International Journal of Plant & Soil Science

Greenhouse and laboratory experiments were conducted to study the adsorption and distribution pattern of zinc in soils amended with different types of biochars. Representative red and black soil samples were collected from plot numbers 125 and 162, respectively, at the Main Agricultural Research Station, Raichur. Maize cob rind, pigeonpea stalk and cotton stalk biochars were applied separately to both soils at 10, 15 and 20 t ha-¹. The soil-biochar mixtures were incubated for up to 120 days at near field-capacity moisture and used for experimentation. The results showed that biochar application at different rates increased soil pH, organic carbon, cation exchange capacity (CEC), water-holding capacity and available major and secondary nutrients, while decreasing bulk density in both soil types. The zinc adsorption data fitted the Freundlich adsorption equation better than the Langmuir equation. Freundlich distribution coefficient (KD) values were higher in black soil treatments than in red soil treatments; therefore, the sorption capacity for zinc was comparatively higher in black soil than in red soil amended with different biochars. Among the biochars, zinc adsorption decreased in the order cotton stalk > pigeonpea stalk > maize cob rind, irrespective of soil type. Furthermore, zinc distribution coefficients were strongly correlated with pH, EC, OC, cation exchange capacity and bulk density. Native zinc was preferentially distributed in the order RES-Zn > CAB-Zn > ORG-Zn > EXC-Zn, whereas adsorbed zinc at the higher addition level (200 μM L−¹) showed a marginal shift compared with the original partitioning of native zinc and followed the sequence CAB-Zn > RES-Zn > ORG-Zn > EXC-Zn.