Abstract: To evaluate compaction meter value and machine drive power roller-integrated compaction technologies, a field study was conducted with 30-m test strips using five granular materials. The test strips were compacted using a prototype CS-533E vibratory smooth drum roller and tested for various compaction parameters using in situ test methods (e.g., nuclear moisture density, dynamic cone penetrometer, plate load tests, etc.). To characterize the roller machine-ground interaction, soil testing focused on measuring soil compaction parameters of the compaction layer, to a depth not exceeding 300 mm . The experimental testing of five test strips provided roller data and in situ measurements for several stages of compaction that were used in performing statistical regression analyses. The relationships between data from the roller-integrated compaction technologies were investigated with special consideration for the relative variation that was observed for each measurement system. Statistical averaging mitigated ...

Abstract: Tree species can differ in their responses to resource availability during the critical phase of establishment, which could influence forest dynamics. In Mediterranean forests, most of the attention has focused on the effects of shade and summer drought on seedling survival, but little is known about the effect of autumn to spring rains on earlier stages of recruitment. A sowing experiment was set up along natural light and water gradients with three co-occurring oak spe- cies (Quercus suber L. (cork oak), Quercus canariensis Willd. (Algerian oak), and Quercus pyrenaica Willd. (Pyrenean oak)) that show limited natural regeneration in southern Spain. Recruitment stages were monitored for 1 year. Models of seed germination, seedling emergence, and seedling survival as well as of overall recruitment patterns were developed as functions of light, soil moisture, and soil compaction. The influence of intraspecific variation in seed mass and emergence time were also tested. Excess soil water levels during the winter reduced germination and emergence and lengthened time to emergence (in waterlogged open areas), which in turn decreased seedling survival during the dry season. Seedlings from larger seeds were more likely to germinate and emerge. The results suggest that temporal and spatial variability of soil water content, mediated by emergence time and seed size, play a crucial role in the regeneration dynamics of Mediter- ranean oak forests.

Abstract: Soil enzymes are linked to microbial functions and nutrient cycling in forest ecosystems and are considered sensitive to soil disturbances. We investigated the effects of severe soil compaction and whole-tree harvesting plus forest floor removal (referred to as FFR below, compared with stem-only harvesting) on available N, microbial biomass C (MBC), microbial biomass N (MBN), and microbial biomass P (MBP), and dehydrogenase, protease, and phosphatase activities in the forest floor and 0–10 cm mineral soil in a boreal aspen (Populus tremuloides Michx.) forest soil near Dawson Creek, British Columbia, Canada. In the forest floor, no soil compaction effects were observed for any of the soil microbial or enzyme activity parameters measured. In the mineral soil, compaction reduced available N, MBP, and acid phosphatase by 53, 47, and 48%, respectively, when forest floor was intact, and protease and alkaline phosphatase activities by 28 and 27%, respectively, regardless of FFR. Forest floor removal reduced available P, MBC, MBN, and protease and alkaline phosphatase activities by 38, 46, 49, 25, and 45%, respectively, regardless of soil compaction, and available N, MBP, and acid phosphatase activity by 52, 50, and 39%, respectively, in the noncompacted soil. Neither soil compaction nor FFR affected dehydrogenase activities. Reductions in microbial biomass and protease and phosphatase activities after compaction and FFR likely led to the reduced N and P availabilities in the soil. Our results indicate that microbial biomass and enzyme activities were sensitive to soil compaction and FFR and that such disturbances had negative consequences for forest soil N and P cycling and fertility.

