Abstract: The Mollisols from the Pampas Region of Argentina have been described as presenting different compactability behaviors under agricultural systems. The purpose of this study was to provide information on the inherent soil factors related to the susceptibility to compaction. Total organic carbon (TOC), texture (CLAY, SILT, SAND), water retention at 0.33 kPa (WR), Proctor maximum bulk density (BD MAX ) and critical water content (CWC) were determined for 26 top-soils selected from the semiarid, subhumid and humid Pampas Region. The selected sites crossed three soil textures (loamy sand, loam and silty loam). It was observed that the compactabilty of these soils could be assessed by inherent properties routinely measured in the laboratory. Their behavior under experimental compaction revealed that TOC had a dominant effect on the susceptibility of these soils to compaction. Higher TOC levels reduced the BD MAX ( r 2 =0.75, p r 2 =0.82, p MAX per unit of water content (susceptibility to compaction, SC) depends on SILT and TOC levels ( r 2 =0.49, p MAX levels were lower than those considered critical for rooting and diminished with increasing TOC, water and SILT contents, in addition to TOC, can determine the potential for compaction in these soils. Based on the need to prevent shallow compaction, continuous no-till systems are possible on soils from the semiarid Pampas Region but not in soils from the subhumid and humid Pampas Region with low TOC.

Abstract: Farmers are concerned that soil compaction will be a problem in the first few years after conversion to strict no-till. The objective of this study was to determine if the changes in depth-incremental soil bulk density during transition to no-till were greater than density changes due to natural variation. We sampled six locations from a no-till field and six locations from a disk field of a soybean [Glycine max (L.) Merr.]-corn (Zea mays L.) rotation and took 12 samples at each of the 12 locations. The soil types sampled were Clarion (fine-loamy, mixed, superactive, mesic, Typic Hapludoll), Nicollet (fine-loamy, mixed, superactive, mesic, Aquic Hapludoll), and Canisteo (fine-loamy, mixed, superactive, calcareous, mesic, Typic Endoaquoll) soils. We divided each 300-mm soil sample into 15 depth-increments, and pooled the 12 samples for each location for each 20-mm depth-increment. Bulk densities ranged from 0.9 to 1.3 Mg m -3 in the top 0 to 20 mm, and 1.2 to 1.6 Mg m -1 for the depth-increments below 20 mm. Comparing the first and last sampling dates for the no-till field, no significant changes in bulk density were detected for any depth-increment; however, for the disk field, increases in significan: bulk density were detected in 10 out of IS depth-increments. Natural causes probably contributed to the bulk density changes that occurred over time in both fields. None of these bulk densities were high enough to restrict root growth. We concluded that concern about soil compaction under no-till management is inappropriate for these structured soils.

Abstract: The concentrations of soil CO2 and O2 at three Long-term Soil Productivity sites located in the Sub-Boreal Spruce biogeoclimatic zone of British Columbia, Canada, were monitored over several growing seasons. These sites were treated with three levels of soil compaction and three levels of organic material removal following forest harvest. Both compaction and depth had a significant effect upon soil CO2 concentrations and average values increased in response to deeper sampling and compaction. Removal of the forest floor and other organic materials had no significant effect upon soil CO2 and O2 concentrations. Mean soil CO2 concentrations varied from site to site and data collected over three growing seasons also showed that mean CO2 values in response to compaction fluctuated significantly from year to year. The high levels of soil CO2 observed in this study (up to 40 000 µ L L−1), especially in response to the compaction treatments, may have had a substantial effect upon whole plant carbon allocation as w...

Abstract: The spatial heterogeneity of N 2 O flux at short distances (0.1-2 m) was characterized in relation to various soil physical and chemical properties and the location of incorporated crop residues in arable soils. Plots were prepared with uniform compaction (either zero or compacted by a laden two-wheel-drive tractor) in two field experiments, one under winter barley (Hordeum vulgare), the other under oil-seed rape (Brassica napus). Flux measurements were made of N 2 O using small chambers (7.3 cm diameter) placed at intervals of approximately 10 cm along a transect (c. 2 m long) across the direction of application of the treatments of compaction and residue incorporation. The flux of N 2 O and many other measurements showed large variation over short distances, particularly when fluxes were small. The spatial variation of the flux was not closely related to the soil properties. Correlations showed that cone resistance, air permeability and closeness to incorporated residues were as important as soil NO 3 , NH 4 and soluble C in determining flux of N 2 O from non-compacted soils. Most properties of compacted soils did not correlate with N 2 O flux. Correlation and multiple regression analysis failed to establish consistent relations between soil environmental variables and N 2 O flux, but principal component regression indicated that, overall, N 2 O flux increased with decreasing distance from straw residues and air permeability, and with increasing cone resistance and wet bulk density.

