PREDICTION OF PHOSPHATE LOSS FROM P-LOADED SOIL PARTICLES IN AQUEOUS SYSTEMS
TOLNER,L., ANAS WAHDAN, FULEKY,GY.
University of Agricultural Sciences Gödöllő, Hungary H-2103
Key words: Aqueous system phosphorous fertilization; P adsorption; P desorption
ABSTRACT
Phosphate ions of the incorporated phosphorous-fertilizer will be more or less strongly bounded on the surface of soil particles.The rate and reversibility of the sorption depend on the dose of phosphorous fertilizer and the time passed after fertilizer application.
Water erosion can carry away the fertilized upper soil layer and deposit it in rivers and lakes. Some part of sorbed phosphate ions will release into the water and causes environmental pollution and eutrification of surface waters.
How phosphate ions will be desorbed from the soil particles - sooner or later - fertilized with phosphorous - will be discussed in this paper.
A calcareous loamy soil of pHH20 7.9 was used in the model experiment. The soil was incubated with 0, 80 and 320 mg kg-1 phosphorus than equilibrated with different rates of phosphorus. After shaking and centrifugation the solid phase was 12 times shaken with distilled water and the desorbed quantity of phosphorous was calculated.
Using the equation used for adsorption, a new model was constructed for description the one and multistep desorption. Parameters of the model help to calculate the reversible and irreversible part of sorbed phosphorous.
Higher fertilizer phosphorus dose produces higher rate of desorbable phosphorus. The model used in this work, developed with the combination of modified Freundlich equation and the mass balance equation, makes it possible the description of multistep desorption and the calculation of potentially desorbable phosphorus amount (Q). The desorbable phosphate quantity nearly increase with the sum of added fertilizer phosphate, 40% of the added P at 0 and 80 mg.kg-1 at previously fertilizer application level and 55% at 320 mg.kg-1 P level.