In determining stress limits to prevent soil compaction, it is important to know the mechanical properties of soils. One important parameter is the precompression stress, which is often used as a ...criterion for soil susceptibility to compaction. A series of uniaxial compression tests on Swedish arable soils was conducted by Eriksson Markpackning och rotmiljö (soil compaction and root environment), Report 126, Division of Agricultural Hydrotechnics, Department of Soil Sciences, Swed. Univ. Agric. Sci., Uppsala, Sweden, 1982 (in Swedish, with English summary). The objective of the present study was to derive precompression stress values from these data.
Eighteen soils, generally classified as Eutric Cambisols and with clay contents ranging from 62 to 863
g
kg
−1 were used. Soil cores (25
mm high, 72
mm in diameter) were sampled at 10
cm intervals to a depth of 1
m and equilibrated at 0.5 or 60
kPa water tension. The cores were then compressed in an oedometer by sequential stresses of 25, 50, 100, 200, 400 and 800
kPa. Precompression stress was determined according to Casagrande The determination of the pre-consolidation load and its practical significance, in: Proceedings of the International Conference on Soil Mech. and Found. Eng. (ICSMFE), vol. 3, Cambridge, MA, 22–26 June 1936, pp. 60–64 and by regression methods.
Precompression stress was higher for subsoils than for topsoils and higher at higher soil water tension, but was difficult to relate to soil physical properties. Values determined according to Casagrande were generally between 100 and 200
kPa. Values determined by regression methods had a smaller range compared to the Casagrande method.
The values of precompression stress indicate a low risk for subsoil compaction on Swedish soils, which is not in line with practical experience in compaction experiments. The concept of precompression stress as a clear transition from small, elastic deformation to larger, plastic deformation could not be supported by the stress–strain relationships obtained in this study. There is an urgent need to design laboratory tests that reflect soil behaviour in the field.
The introduction of six-row sugarbeet harvesters, with total loads of approximately 35
Mg on two axles, caused major concern among Swedish sugarbeet (
Beta vulgaris L.) growers regarding the risk for ...subsoil compaction. A project was started in 1995, which included six long-term field experiments in southern Sweden. The objective was to study effects of heavy axle load traffic during harvest of sugarbeets on penetration resistance, saturated hydraulic conductivity, bulk density and crop yield. Three of the field sites were loams (Eutric Cambisols), two were sandy loams (Eutric Cambisols) and one was sand (Haplic Arenosol). The treatments were: no traffic, four passes by a three-row harvester towed by a tractor (approximately 18
Mg total load on four axles, tyre inflation pressure of tractors 100–150, and 200–250
kPa for the harvester) and one and four passes by a self-propelled six-row harvester (approximately 35
Mg total load on two axles, tyre inflation pressure 200–240
kPa). Traffic was applied late in the autumn at a soil moisture content close to field capacity, but the treatment with four passes with a six-row harvester was also carried out under drier conditions earlier in the autumn.
In the spring after traffic, no significant changes in penetration resistance were found. When measured 2–4 years after traffic, significant changes between treatments were found to 0.5
m depth on three sites. Differences between years are possibly an effect of age-hardening.
Saturated hydraulic conductivity at 0.3 and 0.5
m depth, measured on cores sampled in the spring after traffic, was in several cases reduced by about 90% after four passes with a six-row harvester. As an average for all sites, this traffic significantly reduced saturated hydraulic conductivity and increased bulk density at 0.5
m depth. At two sites, measurements were repeated 4 years after traffic and differences in saturated hydraulic conductivity between treatments were approximately the same as on the first sampling occasion. Despite the great effects on soil physical properties, differences in yield between treatments were mainly small and insignificant.
The data concerning saturated hydraulic conductivity may be useful for modelling the effects of subsoil compaction, for example on erosion and denitrification, since little such data is available in the literature. The results clearly demonstrate to farmers that heavy traffic during harvest of sugarbeet implies a major risk for compaction of the subsoil, which can be seen as a long-term threat to soil productivity.
Terra rossa and eutric cambisol soils were surveyed in Slovenia. At both sites, 6–13 boreholes were drilled in a regular 24 m × 24 m square grid. Soil samples from various depths were taken for gamma ...spectrometric analysis, and radon in soil gas was measured at a depth of 80 cm using an AlphaGuard instrument. The following ranges of activity concentration (Bq kg⁻¹) were obtained for ²³⁸U, ²²⁶Ra, ²²⁸Ra, ⁴⁰K and ¹³⁷Cs: in terra rossa, 64–74, 70–84, 45–49, 293–345, 20–30 and, in eutric cambisol, 55–80, 132–147, 50–57, 473–529, 106–272. Radon activity concentrations in both soils ranged from about 100 kBq m⁻³ to 370 kBq m⁻³.
Field traffic may reduce the amount of air-filled pores and cavities in the soil thus affecting a large range of physical soil properties and processes, such as infiltration, soil water flow and ...water retention. Furthermore, soil compaction may increase the mechanical strength of the soil and thereby impede root growth.
