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 (K-0) and 80 kg (K-80) 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 (KO and non-specifically available K (-Delta K-0) but had no effect on specifically available K (K-X). 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 (alpha) and non-exchangeable pool (beta). However, equilibrium solution K (CK0) in K omission soil was lower than K applied soil. beta was higher than a 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. (C) 2017 Elsevier B.V. All rights reserved.