Verification of traffic-induced soil compaction after long-term ploughing and 10 years minimum tillage on clay loam soil in South-East Norway

Grain yields are presented from a 10-year field trial with four tillage regimes (annual ploughing, harrowing only, ploughing/harrowing alternate years and minimum tillage) on clay loam. We also present soil physical analyses and use the compaction verification tool (CVT) to assess compaction on plots with annual ploughing and minimum tillage, after using slurry tankers with contrasting wheel loads (4.1 Mg, 6.6 Mg) and wheeling intensities (1×/10×) in the 11th trial year, and yields monitored two years after compaction. Winter wheat yields in the period before compaction were strongly affected by tillage, with annual ploughing giving on average 24% higher yield than direct drilling. Both wheat and oats were far less affected in treatments with harrowing only or ploughing/harrowing alternate years, on average within 6% of annual ploughing. Yields after compaction were affected by both previous tillage and compaction intensity. In the first year, single wheeling after annual ploughing gave 23% yield reduction with 4.1 Mg wheel load and 28% reduction with 6.6 Mg wheel load, whilst multiple wheeling gave 14% reduction at 6.6 Mg wheel load. Yield reductions after minimum tillage ranged from 63% (single wheeling with 4.1 Mg) to 100% (multiple wheeling with 6.6 Mg). Similar trends were found in the second year. The soil physical data indicated that all wheeling led to changes in bulk density, pore sizes and permeability in both topsoil and subsoil on both sampled tillage plots. However, effects in the subsoil were partly masked by the soil's high initial bulk density, partly due to its high clay content. The CVT, which plots air capacity against hydraulic conductivity, suggested some harmful compaction on both plots, with the minimum tillage plot being less affected than the ploughed plot. However, yield results did not support this conclusion, indicating that other factors limited yields on the minimum tilled plot.     

Cumulative effect of annually repeated passes of heavy agricultural machinery on soil structural properties and sugar beet yield under two tillage systems

The aim of this study was to determine potential cumulative effects of repeated passes with current heavy agricultural machinery on topsoil (0–0.3 m) and subsoil (below 0.3 m) physical properties of a Luvisol as affected by long-term tillage (annual mouldboard ploughing to 0.3 m depth (MP), shallow-mixing conservation tillage to 0.1 m depth (SM) with a wing-bladed rigid tine cultivator). Moreover, sugar beet yield was determined. Wheeling was conducted with a six-row self-propelled sugar beet harvester representing contemporary heavy agricultural machinery (wheel load 7.8–11.7 Mg, average ground contact pressure 100–145 kPa). Wheeling was applied once per year over three consecutive years after harvest of sugar beet, cereal and cereal, and moreover, independent from regular plot management with light experimental machinery. Soil moisture at wheeling (0–0.6 m depth) was around 100% field capacity in most years, which was secured by irrigation before wheeling if necessary.Repeated wheeling negatively affected penetration resistance, macropore volume (equivalent diameter >50 μm) and air permeability of topsoil (0.05–0.1 m, 0.18–0.23 m) and subsoil (0.4–0.45 m) layers, while biopore number and surface water infiltration remained unaffected. SM compared to MP tillage increased penetration resistance while decreasing macropore volume and air permeability in the 0.18–0.23 m layer, whereas reverse effects occurred in 0.4–0.45 m depth. Sugar beet yield was decreased by wheeling and SM tillage compared to the control treatments. No significant interactions between wheeling and tillage occurred in any parameter investigated.Conclusively, SM tillage did not provide better subsoil resistance against compaction compared to MP treatment under wheeling and soil conditions prevalent in our experiment. Repeated wheeling with heavy agricultural harvest machinery is obviously at risk to exceed the bearing capacity of susceptible soils. Although (i) under regular harvest conditions just small parts of arable fields (except headlands) are wheeled with high loads, (ii) harvest is by far not every year conducted under high soil moisture, and (iii) effects in the subsoil were small, such risks have to be taken into account. Reduction of tillage depth to <0.1 m is not recommended for high yielding sugar beet crops grown on loessial soils.     

