The objective of the study was to determine, under laboratory conditions, the rateof phosphate(V) ions leaching down brown soil horizons under the influence of redistilledwater of pH 6.2. Laboratory tests were conducted to determine the effect of mineral andorganic fertilization on phosphate(V) ion concentrations in brown soil horizons before andafter extraction with water. The content of desorbed PO43– ions was determined in percolatingwater samples. The results indicate that the quantity of desorbed phosphate(V) ionswas affected by the type and rate of fertilization as well as by the dose of the appliedsolvent. The highest desorption of phosphate(V) ions from the brown soil profile was reportedin the treatment fertilized with manure + PK, while the lowest desorption was observedin the plot fertilized with NPK. The maximum desorption of phosphate(V) ionswas noted in soil layers at the depths of 0-25 cm and 26-50 cm. In all filtrate samples, PO43– values significantly exceeded the minimum quantity required to initiate eutrophication.The highest content of phosphate(V) ions, at 64.8 mg PO43– kg–1 soil, was determinedin percolating water from the treatment fertilized with slurry rate II (123.8 t ha–1). Percolating water samples collected in the non-fertilized (control) plot were least abundantin phosphate(V) ions (21.7 mg PO43– kg–1 soil).