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.
Phosphorus Adsorption Isotherms of Some Low Activity Clay Soils As Influenced By Soil Properties and Their Effect on Fertilizer P Recommendations and Yield of Soybean (Glycine Max (L.) Merr.) In Benue State, Nigeria (Published)
The relationship between labile P sorbed to the soil surface and solution P can be described by a quantity-intensity relationship which shows P sorption or desorption as a function of P in the equilibrium solution. Twelve soils in Benue state representing Alfisols, Ultisols and Inceptisols were therefore used to examine the influence of soil properties on the shape and placement of their adsorption curves and yield of soybean. Sorption characteristics were determined in 0.01 M CaCl2 solutions of various P concentrations. For each soil, the amounts of P that gave 0.025, 0.05, 0.075, 0.100, 0.125, 0.150, 0.175, 0.200, 0.225, 0.250 mg kg-1 solution concentrations were estimated from adsorption curves. In the greenhouse, 4 kg of soil from each location was placed in plastic pots. Amount of P estimated from sorption study was added as KH2PO4. The treatments were laid out in Randomized Complete Block Design (RCBD) and soybean seed variety (TGx 1448-2E) was planted and growth and development observed to maturity. Optimum solution P concentration (SPC) was determined for each soil in relation to yield. At harvest, SPC that gave highest grain yield was evaluated for each soil and the quantity of P required (SPR) to achieve this concentration was calculated. Consequently, Odoba would require highest P fertilizer application (604.84 Kg P ha-1), (Tor-Donga 112.31, Abeda-Mbadyul 105.93) would require medium fertilization, (Utonkon 72.75, Katsina-Ala and Ofugo 67.64, Akoodo-Mbakor and Nor 61.26, Ogyoma 39.56, Otobi 33.18 and Abaji-Kpav 22.97 Kg P ha-1)would require low fertilization while Vanam (2.55 Kg P ha-1) would require the least.