This research was carried out in Rio Grande do Sul State, Southern Brazil, during the 1990/1991 summer harvest. The main objective was to evaluate the aggregation and aggregate stability of two clayey soils classified as Dusky Latosol (Haplorthox) and Dark-Red Podzolic (Paleoudult). Two treatments were used in the Haplorthox: grass (Setaria anceps L.); and crop rotation under conventional tillage (wheat (Triticum aestivum) soybean (Glycine max L.)). On the other hand, four treatments were used in the Paleoudult: grass (Digitaria decumbens L.), leguminous (Macroptilium atropurpureum L.), crop rotation under no-tillage (oat (Avena bizantina) corn (Zea mays)) and bare soil. Soil aggregation and aggregate stability were greatly enhanced through the action of the grass roots. Soil aggregation was also related to the contents of organic carbon, oxalate-extractable iron and aluminum, clay and water-dispersed clay. However, these factors were not sufficient to explain differences observed in the weighed mean diameter of soil aggregates among the treatments.
aggregation; roots system; aggregate stability; cropping systems