Potassium status of two clayey calcareous soils treated with zeolite under wetting-drying cycles

Zeolite application to clayey soils may change potassium (K) pools distribution and its release rate. To test this hypothesis, two heavy-textured calcareous soils with different mineralogy (smectitic and mixed by XRD) from southern Iran were selected. Experiment was a completely randomized factorial arrangement. Treatments consisted of two soils and two zeolite levels (0 and 5%) and wetting-drying treatment. Soil samples were incubated in 50% of saturation percentage for 90 days. Then, three wetting-drying cycles were done on samples. Different forms of K and K release to 0.01 M CaCl2, HCl and CH3COOH by 12 successive 15 min extractions of soil samples were determined. Zeolite increased the content of different K forms in soil 1 (smectitic), while it increased soluble and exchangeable K and decreased non-exchangeable K in soil 2 (mixed mineralogy). This may be due to the high CEC (189 cmol(+)/kg) and K content (2.13% K2O) of the used zeolite. Wetting-drying cycles increased non-exchangeable K in soil 1 and exchangeable K in zeolite treated soils. CaCl2 extracted more K than HCl and CH3COOH solutions (682, 281 and 292 mg kg-1, respectively) because Ca ions are more efficient than H ions in replacing K from surface sites in the K-bearing minerals. Zeolite and wetting-drying had no effect on K release from soil 1 while they significantly decreased K release rate from soil 2.