Kinetics of phosphate desorption from different soils as influenced by application of poultry manure and fertilizer phosphorus and its uptake by soybean

Laboratory and greenhouse experiments were conducted to work out the kinetics of P desorption and P uptake by soybean in different soils of Punjab and Himachal Pradesh (India) as influenced by fertilizer P and poultry manure (PM) application. Different kinetic equations were scanned to assess their suitability for explaining the P desorption process. Phosphorus desorption, determined by successive extractions with 0.5 M NaHCO3 solution, increased gradually up to 48 h of extraction in the samples treated with PM and/or P, whereas, in the control it levelled off after about 24 h of extraction. P desorption kinetics were best described by Elovich kinetic equation, closely followed by the Parabolic Diffusion equation. The values of kinetic constants of the Elovich and Parabolic equations increased with the increase in the level of fertilizer phosphorus, with and without PM. A significant linear relationship between the Elovich constant, α (rate of P desorption), and P uptake suggested that the rate of P desorption was a useful parameter to predict the P bioavailability, both from the soil and fertilizer material. Application of PM helped in maintaining crystalline products of phosphate in metastable or poorly crystalline forms in the calcareous and non-calcareous soils, while in the acidic soils, PM might have chelated Fe and Al ions thereby transforming the mineral P towards higher solubility.