Effect of phosphate fertilization on a variable charge soil, under a pasture subjected to grazing

Angélica Sadzawka R.1 y René Bernier y.2

To study ihis effect, samples were taken from an Osorno soil (Typic Dystrandept), at 0-5, 5-10, 10-20, 20-30, and 30-40 cm depths, in plots that had been broadcasted with triple superphosphate, at the rates of 0,37, and 137kg P/ha/year,during a nine years period. ln each sample, total P, organic P, NaHCO3-P, P retention, P sorption capacity, organic C, pH and effective CEC were determined. Phosphate fertilization increased total P only in the upper 5cm and NaHCO3-P in the upper 10cm. From the added P, at a rate of 37 kg P/ha/year, only 33% was accumulated, as organic P; ata rate of 131 kg P/ha/year, 56% was accumulated, of which 17% was as organic P and 39% as morganic P. Phosphate fertilization did not produce changes in soil pH, nor in organic C content, but produced variations in the P sorption capacity and tended to diminish Ihe effective CEO. Results suggest that P retention was mainly produced by adsorption mechanisms, through Al, Fe-humus complexes of the soil.

1 Estación Experimental La Platina (INIA), Casilla 439, Correo 3, Santiago, Chile.
2 Estación Experimental Remehue (INlA),Casilla 1110, Osorno, Chile.