Estimating the Phosphate Fertilizer Need of Soybean (Glycine Max (L) Merr.) In Some Ultisols In Benue State, Nigeria From Their Solution Phosphate Concentration

Abstract

Ultisols in Benue state were studied to determine the solution phosphate concentration (SPC) required to obtain optimum yield of soybean for estimating the P fertilizer requirement of soybean. Soil inorganic P was fractionated using standard procedures. Sorption characteristics were determined in 0.01 M CaCl2 solutions of various P concentrations. 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 concentration were estimated from adsorption curves. In the greenhouse, 4 kg of soil from each location was placed in plastic pots. P estimated was added as KH2PO4. Treatments were laid out in Randomized Complete Block Design. Soybean (TGx 1448-2E) was planted to maturity. The shoot was dried, weighed, milled and digested in a 4:1 HNO3:HClO4 mixture and analyzed for P. SPC was determined in relation to yield. Field trial was conducted at Vanam and phosphate fertilizer quantity that resulted in 0.0, 0.5 SPC, 1.0 SPC, and 2.0 SPC was added per plot, seeds were drilled and replicated thrice. At harvest, SPC that gave highest grain yield was evaluated and the quantity of P required (SPR) to achieve this concentration was calculated. High grain yield was obtained at Vanam and Abaji-Kpav at SPC of 0.025 mg P kg -1 , Ogyoma attained optimum yield at 0.050 mg P kg -1 and Ofugo of 0.075mg P kg -1 , in the green house experiment. The estimated SPC value gave high grain yield in the field trial. Highest P fertilization would be required at Ofugo while Vanam would require the least.