AVAILABILITY OF SOIL PHOSPHORUS BY ANION EXCHANGE RESIN

L. TOLNER and GY. FÜLEKY

Department of Agricultural Chemistry, University of Agricultural Sciences, H-2103 Gödölő (Hungary)

KEY WORDS: desorption, ion exchange, model, phosphorus, resin, soil

The change of any component in soil-solution-resin system has a significant effect on the amount of phosphorus sorbed by resin. The effect is caused by the distribution of P at equilibrium in each phase of the system. The amount of phosphorus retained by soil or remaining in soil solution may not be neglected.
The distribution of phosphorus in soil-solution-resin system may be described by the combination of balance equation and adsorption isotherm:

By this equation the real amount of desorbable phosphate (Q) may be obviously determine.
“T” is the amount of soil suspended in 100 cm³ of water indicating the ratio of soil:solution. The term describing the amount of phosphorus sorbed on the soil may be modelled by the Langmuir isotherm of parameters “A” and “K”. The BET isotherm may be used for the phosphorus sorption of the ion exchange resin. So with the help of P_R—the amount of phosphorus sorbed by resin—the phosphorus content of equilibrium solution (c) may be determined. The model was successfully applied for several soils of Hungary, with different amounts of resin and extreme ratios of soil:solution. On the analogy of the above mentioned studies soil-solution system may be described as well.