Heavy soil loading its consequence for soil structure,strength, deformation of arable soils

The alteration of mechanical soil properties by a single stress application exceeding all previously applied stresses is analyzed for a conventionally tilled and a conservational managed (since 1992) Stagnic Luvisol. Despite the more pronounced compactness of the plough layer under conventional management, it turned out to be less rigid compared to the “relictic” plough layer under conservation management. We assume that wheeling with a sugar beet harvester (rear wheel 140 kPa, front wheel 110 kPa, total mass 37 Mg) resulted in a break up of the plough pan. This was most obvious in the conventionally tilled soil whereas under conservation tillage, the plough pan seemed to resist the induced forces. Our results suggest that a break up of the compact plough layer and the subsequent re‐arrangement of newly formed fragments results in a smaller mechanical stability of the deformed soil. Soil structural changes within the plough pan are also indicated by the alteration of the anisotropy of cohesion and precompression stress, respectively. Altered mechanical properties induced by heavy soil loading affects the soil response to subsequent loading events, which could be shown by finite‐element simulations of stress‐strain properties. The simulations showed that a decrease in soil stiffness reduces the stress attenuation within the plough pan causing compressive and shear stresses to be transmitted into deeper soil levels, while at the same time shear strain increased.     

Soil compaction and stress propagation after different wheeling intensities on a silt soil in South-East Norway

The objective of this study was to evaluate the effect of wheeling with two different wheel loads (1.7 and 2.8?Mg) and contrasting wheeling intensities (1x and 10x) on the bearing capacity of a Stagnosol derived from silty alluvial deposits. Soil strength was assessed by laboratory measurements of the precompression stress in topsoil (20?cm) and subsoil (40 and 60?cm) samples. Stress propagation, as well as elastic and plastic deformation during wheeling were measured in the field with combined stress state (SST) and displacement transducers (DTS). We also present results from soil physical analyses (bulk density, air capacity, saturated hydraulic conductivity) and barley yields from the first two years after the compaction. Although the wheel loads used were comparatively small, typical for the machinery used in Norway, the results show that both increased wheel load and wheeling intensity had negative effects on soil physical parameters especially in the topsoil but with similar tendencies also in the subsoil. Stress propagation was detected down to 60?cm depth (SST). The first wheeling was most harmful, but all wheelings led to accumulative plastic soil deformation (DTS). Under the workable conditions in this trial, increased wheeling with a small machine was more harmful to soil structure than a single wheeling with a heavier machine. However, the yields in the first two years after the compaction did not show any negative effect of the compaction.     

Mechanical weeding effects on soil structure under field carrots (Daucus carota L.) and beans (Vicia faba L.)

The successful production of organic vegetables relies heavily on mechanical weeding, flame weeding and stale seedbeds. These operations involve repeated passes by tractors. Mechanical weeding also involves regular tillage. This combination of repeated tillage and compaction changes soil structure. We studied these structural changes in two fields of organic carrots and one field of beans in eastern Scotland. Structure was described by measuring soil strength with a vane shear tester and a cone penetrometer, by measuring bulk density and by visual assessment. Under beans, vane shear strength below the growing root zone was highly variable and in some areas was high enough to restrict root growth (>50 kPa). The carrots were grown in beds containing crop rows separated by bare soil. The bare soil was regularly weeded mechanically. The structure of this weeded soil in the top 10 cm layer of a loam eventually became disrupted and compacted enough to deter root growth (vane shear strength of 70 kPa). In addition the topsoil and subsoil in the wheel-tracks between the beds became very compact with little distinguishable structure. This compaction extended to the subsoil and persisted into the next cropping season (cone resistance >3 MPa at 35–50 cm depth). Reduced tillage by discing without ploughing was used to incorporate the straw used to protect the carrots overwinter and prepare the soil for the next crop. The resulting topsoil quality was poor leading to anaerobic growing conditions which restricted growth of the following crop and led to losses of the greenhouse gas nitrous oxide. The greatest threat to soil quality posed by mechanical weeding was subsoil compaction by tractor wheeling.     

