Gefügeänderung bei Andosolen Südchiles als Folge der Nutzung seit der Rodung

Changes in soil structure as caused by land use after clearing virgin forest Three groups of volcanic ash soils from southern Chile were investigated to evaluate the change of porosity, penetrometer resistance and packing characteristics of virgin forest soils due to different forms of land use during a variable length of time. The different forms of land use were pasture, arable land and reforestation with Pinus radiata. Afforestation tended to loosen the soil and to increase soil strength, whereas pasture use or a pasture-arable land rotation showed severe compressions. Compressions, as noticed in the ash soils under study, appeared to be more pronounced than is generally observed in mineral soils.     

Soil penetration resistance and tree root development

Current UK guidance suggests that a 'rootable' soil profile of at least 1.0 m depth should be sufficient to allow adequate rooting of the majority of tree species in a range of soil types and climatic conditions [Arboricultural Journal (1995) vol. 19, 19–27]. However, there is some uncertainty as to what constitutes a loosened soil profile in terms of penetration resistance. In this study the root development of Italian alder, Japanese larch, Corsican pine and birch was assessed after 5 years of tree growth. These data were compared to penetration resistance measured using both a cone penetrometer and a 'lifting driving tool' (dropping weight penetrometer). Tree root number and percentage were significantly reduced by increasing soil penetration resistance measured with both the cone penetrometer ( P  <   0.050) and the 'lifting driving tool' ( P  =   0.011 and 0.008 respectively). The vast majority of roots were recorded in soils with a penetration resistance of less than 3 MPa (90.7%) with a significant amount in the less than 2 MPa class (70.2%). Root development of Italian alder, Japanese larch and birch all showed a similar pattern, but Corsican pine appeared to be capable of rooting into more compact soils. The 'lifting driving tool' can be used as an alternative measure of soil penetration resistance. This equipment is more cost effective, easier to use and capable of measurements at a greater depth than the cone penetrometer. The majority of Japanese larch and birch roots (84.3%) were recorded in soils where it took less than 15 impacts to penetrate one 10 cm soil depth increment. The modelled data also suggest that a penetration resistance of 2 and 2.5 MPa relates to 10 and 15 impacts respectively.     

Persistence of soil compaction due to high axle load traffic. II. Long-term effects on the properties of fine-textured and organic soils

The long-term effects of high axle load traffic on soil structure were investigated in three field experiments. Two of the experiments were located on fine-textured mineral soils (Vertic Cambisol). The clay soil had 48 g clay (particle size less than 2 μm) per 100 g in the topsoil and 65 g per 100 g in the subsoil, and the loam soil had clay contents of 30 g and 42 g per 100 g in the topsoil and subsoil, respectively. One experiment was located on an organic soil (Mollic Gleysol) consisting of well-decomposed sedge peat mixed with clay from 0.2 to 0.4–0.5 m depth, and underlain by gythia (organic soil with high clay content). In the autumn of 1981, one pass and four repeated passes with a heavy tractor-trailer combination compacted the soils to 0.4–0.5 m depth. The trailer tandem axle load was 19 Mg on the clay and 16 Mg on the other soils.

For 9 years after the experimental traffic, the main crops grown were spring cereals. During this time, the maximum axle load applied during field operations was 5 Mg and the maximum tyre inflation pressure was 150 kPa. The clay and loam froze to 0.5 m depth for 6 and 2 years, respectively. During several growing seasons all three soils dried and cracked. In the ninth year after the loading, soil penetrometer resistance, saturated hydraulic conductivity (K_sat), macroporosity and number and area of cylindrical biopores were measured and the visual structure of the soils examined.

Compaction in the plough layer was alleviated by ploughing and natural processes, whereas in the subsoil the effects of the compaction were still measurable, in all experiments, in the ninth year after the high axle load traffic. In the clay soil in the 0.3–0.5 m layer and in the organic soil in the 0.28–0.4 m layer, the penetrometer resistance was 22–26% greater and the soil structure more massive in the plots compacted with four passes than in the control plots. In the 0.4–0.55 m layer in all soils, the loading with four passes decreased K_sat by 60–98% and macroporosity (diameter greater than 300 μm) by 37–70%. In the fine-textured mineral subsoils, cylindrical biopores were found in all treatments. The trend of the results was, however, for biopores to be fewer in compacted than in control plots.     