Abstract: The purpose of this experiment was to investigate the influence of soil compaction and water content on root development of 6 month old sengon seedling. The experiment was arranged 3 x 3 factorial experiment within a complete randomized design and 3 replications. The factor number one was soil compaction and factor number two was soil water content. The soil compaction factor consists of 3 levels, which are 1,5 g/cm3 (A1), 1,2 g/cm3 (A2), and 0,9 g/cm3 (A3) respectively, while the soil water content also consists of 3 levels, which are 60,41 % (B1), 49,64% (B2), and 42,86 % (B3) for each level. The parameters were counted which are root number, diameter, root length, biomass, surface area, and root length density. The result was that soil compaction treatment has a significant influence to root number, root length, biomass, surface area, and root length density. On the other hand the soil water content treatment on pF 2,54 until 3,5 and interaction soil compaction and water content have no influence to root number, diameter, root length, biomass, surface area, and root length density. Root number, diameter, length, biomass, surface area and root length density were increased accordingly to the age of the seedling, but the increasing of soil compaction has decreased to the number, length, root length, biomass, surface area and root length density. The secondary root was found more larger than the primary and the tertiary root in term of the root length, surface area and root length density.

Abstract: Earthworms may alter the physical, chemical, and biological properties of a forest soil ecosystem. Any physical manipulation of the soil ecosystem may, in turn, affect the activities and ecology of earthworms. The effects of removing organic matter (logs and forest litter) and severely compacting the soil on native earthworm species were measured in a central USA hardwood region (oak-hickory) forest in the Missouri Ozarks (USA). Soils in this region are characterized by a cherty residuum that is primarily of the Clarksville series (Loamy-skeletal, mixed, mesic Typic Paledults). Earthworms were collected from 0–15 cm depth each spring and fall for 2 years by handsorting, and densities were determined on a per meter square basis. Two native earthworm species, Diplocardia ornata and Diplocardia smithii, were dominant on this site. Organic matter removal decreased the average individual biomass of both species. However, both species responded differently to soil compaction. Soil compaction affected D. ornata adversely and D. smithii favorably. This suggested that the degree of soil compaction was not as restrictive with respect to D. smithii (2 mm diameter) as to D. ornata (5 mm diameter). Moreover, the apparently improved soil environmental conditions resulting from the remaining organic matter in compacted soil enhanced the population and growth of D. smithii. Sampling position on the landscape affected D. ornata but not D. smithii. Soil microbial biomass C and soil microbial biomass N were decreased under soil compaction when the organic matter was removed. Other factors influencing the ecology and activity of these two species will require further study.

Abstract: Heavy agricultural machinery can cause structural degradation in agricultural subsoils. Severe structural degradation impedes plant growth. Therefore, compaction must be limited to layers that can be structurally reclaimed and remoulded with reasonable effort by tillage. The purpose of this study was to investigate the impact of a single pass with a sugar beet harvester on the soil properties of an unploughed Eutric Cambisol. Field measurements and laboratory testing were carried out in Frauenfeld, Switzerland. In addition 2D calculations of strain, stress and subsequent compaction were conducted using a three-phase (soil skeleton, pore water, and air) model for unsaturated soil incorporating a recently developed constitutive law. Model data were compared to the field measurements. Due to the pass of the machinery, the soil was compacted down to a depth of at least 0.15 m and at most 0.25 m. This compaction was indicated by an increase in soil bulk density and pre-consolidation pressure as well as by a decrease in total porosity and macroporosity. The surface displacement measured in the field was consistent with the calculated model data. The calculated and measured stresses at depths of 0.35 and 0.55 m stand in good accordance with each other, whereas at a depth of 0.15 m the pressure measured in the field exceeded the calculated pressure. In this study, we show the degree of compaction due to heavy wheel traffic and the suitability of a model approach to describe compaction processes.