Modification of porespace by tillage in two stagnogley soils with contrasting management histories

The soil porespace was studied in two long-term tillage experiments on two clayey stagnogleys in Southern England. The soils differed in respect of mineral and organic composition and previous management history. In both soils the total volume of pores and the volume fraction of macropores in the topsoil horizon declined with direct drilling compared with annual ploughing. This difference between tillage treatments appeared to develop more slowly in the soil that was formerly under continuous arable cultivation than in the soil that was previously in long-term grassland. Fluid transport coefficients were greater in ploughed topsoil in both soils; however, at the boundaries between topsoil and subsoil, and in the upper subsoil, permeability and gaseous diffusivity were greater after direct drilling. At a long-term arable site, soil was more consolidated below the depth of ploughing or shallow tillage, whereas in a former grassland soil ploughing disrupted the continuity of channel-type macropores.     

Interrelation between soil physical properties and Enchytraeidae abundances following a single soil compaction in arable land

In spring 1995 a silty clay soil was compacted dynamically by wheeling with graded wheel loads up to 6 times. The reaction towards wheeling was recorded immediately. In the following 3 years some soil physical parameters as well as the Enchytraeidae abundances were recorded regularly. To the first wheeling, the soil reacted plastically in vertical direction. The reaction became elastically after the 4th wheeling. After the 6th passage with a 5‒tonnes wheel load soil structure collapsed totally, which can be concluded from the stress ratios. After the wheeling event, abundances of Enchytraeidae decreased obviously compared to uncompacted plots. The increase in air permeability, air capacity, and the decrease of soil bulk density depend on primary tillage events. The recovery of Enchytraeidae abundances developed in parallel. Abundances seem to be regenerated in the 3rd year after the wheeling event. Primary tillage can help to induce biological and macroscopic structural regeneration of the top soil after a compaction event.     

Effect of tractor weight, depth of ploughing and wheel placement during ploughing in an organic cereal rotation on contrasting soils

The relative effects of using light (2–3 Mg) versus heavier (5–7 Mg) tractors, shallow (15 cm) versus deeper (25 cm) ploughing and on-land versus in-furrow wheel placement during ploughing were investigated from 2003 to 2006 in organic rotations (wheat or barley, green manure, oats with peas) and conventionally fertilized barley. Trials were located on loam soil in south-eastern Norway and silty clay loam in central Norway. Ploughing was performed in spring, when the topsoil moisture content was at or below field capacity, using single furrow ploughs that allowed alternative wheel placement and resulted in complete coverage of the surface by wheels each year (ca. 3 times the normal coverage during ploughing). Low tyre inflation pressures (≤80 kPa) were used throughout. The use of a heavy tractor increased topsoil bulk density slightly in the loam soil, and, in combination with in-furrow wheeling, it reduced air-filled pore space and air permeability at 18–22 cm. On the silty clay loam, the use of a heavy tractor did not increase bulk density, but it reduced air-filled pore space throughout the topsoil. In-furrow wheeling reduced air-filled pore space in this soil also, compared to on-land wheeling. Penetration resistance was in this soil always greater at 15–25 cm depth after shallow than after deep ploughing, especially with in-furrow rather than on-land wheeling. Shallow ploughing led on both soils to marked increases in perennial weed biomass compared to deep ploughing. Earthworms were hardly affected by the treatments, but in the loam in 2006 a higher number of individuals were found where the light rather than the heavy tractor had been used. Few significant treatment effects were found on grain yield and quality. Deep ploughing with a light tractor gave the highest wheat yield and protein content in 2 years on the loam soil, and on the silty clay loam the yield of conventionally fertilized barley was higher after deep than after shallow ploughing. In summary, limited evidence was found to support the use of on-land rather than in-furrow wheeling when ploughing is performed at favourable soil moisture and with tractor weights < 5 Mg. There is, however, reason to be wary of using heavy tractors (>5 Mg), even under such conditions. With regard to ploughing depth in organic rotations dominated by cereals, the need to combat perennial weeds by deep ploughing weighs probably more heavily than any possible beneficial effect of shallow ploughing on stimulating nutrient turnover.     

