Eight-year long potassium fertilization effects on quantity/intensity relationship of soil potassium under double rice cropping

Present research was undertaken to understand the effect of long-term potassium (K) fertilization @ 0 kg (K0) and 80 kg (K80) K ha−1 on the quantity/intensity (Q/I) parameters for K in soil and characterize the Aeric Haplaquept soil for K supplying capacity under long-term continuous rice cropping. The study involved laboratory experiments on Q/I parameters of the soils in different depths (0-75 cm depth) from long-term K management experimental field. The Q/I parameters showed a linear relationship for both K omission and K fertilized soils at different depths. Omission of K decreased the equilibrium K concentration ratio (CR0K) compared to K applied to the soil and slightly decreased the labile K (KL) and non-specifically available K (-ΔK0) but had no effect on specifically available K (KX). The K omission increased the potential buffering capacity (PBCK) compared to K fertilized soil. Potassium management had little effect on equilibrium exchangeable K (EK0), magnitude of the conversion of added K to exchangeable pool (α) and non-exchangeable pool (β). However, equilibrium solution K (CK0) in K omission soil was lower than K applied soil. β was higher than α in both the K management conditions. The PBCK for non-exchangeable pool was also higher than exchangeable pool both in K omission and K fertilized soils. Potassium management influenced critical solution K (CKr) and critical exchangeable K (EKr) but had no effect on minimum exchangeable K (Emin). Since the exchangeable K (EK), EKr and EK0 is very close to Emin it is concluded that EKr and Emin should be consider in interpreting the K fertility specially the EK of soil under long-term wetland double rice cultivation.