ChileanJAR

Total P was determined in 17 samples from volcanic soils of Southern Chile. Samples were taken both from uncultivated and cultivated (usually wheat) plots. The levels of total P were high, specially in Río Bueno, Osorno and Purranque soils. Fertilizer P accumulates markedly, particularly in Metrenco and Loncoche soils. Organic-P was determined by applying two different methods: Mehta et al (1954) and Steward and Oades (1972), that incorporates ultrasonic-dispersion. The method of Mehta et al produced a considerable hydrolitic effect and theref ore the Steward and Oades’method is recomended for these soils, but introducing some slight modifications. Organic-P accounted for approximately 50% of total-P in alI the samples, and the ratio humic-P/fulvic-P fluctuated between 1.2 and 19. The C/P ratios of the isolated humic acids were higher than 20; this help to support the hypothesis that the forms of organic-P found would preferentially inc lude high molecular weight compounds, of the type HA-P and HA-Al-P, HA being a polyfunctional macromolecule.