Abstract
The effects of soil tillage and crop rotation on humic substances of an Oxisol from southern Brazil were studied. Soils were sampled from conventional (CT) and no-tillage (NT) systems applied to soybean-wheat (S-W) and soybean-lupine-maize-wheat (S-L-M-W) rotations. Two additional samples from soils with secondary forest and eucalyptus were collected. Humic substances (HS) were extracted by chelating ion exchange resin and water. Grey humic acids (GHA), brown humic acids (BHA) and fulvic acids (FA) were analysed chromatographically on controlled pore glass. As expected, cultivation and tillage led to a decrease in soil organic carbon content. This diminution was somewhat lower in conventional tillage with S-L-M-W, compared with S-W rotation. The total amount of extractable HS was higher for forest soils. Cultivated soils with both CT and NT showed higher contents of GHA than BHA and FA. Crop rotation had an important influence on the quality of the organic matter as the S-W rotation with both CT and NT showed the highest GHA contents. Soils with eucalyptus exhibited the highest amount of extractable humic substances among the investigated soils.
Published Version
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