The intensive agricultural traffic on soils under coffee can cause excessive compaction, mainly when vehicles pass under inadequate soil moisture conditions, promoting yield decreases. Our objectives were: a) to assess the degradation of soil structure in the tractor track (TT) and the harvester track (HT), based on soil physical properties and load bearing capacity as related to the soil matric potential in three layers, b) to calculate the critical matric potential to prevent additional soil compaction by a Massey Ferguson wheel tractor model 275 and a Jacto KTR Advance harvester on a clayey Red Latosol (Oxisol). The study was carried out at the Epamig Research Farm in Patrocínio, State of Minas Gerais, Brazil. Undisturbed soil samples were collected (layers 0-3, 10-13 and 25-28 cm) from five trenches. The models of soil bearing capacity (σp) in function of soil matric potentials were determined in uniaxial compression tests with the undisturbed soil samples, at different soil matric potentials. In addition, soil samples were collected in six trenches (layers 0-3, 10-13 and 25-28 cm) for the determination of soil physical properties in the TT and HT. Transactions with the tractor degraded the soil structure more than operations with the harvester, since soil bulk density, microporosity and preconsolidation pressure were higher in the tractor track (TT) than in the harvester track (HT). The critical matric potential of TT was -51 kPa (0.36 m³ m-3) and the critical matric potential of HT -291 kPa (0.30 m³ m-3).
compactation; pressure preconsolidation; matric potencials
