Compaction by wheels: a numerical model for agricultural soils

A simple, numerical model was developed to predict changes in soil dry bulk density resulting from the passage of wheels. The model uses Söhne's solutions to estimate stress increases, and empirical isotropic stress-strain data to predict soil volume changes. Predicted and measured increases in bulk density, resulting from the passage of various agricultural vehicles, compared favourably at most depths but the model underestimated the compaction of loose soil in close proximity to underlying dense layers. The model may also be used to compare the compaction caused by various types and arrangements of wheels and to assess the contribution made by a particular input variable. Examples of such uses are given.     

Technical solutions to reduce the risk of subsoil compaction: effects of dual wheels, tandem wheels and tyre inflation pressure on stress propagation in soil

The use of heavy machinery is increasing in agriculture, which induces increased risks of subsoil compaction. Hence, there is a need for technical solutions that reduce the compaction risk at high total machine loads. Three field experiments were performed in order to study the effects of dual wheels, tandem wheels and tyre inflation pressure on stress propagation in soil. Vertical soil stress was measured at three different depths by installing probes into the soil horizontally from a dug pit. In one experiment, also the stress distribution below the tyre was measured. Beneath the dual wheels, vertical stresses at 0.15 and 0.3 m depth were lower between the two wheels than under the centre of each wheel, despite the gap between the wheels being small (0.1 m). At 0.5 m depth, vertical stress beneath the wheels was the same as between the two wheels. The stress interaction from the two wheels was weak, even in the subsoil. Accordingly, measured stresses at 0.3, 0.5 and 0.7 m depth were highest under the centre of each axle centre line of tandem wheels, and much lower between the axles. For a wheel load of 86 kN, tyre inflation pressure significantly affected stress at 0.3 m depth, but not at greater depths. Stress directly below the tyre, measured at 0.1 m depth, was unevenly distributed, both in driving direction and perpendicular to driving direction, and maximum stress was considerably higher than tyre inflation pressure. Calculations of vertical stress based on Boussinesq's equation for elastic materials agreed well with measurements. A parabolic or linear contact stress distribution (stress declines from the centre to the edge of the contact area) was a better approximation of the contact stress than a uniform stress distribution. The results demonstrate that stress in the soil at different depths is a function of the stress on the surface and the contact area, which in turn are functions of wheel load, wheel arrangement, tyre inflation pressure, contact stress distribution and soil conditions. Soil stress and soil compaction are a function of neither axle load nor total vehicle load. This is of great importance for practical purposes. Reducing wheel load, e.g. by using dual or tandem wheels, also allows tyre inflation pressure to be reduced. This reduces the risk of subsoil compaction.     

Interpretation and presentation of cone resistance data in tillage and traffic studies

Recommendations are made regarding the analysis and presentation of cone resistance data. Methods for eliminating extreme readings due to stones are compared and the effects of stones on variability and treatment comparisons are discussed. Results showed very high variability between positions, even at 100 mm separation. Measurements separated by more than 1 m were independent of each other except where trends in other soil properties influenced cone resistance. The assessment of compaction under wheels is described for cone resistance measurements made under the rut centre-line. Parameters are derived from measurements made on two-dimensional, vertical grids to quantify the depth, extent and intensity of compaction and loosening. The usefulness of penetrometers in tillage and traffic studies is discussed.     

Evaluating the performance of a soil compaction sensor

One of the most significant soil parameters affecting root growth is soil compaction. It is therefore important to be able to determine the presence of compacted layers, their depth, thickness and spatial location without the necessity of digging a large number of holes in the field with either a spade or backhoe. Previous investigations have identified soil compaction by different methods such as: using ground penetrating radar, acoustic systems, vertical and horizontal penetrometers and instrumented wings mounted on the faces of tines. Linking the output from these sensors to global positioning systems would give an indication of the spatial patent variation. The aim of this study was to evaluate the performance of a soil compaction profile sensor in both controlled laboratory and field conditions. The sensor consisted of a series of instrumented flaps; a flap is defined as the sensing element which comprises one half of a pointed leading edge to the leg of a tine to which strain gauges are placed on the rear face of the flap. Studies measured the effect of compaction on the changes in the soil resistance acting upon a flap face in a soil bin laboratory and under field conditions. The results indicated that the sensor was sensitive to differences in soil strength at different depths in soils. A technique was developed to identify the soil compaction resulting from different tyre inflation pressures and loads. The soil compaction profile sensor was tested on a number of fields in south‐eastern England to determine the changes in soil strength below the wheelings of a pea harvester operating at different tyre inflation pressures.     

