CHARACTERISTICS OF PHOSPHATE ADSORPTION AND DESORPTION IN ALBIC SOILS
Xia Hanping (South China Institute of Botany, Academia Sinica, 510650) Gao Ziqin (Institute of Applied Ecology, Academia Sinica, Shenyang)
The characteristics of phosphate(P) adsorption and desorption by 4 albic soils collected from the Three-River Plain. The experimental results showed that the soils had very strong ability to adsorb P. The whole process of adsorption was divided into the initially fast reaction (within 24 hours) and the slow reaction thereafter. In all kinetic models examined in this study, the Langmuir-type equation most perfectly modeled the kinetic processes of P sorption. The properties of P adsorption suggested that there were two populations of adsorbed sites which differed in the affinity for P, and therefore the sorption of P may be described using two-surface Langmuir equation. The process of P desorption had an evident hysteresis phenomenonn at high P concentration. The characteristics of successive desorption further indicated the presence of two forms of adsorbed sites or regions, one adsorbed P tightly, another loosely.Organic matter (O. M.) significantly affected P sorbtion by soils. The addition of O. M. could increase the amount of P adsorbed but it could be conductive to P desorption as well. The higher the content of O. M. the more easily the adsorbed P, especially at low P concentration. After O. M. was removed, P was more tightly adsorbed by soils, and therefore the desorption rate decreased evidently.