancing cation and anion exchange capacity of rice straw biochar by chemical modification for increased plant nutrient retention

Abstract

Biochar, a potential alternative of infield crop residue burning, can prevent nutrient leaching from soil and augment soil fertility . However, pristine biochar contains low cation (CEC) and anion (AEC) exchange capacity. This study developed fourteen engineered biochar by treating a rice straw biochar (RBC-W) first separately with different CEC and AEC enhancing chemicals, and then with their combined treatments to increase CEC and AEC in the novel biochar composites. Following a screening experiment, promising engineered biochar, namely RBC-W treated with O 3 -HCl-FeCl 3 (RBC-O-Cl), H 2 SO 4 -HNO 3 -HCl-FeCl 3 (RBC-A-Cl), and NaOH-Fe(NO 3 ) 3 (RBC-OH-Fe), underwent physicochemical characterization and soil leaching-cum nutrient retention studies. RBC-O-Cl, RBC-A-Cl, and RBC-OH-Fe recorded a spectacular rise in CEC and AEC over RBC-W. All the engineered biochar remarkably reduced the leaching of NH 4 + -N, NO 3 − -N, PO 4 3− -P and K + from a sandy loam soil and increased retention of these nutrients. RBC-O-Cl at 4.46 g kg −1 dosage emerged as the most effective soil amendment increasing the retention of above ions by 33.7, 27.8, 15.0, and 5.74 % over a comparable dose of RBC-W. The engineered biochar could thus enhance plants' nutrient use efficiency and reduce the use of costly chemical fertilizers that are harmful to environmental quality.