Abstract: In Brazil, most Eucalyptus stands have been planted on Cerrado (shrubby savanna) or on Cerrado converted into pasture. Case studies are needed to assess the effect of such land use changes on soil fertility and C sequestration. In this study, the influence of Cerrado land development (pasture and Eucalyptus plantations) on soil organic carbon (SOC) and nitrogen (SON) stocks were quantified in southern Brazil. Two contrasted silvicultural practices were also compared: 60 years of short-rotation silviculture (EUCSR) versus 60 years of continuous growth (EUCHF). C and N soil concentrations and bulk densities were measured and modelled for each vegetation type, and SOC and SON stocks were calculated down to a depth of 1 m by a continuous function. Changes in SOC and SON stocks mainly occurred in the forest floor (no litter in pasture and up to 0.87 kg C m_2 and 0.01 kg N m_2 in EUCSR) and upper soil horizons. C and N stocks and their confidence intervals were greatly influenced by the methodology used to compute these layers. C/N ratio and 13C analysis showed that down to a depth of 30 cm, the Cerrado organic matter was replaced by organic matter from newly introduced vegetation by as much as 75-100% for pasture and about 50% for EUCHF, poorer in N for Eucalyptus stands (C/N larger than 18 for Eucalyptus stands). Under pasture, 0-30 cm SON stocks (0.25 kg N m_2) were between 10 and 20% greater than those of the Cerrado (0.21 kg N m_2), partly due to soil compaction (limit bulk density at soil surface from 1.23 for the Cerrado to 1.34 for pasture). Land development on the Cerrado increased SOC stocks in the 0-30 cm layer by between 15 and 25% (from 2.99 (Cerrado) to 3.86 (EUCSR) kg C m_2). When including litter layers, total 0-30 cm carbon stocks increased by 35% for EUCHF (4.50 kg C m_2) and 53% for EUCSR (5.08 kg C m_2), compared with the Cerrado (3.28 kg C m_2), independently of soil compaction. (Resume d'auteur)

Abstract: To evaluate roller-integrated machine drive power (MDP) technology for predicting the compaction parameters of cohesive soils considering the influences of soil type, moisture content, and lift thickness on machine power response, a field study was conducted with 15-m test strips using three cohesive soils and several nominal moisture contents. Test strips were compacted using a prototype CP-533 static padfoot roller with integrated MDP technology and tested using various in situ compaction measurement devices. To characterize the roller machine-soil interaction, soil testing focused on measuring compaction parameters for the compaction layer. Variation in both MDP and in situ measurements was observed and attributed to inherent variability of the compaction layer and measurement errors. Considering the controlled operations to create relatively uniform conditions of the test strips, measurement variability observed in this study establishes a baseline for acceptable variation in production operations using MDP technology in cohesive soils. Predictions of in situ compaction measurements from MDP were found to be highly correlated when moisture content and MDP-moisture interaction terms were incorporated into regression models.

Abstract: Management of the vineyard floor affects soil and crop productivity, as well as runoff and sediment that leave the vineyard. In Monterey County, weed control is typically conducted in a 4-foot-wide area under the vines, while cover crops are planted in the middles between vine rows. This 5-year multidisciplinary study in a low rainfall vineyard evaluated the impact of weed control strategies (cultivation, pre-emergence and post-emergence herbicides) in the vine rows, factorially arranged with three cover-crop treatments in the middles. We studied soil compaction, moisture and runoff; vine and soil nutrition; soil microbial biomass and mycorrhizae; and grape yield and quality. The late-maturing 'Trios 102' triticale used more water during the vine growing season than the earlier maturing 'Merced' rye. Cover crops increased organic matter and microbial biomass in the middles and reduced sediment loss. Weed control treatments did not affect crop yield or soil nutritional and microbiological parameters, but cultivation increased soil compaction at 4 to 7 inches deep. Weed control strategies and cover crops must be chosen carefully to maximize benefits and minimize negative environmental impacts.

Abstract: A field and laboratory study was carried out to study the effect of pressure and temperature on the compaction of asphalt pavements. Density, temperature, number of passes, and type of roller were recorded in the field at four different paving projects in Wisconsin, with binder and mixture samples obtained from each project. Compaction in the field occurred at temperatures that ranged from 125 to 60°C. Densification was achieved only for temperatures above the 70-80°C range. Roller contact pressures were estimated between 300 and 700 kPa during the compaction process. Laboratory compaction was performed with Superpave gyratory compactor using the field compaction temperatures and contact pressures. The lab compaction results confirmed that below a certain temperature limit densification decreased significantly. Binder testing was performed to determine the binder viscosities in the full range of field compaction temperatures observed. The upper limit of viscosity for significant reduction in densification was estimated to be 50 Pa s. A procedure for identifying the lowest temperature at which acceptable densification rate can be achieved is proposed based on testing using the dynamic shear rheometer. The determination of the lower temperature limit for compaction is an important task that is absent in the current specifications.

Abstract: For successful designs of geotechnical structures, rational determination of the engineering properties of soils is an important process. In this context, compaction parameters, maximum dry unit we...