Two mechanisms for age-hardening of soil

Soil samples from Germany, Israel and USA were moulded at water contents around the lower plastic limit and compacted with uniaxial pressures c . 20-200 kPa. The samples were stored at constant water content. At intervals after moulding, the strengths of sub-samples were measured with a small penetrometer.
The soils showed increases in strength with time. Two types of behaviour were observed and explained by a simplified theory for soil strength. With the German and Israel soils, penetrometer strength increased by the same absolute amount irrespective of compaction pressure. This indicates that new particle-particle bonds were being formed at a rate which was not affected by compaction. With the USA soils, the ratio of penetrometer strength/initial strength increased with time and was independent of compaction pressure. This indicates that existing particle-particle bonds were being reinforced by a cementation mechanism. Evidence is presented which suggests that age-hardening by this second mechanism may be inhibited by soil organic matter.     

Changes in penetration resistance of Ultisols from southern China as affected by shearing

Shear stresses and soil properties modified due to stress play an important role during formation of seals in a series of rainfall events and during tillage. The objectives of the study were to evaluate the effects of the penetrometer geometry on the penetration resistance as affected by shearing under different initial soil conditions and to use the information on soil strength to elucidate shearing process. Nine homogenous air-dried soils (<2 mm) were sprayed and stored so as to obtain equilibrium soil water contents. The moist soils were sheared by horizontal displacement of layers of soil particles/aggregates in between hands in one direction. The soil cores were prepared with comparable bulk density before the measurement of maximum penetration resistance (P_max) with a small flat tip and a cone tip penetrometers. At a wide range from 0.05 to 6.2 MPa, P_max was linearly correlated between the small flat tip and the cone tip penetrometers. The conversion ratio was higher under the saturation condition irrespective of the shearing effect. The penetrometer with the small flat tip was more sensitive for the weak soils. Shearing generally increased P_max in most cases, but it decreased P_max for some sandy soils under both saturated and unsaturated conditions and for a clayey soil under the saturated condition. The soil consisting of swelling clay exerted a decrease in P_max. Rearrangement and/or sliding of particles/aggregates and increase in soil suction during shearing were attributed to the increase in P_max. Increase in porosity due to the aggregation during shearing was ascribed to the decrease in P_max. In addition, it was shown that agricultural cultivation resulted in a reduction in soil strength.     

Soil penetrometer resistance spatial variability in a Ferralsol at several soil moisture conditions

The penetrometer resistance (PR) spatial variability in a Ferralsol under different soil moisture conditions was characterized through statistical and geostatistical methods. PR measurements were made in a 10-row, 10-columns, 3-m spacing grid at 20–30 cm depth using a hand-pushing penetrometer. Measurements were made for dry soil conditions (before irrigation) as well as 2 and 24 h after irrigation. The soil bulk density (BD) and the relative topographical altitudes (RT) were measured at the same locations. The PR spatial variability is normally distributed for dry soil conditions and after irrigation-water redistribution. A normal distribution fits also to the BD spatial variability. PR mean and coefficients of variations are lower for wet soil conditions and vary notably according to the soil moisture condition. The PR semivariance values are much higher for dry soil conditions than those found for wet soil conditions. However, the semivariogram of PR before irrigation shows almost a pure nugget effect. Irrigation yields a spatial structure in PR measurements. Despite the differences in the shown spatial structure, the range of the PR semivariograms before and 24 h after irrigation is about 8–10 m, which is very similar to the range of the BD semivariogram. The correlation coefficients between PR and the other measured variables are very small before and after irrigation, which could lead to the conclusion that those variables are not related at all. However, according to the co-dispersion coefficients plotted as a function of the separation lag, the correlation between those variables changes according to the separation distance. Particularly, PR and the RT show correlation 24 h after irrigation only for lags between 5 and 12 m. The results pointed out that PR spatial variability depends on soil moisture condition, soil BD and on several local features as microtopography.     

A comparison of five instruments for measuring soil strength in cultivated and uncultivated cereal seedbeds

A torsional shear box, shear vane. cone penetrometer, drop-cone penetrometer and pocket penetrometer were used to measure soil strength at several depths less than 150 mm in cultivated and uncultivated seedbeds in a loam and a sandy clay loam. From the shear box results, cohesion was higher and the angle of friction was lower in the sandy clay loam than in the loam. Angle of friction was independent of cultivation but cohesion was higher in uncultivated than in cultivated soil. Despite these differences cone resistance was similar in both soils above 70 mm depth. Vane shear strength and drop-cone penetration, although empirical, indicated strength differences between soils and cultivations similar to those found with the torsional shear box. Vane shear strength, at 42 kPa, was about twice as high as cohesion in the sandy clay loam and, at 33 kPa, over four times as high as cohesion in the loam. These overestimates increased with increasing bulk density. The range of measurement of the pocket penetrometer was inadequate to cover the range of soil strengths encountered. The coefficient of variation within plots for cone resistance decreased from 76 per cent at 10 mm depth to about 22 per cent at 70 mm depth and below, and for vane shear strength it was 33 per cent near the soil surface. The drop-cone penetrometer results were the most variable, reflecting the log-normal distribution of penetrations. The cone penetrometer was the fastest method, followed by the shear vane, drop-cone penetrometer and torsional shear box in that order.     

