Laboratory, pot and field studies were conducted with some low activity clay Soils in Benue State to evaluate their potassium (K) supplying capacity using equilibrium parameters as measured by quantity, intensity and activity indices. The soils were Daudu, Tse-Kough, Tse-Agbakor and Mbachor. Farmers’ fields were used to verify the findings of these experiments. Routine soil analysis was done using standard procedures. Potassium fractions were estimated using standard procedure. The Total K content of the soils varied from 57.06 C mol Kg-1 at Daudu to 64.63 C molkg-1 at Mbachor with the non exchangeable K constituting 57.16%, 0.40% and 0.13% respectively of the total K in the soils. The potassium buffer capacity (PBC) which measures the ability of the soils to maintain K intensity in solution ranged from 1.98 at Daudu to 3.56 at Mbachor indicating a slow release of K in these soils. The specifically bonded K which constituted the bulk of the labile K (KL) was generally low. Response of Soybean (Glycine max merr. (L) to K application was observed in all the soils studied and the critical K value for optimum yield of the crop using standard procedure was determined to be 0.33 C mol Kg-1. It was concluded that response of Soybean to K application would be probable in the Daudu and Tse-Kough Soils while response to K application will not be probable with the Tse-Agbakor and Mbachor Soils.
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