The objective of this study was to evaluate the effects of different mechanical loads on soil physical properties of a Eutric Cambisol with loam sandy texture. The soil load distribution (kPa) was measured in situ by sensors placed in different soil layers. The soil physical properties evaluated were the bulk density (Ds) and the soil penetration resistance (RP) on sugarbeet (Beta vulgaris L.) row and interrow down to 0.30 m depth. The treatments were: without extra pressure exerted by the sowing machine, or no-compaction (SC); low pressure exerted by the sowing machine, named low load (BC); high pressure exerted the sowing machine, named high load (AC) and load pressure exerted by the tractor wheels used in the seedbed preparation, or tractor load (CT). The soil load distribution data indicated that the 0-0.10 m layer had soil stresses values higher than 120 kPa, which are considered very high. The increase on soil stresses from treatments SC to AC caused higher stress on topsoil than in the 0.10-0.20 m depth, while that under CT treatment showed higher stress at the 0.10-0.20 m layer. As a consequence of the soil stress load it was verified an increase on Ds in the more superficial soil layer (0-10 cm), and it followed the sequence: SC<BC<AC<CT. The RP was higher than 2.0 MPa at the 0.10-0.15 m layer under conventional tillage for the CT treatment. Under minimum tillage the RP reached values above of 1.5 MPa in all treatments, and values higher than 2.5 MPa were observed below the 0.25 m soil layer. The soil under treatments SC, BC and AC presented significant differences in RP between row and interrow positions at the 0.10-0.15 m layer; higher RP values were found for the row position. In general, the CT treatment showed higher Ds and RP values due to the greater stress applied on the soil.
soil compaction; bulk density; resistance to penetration; seedbed