Soil compaction and soil management – a review

Soil compaction is an important component of the land degradation syndrome which is an issue for soil management throughout the world. It is a long standing phenomenon not only associated with agriculture but also with forest harvesting, amenity land use, pipeline installation, land restoration and wildlife trampling. This review concentrates on the impact of soil compaction on practical soil management issues, an area not previously reviewed. It discusses in the context of the current situation, the causes, identification, effects and alleviation of compaction. The principal causes are when compressive forces derived from wheels, tillage machinery and from the trampling of animals, act on compressible soil. Compact soils can also be found under natural conditions without human or animal involvement. Compaction alters many soil properties and adverse effects are mostly linked to a reduction in permeability to air, water and roots. Many methods can be used to measure the changes. In practical situations, the use of visual and tactile methods directly in the field is recommended. The worst problems tend to occur when root crops and vegetables are harvested from soils at or wetter than field capacity. As discussed by a farmer, the effects on crop uniformity and quality (as well as a reduction in yield) can be marked. By contrast, rendzinas and other calcareous soils growing mainly cereals are comparatively free of compaction problems. The effect of a given level of compaction is related to both weather and climate; where soil moisture deficits are large, a restriction in root depth may have severe effects but the same level of compaction may have a negligible effect where moisture deficits are small. Topsoil compaction in sloping landscapes enhances runoff and may induce erosion particularly along wheeltracks, with consequent off‐farm environmental impacts. Indirect effects of compaction include denitrification which is likely to lead to nitrogen deficiency in crops. The effects of heavy tractors and harvesters can to some extent be compensated for by a reduction in tyre pressures although there is concern that deep‐seated compaction may occur. Techniques for loosening compaction up to depths of 45 cm are well established but to correct deeper problems presents difficulties. Several authors recommend that monitoring of soil physical conditions, including compaction, should be part of routine soil management.     

Physical Properties as Indicators of Oil Penetration in Soils Contaminated with oil Lakes in the Greater Burgan Oil Fields,Kuwait

Measurements were made on 60 samples to determine the physical properties of the soil profiles contaminated with oil lakes in Al-Ahmadi and Burgan oil fields which include 80% of the Greater Burgan oil wells in southern Kuwait. The two soil profiles have similar saturation percentages, field capacities, wilting coefficients, low available water capacities due to statification and very low matric potential, and high bulk densities due to compaction by vehicle wheels. The fluviatile origin, relatively poor sorting and unstable structure of the Burgan soil layers have led to lower hydraulic conductivity and permeability, thereby restricting oil penetration mainly to the upper 25–45 cm layer. In contrast, the eolian origin, excellent sorting and stable structure of Al-Ahmadi soil layers have resulted in higher hydraulic conductivity and permeability, and hence allowed the spreading of oil over much greater depths (down to 150 cm). The very low values of the hydraulic conductivities and available water capacities of the zone(s) lying below the impervious Gatch (caliche) layer in the two soil profiles suggest that this layer could act as a moisture barrier impeding any further downward oil penetration.     

The calibration of a high resolution gamma-ray transmission system for measuring soil bulk density and an assessment of its field performance

The calibration of a high resolution gamma-ray density probe and a simple experiment comparing the probe with an earlier, lower resolution version are described. An assessment is made of the performance of the probe in three experiments investigating compaction by tractor wheels, two of which were in the field and the third in an indoor soil tank. A linear calibration relationship was obtained, although the addition of a quadratic term improved the fit of the curve slightly. The probe was found to be much more accurate than the earlier version within 100 mm of the soil surface where treatment effects were largest and most numerous in the field experiments, and thin layers of high density could be detected. Over the 15 month period of the experiments, the stability of the system was found to be satisfactory.     