Effects of 'Agri-SC' soil conditioner on the erodibility of loamy sand soils in East Shropshire, UK: preliminary results

Abstract. The effect of Agri-SC' soil conditioner on the erodibility of loamy sand soils has been investigated at the Hilton experimental site, Shropshire, since March 1988. Factors measured have included runoff and erosion, soil structure, crust strength, splash susceptibility, aggregate stability, soil micromorphological properties, response to compaction and penetrometer resistance.
Treatment decreased runoff and erosion rates, bulk density, splash erosion, crust strength and penetrometer resistance, and increased pore space and aggregate stability. The effects on crust strength, aggregate stability and bulk density were statistically significant. The results suggest that applications of 'Agri-SC' could have beneficial effects for soil conservation.     

Influence of failure mode induced by a horizontally operated single-tip penetrometer on measured soil resistance

Excessive soil compaction has negative effects for agriculture and the environment. Measurement of soil strength is a common indirect measure of soil compactness. In the context of precision farming, on-the-go soil mechanical resistance measurements using single- and multiple-tip horizontal sensors have been developed. It has been reported that there was a significant relationship between soil mechanical resistance values measured with both vertically operated cone penetrometer and horizontally operated sensors only for relatively deep layers. It was hypothesized that the differences in horizontally measured soil resistance in different soil layers could be explained by different failure modes. The objective of this research was to develop a horizontal soil mechanical resistance sensor and to observe the failure mode in front of it while penetrating soil at three different depths. A single-tip horizontal penetrometer was equipped with a 30° prismatic tip and had a base area of 324 mm². The prismatic tip was mounted horizontally to an S-shaped load cell housed inside a shank. A data-logging system was also developed to record measurements with 10 Hz sampling rate. The sensor was tested in a field with silty clay loam soil at three depths of 20, 25 and 30 cm. Cone index (CI) values were obtained with 1 cm depth increments and 1 m horizontal intervals along each transect for comparison using a standard cone penetrometer. The results showed that average horizontal soil mechanical resistance index (HRI) values for both depths of 20 and 25 cm were similar due to the brittle failure mode in both cases. However, when the tip was operated below the critical depth of the sensor, the value of HRI at 30 cm depth increased three times when compared with 20 or 25 cm depth values. This was due to change in failure mode from brittle to compressive mode below the critical depth. There was a significant relationship (R² = 0.75) between HRI and CI for the 30-cm depth, whereas for shallower depths the relation was not significant. It can be concluded that the correlation between measurements obtained with the vertically and horizontally operated penetrometers would be significant as long as both produced the same soil failure mode.     

The efficacy of three techniques to alleviate soil compaction at a restored sand and gravel quarry

Reinstated soil at restored sites often suffers from severe compaction which can significantly impede root development. Several methods, such as ripping and complete cultivation, are available to alleviate compaction that may occur as a result of soil reinstatement. This paper examines the effectiveness of the industry standard industrial ripper and a prototype modern ripper, the Mega‐Lift, in comparison with the recommended best practice method of complete cultivation. An investigation of the penetration resistance of the soil at a restored sand and gravel quarry was carried out using a cone penetrometer and a ‘lifting driving tool’ (dropping weight penetrometer) 3 years following cultivation. All the cultivation treatments reduced soil compaction to some degree compared with the untreated control. However, the penetration resistance values suggest that rooting would be restricted at relatively shallow depths in the plots cultivated using the industrial and Mega‐Lift ripper; penetration resistance exceeded 2 MPa within the first 0.33 m. Complete cultivation maintained penetration resistance values of less than 2 MPa within the depth limit of the penetrometer of 0.42 m. In addition, the results from the ‘lifting driving tool’ indicate that soils treated using complete cultivation remained significantly looser than those treated with the ripper to a depth of at least 0.80 m. The results demonstrate that complete cultivation remains the most effective method of alleviating soil compaction on restored sites, although it is recognized that its relatively high cost may restrict the uptake of the technique.     

