Effect of vermicompost on Phosphorus adsorption in calcareous soils compared to other organic amendments

Organic amendments are used in soils, with a goal of improving soil properties such as fertility and nutrition. This study was conducted to evaluate and compare the effect of vermicompost, on the phosphorus (P) isotherm, phosphorous buffering capacity (PBC) and standard phosphorus requirements (SPR) with more commonly used sheep manure, poultry manure and grape waste in five vineyard calcareous soil of Malayer area in Hamadan province. Organic amendments were added to soils at the rate of 2 % and the samples were incubated for one month at 25±2 ᵒC and field capacity. Isotherm experiments in treated and control soils were carried out by concentrations of P ranging from 0 to 200 mg kg-1 of KH2PO4 in the presence of 0.01 M CaCl2. Phosphorus sorption curves were well fitted to the Freundlich and Van-Hay equations. Incorporation of organic amendments increased soils available P, and decreased Kf constant, PBC and SPR in treated soils. The SPR average of control soils were 17.1 mg kg-1, while in treated soils ranged from 9.3 to 14.5 mg kg-1.  The PBC average of treated soils, with vermicompost, sheep manure, poultry manure and grape waste decreased 41.0, 37.9, 29.9 and 21.6 % than PBC average of control soils, respectively. The results indicated that conventional soil amendments such as sheep manure and poultry manure in vineyard soil can be replaced with vermicompost, an organic fertilizer with low salinity and natural pH which increases P availability in soil. We suggest further studies on P leaching from vermicompost treated soils.