Soil compaction in cropping systems: A review of the nature, causes and possible solutions

Soil compaction is one of the major problems facing modern agriculture. Overuse of machinery, intensive cropping, short crop rotations, intensive grazing and inappropriate soil management leads to compaction. Soil compaction occurs in a wide range of soils and climates. It is exacerbated by low soil organic matter content and use of tillage or grazing at high soil moisture content. Soil compaction increases soil strength and decreases soil physical fertility through decreasing storage and supply of water and nutrients, which leads to additional fertiliser requirement and increasing production cost. A detrimental sequence then occurs of reduced plant growth leading to lower inputs of fresh organic matter to the soil, reduced nutrient recycling and mineralisation, reduced activities of micro-organisms, and increased wear and tear on cultivation machinery. This paper reviews the work related to soil compaction, concentrating on research that has been published in the last 15 years. We discuss the nature and causes of soil compaction and the possible solutions suggested in the literature. Several approaches have been suggested to address the soil compaction problem, which should be applied according to the soil, environment and farming system.

The following practical techniques have emerged on how to avoid, delay or prevent soil compaction: (a) reducing pressure on soil either by decreasing axle load and/or increasing the contact area of wheels with the soil; (b) working soil and allowing grazing at optimal soil moisture; (c) reducing the number of passes by farm machinery and the intensity and frequency of grazing; (d) confining traffic to certain areas of the field (controlled traffic); (e) increasing soil organic matter through retention of crop and pasture residues; (f) removing soil compaction by deep ripping in the presence of an aggregating agent; (g) crop rotations that include plants with deep, strong taproots; (h) maintenance of an appropriate base saturation ratio and complete nutrition to meet crop requirements to help the soil/crop system to resist harmful external stresses.     

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.     

SoilFlex: A model for prediction of soil stresses and soil compaction due to agricultural field traffic including a synthesis of analytical approaches

Soil compaction is one of the most important factors responsible for soil physical degradation. Soil compaction models are important tools for controlling traffic-induced soil compaction in agriculture. A two-dimensional model for calculation of soil stresses and soil compaction due to agricultural field traffic is presented. It is written as a spreadsheet that is easy to use and therefore intended for use not only by experts in soil mechanics, but also by e.g. agricultural advisers. The model allows for a realistic prediction of the contact area and the stress distribution in the contact area from readily available tyre parameters. It is possible to simulate the passage of several machines, including e.g. tractors with dual wheels and trailers with tandem wheels. The model is based on analytical equations for stress propagation in soil. The load is applied incrementally, thus keeping the strains small for each increment. Several stress–strain relationships describing the compressive behaviour of agricultural soils are incorporated. Mechanical properties of soil can be estimated by means of pedo-transfer functions. The model includes two options for calculation of vertical displacement and rut depth, either from volumetric strains only or from both volumetric and shear strains. We show in examples that the model provides satisfactory predictions of stress propagation and changes in bulk density. However, computation results of soil deformation strongly depend on soil mechanical properties that are labour-intensive to measure and difficult to estimate and thus not readily available. Therefore, prediction of deformation might not be easily handled in practice. The model presented is called SoilFlex, because it is a soil compaction model that is flexible in terms of the model inputs, the constitutive equations describing the stress–strain relationships and the model outputs.     