Abstract: Preliminary results of small-scale model compaction grouting tests performed in a geotechnical centrifuge are presented. The soil response to a one-stage grout bulb injection in dry uniform sand was examined at various prototype depths, and the effects of grout composition on grout bulb development and shape and on soil response are evaluated. Preliminary results indicate that the shape of the injected grout bulb is a function of overburden pressure. For specific grouting conditions, there is a maximum size that the grout bulb will achieve. Observed soil deformations were similar to those observed in models of deep uplift anchors. The addition of either clay or fly ash to the grout mix reduced the ability to sustain high injection pressures.

Abstract: The long-term effects on soil compaction by different traffic intensities during forestry harvester operation were evaluated in field experiments on heavy clay, vertic Argiudol. A conventional 2WD 73.5 kW engine power tractor with a trailer, 4.2 Mg and 3.75 Mg total load respectively, were used on a multiclonal Populus deltoides (Marsh) 3x3 plantation. There were four treatments: one pass, five pass and ten repeated passes with the tandem over the same track, and a control plot without experimental traffic. Moisture content, bulk density and penetrometer resistances were evaluated before and immediately after the traffic treatments and three years later. Effects of induced soil compaction by traffic were especially marked on topsoil, with cone index increments between 76 and 16% in the first 40 cm of the surface layer after treatments. Bulk density had a similar tendency but limited to a 15 cm depth. Three years later, only subsoil cone index in the track line, below 20 cm depth, was significantly higher than the interline track soil cone index. The 10 passes treatment had significant differences compared to the 1 pass and no traffic control plot treatments from the surface layer to 50 cm depth, without differences with the 5 passes treatment in most of the studied soil layers. Subsoil compaction may be induced by repeated traffic with low axle load and their effects persist for a very long time.

Abstract: Yields of arable crops are commonly lower on the crop margins or headlands, but the nature of the relationship between yield and distance from the crop edge has not been clearly defined, nor have the reasons for lower marginal yields. Surveys of 40 winter wheat headlands were carried out in 2 years to determine how yield changed with distance, and what factors might influence this relationship. Two field experiments were also conducted over 3 years in winter cereal headlands, in which the effect of distance was measured under conservation headland and conventional (fully sprayed) management. Yields in the headland surveys varied from 0.8 to 10.2 t/ha. An inverse polynomial regression model was fitted to yield and weed data. Best fits were obtained by using separate parameters for each site. Adjusting yields to take account of weed dry matter improved the non-linear fit between yield and distance from crop edge. Field experiments provided similar results but the non-linear relationship was not as apparent. There was a negative relationship between soil compaction, as measured by a cone penetrometer, and yield in one field experiment, where soil density values were relatively constant. No relationship was found between pattern of nitrogen fertilizer application and yield. Conservation headland management resulted in lower yield at one experimental site, especially in the third year, but not at the other site. Where yields were affected, weed dry matter was higher in conservation headland plots than in fully sprayed plots. Although greater weed competition appears to account for at least part of the observed yield reductions on headlands, the role of other factors, particularly soil compaction, needs further study. Increased weed infestation may be an indirect result of reduced crop competition caused by other adverse conditions.

Abstract: Recreational use of wild lands can create areas, such as campsites, which may experience soil compaction and a decrease in vegetation cover and diversity. Plants are highly reliant on their roots' ability to uptake nutrients and water from soil. Any factors that affect the highly specialized root hairs ("feeder cells") compro- mise the overall health and survival of the plant. We report here initial data in our investigation of how of soil compaction affects plant roots, using the common bean as a dicot model. Soil compac- tion decreases overall plant growth and causes changes in root hair morphology and the F-actin cytoskeleton, critical to the function of root hairs. In addition, rates of cytoplasmic streaming, which facilitate nutrient and water uptake, are reduced in root hairs from compacted treatments. When plants were removed from compacted soils, higher amounts of total C, N and Ca were found compared to those of controls. We discuss these data in the context of rehabilita- tion methods in impacted wilderness areas.