Simultaneous measurement of soil water and soil hardness using a modified time domain reflectometry probe and a conventional cone penetrometer

Soil strength and water content are important indices for assessing soil resistance to root growth and soil compaction both of which affect other soil properties. Therefore, simultaneous measurement of soil penetration resistance (PR) and soil water content can aid agricultural land management. We measured PR with a conventional cone penetrometer, followed immediately by determining water content using a modified TDR probe inserted into the penetrometer hole. From the results of a field feasibility test, soil water content was measured satisfactorily and correlated well with data obtained by the gravimetric method, except for those data from near the surface owing to soil disturbance when the cone penetrometer was extracted after the PR measurements. Field results demonstrate that PR and soil water content have three‐dimensional variability, with a markedly different distribution pattern between cultivated and subsoil layers at the field scale. Overall, the variability in the PR and soil water data is similar to that reported in previous studies. We conclude that our method produces results helpful to field management of soil and water because it is based on a simple and easy technique for the simultaneous measurement of soil water content and PR.     

东北黑土有机碳的分布及其损失量研究

为了分析东北黑土土壤有机碳(SOC)的分布特征及其开垦以来黑土SOC的损失程度,我们于2004～2005年在黑龙江和吉林两省采集了32个自然黑土剖面样品,在每个自然黑土样品附近对应采集32个景观条件相似的耕作黑土样品。结果表明,自然黑土样品0～30cm土层SOC含量平均为32.20 g kg-1,最高可达63.46 g kg-1,黑龙江省自然黑土SOC含量(34.55 g kg-1)高于吉林省(23.80 g kg-1)。耕作土壤SOC平均含量为22.71 g kg-1,远低于自然土壤。受温度的影响,随着纬度的增加,自然黑土与耕作黑土SOC含量逐渐递增。由于土壤侵蚀以及耕垦和去除作物残留物等农业管理措施的综合作用,使得耕作黑土表层SOC含量小于自然黑土。与自然黑土相比,耕作黑土0～10cm土层SOC损失量在26.84%～46.57%之间,亚表层损失相对较少。黑土SOC含量下降也是土壤水土流失致使黑土层变薄的一个直接表现。耕作黑土表层流失厚度可以通过自然与耕作黑土剖面SOC含量的分异差值来估算。通过对土壤剖面上SOC的分布进行校正剔除土壤侵蚀的影响后得到的同等深度SOC含量的差值才可视为由耕作以及有机质输入量差异等因素造成的SOC损失量。未经校正而进行的自然黑土和耕作黑土同一深度SOC含量的比较可能过高估计了农业管理措施对土壤SOC损失量的影响。     

Soil strength and crop emergence in direct drilled and ploughed cereal seedbeds in seven field experiments

Cone resistance and vane shear strength were measured in the top 50–100 mm of seven soils. Bulk density and water content were also measured in the same layer by coring. At each site cone resistance and vane shear strength tended to decrease with increasing water content and decreasing bulk density down to 1300 kg m-3, but at lower densities they were not related to bulk density. Cone resistance and vane shear strength tended to decrease with increasing coarseness of texture but also depended on soil structure and organic matter content. Plant populations, mainly spring barley, were reduced in soils with cone resistances and vane shear strengths greater than 2500 kPa and 65 kPa respectively. Such high strengths in undisturbed soils were associated with wheeling during harvesting, were apparently independent of soil type and, at the only site of measurement, apparently decreased during weathering in the subsequent season. In contrast to the cone penetrometer, the vane shear tester has minimal shaft friction in undisturbed soils and is more sensitive to soil differences and less sensitive to water content differences than the penetrometer. It is apparently more suitable for indexing the suitability of undisturbed soils for the penetration of direct drill coulters and for subsequent plant establishment.     

