Evaluation of fertilizers solubility and phosphate release in slightly acidic arable soil

The geochemical reactivity of single superphosphate (SSP), triple superphosphate (TSP), phosphate rock (PR), partially acidulated phosphate rock (PAPR) and potassium dihydrogen phosphate (KH2PO4) was evaluated in an incubation trial. The soil was Anthrosols, Ap horizon (Sandy loam). Solubility equilibrium of phosphates was calculated by phosphate (P-Pot=logH(2)PO(4) - pH) and calcium (Ca-Pot=logCa + 2pH) potentials. Next, activity ratio (AR degrees) and Woodruff potential (F) were considered for estimating phosphate dynamics in the soil. Data showed that phosphate potentials stressed on significant solubility process and varied accordingly to the rates of the fertilizers: -5.50, -4.81, -4.47 and -4.09 for 0, 50, 100 and 150kg P ha(-1). The values of the Woodruff potential (F) varied widely from -1929 to 8573 cal mol(-1), i.e., from marginal supplying power in the case of the control treatment to very high supplying power for the TSP (Triple superphosphate). These findings are of practical value for the following reasons: TSP and KH2PO4 are recommended for quick and high P supply to plants; SSP and PAPR for moderate supply and finally PR for slow and low supply. Phosphorus efficiency should be treated with priority particularly for areas with intensive cropping and susceptibility to runoffs.