Abstract: A practical model of the soil structure dynamics in ploughed fields can be a powerful aid to farmers attempting to optimise their management practices. This paper describes a compartmental model that simulates the changes over several years in an indicator of the effects of cropping systems on soil structure. This indicator, the proportion of severely compacted clods in the ploughed layer, was measured in two plots at the INRA Experimental Centre at Grignon (Yvelines, France), where two cropping systems produced very different compaction conditions in a silt loam. The ploughed layer was considered to be a set of elementary compartments delimited by the wheel tracks and actions of tillage tools. The percentage of severely compacted clods in each elementary volume changed with time due to transfer between compartments during mouldboard ploughing, compaction and fragmentation. The proportion of severely compacted clods changed exponentially until it reached a plateau, after about 8 years. The equilibrium values of the indicator were very similar to those measured in the experimental plots. The model was very sensitive to the rate at which severely compacted clods were lost, probably because the vertical distribution of these clods in the soil profile was not taken into account in this compartmental model. The model in its present state can be used to compare the effects on soil structure of various technical changes.

Abstract: The effects of soil compaction under water deficit conditions during the reproductive stage on the grain yield of rice were examined with various cultivar s. In a field experiment, three rice cultivar s were grown in compacted and non-compacted upland conditions and irrigation was terminated at the early reproductive stage. The grain yield and total dry weight (DW) at maturity was similarly reduced by soil compaction regardless of the rank of the cultivars in drought resistance. However, the yield was superior in the cultivars that showed higher yield and DW under non-compacted conditions. In greenhouse experiments, six rice cultivars were grown in the pot of 1.0 meter in depth containing soil at three levels of soil bulk density (SBD), and water supply was reduced by lowering the water table during the reproductive stage. The effects of SBD on DW and grain yield were similar among six cultivars. In both field and pot experiments the yield reduction was predominantly caused by a smaller number of ...

Abstract: The aim of this experimental study was to determine the effect on soil porosity and compaction of the number of the tractor passes on the soil surface. The soil has a sandy loam texture. A tractor passed once, twice, and four times while the water content of soil was near field capacity. Numbers of tractings increased soil bulk density and compaction, and decreased total porosity, void ratio, air porosity and drainage porosity. One and two tractor passes did not markedly affect the percentage of porosity kept at field capacity porosity, but four tractor passes improved it.

Abstract: McBride, R.A., McLaughlin, N.B. and D.W. Veenhof. 2000. Performance of wheel and track running gear on liquid manure spreaders. Can. Agric. Eng. 42:019-025. A field experiment was conducted to characterize soil-vehicle interactions and to measure tractor power/fuel requirements when hauling a fully loaded tank spreader (18 m) fitted with rubber tracks (2721x635), high flotation tires (28L26) or conventional truck tires (445/65R22.5). A second objective was to apply an existing soil compaction model to the data from this field trial and to determine if its estimates of wheel rut depth were reasonable. The experiment was carried out in late autumn on a harvested soybean field (silt loam soil) located in southwestern Ontario. Fuel consumption and drawbar draft were measured during the traffic treatments with an instrumented tractor, and selected soil properties were measured afterwards. An analytical-type soil compaction model was used to estimate the wheel rut depth for the two pneumatic tire treatments. The type of running gear had a highly significant effect on both drawbar draft and fuel consumption (p < 0.001), with the tracks having the highest values (mean 24.6 kN and 21.5 L/h, respectively) and the flotation tires having the lowest (mean 13.9 kN and 16.9 L/h, respectively). The truck tires left ruts with a mean depth of 42.3 mm, while the flotation tires left cleat impressions that were barely discernable. A pedotransfer function was used to estimate the preconsolidation stress (26 kPa) and compression index (0.173) of the plow layer soil and, with these and other input data, the soil compaction model estimated rut depths that were quite comparable to those observed. The only ruts produced by the tracks were those of the track grousers (about 48 mm deep), but extensive soil shearing was evident. The tracks and truck tires produced significantly higher (p < 0.05) measured dry bulk densities at a depth of 150 mm when compared to those induced by the flotation tires. Soil cone penetrometer measurements were not as conclusive in distinguishing the impact of the running gear treatments on soil structural conditions. In general, however, flotation tires appeared to be the preferred running gear option with respect to several key parameters (fuel consumption, drawbar draft, wheel rut depth, dry bulk density) under these particular soil and loading conditions.

Abstract: The effect of a long term of soil compaction on dry matter production (DMP) and water use in rice cultivated under limited water supply during the reproductive stage is unknown. Our objectives were...