Abstract: With the objective of evaluating the growth of cover crops under different levels of soil compaction an experiment was installed under greenhouse conditions. A completely randomized block design was used with four replications, in which the treatments consisted of a factorial with four vegetal species of cover crops: Cajanus cajan, Sesamum indicum L., Pennisetum glaucum L. cultivar ADR 300 and Chenopodium quinoa Willd., in four levels of subsurface compaction (soil bulk density: 1.18; 1.34; 1.51 and 1.60 Mg m-3) in a Typic distropheric Red Latosol. The compaction of the subsurface soil was restrictive to the root growth of the studied species, concentrating them in the upper layer. The Pennisetum glaucum cultivar ADR 300 excelled in the production of dry matter and was able to develop in the compacted layers and below them. The increase of soil density in the compacted layer did not influence the root length density of the Cajanus cajan, Sesamum indicum and Chenopodium quinoa, however these species had inferior performance when compared with the Pennisetum glaucum (L.) cultivar ADR 300, which presented greater root length density in all layers and densities.

Abstract: Summary Compaction is a major cause of soil degradation. It affects not only the porosity of the soil, but also the soil’s hydrostructural stability. Soil that is restored after temporary removal is particularly sensitive to compaction. We investigated the effects of trafficking with a heavy combine harvester on the shrinkage behaviour of a restored soil that had been gently cultivated for several years. We tested the hypothesis that compaction decreases the hydrostructural stability of restored soil by analysing simultaneously measured shrinkage and water retention curves of undisturbed soil samples. Shrinkage strongly depended on clay and organic carbon content. Taking account of this influence and normalizing the shrinkage parameters with respect to these soil properties, we found pronounced effects of trafficking on shrinkage. Ten passes with the combine harvester decreased the structural porosity by about 40% at maximum swelling and by about 30% at the shrinkage limit and increased the bulk density by 8% at maximum swelling and by 10% at the shrinkage limit, but did not significantly affect the porosity of the soil plasma. Moreover, trafficking modified shrinkage, increasing the slopes of the shrinkage curve in the basic and structural shrinkage domains by about 30% and more than 150% after 10 passes, respectively. Evidently the aggregate structure was strongly destabilized. The results indicate that the hydrostructural stability of the soil was still very sensitive to compaction by trafficking even 5 years after restoration. The analysis of shrinkage seemed well suited for the assessment of compaction effects on soil structure.

Abstract: Considerable research has been conducted on the erosion of cohesive soils, yet predictive models remain rudimentary at best and few design data are available. This research summarizes the current knowledge on cohesive soil erosion. Cohesive soil erosion is a complex phenomenon, determined not only by soil properties and flow hydraulics, but also by the chemical interaction between the soil pore water and the eroding fluid. While noncohesive soils erode as individual grains, cohesive soils erode as aggregates; thus, interped bonding is also important. The erosion resistance of cohesive soils is further affected by changes in the amount and physical state of soil pore water: significant increases soil erodibility have been correlated to freeze-thaw cycling. Considered a soil property, soil erodibility expresses the rate at which a soil will erode, once erosion starts. Typically, the erosion rate of cohesive soils is predicted using a model relating soil erodibility to a measure of the hydraulic forces on the soil. The most common expression is known as the excess shear stress equation, which states the erosion rate is proportional to the difference between the applied boundary shear stress and the soil critical shear stress. Originally used for noncohesive soils, the critical shear stress is defined as the hydraulic stress at which a soil will erode. For cohesive soils, critical shear stress is difficult to predict accurately; there is no precise definition of critical shear stress as there is rarely a defining the point at which erosion starts. Several researchers have developed empirical relationships between the critical shear stress of cohesive soils and soil properties, but the prediction of fluvial entrainment rates based on soil physical properties has had limited success. This lack of adequate methods to predict soil erodibility and critical shear stress for cohesive soils has led to the development of several field test methods using an impinging jet. Ongoing research is comparing these test methodologies.