Mitigation of subsoil recompaction by light traffic and on-land ploughing: I. Soil response

Mechanically loosened subsoil has been shown to be prone to recompaction. We addressed a sandy loam that had been mechanically loosened by a subsoiler to a depth of 35 cm in 1997 and again in 1998. Perennial grass/clover was grown with limited traffic intensity in 1999 and 2000. A recompaction experiment was conducted in 2001 and 2002 when the soil was grown with oat and winter wheat, respectively. Using the formerly loosened plots, on-land ploughing was compared with traditional mouldboard ploughing with the tractor wheels in the furrow. In addition, the loosened plots were either light-trafficked (<6 Mg axle load and <100 kPa inflation pressure) or heavy-trafficked (10–18 Mg axle load and 200 kPa inflation pressure), respectively. Finally, the soil loosened by non-inversion deep tillage was referenced with a conventional ploughing–harrowing tillage system that never received the subsoil treatment. The conventional treatment was also grown with the grass/clover in 1999 and 2000. On-land ploughing and light traffic was applied in 2001 and 2002 instead of traditional ploughing and traffic for the conventional treatment. Penetration resistance and bulk density was recorded in the field. Undisturbed soil cores were taken in 1998, 1999 and 2002 from the 7–14, 18–27 and 25–30 cm layer and used for measuring total porosity, pores >30 μm and air permeability at −100 hPa matric potential. The results showed that on-land ploughing mitigated recompaction of the upper part of the formerly loosened subsoil. In contrast, only small differences in recompaction between heavy and light traffic were observed. The mitigation of subsoil recompaction was needed for the loosened soil to provide an upper subsoil with similar—not better—pore characteristics than the non-loosened soil in the conventional treatment. The structural conditions in the plough pan improved for the conventional treatment from 1998 to 2002 as indicated by an almost doubling in air permeability. This was interpreted as being related to the growing of grass/clover ley in 1999 and 2000 combined with a shift from traditional tillage and traffic to on-land ploughing and light traffic when growing cereals in 2001 and 2002. Results on root growth and crop yield are reported in an adjoining paper.     

Effects of agricultural machinery with high axle load on soil properties of normally managed fields

In a field study, conducted on 10 conventionally managed field sites in Germany, the effects of high axle loads (15–25 Mg) on soil physical properties were investigated. Soil texture classes ranged from loamy sand to silty clay loam. All sites were annually ploughed, and one site was additionally subsoiled to 40 cm depth. In the context of common field operations wheeling was performed either by a sugar beet harvester (45 Mg total mass, 113 kPa average ground contact pressure) or a slurry spreader (30 Mg total mass, 77 kPa average ground contact pressure). Soil moisture conditions varied from 3.2 to 32 kPa water tension during this pass. Penetration resistance was measured before the pass. Soil cores were collected in a grid scheme at each site before and after the machine passed. Bulk density, aggregate density, air-filled porosity and air permeability at seven distinct soil water tensions ranging from 0.1 to 32 kPa were determined in these cores taken from three layers (topsoil, plough pan and subsoil).At most sites, a pass by the sugar beet harvester or slurry spreader strongly affected topsoil properties. Bulk density and aggregate density increased while air-filled porosity and air permeability decreased. The plough pan was already severely compacted before wheeling: therefore changes were small. The subsoil showed no changes or only minor signs of compaction. Only at one site, which was subsoiled the year before, significant signs of compaction (i.e. changes in bulk density, air-filled porosity and air permeability) were detected in subsoil layers.The results show that using present-day heavy agricultural equipment does not necessarily lead to severe subsoil compaction in soils where a compacted plough pan already exists. However, fields which were subsoiled leading to an unstable soil structure are in serious danger of becoming severely compacted.     

