The maintenance of a good soil physical quality is essential to preserve the environment and maximize crop yields. A compacted soil can affect soil density, porosity and penetration resistance, influencing root growth. The purpose of this study was to evaluate the physical quality of an Oxisol, clay texture, with the soybean cultivar CAC-1, at four compaction and three irrigation levels, using the soil physical properties, as well as the relationship of root system with the crop yield. The experiment had a randomized block design, with split plots and four replications. The compaction levels were: C0 = 0, C2 = 2, C4 = 4, C6 = 6 passes of a tractor weighing 11 tons, at the same place. Undisturbed soil was sampled between the soybean rows, to determine the physical properties (layers 0-0.10 and 0.10-0.20 m). Soybean yields were highest at a soil penetration resistance of 0.71 Mpa. Root growth was inhibited by increased soil compaction.
yield; root system; soil resistance
