PERSISTENCE OF MECHANICAL INTERVENTIONS EFFECT FOR SOIL DECOMPACTION IN NO-TILLAGE SYSTEMS

Compaction has become one of the main causes of soil degradation in agricultural areas. It is directly related to the soil management system, often requiring decompaction practices to mitigate the problem. This study aimed to determine the duration of the effects of mechanical soil decompaction, e. g., by plowing and chiseling, associated with soil breaking devices on the seeders, for example disks and disk-ripper, to mitigate the compaction of soil under no tillage; soil physical properties and the force exerted by the traction bar were evaluated. The study was carried out in Coxilha, in the north region of Rio Grande do Sul (Brazil) (28 degrees 10' 18.7 '' S, 52 degrees 22' 39.89 '' W), on a Red Oxisol. The experiment was installed in 2001, in an area for eight years under no-tillage (NT). In this area, mechanical interventions of soil plowing and chiseling were annually performed, prior to summer crop planting. The treatments consisted of one control (uninterrupted NT for 16 years) and six NT periods (7.5; 6.5; 5.5; 4.5; 3.5, and 2.5 years) after chiseling and plowing in the main plots. In the subplots, two fertilizer treatments were applied in the sowing furrow (disks or disk-ripper). The experiment was evaluated in a randomized block design in split plots and three replications. Results indicated the existence of soil compaction in the subsurface layer (7-15 cm), evidenced by increases in soil density and reduction in soil total porosity and macroporosity in all treatments. It was observed that the effects of mechanical intervention to mitigate compaction and improve the soil structure were ephemeral, with a durability of up to two and a half years after chiseling for total porosity and macroporosity and for soil density in the plowing treatments. For the other parameters, these benefits were no longer detectable less than two and a half years after intervention. Mechanical intervention caused no alterations in the force exerted by the traction bar, in comparison with the control. However, the soil breaking mechanism of the disk-ripper on the seeder was effective in altering the appraised parameters, increasing soil macroporosity and reducing microporosity, soil density and traction force, thus mitigating soil compaction.