A study was conducted to compare the methods of Olsen, Bray N° 1, Bray N° 2 and Truog as to their reliability in predicting P response on selected soils. Wheat was grown in eight pot experiments on samples of the Arrayán, Mañil ("trumaos"), Mirador y San Carlos ("red clays" soils) senes in Ñuble. Dry matter yields and P uptake were considered as response indexes. The simple correlation coefficients, r, were calculated between soil-P values, and their logarithms, and the P response. The r-values obtained with the Olsen method were significant at least at the 5% level, and were higher than those obtained with the Bray N° 1, Bray N° 2 and Truog methods. The r-values with the Olsen method were: P-Olsen vs. % yield, r=0,823*; P-Olsen vs. % P-Absorption, r=0,897**; log P-Olsen vs. % yield, r=868**, and log P-Olsen vs. % P absorption, r=0,910**.

1 Ing. Agr., M. S., Estación Experimental Quilamapu, Instituto de Investigaciones Agropecuarias, Casilla 426, Chillán, Chile.