KINETICS OF PHOSPHORUS DESORPTION IN RED MEDITERRANEAN SOILS (ALFISOLS)

The kinetics of phosphorous (P) desorption by ten Red Mediterranean so ils was studied. By the addition of several amounts of P fertilizers a t different water/soil ratios and different contact times, the amount of P fertilizer required for this category of Greek soils in order to avoid environmental pollution from overdoses was determined. The exper imental data led to the same desorption model as given by SHARPLEY (19 81) Pd=kPot(a)w(b); where Pd is the amount of P desorbed in time t, at a water/soil ratio w, with Po the initial amount of desorbable P pres ented in the soil, and K, a and b constants for a given soil. The valu es of K, a and b constants for each soil are nearly the same over a ra nge of experimental conditions consequently we suggest that mean value s of the constants for each soil can be used in the Sharpley model to describe P release for all the agricultural uses for this category of Greek soils, Exchangeable Fe and Mn and the low C.E.C. of Red Mediterr anean soils influenced positively the desorption-time relationship.