Effects of freeze–thaw cycles on phosphorus adsorption and desorption in the black soil of northeastern China

Abstract

Frequent freeze–thaw cycles (FTCs) can profoundly affect the chemical properties of soils. We conducted laboratory experiments to explore the effects of freeze–thaw treatments on phosphorus (P) adsorption (Pads) and desorption (Pdes) and to determine the capacity of P retention (Pret) via Pads and Pdes in the fertile black soil of northeastern China. The effects of 0, 1, 3, 6, and 10 FTCs on soil P adsorption and desorption were determined. Each cycle consisted of freezing for 12 h at −10 °C and thawing for 12 h at +7 °C, mimicking a diurnal pattern, at initial soil-moisture contents of 20%, 30%, 40%, and 50% and at amounts of added P of 10, 20, 40, 60, and 80 mg P L−1. Pads increased significantly with increasing amounts of added P. The freeze–thaws of black soils significantly decreased Pads and buffering capacities, which would promote the release of adsorbed P and increase the risk of reducing soil P. High moisture content also affected the behavior of soil P adsorption by reducing adsorbed P as the number of FTCs increased. The P-isotherm data for all soils at equilibrium-P concentrations fit the Langmuir equation well (R2 = 0.93 or higher). Pads had exponential and linear relationships with Pdes capacity and Pret capacity, respectively.