Seedbed compaction produced by traffic on four tillage regimes in the rolling Pampas of Argentina

The main function of primary tillage is to increase the soil's structural macro-porosity, but during secondary tillage operations over these freshly tilled soils, traffic causes significant soil compaction. In terms of soil conservation however, there is evidence that direct sowing is a more sustainable system, even though there is still insufficient information about the rheology of a non-tilled soil under traffic. The objective of this study was to compare the traffic intensity and soil compaction caused by four different tillage regimes currently used by Argentinean farmers (1 direct sowing with a tractor and planter weighing 127 kN and 3 conventional tillage systems with equipment weighing 55.2 kN). The work was performed in the east of the Rolling Pampa region, Buenos Aires State, Argentina at 34°25′S, 59°15′W. Variables measured were: (1) cone index in the 0–450 mm depth profile; (2) bulk density; (3) total soil porosity; and (4) rut depth. (a) Results indicated that in the depth range 0–150 mm with all tillage treatments, bulk density and cone index values generated by tractor traffic were greater than the 1.3 Mg m⁻³ and 1400 kPa respectively. Similarly in deeper layers these parameters were greater than 1.45 Mg m⁻³ and 2000 kPa respectively. Measurements revealed that traffic reduced topsoil porosity under direct sowing by an average of 7% and under conventional tillage by 7.6–14.8% confirming that both systems cause both topsoil and subsoil compaction.     

Changes in the weed communities as affected by different primary soil tillage and deep loosening

Long-term soil cultivation at the same depth affects soil characteristics and crop productivity. The aim of the study was to investigate the impact of a long-term different intensity soil tillage methods and deep loosening on weed number, weed agrobiological group and soil seed bank changes in till Bathygleyic Dystric Glossic Retisol soil under the climatic conditions of the Western Lithuania (geographical coordinates 55°43′38″N, 21°27′43″E). The study included different soil tillage methods (conventional ploughing, shallow ploughing and shallow ploughless tillage) and deep loosening. During investigational years, the greatest weed number in crops and the greatest weed seed number in the seed bank were determined in the soil reduced tillage (shallow ploughing and shallow ploughless tillage). The weed number in crops of conventional ploughing soil was 35.8% lover compared to reduced tillage soil. The weed seed number in the seed bank of conventional ploughing was 49.6% lover compared to reduced tillage Decreasing soil tillage intensity resulted in weed seeds concentration in the upper topsoil. A one-time deep loosening had a significant effect during the crop rotation: the weed number in crops and weed seed number in the seed bank were determined to have increased by 26.6% and 51.6% in conventional ploughing soil and by 11.9% and 23.2% shallow ploughless soil respectively. However, after deep loosening, the number of Poa annua in crops decreased 2.9 times in plots of conventional ploughing and 1.7 times – in plots of shallow ploughing soil.     

Wirkung mechanischer Belastung auf Gefüge und Ertragsleistung einer Löss‐Parabraunerde mit zwei Bearbeitungssystemen

Effect of mechanical stress on structure and productivity of a loess‐derived Luvisol with conventional and conservation tillage In Germany farmers are committed to caring for the land by a soil protection law. Yet vehicles with ever increasing axle load endanger productivity and environmental quality of arable soils. In spring of 1995 a field experiment was startet on a wet silty Luvisol to test the effect of single mechanical loading on soil and crop characteristics, when managed by mouldboard ploughing (PL) or conservation tillage (CT). CT soils are considered to be more resistant against compactive stresses and to recover from degeneration more rapidly than PL soils. Beside an unwheeled control the loading treatments were light (2 × 2.5 t; number of wheel passes times wheel load); medium (2 × 5 t) and high (6 × 5 t). In 1995 even light loading of the PL soil caused a significant yield decline by 50% in spring barley, but this happened on CT soil only with high loading. In subsequent years with winter wheat and winter barley yield decline was less distinct. Loading of PL soil reduced total root length (from 4 to 1 km m⁻²) and rooting depth (from 70—90 to 40—70 cm), but on CT soil only root length was diminished by high loading. A tillage‐traffic pan (30—35 cm) hindered subsoil rooting in PL, which was favored in CT by earthworm channels. High loading caused compaction to at least 50 cm depth. Within the pan of the PL soil, penetration resistance attained 5 MPa and bulk density 1.65 g cm⁻³. In the CT soil the zone of maximum compaction was closer to the surface (15—25 cm). In PL soil the saturated hydraulic conductivity and the O₂‐diffusion coefficient gradually decreased with loading, but in CT soil only with heavy loading. The compacted top soil was broken in subsequent years by ploughing (PL: 25 cm) or rotary implements (CT: 5—8 cm). With PL, structure in the pan layer and subsoil did not recover, and rooting depth was still limited. Some restoration, however, was indicated with CT. Here transmitting properties increased in time, which was attributed to the reconstruction of root and earthworm channels, as demonstrated by computer tomography. We conclude that in silty soils compacted layers below ploughing depth will hardly be regenerated by internal processes. CT soils are less susceptible to loading, but high stresses are harmful too. Therefore recommending CT as a measure for protecting soil from compaction would not be enough, considering the present development towards heavy field machinery.     

