Soil structure under tillage systems with and without cultivation in the off-season

Conservation systems, such as no-tillage, follow as principles the absence of soil tillage, formation and maintenance of vegetation cover, and crop rotation. Nevertheless, when one principle is not adequately adopted there may be alterations in soil aggregation and porosity. Thus, this study aimed to evaluate physical attributes and organic carbon of the soil in an area with tillage and fallow in the off-season and in areas without soil tillage, with fallow and with crop in the off-season. The soil of the three areas was characterized as an Oxisol with clayey texture. For more than 10 years, corn has been the main crop grown in the season period in the three areas: conventional soil tillage system with fallow in the off-season (CTS), no-tillage system with fallow in the off-season (NTS-f), and no-tillage system with grass-grass succession (NTS-g). Each area was sampled at 20 random points and soil samples were collected from the layers, 0–0.1 m, 0.1–0.2 m and 0.2–0.3 m. The data were subjected to multivariate factor analysis, where two factors were identified, called “soil aggregation” and “soil porosity”. Through the “soil aggregation” process, it was found that clay is essential for the formation of aggregates with diameter of up to 2.0 mm, while soil organic carbon influences the formation of macroaggregates. The “soil aggregation” was higher in the area under NTS-g, and lower in the areas under NTS-f and CTS. The practice of fallow in the off-season in a no-tillage system proved to be harmful to soil structuring, especially in relation to soil aggregation. In the area under CTS there was greater "soil porosity" in the 0–0.1 m layer, but this effect is temporary, due to the large amount of microaggregates generated in this system, which over time obstructs soil pores and causes lower porosity than that determined under the no-tillage system.