The response of soybeans (Glycine max (L.) Merrill) to the direct and residual effect of liming in relation to soil acidity, Al and Mn toxicities and P availability was studied in five Oxisols of Southern Brazil under successive wheat (Triticum aestivum L.)‐soybean cropping. Yield responses to liming were highly significant due to the high exchangeable Al and extractable Mn, the low pH, exchangeable Ca + Mg, and available P found in these soils. Optimum yields were obtained when liming adjusted Al from 0.1 to 0.5 meq/100g (1.5% Al saturation), soil pH from 5.2 to 5.7 and Ca + Mg from 5.7 to 8.5 meq/100g. Liming also increased root nodulation and reduced P fixation and Mn levels in the soil.

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Five soil profiles developed on andesitic volcanic ash, under welldrained conditions and at various elevations associated with different climatic conditions, were studied.These soils varied in profile development and degree of weathering from Incipient Ando soil (Umbric Vitrandept), Mature Ando soil (Typic Dystrandept), and Senile Ando soil (Hydric Dystrandept) to Incipient Latosol (Typic Humitropept) and Mature Latosol (Typic Palehumult).Profile development associated with time of ash deposition and climate and recognized by virtue of morphological properties was closely related to progressive weathering and a consistent evolution of physical, chemical, and mineralogical properties, as well as to an increasing degradation of the native soil fertility.This investigation served as a basis for developing a working hypothesis on the genesis of volcanic ash soils from Regosols and Ando soils to Latosols.