Effects of traffic on soil aeration, bulk density and growth of spring barley

This paper reports the results of field experiments on several different soils to quantify the effects of different numbers of passes of vehicular traffic on soil aeration status (measured in terms of oxygen diffusion rate, ODR and redox potential, Eh), soil bulk density and development of spring barley. In a further series of field experiments, the effects of single and dual wheels were compared and the effectiveness of a soil loosener operating behind the wheels was evaluated. Additionally, some microplot experiments are reported in which a range of known values of soil bulk density were produced and the effects on soil aeration and development of spring barley were evaluated. It is shown that repeated wheeling, even by a tractor of only about 2 tonnes weight, can produce soil conditions in which aeration can be limiting for crop growth. The use of dual wheels resulted in lower values of soil bulk density and associated greater soil aeration. The loosener alleviated the compaction produced by wheels and also improved soil aeration. For a sandy loam soil, greatest root growth and crop yield occurred at a bulk density of 1.43 Mg m⁻³. Soil aeration as a component of soil physical quality is discussed.     

Zero-tillage furrow opener effects on seed environment and wheat emergence

Optimum emergence is necessary to attain maximum crop yields, particularly in reduced and zero-tillage systems. However, zero-tillage seeder performance under zero-tillage conditions is not always adequate, and thus may limit potential yield benefits from this soil and water conserving practice.

A study was conducted to measure the range of influence of zero-tillage openers on some soil physical properties of the soil-seed environment. Furrow opener design has direct consequences on soil surface disturbance, furrow compaction levels, and post-seeding soil water requirements in the seed row. While soil temperature and wheat cultivar differed between two distinct field trials, furrow opener designs conducive to adequate compaction of seed furrow with press wheels consistently resulted in better wheat emergence, when soil water potentials were not limiting.

This study demonstrates that seeding tool design has a quantifiable influence on seed furrow properties, and that this information can be used to develop precise guidelines for future designs of furrow openers and press wheels.     

Compaction of virgin soil by mechanized agriculture in a semiarid environment

Soil compaction was assessed in terms of soil strength as measured with a penetrometer. Penetrometer resistance was measured on virgin soil and on the same soil after one and after five passes of a 7,610 kg tractor. Also, comparative studies were made of strength profiles of soils in arable fields and in adjacent areas of virgin soil. The strength of virgin soil was increased by wheel traffic and agricultural operations in all cases. The increase in soil strength was significant down to 0.3 m, which is considerably greater than the normal depth of tillage in the area (0.05 m). Reduction in the coefficient of variation of penetrometer strengths after the passage of wheels was taken as evidence for associated losses of soil structure. Virgin soils provide important reference sites for assessing the impact of agriculture in an area.     

Changes in the properties of a Vertisol and responses of wheat after compaction with harvester traffic

Soil compaction has been recognised as the greatest problem in terms of damage to Australia’s soil resource. Compaction by tractor and harvester tyres, related to trafficking of wet soil, is one source of the problem. In this paper an array of soil properties was measured before and immediately after the application of a known compaction force to a wet Vertisol. A local grain harvester was used on soil that was just trafficable; a common scenario at harvest. The primary aim was to determine the changes in various soil properties in order to provide a “benchmark” against which the effectiveness of future remedial treatments could be evaluated. A secondary aim was a comparison of the measurements’ efficiency to assess a soil’s structural degradation status. Also assessed was the subsequent effect of the applied compaction on wheat growth and yield in the following cropping season. Nine of the soil properties measured gave statistically significant differences as a result of the soil compaction. Differences were mostly restricted to the top 0.2 m of the soil. The greatest measured depth of effect was decreased soil porosity to 0.4 m measured from intact soil clods. There was 72% emergence of the wheat crop planted into the compact soil and 93% in the uncompact soil. Wheat yield, however, was not affected by the compaction. This may demonstrate that wheat, growing on a full profile of stored soil water as did the current crop, may be little affected by compaction. Also, wheat may have potential to facilitate rapid repair of the damage in a Vertisol such as the current soil by drying the topsoil between rainfall events so increasing shrinking and swelling cycles. If this is true, then sowing a suitable crop species in a Vertisol may be a better option than tillage for repairing compaction damage by agricultural traffic.     

