Evaluation of Extractants and Quantity-Intensity Relationship for Estimation of Available Potassium in Some Calcareous Soils of Western Iran

摘要

Accurate estimation of the available potassium (K+) supplied by calcareous soils in arid and semi-arid regions is becoming more important. Exchangeable K+, determined by ammonium acetate (NH4OAc), might not be the best predictor of the soil K+ available to crops in soils containing micaceous minerals. The effectiveness of different extraction methods for the prediction of K-supplying capacities and quantity-intensity relationships was studied in 10 calcareous soils in western Iran. Total K+ uptake by wheat grown in the greenhouse was used to measure plant-available soil K+. The following methods extracted increasingly higher average amounts of soil K+: 0.025 M H2SO4 (45 mg K+ kg-1), 1 M NaCl (92 mg K+ kg-1), 0.01 M CaCl2 (104 mg K+ kg-1), 0.1 M BaCl2 (126 mg K+ kg-1), and 1 M NH4OAc (312 mg K+ kg-1). Potassium extracted by 0.01 M CaCl2, 1 M NaCl, 0.1 M BaCl2, and 0.025 M H2SO4 showed higher correlation with K+ uptake by the crop (P < 0.01) than did NH4OAc (P < 0.05), which is used to extract K+ in the soils of the studied area. There were significant correlations among exchangeable K+ adsorbed on the planar surfaces of soils (labile K+) and K+ plant uptake and K+ extracted by all extractants. It would appear that both 0.01 M CaCl2 and 1 M NaCl extractants and labile K+ may provide the most useful prediction of K+ uptake by plants in these calcareous soils containing micaceous minerals.