Effect of soil organic matter, electrical conductivity and sodium adsorption ratio on tensile strength of aggregates

The properties of soils affected by salinity and processes involving degradation of soil structure have been partly recognized. However, the effects of saline and sodic conditions on mechanical and physical properties of soils have been studied to a lesser extent. In this research, the effects of electrical conductivity (EC) and sodium adsorption ratio (SAR) on soils possessing various amounts of organic matter were assessed under laboratory conditions. The soils contained a uniform clay type, predominantly Illite. The major difference of the soils was their amount of organic matter content. The treatments consisted of solutions with definite EC and SAR (two levels of EC: 0.5 and 4 dS/m and three levels of SAR: 0, 5 and 15). The amount of tensile strength was dependent on organic matter, EC, and SAR in a way that with the increase of SAR, the tensile strength decreased. In similar SAR, treatments with higher EC exhibited greater tensile strength. Also, the soils with higher organic matter showed greater tensile strength. The analysis of variance showed the significant difference (at 1%) between the mean of parameters analyzed (soil type, sampling depth, EC, and SAR). The order of averages of tensile strength were: permanent pasture (Agropyron elengatum)Festuca arusdinaceae)相似文献   

Scale- and location-dependent correlations of soil strength and the yield of wheat

The relationship between soil strength and crop yield may be summarized by a linear correlation coefficient (usually negative). It is likely, however, that this over-simplifies a complex situation in which the relationship between these variables depends on spatial scale and location. We used the wavelet transform to assess this scale- and location-dependence. We established a transect on an arable field in Eastern England, and studied the correlations of soil strength (top- and subsoil) with crop yield. The transect comprised 267 contiguous 0.72 m × 0.72 m plots. Measurements were taken during two consecutive growing seasons of winter wheat (harvest dates of August 2004 and 2005). Soil strength was measured with a penetrometer in the spring of each growing season. As expected, the overall correlation of soil strength with yield was negative but weak. Wavelet analysis revealed that, at fine spatial scales, topsoil and subsoil strength were correlated more or less equally with yield; however, at coarse spatial scales, topsoil strength had a stronger correlation with yield than did subsoil strength. The correlation of topsoil strength with yield at fine spatial scales (corresponding to about 1 m on the ground) was negative. A likely source of this fine-scale variation was the soil compaction associated with tractor wheelings. The correlation of topsoil strength with yield at the coarsest spatial scale (corresponding to about 50 m on the ground) was positive. This correlation was temporally stable, and might have reflected how soil strength can act as a proxy for other soil attributes. In the 2005 growing season, we found evidence that, at intermediate spatial scales, the correlation of soil strength with yield changed depending on the position on the transect. This was probably due to an interaction between the compaction associated with tractor wheelings and the local soil conditions. There was no evidence of such location-dependence in the correlation of soil strength with yield in the 2004 growing season. In summary, the effect of soil strength on crop yield was not expressed in a constant negative correlation across all spatial scales and locations: the negative correlation occurred mainly at fine spatial scales, and the correlation changed according to the position in the landscape and the prevailing local soil conditions.     

Shear strength of surface soil as affected by soil bulk density and soil water content

This paper proposes a new method to measure the soil strength parameters at soil surface in order to explain the processes of soil erosion and sealing formation. To simulate the interlocks between aggregates or particles within top 2 mm of the soil, a piece of sandpaper (30 particles cm⁻²) was stuck on the bottom face of a plastic box of diameter of 6.8 cm with stiffening glue and used as shear media. The soil strength for the soils from sandy loam to clayey loam was measured with penetrometer and the new shear device at soil surface at different bulk density and soil water content. The normal stresses of 2, 5, 8, 10 and 20 hPa were applied for the new shear device. The results indicated that significant effect of bulk density on soil strength was detected in most cases though the difference in bulk density was small, ranging from 0.01 to 0.09 g cm⁻³. It was also indicated that the measurement with the new shear device at soil surface was reproducible. The changes in soil shear strength parameters due to changes in bulk density and soil moisture were explainable with the Mohr–Coulomb’s failure equation and the principles of the effective stress for the unsaturated soils. The implications of the method were later discussed.     

Improvement of the physical fertility of a degraded Alfisol with planted and natural fallows under humid tropical conditions

Abstract. Topsoil (0–15 cm) bulk density, aggregate stability, soil dispersibility, water retention and infiltration were measured between 1989 and 1996 on an Alfisol under rehabilitation in southwestern Nigeria. The planted leguminous species were Pueraria phaseoloides, Senna siamea, Leucaena leucocephala, Acacia leptocarpa and A. auriculiformis. Also, plots with natural fallow and maize/cassava intercropping were included. Level (minimum) and mound tillage with hoes was adopted for the cultivated areas under study after 4 and 6 year fallow periods. Under fallow, the soil bulk density decreased from1.56 to 1.11 t m73.The continuously cropped treatment (level tillage) had significantly higher bulk density than the fallowed subplots after 6 years. Mean soil penetrometer resistance ranged from 75 to 157 kPa for fallowed plots and from 192 to 295 kPa for the continuously cropped (level tillage) subplot. Surface soilwater contentswere similar for all the treatments during the soil strength measurements. Although soil aggregates were generally of low stability and not well formed, they were improved by fallowing.
Soil structural improvement by planted fallows was similar to that by natural fallow, but the trees were more promising for long-term fallow (>6 years) than the herbaceous P. phaseoloides. However, the improvement in soil structure after 4 or 6 year fallow could not be maintained in subsequent cropping. Furthermore, the significant improvement in soil bulk density caused by A. auriculiformis and natural fallow was more rapidly lost on the cultivated subplots compared with other fallow treatments. Thus, soil structure recovery under a fallow does not imply a sustained improvement when stress is applied to this soil. Post-fallow soil management options such as residue incorporation and tillage to ameliorate compaction or soil strength will be necessary to enhance the improvements by fallow species.     

