Soil phosphate desorption by successive extractions with iron oxide-impregnated paper strip

The kinetics and amount of phosphorus (P) release from five Italian soils w ith and without added P, were assessed by a successive soil P extraction pr ocedure using iron (Fe) oxide-impregnated paper strips to characterize the residual effectiveness of added P. Following P application to soils (0, 25, 50, and 100 mg kg(-1) soil), P removed in the first extraction (strip P), P released in ten extractions (total P), and soil P sorption saturation (P- saturat) increased for all soils. The rate of P release decreased with succ essive strip extraction of soil [Strip P=a*(extraction number)(b); R-2 of 0 .89-0.99], with the exponent b decreasing as the saturation of soil P sorpt ion capacity increased. Both initial P and total P released to strips incre ased with soil P saturation.