Phosphorus Sorption Characteri stics in Relation to Soil Properties in Some Calcareous Soils of Western Azarbaijan Province

Abstract

Phosphorus (P) sorption in soils is a key process governing its availability to crops. There has been scanty information available on the P sorption characteristics of calcare- ous soils of Western Azarbaijan Province, Iran . In this study, P sorption characteristics and their relationship to soil properties were determined in 36 soil samples belonging to 15 agricultural soil series located in the sout h of Urmia, Western Azarbaijan Province. Total CaCO 3 contents ranged from 10 to 48.5%. Active CaCO 3 contents ranged from 1.7 to 20% and were significan tly related (r = 0.61, P <0.001) to the total CaCO 3 of the soils. NaHCO 3 -extractable P contents ranged from 4 to 38 mg P/kg soil. The amount of P sorbed by the soils differed among various soil series. The results sh owed that equilibrium solution P concentration (EPC) was lower (<0.2 mg/L) than the requirement for most crops. The amount of P adsorbed by the soil s at 0.2 mg/L EPC ranged from 5 to 114 mg/kg soil. The phosphate adsorption was well described by the Freundlich (r 2 = 0.96) and Langmuir (r 2 = 0.88) isotherms. The Lang muir maximum adsorption (X m ) and Freundlich coefficient (a F ) estimated from Langmuir and Freundlich equations ranged from 127 to 238 mg P /kg soil and from 43 to 211 mg P/kg, respectively. Soil clay content was significantly related to the soil P sorption indices, P 0.4 (P sorbed at 0.4 mg P/L, r = 0.40, P <0.01), PBC (P buffering capacity, r = 0.54, P <0.001), a F (r = 0.48, P <0.01), and X m (r = 0.40, P <0.01). Total CaCO 3 and active CaCO 3 were found to be less important factors affecting P adsorption