Methods of Available Potassium Assessment in Selected Soils of Kwara State, Nigeria

Responses to potassium (K) by potted Sorghum (Sorghum bicolor) were determined in soils taken from four Local Government Areas in Kwara State and regressed with K extracted with five laboratory methods. Results showed that without K application, dry-matter yields were relatively high and responses to 15 kg, 30 kg and 60 kg K ha-1 were negative and not significant in the soils derived from basement complex and sandstones. When dry matter yields without K application were less than 9.00 g/pot, there were no significant responses to K application and responses were significant only when they were more than 9%. Potassium extracted with N NH4OAc pH 7.0 gave the best indication of dry matter yields when K was not applied, with the equation, Y = 0.005X + 3.1902, r = 0.1622. Significant responses were obtained in soil testing with less than 15 kg K ha-1 with this method. Furthermore, K extracted with hot N HNO3 was almost equal with a higher value in virtually all soils to exchangeable K extracted with N NH4OAc and could be used in place of this extractant as it also accounts for the replenishable form of K in soil.Keywords: A-value, extractants, K status, % K response, Sorghum, uptak