Phosphorus Sorption by Saline Soils of Western Transbaikalia

The sorption of phosphorus by salt marshes of the dry-steppe zone of the Republic of Buryatia from an aqueous solution of KN₂PO₄ in the concentration range from 0.25 to 5.0 mM/L (mmol/L) was studied under static conditions. The interaction time is 24 hours with a soil: solution ratio of 1 : 10. The amount of sorbed phosphorus was calculated from the difference in its content in the initial solutions and in the filtrates of soil suspensions. Based on experimental data, phosphorus adsorption isotherms were constructed by soil and sorption parameters were calculated using the Langmuir and Freundlich equations. Typical and quasi-clay Solonchaks have relatively high sorption properties with respect to phosphorus. The value of the maximum adsorption capacity (Amax) in the humus horizons of these soils varied in the range of 23.04–42.74 mM P/kg, in the underlying horizons 16.26–30.39 mM P/kg. In general, all soils, with the exception of the sorov Solonchaks, had an Amax value in the range of 17.70–42.74 mM P/kg. A low sorption value of phosphorus was found in the Solonchaks of sorovy. The Langmuir adsorption constant (K_L) varied in the range of 0.3–14.0 l/mmol. Solonchaks dark and typical most strongly bind phosphorus. The Freundlich coefficient (K_F) in the studied soils varied in the humus horizon from 5.34 to 63.43 mM P/kg, in mineral from 1.74 to 22.68 mM P/kg. The distribution coefficient (Kd) ranged from 1.95–145.04 l/kg with high values for quasi-clay Solonchaks and low for sorov Solonchaks. The correlation between Kd and Amax was estimated as average (r = 0.51), Kd and K_L – high (r = 0.84, p ≤ 0.05). The studied soils according to the values of SPR (the amount of phosphorus that must be sorbed by the soil to maintain a concentration of P = 0.2 mg/kg (0.0065 mM/l) in soil solution) from (0.0723 to 3.4836 mM/kg) refer to weakly absorbing phosphorus. According to the ability to sorb phosphorus, soils form the following decreasing series: quasi-glay solonchaks > typical solonchaks > dark solonchaks > glay solonchaks >alluvial light humus saline > sorov solonchaks.