Different weed managements in coffee have led to structural changes, affecting the soil physical quality. Therefore, information on the load bearing capacity of the soil under different weed managements is essential to establish a sustainable soil management under coffee. The objectives of this study were to: (a) assess the influence of different weed managements over three decades on the load bearing capacity of a Dystroferric Red Latosol (LVdf) cultivated with coffee on the Epamig Farm in São Sebastião do Paraíso, Minas Gerais State (Latitude de 20 º 55 ' 00 " S and Longitude 47 º 07 ' 10 " W); (b) determine the maximum stress (σmax) exerted by a tractor; (c) establish the critical water content (θcrítica) for tractor traffic. The following weed managements were assessed: no weeding (SCAP); hand weeding (CAPM); post-emergence herbicide (HPOS); mowing (ROÇA); rotary tiller (ENRT); tandem disk harrow (GRAD) and pre-emergence herbicide (HPRE). In each management system 15 undisturbed soil samples were collected randomly in the coffee inter-rows in the layers 0-3, 10-13 and 25-28 cm, totaling 315 soil samples. Additionally, 15 samples per layer were collected in a native forest (MATA). The equipment used in coffee management was coupled to a Valmet® model 68 tractor for coffee. To determine θcrítica for tractor traffic, only the stress was considered that did not exceed the internal strength of the soil expressed as precompression stress. The undisturbed soil samples were used to determine precompression stress (σp) at different volumetric water contents (θ) and then bulk density (Bd). Disturbed samples were used to analyze particle size distribution, organic carbon (OC) and total oxides. Load bearing capacity (LBC) between precompression stress and volumetric water content was calculated (σp = 10(a+bq)) to assess the possible effects of weed management systems on soil structure. The maximum stress caused by the Valmet® tractor (inflation pressure of the front tires 6-16 of 172 kPa) was 220 kPa. The lowest critical water content was 0.27 cm³ cm-3 for the Dystroferric Red Latosol under no weeding in the 0-3 cm layer and the highest 0.48 cm³ cm-3 for the soil managed with pre-emergence herbicide in the 0-3 cm layer. The weed management with disk harrow and pre-emergence herbicide led to crusting on the soil surface and increased bulk density and precompression stress. The load bearing capacity of the soil under native forest was lower in the three layers studied compared to the soil under coffee and different weed managements. The different weed managements used in the interrows did not influence soil bulk density and organic carbon content of Latossol, in the 25-28 cm layer, compared to the soil under native forest (MATA).
precompression stress; stress distribution; organic carbon; critical water content; weed management; soil compaction
