Potassium isotherm partitioning based on modified quantity‐intensity relation and potassium buffering characterization of soils of North India

Background : Potassium (K) availability in soil and plant uptake is restrained by the dynamic interactions among the different pools of K. Aims : To understand these interactions, a study was undertaken to assess the quantity–intensity (Q/I) and buffering characteristics of rainfed maize ( Zea mays L.) growing soils. Ten contrasting soils were evaluated for K partitioning changes in exchangeable K (ΔEK) and non‐exchangeable K (ΔNEK) pools in the soil‐solution phase and buffering characteristics using a modified version of Q/I approach. Results : The partitioned Q/I isotherms showed strong adsorption with the increase in K concentration ratio (CR K ) and the changes due to ΔEK were higher than changes due to ΔNEK. Total buffering capacity (PBC K ) significantly correlated ( r = 0.92, p <0.01) with clay content with a major share contributed by buffering capacity owing to non‐exchangeable K (PBC Δ NEKK) rather than exchangeable K (PBC Δ EKK). The fixation capacity (β) factor, the magnitude of added K converted into a non‐exchangeable pool, ranged from 41 to 63%, whereas release (α) factor, the magnitude of added K converted to the exchangeable pool, ranged from 19 to 36%. Both threshold solution K (CK r ) and threshold exchangeable K (EK r ) values were found to be high in Satran clay loam (S2) and lower in Doon silty clay loam (S3) soils. The equilibrium exchangeable K (EK o ) was found close to minimum exchangeable K (E min ) in Doon silty clay loam (S3) and Babaweyl sandy clay loam (S1) soils and overall E min constituted about 8.94 to 0.57% of the EK o . Conclusion : It may be concluded that K Q/I isotherm partitioning provides a valuable insight to assess the dynamic relations. The ratio of α/β (K recharge index) could be used to evaluate the K enrichment capacity of soil to K additions while EK r and E min can be potentially useful in the elucidation of exchangeable K as K fertility index especially in soils with poor K fertilizer management.