Phosphorus Sorption by Saline Soils of Western Transbaikalia

The sorption of phosphorus by solonchaks of the dry-steppe zone in the Republic of Buryatia from water solution of KN 2 PO 4 in the concentration from 0.25 to 5.0 mM P/L was studied under static conditions. The interaction period was 24 hours, and the soil to solution ratio was 1 : 10. The amount of adsorbed phosphorus was calculated as the difference of its content in the initial solutions and in the filtrates of soil suspensions. Based on the experimental data, we constructed isotherms of phosphorus adsorption by soil and calculated sorption parameters using the Langmuir and Freundlich equations. Typical and quasigley solonchaks were characterized by relatively high phosphorus sorption properties. The maximal adsorption capacity ( A max ) varied within 23.04–42.74 mM P/kg in the humus horizons of these soils and within 16.26–30.39 mM P/kg in deeper horizons. In general, the range of A max was 17.70–42.74 mM P/kg in all soils, except for sor solonchak, where the sorption capacity of phosphorus was low. The Langmuir adsorption constant ( K L ) varied in the range of 0.3–14.0 L/mM. Dark and typical solonchaks were characterized by the strongest binding of phosphorus. The Freundlich coefficient ( K F ) in the studied soils varied from 5.34 to 63.43 mM P/kg in the humus horizon and from 1.74 to 22.68 mM P/kg in the underlying mineral horizons. The distribution coefficient ( K d ) ranged within 1.95–145.04 L/kg and was high for quasigley solonchaks and low for sor solonchaks. There was a moderate correlation between K d and A max ( r = 0.51) and high between K d and K L ( r = 0.84, p ≤ 0.05). According to the standardized phosphorus retention ( SPR ) (the amount of phosphorus that should be sorbed by the soil to maintain concentration of P = 0.2 mg/kg (0.0065 mM/L) in soil solution), the studied soils were assigned to the group with weak phosphorus sorption (SPR was from 0.0723 to 3.4836 mM/kg). According to the phosphorus sorption capacity, the soils were arranged into the following sequence: quasigley solonchak > typical solonchak > dark solonchak > gley solonchak > alluvial light-humus saline soil > sor solonchak.