Abstract: Conversion of forested lands to agriculture, including cultivation and pasture has been linked to land degradation, including soil compaction, reduced soil fertility and increased salinity hazard. The Queensland Government is currently providing incentives for landholders to plant ex-pasture and cropping areas with hardwood plantations. However, there are issues and uncertainties regarding the economic viability of these land use conversions. Carbon credits resulting from additional carbon (C) sequestration achieved in the plantations are now recognised under the Kyoto Protocol, but the nature of the carbon trading scheme that will apply is still unclear, as Australia has not ratified the Protocol. This study compared the total soil C under native scrub (subtropical dry vine forest), grazed pasture, cultivation and spotted gum (Corymbia citriodora subspecies variegata) forest on the Red Ferrosol soils of the Kingaroy region in southeast Queensland (SEQ). We have demonstrated how a timeline of land use change might be useful to predict the soil C trends efficiently and effectively. Cumulative soil C (including surface litter and particulate organic matter) to 1.2 t m-2 dry soil ranged from 72 t ha-1 at the cultivated site to 281 t ha-1 under the mature spotted gum forest. The estimated annual rates of soil C loss under cultivation in last 55 years (1950-2005) was 2.1% and the estimated annual rate of soil C gain in pasture in last 23 years (1983-2005) was 1.1%. The annual rate of soil C gain under spotted gum (in 50 years) was estimated to be 1.4%. Therefore there is considerable potential for spotted gum plantations to sequester soil C when planted on ex-agricultural land in SEQ.

Abstract: The North Otago Rolling Downlands (NORD) of New Zealand is currently undergoing a large change in land use with subsequent intensification as a result of a new large community irrigation scheme. To assess the effect of this change, a 4-year monitoring survey was established on two common Pallic soil types of the area to determine the influence of irrigation term (short, 5 years) and grazing animal (cattle vs. sheep) on a range of physical and organic matter soil quality parameters. This 4-year survey also included the historical land use of dryland sheep farming in the absence of irrigation water. Irrigation term had no significant (P > 0.05) effect on soil physical parameters (percentage macroporosity and bulk density) for 3 of 4 years and no significant effect (P > 0.05) on topsoil total carbon or nitrogen contents. However, irrigation term had a significant (P < 0.01) but biologically small effect on the ratio of carbon to nitrogen with narrowing of the range under longer term irrigation. A significant difference between the dryland and irrigated surveys was found for macroporosity (dryland sheep 17.3% v/v vs. irrigated sheep 13.4% v/v; P < 0.001) and for the C:N ratio (dryland sheep 10.7 vs. irrigated sheep 10.2; P < 0.05). The change in macroporosity under irrigation is likely to take effect within 1 or 2 years of land-use change as little discernable differences in soil physical properties were evident from land under short- or long-term irrigation.

Abstract: Ecologically effective mine reclamation is characterized by the return of pre-mining floral and faunal communities. Excessive soil compaction typically results in delayed succession and low species diversity on reclaimed mine lands. We compared small mammal abundance and diversity among three levels of compaction in reforestation plots on an eastern Kentucky surface mine during 2004 and 2005. Compaction levels included 1) no compaction (loose-dumped), 2) light compaction (strike-off), and 3) high compaction (standard reclamation). Peromyscus leucopus (White-footed Mouse) made up 98% (295 of 300) of all individuals captured. In 2004, loose-dumped plots had more White-footed Mice (n = 108, mean = 36, SE = 0.58) than high-compaction plots (n = 62, mean = 20.6, SE = 3.10). Strike-off plots had more White-footed Mice (n = 59; mean = 19.6, SE = 0.66) than loose-dumped (n = 46, mean = 15.3, SE = 1.45) or high-compaction (n = 20, mean = 6.6, SE = 2.19) plots in 2005. Canopy cover and large rocks that cre...

Abstract: The Burruyacu district (Tucuman province, Argentina) is a farming frontier in the western Chaco plain, at the foothills of the sub-Andean mountain ranges, where agricultural land-uses are in conflict with the conservation and management of the Chaco forest. Over the last decades, large-scale farming rapidly expanded due to population pressure, attractive market prices, easy accessibility, favourable annual rainfall, fertile soils, and flexible land tenure. Cropland extension, mainly for heavily mechanized soybean production, has resulted in important reduction of the Chaco forest and also caused physical soil degradation, especially soil compaction, and soil erosion. Land suitability was assessed using the Food and Agriculture Organization (FAO) framework for a set of crops ecologically adapted to the area, including soybean, maize, wheat, sugarcane, citrus, and safflower. Only 16% of the study area has high suitability for most of the selected crops. Major limitations for cropping are low annual rainfall and flooding in the east of the study area, and topography (slope) and flooding in the west. As climate varies over relatively short periods of time, with recurrent cycles of dry and rainy years, land suitability for the selected crops was also assessed under extreme but realistic climatic conditions. Under rainy-year conditions, almost all the study area is unsuitable or marginally suitable for most of the crops. Under dry-year conditions, the study area is unsuitable for all crops, except safflower, which is more drought-resistant. This article proposes alternatives to the mono-cropping of soybean with the aim to help farmers make adequate decisions on land-use and management under deteriorating environmental conditions and for addressing the issue of competitive land uses in the context of land-use planning.