Effect of dairy slurry application on soil compaction and corn (Zea mays L.) yield in Southern Wisconsin

As stocking rates on Wisconsin dairy farms continue to increase, one possible nutrient management solution is to haul slurry to nearby grain farmer's fields. Although the nutrient and soil building benefits of manure are well known, many grain farmers are hesitant to apply manure on their fields due to potential soil compaction. Studies were initiated to evaluate the effects of tanker-applied slurry on soil compaction and corn (Zea mays L.) yield. An on-station trial was established to address the issues of compaction caused by manure tankers, repeated traffic associated with field headlands, and the possible ameliorating effect of manure itself on corn yield. In addition, 15 replicated on-farm trials were established to evaluate the impact of single pass manure applications on soil compaction and yield. These predominately fall applications were conducted when the host farmer felt that the soil would support tanker traffic. Due to its portability and instrument sensitivity, compactness was evaluated with a data-logging hand held penetrometer.Results from the on-station trial indicate that multiple passes did increase compactness above single-pass traffic and the check. The slurry itself did not attenuate the effect of traffic on soil compaction, nor on yield. Despite yield reductions estimated from in-track samples in both years of 6% (one-pass traffic) and 22% (six-pass traffic) in this study, whole plot corn yields were not reduced due to compaction. The on-farm trials indicated that manure application technique does affect compaction patterns; with broadcast application resulting in less area trafficked by the tanker than injection application, and therefore less area compacted. The narrower gauge truck tires used at some sites led to significantly higher penetrometer readings compared to the control, but this was not the case at sites with wider tractor tires. As in the on-station work, although compaction led to higher penetrometer readings, whole plot corn yields in compacted plots were not adversely affected compared to the control. These results suggest that, in the first year after slurry application, on predominantly prairie derived soils; well-timed applications of dairy slurry do not cause extensive soil compaction nor a reduction in corn yields. This study did not look at the potential residual effects that may positively (>soil organic matter) or negatively (residual soil compaction) impact subsequent crops.     

Influence of single passes with high wheel load on a structured, unploughed sandy loam soil

In a field experiment, a sandy loam was subjected to single passes with a sugar beet harvester at two different soil water potentials. Different hopper fillings resulted in ground contact pressures of 130 kPa (partial load) and 160 kPa (full load) underneath the tyre. Bulk density, macroporosity (equivalent pore radius >100 μm), penetrometer resistance, air permeability and pre-consolidation pressure were measured within and next to the wheel tracks at depths of 0.12–0.17, 0.32–0.37 and 0.52–0.57 m. Furthermore, the soil structure at two horizons (Ahp 7–24 cm, B(C) 24–38 cm) was visually assessed and classified.

The moist plot responded to a wheel load of 11.23 mg (160 kPa) with an increase in bulk density and pre-consolidation pressure as well as with a decrease in air permeability and macroporosity at a depth of 0.12–0.17 m. With a wheel load of 7.47 mg (130 kPa) on the moist plot and with both wheel load levels on the dry plot, only slight changes of the soil structure were detected. At a depth of 0.32–0.37 and 0.52–0.57 m, the measurements did not indicate any compaction. An ANOVA indicates that the factor “soil water potential” and the factor “wheel load” significantly influence the bulk density at a depth of 0.12–0.17 m. No interactions occurred between these two factors. The wheel traffic on the test plot had no effect on the yield of winter wheat planted after the experimental treatment.

Bulk density, macroporosity and pre-consolidation pressure proved to be sensitive to detect compaction because they varied only slightly and are easy to measure. In contrast, the standard deviation of air permeability is large. The soil structure determined visually in the field confirms the values measured in the laboratory. The results of the penetrometer resistance measurements were not explainable.