Study of phosphorus sorption behaviour in cultivated soils of Khoy region

Phosphorus (P) is an essential nutrient that its bioavailability controlled by sorption and desorption process. To study the behavior of phosphorus (P) sorption in agricultural soils of Khoy region, bath experiments were carried out with 60 cultivated soil samples and 9 initial P concentrations from 0 to 30 mg L-1 in 0.01M CaCl2 as a background solution. After equilibrium, remaining amount of P in solution was measured and the experimental sorption data were fitted to Langmuir, Freundlich and Temkin models. Based on coefficient of determination (R2) and standard error of estimate (SE), Langmuir isotherm models, is relatively better fitted to experimental data compared with Freundlich and Temkin models. The maximum mono layer sorption of Langmuir (qmax) varied from 135 to 486 mg kg-1 and energy parameter of Langmuir (KL) varied from 0.09 to 0.52 L mg-1. Also, Freundlich sorption capacity (KF) and intensity (n) parameters was varied from 16.0 to 123.4 mg kg-1 and 1.1 to 2.4 respectively, and Temkin equation constants, A and KT varied from 10.3 to 196.3 mg kg-1 and 17.3 to 88.7 L mg-1, respectively. The soils with high clay and CaCO3 showed maximum qmax, KF and A, and mentioned sorption parameters significantly correlated with clay and CaCO3. The result showed that the amount of equilibrium P concentration (EPC) values varied from 0.01 to 0.89 mg l-1, 0.35 mg l-1 on average for the cultivated soils. Also, there was a highest significant correlated between EPC and extractable phosphorus with sodium bicarbonate (r = 0.90**). The Potential buffering capacity (PBC) values was from 3.2 to 122.4 and 33.5 mg kg-1 on average. PBC significantly correlated with soil clay content (r= 0.80**) and amount of calcium carbonate (r=0.43**).