Abstract: Yield variability of spring pea (Pisum sativum L.) in farmers' fi elds is mainly due to soil compaction at sowing and abiotic stresses during the reproductive period. Winter peas fl ower earlier, and thus should be less sensitive to abiotic stress at the end of the cycle, but because of their sensitivity to frost they must be sown late in autumn when soils are very wet. Pea breeders are working on new winter cultivars that are more resistant to frost and highly sensitive to photoperiod and that could be sown earlier in autumn under better soil conditions. Our aim was to measure crop growth, development, and seed yield of diff erent types of pea cultivars using factorial experiments that evaluated the eff ect of soil structure, sowing period, and cultivar at two sites in France. Compaction reduced seed yield by 18% at Grignon and 6% at Estrees-Mons, but had no signifi cant eff ect on crop development. November sowings resulted in increased seed yield of about 1 t ha–1 at both sites compared with spring sowings, and were associated with larger numbers of reproductive nodes and seeds m–2. Cultivars exhibited contrasting characteristics in terms of mean seed dry weight, seeds m–2, and number of reproductive nodes, but fi nal seed yields were similar within sowing periods. Th e ability of the crop to convert crop gro

Abstract: The objective of this work was to evaluate the physical quality of soil in pastures under continuous grazing. The pastures were established with Bermudagrass coastcross (Cynodon dactylon) intercropped or not with the perennial peanut (Arachis pintoi). The intercropped pasture was fertilized with 0, 100 and 200 kg ha-1 nitrogen (N) per year and the single-cropped pasture was fertilized with 200 kg ha-1 N per year, totaling four treatments. The experiment was established in 2002 in a Haplorthox (Rhodic Ferralsol) in Paranavai, northwestern of Parana, Brazil, using a randomized complete block design, with two replications. Between 2002 and 2007 the stocking rate was based on forage offer level. In March and November 2007, undisturbed soil samples were collected from 0-75 and 75-150 mm depths for the evaluation of soil bulk density, soil porosity, and soil air and water storage capacity. Continuous grazing with stocking rates controlled as a function of the pasture production did not damage the soil physical quality. The soil water storage capacity is a sensitive indicator to assess the effects of stocking rate intensification on soil physical quality.

Abstract: The knowledge of the pressure levels that can be applied to the soil under different weed management system (WMS) is importante for coffee plantations management. The objective of this study was to evaluate the influence of different weed management systems on the susceptibility to compaction of a Red-Yellow Latossol (Oxisol) (LVA) using soil support capacity (CSC) models. This study was carried out at the Epamig Research Farm in Patrocinio, state of Minas Gerais, Brazil, in a coffee plantation using Ruby 1192 coffee variety in a 3.8 x 0.7 m spacing, planted in February 1999. Four WMS were used and the soil samples were collected in-between the rows under the following management systems: (1) no weed control (SC); (2) hoe-weeded (CM); (3) weed control with post-emergence herbicide Glyphosate (HPOS); (4) weed control with pre-emergence Oxyfluorfen (HPRE). Fifteen undisturbed soil samples from each system were collected (in the layers 0-3, 10-13 and 25-28 cm) in July 2004, totaling 180 samples. The undisturbed soil samples were equilibrated at different moisture contents and subjected to the uniaxial compression test to obtain the soil CSC models. Results suggested that the support capacity of the LVA decreases in the center of the inter rows in the following order: HPRE in the 0-3 cm layer > CM in the 10-13 cm layer > SC in the 0-3, 10-13, 25-28 cm layers = HPOS in the 0-3, 10-13, 25-28 cm layers = CM at 0-3 and 25-28 cm layers = HPRE in the 10-13 cm layer > HPRE in the 25-28 cm layer. Weed control with HPRE in the 25-28 cm layer was most susceptible, while HPRE in the 0-3 cm layer was most resistant to soil compaction. The management systems SC and HPOS in the 0-3, 10-13, 25-28 cm layers and the managements CM in the 0-3 and 25-28 cm layers and HPRE in the 10-13 cm layer were equally susceptible to soil compaction.