Infiltration in reclaimed mined land ameliorated with deep tillage treatments

Reclamation of mined land with heavy machinery can result in soil compaction. Compaction increases soil bulk density and reduces porosity, water infiltrability, root elongation and crop productivity. Mine operators have used deep tillage equipment to alleviate the compaction problem. The main objectives of this study were to examine (1) the effect on infiltration in reclaimed surface mined land of a deep tillage treatment, and (2) the subsequent changes in infiltration after the amelioration. The experiment was conducted at the Horse Creek Mine near Conant, Perry County, IL, USA. The soil was classified as Schuline series, which is a fine, loamy, mixed, mesic, Typic Udorthents. The treatments included tillage depths of 20 (as a control), 40, 60 and 80 cm. Infiltrometers and runoff plots were installed to evaluate infiltration and rainfall-runoff relationships affected by the treatments. Results indicated that the steady infiltration rates of the 40- and 60-cm tillage treatments were lower than that of the control treatment successively during the experimental period for 3 years. Results also revealed that the 80-cm tillage treatment increased infiltration and reduced surface runoff most. Even though the beneficial effects declined over a 3-year test period, the 80-cm tillage is recommended in the amelioration of soil compaction because tillage depths less than 80 cm did not enhance water infiltration rate much.     

Soil compaction: identification directly in the field

The compaction of soil alters its structure, increases its bulk density and decreases its porosity. These changes can be detected by careful and systematic visual and tactile examination directly in the field. These changes also reduce the permeability of soil to water and air and may alter the pattern of root growth. Further signs of compaction may be induced such as the creation of waterlogged zones or of dry zones caused by shallow rooting denying access to deeper reserves of water. Furthermore, there may be a reduction in nutrient uptake from dry soil. Under wet conditions anoxic pockets may form with associated biochemical changes, some of which are visible. Changes in mineral nitrogen may take place through denitrification and a reduction in nitrification. The criteria used to identify compaction in the field include patterns of crop growth, pale leaf colours, waterlogging on the surface or in subsurface layers above compaction, an increase in soil strength, changes to soil structure, soil colour and the distribution of roots and of soil moisture. Manifestation of soil compaction in crops is also dependent on the weather and is influenced by crop type and variety, and stage of growth. Many soil‐borne diseases are made worse by stress to the crop which might be induced by compaction caused by drier or wetter conditions in the root zone. Where, when and how to identify compaction in the field are discussed and the techniques used are described. Specific examples of the identification of compaction are given, covering a wide range of situations.     

Cattle trampling and soil compaction on loamy sands

Abstract. Field investigations on loamy sand soil showed that compaction by cattle trampling increased soil bulk density and cone penetrometer resistance. Trampling produced very dense zones at depths of 7–10.5 cm, which impeded drainage, despite the presence of large macropores. Soil structural and hydrological changes caused by hoof compaction can result in serious pasture management problems. Compaction simulation experiments on saturated turf indicated that most severe structural damage occurs on initial compaction.     

Anwendbarkeit geophysikalischer Prospektionsmethoden zur Bestimmung von Bodenverdichtungen und Substratheterogenitäten landwirtschaftlich genutzter Flächen