Vertical distribution of soil properties under short‐rotation forestry in Northern Germany

Short‐rotation forestry (SRF) on arable soils has high potentials for biomass production and leads to long‐term no‐tillage management. In the present study, the vertical distributions of soil chemical and microbial properties after 15 y of SRF with willows and poplar (Salix and Populus spp.) in 3‐ and 6‐year rotations on an arable soil were measured and compared to a pertinent tilled arable site. Two transects at different positions in the relief (upper and lower slope; transect 1 and 2) were investigated. Short‐rotation forestry caused significant changes in the vertical distribution of all investigated soil properties (organic and microbial C, total and microbial N, soil enzyme activities), however, the dimension and location (horizons) of significant effects varied. The rotation periods affected the vertical distribution of the soil properties within the SRF significantly. In transect 1, SRF had higher organic‐C concentrations in the subsoil (Bv horizon), whereas in transect 2, the organic‐C concentrations were increased predominantly in the topsoil (Ah horizon). Sufficient plant supply of P and K in combination with decreased concentrations of these elements in the subsoil under SRF pointed to an effective nutrient mobilization and transfer from the deeper soil horizons even in the long term. In transect 1, the microbial‐C concentrations were higher in the B and C horizons and in transect 2 in the A horizons under SRF than under arable use. The activities of β‐glucosidases and acid phosphatases in the soil were predominantly lower under SRF than under arable use in the topsoil and subsoil. We conclude, that long‐term SRF on arable sites can contribute to increased C sequestration and changes in the vertical distribution of soil microbial biomass and soil enzyme activities in the topsoil and also in the subsoil.     

Seasonal dynamics in wheel load‐carrying capacity of a loam soil in the Swiss Plateau

Subsoil compaction is a major problem in modern agriculture caused by the intensification of agricultural production and the increase in weight of agricultural machinery. Compaction in the subsoil is highly persistent and leads to deterioration of soil functions. Wheel load‐carrying capacity (WLCC) is defined as the maximum wheel load for a specific tyre and inflation pressure that does not result in soil stress in excess of soil strength. The soil strength and hence WLCC is strongly influenced by soil matric potential (h). The aim of this study was to estimate the seasonal dynamics in WLCC based on in situ measurements of h, measurements of precompression stress at various h and simulations of soil stress. In this work, we concentrated on prevention of subsoil compaction. Calculations were made for different tyres (standard and low‐pressure top tyres) and for soil under different tillage and cropping systems (mouldboard ploughing, direct drilling, permanent grassland), and the computed WLCC was compared with real wheel loads to obtain the number of trafficable days (NTD) for various agricultural machines. Wheel load‐carrying capacity was higher for the top than the standard tyres, demonstrating the potential of tyre equipment in reducing compaction risks. The NTD varied between years and generally decreased with increasing wheel load of the machinery. The WLCC simulations presented here provide a useful and easily interpreted tool to guide the avoidance of soil compaction.     

