Agricultural machinery traffic may lead to a restrictive state of soil compaction for crop yields in no-tillage systems. This study was conducted at the University of Cruz Alta, in Cruz Alta, State of Rio de Janeiro, Brazil. The main objective was to evaluate the effects of soil management systems and compaction states on selected soil physical properties and on yield of six soybean cultivars. The experiment was conducted on an Oxisol with 427 g kg-1 of clay, prior under no-tillage. The experimental design was randomized blocks with five treatments and four replications. The treatments consisted of management systems and compaction stages: continuous no-tillage (NT0) without additional soil compaction, NT with one pass of a compacting-wheel 2.0 Mg weight (NT1), NT with three passes of the compacting-wheel (NT2), NT with five passes of the compacting-wheel (NT3), and NT chisel-plowed without secondary tillage (Chisel). Soil physical properties were determined during the cropping season including soil penetration resistance (PR), bulk density (Bd), and porosity (total-Tp, macro-Mac, and micro-Mic). Soil compaction states induced by the compacting wheel increased Bd and PR and decreased soil porosity at 0 to 0.10 m-depth. There were direct relationships between Bd, Mic and PR, and an inverse relationship between bulk density and Mac as the state of compaction increased. The soybean cultivars behaved similarly in all states of soil compaction. The chiseling of soil under eight year no-tillage did not result in an increased soybean yield. When PR values were under 2.6 MPa, Bd values under 1.51 Mg m-3, and Mac values over 0.10 dm³ dm-3, there were no restrictions for soybean crop.
soil structure; soil porosity; soil strength; soybean production
