Contribution of non-exchangeable potassium on its quantity-intensity relationships under K-depleted soils

ABSTRACT

Quantity-Intensity (Q/I) parameters were used for elucidating the role of buffering properties of soils through K depletion. Winter wheat was sown in a greenhouse pot experiment until K-depletion and soils were analyzed with NH₄OAc and NaBPh₄ (1 min incubation period). Q/I isotherms (partitioned in exchangeable and non-exchangeable form) were constructed for the soils before and at the end of the K-exhaustion experiment. Results showed that NaBPh₄-K correlated better than NH₄OAc-K with intensity parameter (AR_e^K) or labile K (-ΔΚ₀) in K-depleted soils (r = 0.41 and 0.70), indicating the importance of non-exchangeable K in K dynamics. The latter was confirmed from the comparison of buffering characteristics between initial and K-depleted soils which showed that among the soils studied there was a group whose increase in buffering capacity (PBC^K_t) was due to non-exchangeable K fixation. Furthermore, NaBPh₄-K was well predicted by the sum of exchangeable K and the quantity of K that has to be applied to achieve K balance as derived from Q/I isotherms (EK₀ + CK₀). Finally, relationships were found between Q/I parameters of the initial soils (-ΔΚ_0i, ΕΚ_0i, ΕΚ_ri, CK_0i) and the K-depleted ones (ΕΚ_rd, ΕΚ_0d, CK_0d, CK_rd) which allowed corresponding prediction of the initial parameters (r² = 0.78–0.87).