Soil functions and quality are closely linked to soil structure. The effect of management practices on the recovery of the aggregation of a physically degraded soil was studied based on the distribution of water-stable aggregates and single particles (diameter classes 9.51-4.76, 4.76-2.00, 2.00-0.25, 0.25-0.053, < 0.053 mm) and carbon stock (C) in the surface layer (0-7.5 cm) of a Paleudult in the Central Depression region of the state of Rio Grande do Sul, Brazil, under different management systems. The following systems were evaluated in experimental plots after 17 years: soil without plants and without tillage (fallow); no-till Lablab purpureus and maize (Zea mays) (Lablab/m); no-till Cajanus cajan (pea/m) and maize; perennial pasture of Digitaria decumbens (Pangola grass). The following systems were evaluated after 15 years: conventional tillage and no-till Avena strigosa and maize (CT a/m and NT a/m, respectively) Avena strigosa + Vicia sativa and maize + Vigna unguiculata (CT av/mu and NT av/mu, respectively). A conventionally tilled area was also evaluated after 30 years of grain cultivation (crop) and native grassland (NGr), representing the degraded state and the native ecosystem of this soil, respectively. Undisturbed soil samples collected in two seasons (September 1999 to September 2000) were evaluated in six replications per management system. Data were analyzed by ANOVA and Tukey's test (5 %) to detect differences between management systems. In the NGr, 76.4 % of the soil aggregates consisted of 63.8 % macroaggregates and of 23.6 % of single particles, and a C stock of 20.0 Mg ha-1. The agricultural use with intense soil tillage and low residue application (crop) reduced the proportion of soil aggregates to 49.9 % and raised single particles to 50.1 %, while the C stock decreased to 11.8 Mg ha-1. From this condition, 15 years of the untilled system with greater diversity of plant species and high residue application (NT av/mc) raised the proportion of soil aggregates to 70.7 % and of macroaggregates to 53.5 %. Perennial pasture (Pangola) increased the proportion of soil aggregates to 74.1 % and of macroaggregates to 61.8 %, equaling NGr. The systems NT av/mc, pea/m and Lablab/m recovered C stocks to the level of NGr. Although Pangola had the highest soil aggregation rates, the C stock was lower than in the said systems, emphasizing the positive action of a dense root system in the recovery of soil aggregation.
macroaggregates; single particles; organic matter; crop systems; soil quality
