JWSS - Journal of Water and Soil Science

To study the behaviour of phosphorus (P) sorption in the agricultural soils of Khoy region and the effect of long-term cultural management with the application of poultry manure on the P sorption parameters, bath experiments were carried out with 16 soil samples (8 cultivated and 8 virgin soils) and 9 initial P concentrations from 0 to 30 mg L-1 in 0.01M CaCl₂ as a background solution. After equilibrium, the remaining amount of P in solution was measured and the experimental sorption data were fitted to the Langmuir (R²=0.93-0.99) and Freundlich (R²=0.87-0.99) models. The results showed that P sorption was increased with enhancing the initial P concentration, eventually reaching the steady-state plateau. Based on the coefficient of determination (R²) and the standard error of estimate (SE), both isotherms models, Langmuir and Freundlich, showed a relatively good fit to the experimental data. The maximum mono layer sorption of Langmuir (qmax) varied from 233 to 486 and from 340 to540 mg kg^-1, and the energy parameter of Langmuir (KL) ranged from 0.12 to 0.50 and from 0.22 to 0.71 for the cultivated and virgin soils, respectively. Freundlich sorption capacity (KF) and intensity (n) parameters showed the same trends and KF varied from 36.4 to 123 and 59.3 to 145.2; also n varied from 1.18 to 1.50 and 1.47 to 1.71 in the cultivated and virgin soils, respectively. Consequently, all sorption parameters and the buffering indices showed a decreasing trend in the cultivated soils, as compared to the corresponding virgin soils and the cultural and fertilization management; especially, the application of the poultry manure in this region reduced phosphorus sorption by soil and then increased phosphorus availability to plants. Hence, less fertilizer would be needed to maintain a favourable P concentration in the soil solution for the optimum plant growth.

can provide useful information about P adsorption and the factors affecting it. A batch experiment was performed with phosphorus concentrations (0 to 35 mg/L) in two soils with different electrical conductivity (EC) (2 and 15 dSm^-1) by a variety of biochar treatments including simple apple-grape biochar (BC), rock phosphate- biochar (BC-RP), enriched-biochar (BC-H₃PO₄-RP), enriched-biochar (BC-HCl-RP), triple superphosphate (TSP), and control (Cont). The results indicated that phosphorus sorption capacity varied between the soils. Biochar treatments were effective in reducing the phosphorus adsorption of both soils. Due to BC-H₃PO₄-RP and BC-HCl-RP treatments, the maximum phosphorus adsorption of soils decreased in S1 soil by 14 and 23 % and in S2 soil by 26 and 19%, respectively. Also, the use of these treatments decreased the parameters of Langmuir absorption intensity (K_L) of S1 soil to 0.085 and 0.066, respectively and S2 soil to 0.11 and 0.15, L/mg respectively, and Freundlich absorption capacity (K_F) of S1 soil decreased to 19.2 and 22.5 and S2 soil to 28.2 and 28.1 L/kg, respectively. Enriched biochars significantly reduced the buffering indices of both soils indicating phosphorus adsorption decreased and increased the availability of phosphorus for the plant. The standard phosphorus requirement of S2 soil was lower than S1 soil by both equations. Therefore, enriched biochar can be an effective strategy to increase phosphorus availability and reduce the use of chemical fertilizers in saline and non-saline conditions; however, more field studies are needed for a clear understanding of the potential of P-enriched biochar as a fertilizer alternative.