Kinetics of non-exchangeable potassium release and availability in some calcareous soils of western Iran

摘要

The rate of non-exchangeable K~+ release from soils can significantly influence K~+ fertility of soils. There are few studies about the relationship between the kinetics of K~+ release and plant K~+ uptake for calcareous soils. The objectives of thisstudy were (i) to determine the kinetics of non-exchangeable K~+ release from some calcareous soils and (ii) to compare the effectiveness of different extraction methods for the prediction of K-supplying capacities. The kinetics of non-exchangeable K~+ release by successive extractions with 0.01 M CaCl_2, extractable K' using different soil extractants, and total K~+ uptake by wheat was studied in surface samples of 10 calcareous soils in western Iran. Total K~+ uptake by wheat grown in the greenhouse was used to measure plant-available soil K~+. The kinetics of non-exchangeable K~+ release from soils consisted of two phases and was best described by Elovich, power and parabolic models. Elovich b values were correlated with K~+ uptake by wheat (r = 0.785). This finding shows that the process of K' release is initiated by a low K~+ concentration in the soil solution and not by cation exchange. The following methods extracted increasingly higher average amounts of soil K : 0.1 M HNO_3 (194 mg K~+ kg~(-1)), 2 M NaCl (251 mg K~+ kg~(-1)), 1 M NaOAc (295 mg K~+ kg~(-1)), 1 M NH_4OAc (312 mg K~+ kg~(-1)) and 1 M HNO_3 (737 mg K~+ kg~(-1)). Potassium extracted by 0.1 M HNO_3, 2 M NaCl and NaOAc showed higher correlation with K~+ uptake by the crop (r = 0.876, 0.790 and 0.758, respectively) than did NH_4OAc (r = 0.689), which is used to extract K~+ in the soils of the studied area.