Abstract: Two grazing trials were conducted on a Vertosol in central Queensland to assess the effects of stubble grazing by cattle on soil properties and subsequent crop performance. Two adjacent contour bays were selected for two treatments (grazed and ungrazed) in each trial. Both trials were conducted following a grain sorghum crop. In trial 1 (during 1996) the surface soil was dry throughout grazing. In trial 2 (during 1998) the surface soil became saturated during grazing after 125 mm of rain. Soil physical properties including bulk density, shear strength, cone index and hydraulic conductivity were measured pre-and post-grazing in both trials and the response of wheat crops sown after grazing was assessed. The area was then double-cropped to sorghum to measure any further residual impacts. After grazing on dry soil, hoof marks were barely evident and no significant change was found in any soil physical property or the establishment or yield of a subsequent wheat crop. After grazing on saturated soil, there were visible hoof marks 49 mm deep and increases in soil shear strength, cone index and drawbar power requirement. The following wheat crop had reduced dry matter at 32 days and reduced grain yield. There was no immediate change in ground cover and no effect on wheat establishment following direct-drilling 37 days after the cattle were removed. In a sorghum crop following the wheat crop, there were no carryover effects on any soil physical property or on crop yield. We conclude that under a similar regime to that of trial 1 (dry soil and no rainfall during grazing), adverse effects of stubble grazing are unlikely. It follows that if grazing can be restricted to times when the surface soil is dry enough to minimise compaction by animals, there is little risk of adverse effects on subsequent crop performance.

Abstract: The widespread use of heavy equipment during timber harvesting and site preparation can lead to reduced soil productivity and warrants development of new methods to assess compaction. We evaluated the effects of soil particle density, organic matter, particle size distribution, extractable oxides, and plastic and liquid limits on the maximum bulk density (MBD) of forest soils in British Columbia. Soil samples were collected from 33 sites throughout British Columbia, covering the major forest and soil types of the province. The standard Proctor test was used to determine MBD and related parameters, including the gravimetric water content (W MBD ) and porosity (f MBD ) at which MBD was achieved. The signifi cance levels of single soil properties in predicting MBD were in the order plastic and liquid limits, organic matter, oxalate-extractable oxides, and particle size distribution. For all samples, liquid limit and clay were most closely related to MBD (R 2 = 0.83). Addition of organic matter to the model increased the regression coeffi cients, and oxidizable organic matter caused a greater increase than did total C. Stratifi cation of the sample set into groups based on plasticity led to higher R 2 values in multiple regressions, and different soil properties were important for nonplastic soils than for those with high, moderate, and low plasticity. Prediction with multiple regression explained the most variation in MBD for nonplastic soils, while properties of highly plastic soils explained the least variation in MBD and moderately plastic soils were intermediate. Based on our fi ndings, we propose an approach for using MBD to help better interpret bulk density data in forest soil compaction studies. Abbreviations: BWBS, Boreal White and Black Spruce biogeoclimatic zone; CDF, Coastal Douglas-fi r biogeoclimatic zone; CWH, Coastal Western Hemlock biogeoclimatic zone; f, porosity; f MBD , porosity at MBD; ICH, Interior Cedar‐Hemlock biogeoclimatic zone; IDF, Interior Douglas-fi r biogeoclimatic zone; LTSP, Long-Term Soil Productivity Study; MBD, maximum bulk density; PCA, principal component analysis; SBS, Sub-Boreal Spruce biogeoclimatic zone; gravimetric water content at which MBD was achieved.

Abstract: The impact of wood loads on bulk density and preconsolidation pressure and of harvester and forwarder traffic on rut depth, bulk density and preconsolidation pressure of two Ultisols were examined in this study. Our objective was to quantify the threshold beyond which significant soil compaction and rutting would occur. This study was carried out in the county of Eunapolis, state of Bahia, Brazil, (16 o 23 ' 17 '' S and 39 o 10 ' 06 '' W; altitude 80 m asl) in two Ultisols (PAd2 and PAd3) with different texture classes, in experimental areas with eucalypt plantation. The study involved measurements at the wood load site and machine driving at specific locations in the forest during logging operations. The treatments consisted of one harvester pass and, 8, 16 and 40 passes of a fully loaded forwarder. Thresholds were established based on the rut depth and percentage of preconsolidation pressure values in the region of additional soil compaction defined in the bearing capacity model. The percentage of soil samples with values of preconsolidation pressure in the region of additional soil compaction indicated a greater susceptibility of PAd3 than of PAd2 to soil compaction. The threshold levels established here based on preconsolidation pressure and rut depth indicated that no more than eight forwarder passes should be allowed in loading operations in order to minimize soil compaction.