不同土壤水吸力与耕作方式对土壤压缩—回弹特性的影响

[目的]合理耕作方式是缓解土壤压实、提升土壤生产能力的有效措施,而土壤水分是影响土壤机械物理性能的重要因素,直接影响土壤耕作质量.通过研究不同土壤水吸力和耕作方式下土壤压缩曲线及模型拟合效果,分析土壤回弹—再压缩曲线变化及机械力学参数(预固结压力、压缩指数和回弹指数)差异,以期为农田土壤耕作和培肥提供科学依据.[方法]...     

Prevention strategies for field traffic-induced subsoil compaction: a review: Part 1. Machine/soil interactions

Subsoil compaction is a severe problem mainly because its effects have been found to be long-lasting and difficult to correct. It is better to avoid subsoil compaction than to rely on alleviating the compacted structure afterwards. Before recommendations to avoid subsoil compaction can be given, the key variables and processes involved in the machinery–subsoil system must be known and understood. Field traffic-induced subsoil compaction is discussed to determine the variables important to the prevention of the compaction capability of running gear. Likewise, technical choices to minimise the risk of subsoil compaction are reviewed. According to analytical solutions and experimental results the stress in the soil under a loaded wheel decreases with depth. The risk of subsoil compaction is high when the exerted stresses are higher than the bearing capacity of the subsoil. Soil wetness decreases the bearing capacity of soil. The most serious sources of subsoil compaction are ploughing in the furrow and heavy wheel loads applied at high pressure in soft conditions. To prevent (sub)soil compaction, the machines and equipment used on the field in critical conditions should be adjusted to actual strength of the subsoil by controlling wheel/track loads and using low tyre inflation pressures. Recommendations based on quantitative guidelines for machine/soil interactions should be available for different wheel load/ground pressure combinations and soil conditions.     

Soil stress as affected by wheel load and tyre inflation pressure

The relative importance of wheel load and tyre inflation pressure on topsoil and subsoil stresses has long been disputed in soil compaction research. The objectives of the experiment presented here were to (1) measure maximum soil stresses and stress distribution in the topsoil for different wheel loads at the same recommended tyre inflation pressure; (2) measure soil stresses at different inflation pressures for the given wheel loads; and (3) measure subsoil stresses and compare measured and simulated values. Measurements were made with the wheel loads 11, 15 and 33 kN at inflation pressures of 70, 100 and 150 kPa. Topsoil stresses were measured at 10 cm depth with five stress sensors installed in disturbed soil, perpendicular to driving direction. Contact area was measured on a hard surface. Subsoil stresses were measured at 30, 50 and 70 cm depth with sensors installed in undisturbed soil. The mean ground contact pressure could be approximated by the tyre inflation pressure (only) when the recommended inflation pressure was used. The maximum stress at 10 cm depth was considerably higher than the inflation pressure (39% on average) and also increased with increasing wheel load. While tyre inflation pressure had a large influence on soil stresses measured at 10 cm depth, it had very little influence in the subsoil (30 cm and deeper). In contrast, wheel load had a very large influence on subsoil stresses. Measured and simulated values agreed reasonably well in terms of relative differences between treatments, but the effect of inflation pressure on subsoil stresses was overestimated in the simulations. To reduce soil stresses exerted by tyres in agriculture, the results show the need to further study the distribution of stresses under tyres. For calculation of subsoil stresses, further validations of commonly used models for stress propagation are needed.     

Prevention of traffic-induced subsoil compaction in Sweden: Experiences from wheeling experiments

Abstract

In this paper we describe the susceptibility of Swedish subsoils to compaction and discuss strategies for prevention of traffic-induced subsoil compaction against the background of experiences from wheeling experiments conducted in Sweden during recent years. The susceptibility of Swedish subsoils to compaction must be considered high because subsoils are often wet during field operations and machinery with high wheel loads is used. The risk of subsoil compaction could be reduced by technical solutions, such as the use of dual and tandem wheels instead of single wheels, low tyre inflation pressure or tracks. However, each of these solutions has its limitations. Results from several wheeling experiments on different soils indicate that residual deformations occur even when the applied stress is lower than the precompression stress. Hence, soil compaction could not be avoided completely by limiting the applied stress to the precompression stress.