Applicability of geophysical prospecting methods for mapping of soil compaction and variability of soil texture on farm land The increasing degree of mechanization in agriculture has resulted in the use of more powerful and heavier tractors and machines. Consequently, mechanical burden to soils has increased, too, which can lead to persistent subsoil compaction at depths below 30 cm. In soils damaged by compaction soil functions like transportation of water and air decrease. Because of that, conditions for plant growth are getting worse and the soils' natural regulation functions could be impaired. In order to take counteractive measures, it is necessary to get information about the status of soil compaction. Up to now, the status of soil compaction can only be determined at single points in laboratory measurements or with less accuracy in field measurements. Therefore, the demand for an efficient planar‐mapping system arises. The applicability of different geophysical prospecting methods with regard to this problem has been examined. For this purpose, geophysical and soil measurements were performed in a field with conventional agricultural land use in Schleswig‐Holstein (Germany) on a young moraine site. We applied GPR (Ground Penetrating Radar) with main frequencies 500 MHz and 900 MHz, supplemented by inductive electromagnetic technique (EM) using the Ground Conductivity Meter EM38 and high‐resolution refraction seismic using compressional and shear waves. Differences in soil type were found by all these geophysical methods and confirmed by soil measurements, therefore, locations with higher risk for compaction (loamy soils) could be distinguished from locations with lower risk (sandy soils). Under humid conditions, radar data showed strong reflections at a depth of approx. 30 cm. During summer, under dry conditions, these reflections did not occur. This temporal variation of radar reflections can be explained by variable water layers inside the soil, which can be regarded as an indicator for compacted soil. The seismic investigation was performed along short (12 m) profiles with dense (20 cm) sensor spacing. Excellent data quality showed that this sort of measurement, known from engineering geophysics, is also feasible for soil investigations. We performed both compressional‐ (P‐) and shear‐(SH‐) wave refraction studies. Differences in soil type of subsoil affected especially seismic velocities of P‐waves. Whether or not areas of compacted soil can be detected is still unknown, because deeper soil horizons of our test area showed only uniformly strong compaction with little contrasts.     

Mechanical and biological approaches to alleviate soil compaction in tropical soils: assessed by root growth and activity (Rb uptake) of soybean and maize grown in rotation with cover crops

Chiselling has been used to alleviate soil compaction but cover crops with deep, vigorous roots can improve root growth and activity of the cash crop for a longer time. The determination of root activity in addition to root mass or length may improve the understanding of plant response to compaction. The objective of this experiment was to evaluate root growth and activity as affected by the alleviation of soil compaction using mechanical and biological methods. The experiment was conducted in Botucatu, São Paulo, Brazil, from 2009 to 2011, on a clay, Typic Rhodudalf soil. Crop rotations including pear millet (Pennisetum glaucum), soybean (Glycine max), grain sorghum (Sorghum bicolor), maize (Zea mays), ruzi grass (Brachiaria ruziziensis) and castor bean (Ricinus communis) in plots, either chiselled or not. Root growth was assessed by core sampling and root activity was determined indirectly using rubidium injected at several depths as a marker. Root activity was instrumental in interpreting the effects of tillage and crop rotations on soil amelioration. Compared with the initial compacted condition, chiselling increased root growth and activity just for the first 18 months of the experiment, but crop rotations, mainly including ruzi grass and castor bean, increased root growth and activity in the soil profile from the second year on. Generally, root mass was poorly correlated with root activity, except in the case of ruzi grass. Introduction of ruzi grass plus castor bean into the cropping system improves not only root growth and activity in the soil profile but also soybean yield.     

Compaction characteristics of towed wheels on clay loam in a soil bin

Wheel induced soil compaction is an ongoing concern in mechanized agriculture. This experimental study was performed with the aim to evaluate whether soil compaction is related to stresses induced by towed wheels. Soil bin studies were conducted and soil compaction variables were measured under two towed tires, with different tread patterns, commonly used in Turkey. Tests were carried out at three tire loads (3.5, 5.5 and 7.5 kN) and two forward velocities (0.8 and 1.4 m/s) on a clay loam. To determine soil compaction, surface sinkage, subsurface layer deformation, compaction index, penetration resistance and bulk density were measured. With increasing vertical load, average contact pressure of tires increased from 39.3 to 68.5 kPa. In different trials, surface sinkage, compaction index, penetration resistance and bulk density varied from 46 to 86 mm, 0.18 to 0.48, 1472 to 2530 kPa and 1.31 to 1.70 Mg m⁻³, respectively. The soil contact projected area of tire 2 was approximately 10% greater than tire 1. The greater contact surface reduced the compaction at the soil surface and subsurface, but the tire load was still the dominant factor in the 0–20 cm depth range used in this study. According to the experimental results, decreasing contact duration with increasing forward velocity decreased soil compaction. Tire load and type affected soil deformation characteristics stronger than forward velocity.