Improper tillage operations cause serious problems of soil conservation, above all compaction, causing pore space reduction of mainly the macropores, and affecting the physical-hydric properties. The purpose of this study was to verify the influence of different periods of management systems on the maximum density of a Red Oxisol in Jaboticabal, São Paulo State, and establish correlations with soybean yield, relative density and the soil critical moisture for compaction. The experiment was arranged in a completely randomized design with a split-plot arrangement (five management systems and three layers) with four replications. The five systems consisted of: 5 years of no-tillage (SPD5), 7 years of no-tillage (SPD7), 9 years of no-tillage (SPD9), conventional tillage system (SPC) and an adjacent area of native forest (MN). The maximum soil density (DSMax), critical moisture content for compaction (UGC), relative soil density (DSR), particle size, porosity, and level of soil organic matter were determined in the soil layers 0-0.10; 0.10-0.20 and 0.20-0.30 m. The results showed that the behavior of soil compaction curves was similar in all layers of all treatments and soil organic matter content did not explain the small changes in DSMax. On the Red Oxisol under study, the mechanical operations required for the management systems can be performed in a moisture content range of 0.13-0.19 kg kg-1, without causing physical degradation. It was found that the optimum Dsr and critical moisture for compaction were 0.86 and 0.15 kg kg-1, respectively, whereas the soybean yields were similar after the different periods of management systems.
standard Proctor test; conservation system; Glycine max
