The Effect of Vermicompost on Transformation Rate of Available P Applied as Chemical Fertilizer in a Calcareous Clay Soil

The effects of vermicompost (VC) (0% and 1% w/w) on treated calcareous clay soil with 0 and 50mg phosphorus (P) kg(-1) as calcium phosphate [Ca(H2PO4)(2).H2O] was investigated. The soil samples were incubated for 7, 30, 60, 120, and 150 d at 25 +/- 1 degrees C and Olsen-P was measured after each incubation time. Results showed that Olsen-P increased 36% and 38% after VC addition in treated soil with 0 and 50mg P kg(-1), respectively. Recovery of Olsen-P in treated soils with VC, combined fertilizer VC +P, and fertilizer P was 42%, 42%, and 17%, respectively. The rate coefficient in treated soils with fertilizer, VC, and combined fertilizer VC +P was 0.033, 0.026, and 0.023mg kg(-1) d(-1/2), respectively. It seems that the process that leads to the decrease in available P in amended soils, is controlled by P diffusion into sorption sites in micropores of aggregates.