The objective of this research was to test the hypotheses that: (1) the degree of soil displacement during field traffic depends largely on the soil water content, and (2) the depth to which the soil is displaced during field traffic can be predicted on the basis of the soil precompression stress and calculated soil stresses. In 1999, field measurements were carried out on a Swedish swelling/shrinking clay loam of stresses and vertical soil displacement during traffic with wheel loads of 2, 3, 5 and 7
Mg at soil water contents of between 11 and 35% (w/w). This was combined with determinations of soil precompression stress at the time of the traffic and predictions of the soil compaction with the soil compaction model SOCOMO. Vertical soil displacement increased with increased axle load. In May, the soil precompression stress was approximately 100
kPa at 0.3, 0.5 and 0.7
m depth. In August and September, the soil precompression stress at 0.3, 0.5 and 0.7
m depth was 550–1245
kPa. However, when traffic with a wheel load of 7
Mg was applied, the soil displacements at 0.5
m depth were several times larger in August and September than in May, and even more at 0.7
m depth. An implication of the results is that the precompression stress does not always provide a good indication of the risk for subsoil compaction. A practical consequence is that subsoil compaction in some soils may occur even when the soil is very dry. The SOCOMO model predicted the soil displacement relatively well when the soil precompression stress was low. However, for all other wheeling treatments, the model failed to predict that any soil compaction would occur, even at high axle loads.
The measured soil stresses were generally higher than the stresses calculated with the SOCOMO model. Neither the application of a parabolic surface load distribution nor an increased concentration factor could account for this difference. This was probably because the stress distribution in a very dry and strongly structured soil is different from the stress distribution in more homogeneous soils.
Traffic with high wheel loads in combination with high inflation pressure implies a risk for subsoil compaction, but effects will depend on the soil strength. Soil displacement during traffic with a ...heavy sugarbeet harvester (total load approximately 35
Mg on two axles) was determined at 0.3, 0.5 and 0.7
m depths during harvesting in the autumn. Measurements were made on one occasion on a clay loam (Eutric Cambisol) and a sand (Haplic Arenosol), and at different water contents on a sandy clay loam (Eutric Cambisol). Soil mechanical properties (precompression stress and shear strength) were determined for each traffic occasion. Field measurements were also compared with model computations of soil compaction, based on calculation of soil stresses and on the mechanical properties measured. On the sandy clay loam in the driest condition, displacement occurred only at 0.3
m depth, while it was registered down to 0.7
m depth in the wettest condition, when soil moisture was around field capacity. On the clay loam and the sand there was displacement down to 0.5 and 0.7
m depth, respectively. Model predictions of compaction correlated well with the depth to which displacement was measured in the field. One important task in subsoil compaction research is to define methods to determine soil mechanical properties that are easy to use and that still make it possible to predict compaction. The results clearly demonstrate that heavy sugarbeet harvesters may cause compaction to more than 0.5
m depth during normal field conditions in the autumn, with soil water content as the most decisive factor.
The vertical distribution of weed seeds in soil is crucial because seedling emergence varies with seed depth, whereas lateral soil displacement during mouldboard ploughing contributes to weed ...dispersal within the tilled field. In order to model vertical and lateral seed displacements during ploughing, an existing model describing soil particle movements for different ploughing characteristics (depth and width) and soil structures was adapted to integrate the effect of a skim-coulter. This model was tested in two field trials, in Northern France, using coloured plastic beads to imitate weed seeds. The trial in Dijon was set up on an eutric cambisol and comprised both compacted and uncompacted soil. The second trial was set up at Grignon, on an orthic luvisol which was left uncompacted before ploughing. The model correctly simulated the lateral displacement (LD) and the final vertical co-ordinate of the beads as a function of their initial location, soil structure before ploughing and ploughing parameters (ploughing depth and width; skim-coulter depth and width). The model was then used to calculate seed transfer matrixes describing vertical seed movements between seed bank layers and vertical seed distributions for different conditions and plough modes. The results were consistent with those of Cousens and Moss Weed Res. 30 (1990) 61–70. Simulations were performed to test the effect of different ploughing modes on the time changes in the vertical distribution of weed seeds and to show how the model can be used to manage weed seed concentration in the top layer by soil tillage. Furthermore, simulations showed that the vertical distribution of the seed bank could be extremely variable, depending on plough characteristics, soil structure or initial seed distribution. Although further studies are needed on the long-term seed movements under the influence of secondary tillage and climate, this model can be useful for evaluating different tillage modes on seed dispersal within the ploughed layers.
Subsoil compaction has become a problem of world-wide concern, especially under highly mechanised agricultural practices. Severe structural degradation impedes plant growth. Therefore, compaction ...must be limited to layers which can be structurally reclaimed 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. In autumn 1998 and 1999 field measurements and laboratory testing were carried out in Frauenfeld, Switzerland. The wheel loads were 107
kN in 1998 and 108
kN in 1999. Changes of bulk density, total porosity, macroporosity and pre-consolidation pressure show that compaction effects were restricted to the topsoil (0–0.25
m depth). Below 0.25
m depth no changes were measured. The compaction beneath the tyre was modelled with a two phase finite element model in the framework of critical state soil mechanics. The model predicts the degree and depth of compaction of an Eutric Cambisol caused by a single pass in Switzerland. Modelled data and field results agree quite well.
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.
