Effect of Sheep Manure and Municipal Waste Vermicomposts on Availability of Phosphorus Fertilizer in a Calcareous Soil

The effect of organic amendments on phosphorus (P) availability over time is important for developing P fertilizer and organic amendment management practices in soils. This study was conducted to determine the effect of two types of vermicompost, namely, sheep manure (SMV) and municipal waste (MWV), on P availability, its mineral species and fractions in a calcareous sandy loam soil treated with three kinds of phosphorus fertilizer (rock phosphate (RP), diammonium phosphate (DAP), and triple super phosphate (TSP) during 90 days. Available P data during the incubation period were fitted using the power function equation to describe P transformation rate. The geochemical visual MINTEQ was used to calculate saturation indices and mineral P species in solution at the first and last days (nineteenth day) of incubation. By the end of the incubation period, there was no significant difference (P 15≤"> 0.05) between the amounts of available P released in the treated and the control soils, except in soils containing TSP treated with MWV and soils containing DAP treated with SMV and MWV. These results suggest high P fixation capacity in studied soil. Phosphorus transformation rate (the b constant of power function equation) ranged from -0.059 mg kg -1 day -1 (soil treated with SMV) to -0.140 mg kg -1 day -1 (soil treated with TSP). The highest “a” constant of power function was observed in soils treated with TSP and DAP and MWV. As compared to application of phosphorus fertilizer alone, vermicomposts applications with P fertilizer decreased P transformation rate in soils. Available P in soils treated with VWM was higher than with VSH. Phosphorus fractionation at the first and nineteenth day of incubation showed that carbonate and residual fractions were the dominant fractions, respectively. The results showed that P release was controlled by the dissolution rate of hydroxylapatite, and HPO4-2 was the dominant P specie during the incubation.