Kinetics of nonexchangeable‐potassium release and plant response in some calcareous soils

Abstract

Abstract Nonexchangeable K + constitutes a slowly available reserve that may significantly influence K + fertility of soils. Laboratory and greenhouse experiments were conducted to characterize the K + supply and nonexchangeable K + –release kinetics in 10 calcareous soils using 0.01 M CaCl 2 and 0.01 M oxalic acid extractions. Total K + uptake by wheat ( Triticum aestivum L.) grown in the greenhouse was used to measure plant‐available K + . The release of K + was characterized by an initial fast rate followed by a slower rate. The nonlinear relationship in the early stages of the K + release may be attributed to the edge sites, and release of K + from interlayer exchange sites may be responsible for the second part of the K + release. Kinetics of K + release was described best with power function, which showed the best fit of the four models tested. Parameters of kinetics models in 0.01 M CaCl 2 were significantly related to K + uptake by wheat. Potassium release was also correlated to initial NH 4 OAc‐extratable K + and to HNO 3 ‐extractable K + .