Abstract: Extent and persistence of soil and crop responses to subsoil compaction caused by vehicles with high axle loads are reviewed and methods to protect the subsoil from permanent deterioration are discussed Traffic by vehicles with high axle loads on soils with high moisture contents generally causes deep subsoil compaction At an axle load of 10 Mg, compaction typically penetrates to a depth of 50 cm With still higher loads, compaction to a depth of 1 m has been reported Subsoil compaction is very persistent At depths of more than 40 cm it is virtually permanent even in clay soils in regions with annual freezing Deep subsoil compaction also causes persistent and possibly permanent reductions of crop yields Complete amelioration by mechanical loosening is usually impossible and definitely expensive From a soil productivity point of view, limits for mechanical stresses in the subsoil are needed These may have the form of axle load limits for the vehicles or a combination of limits for the axle load and for some other important factors, such as the ground contact pressure of the running gear or the per cent water saturation of the soil at the time of trafficking Guidelines for such limits should preferably be worked out in an international joint effort

Abstract: This study used a database to explore the relationship between hydraulic conductivity, compositonal factors of the soil, and compaction conditions. The data were collected from 66 landfills at various locations in North America. The study used graphs and multivariate regression to identify compositional and compaction variables that correlate with hydraulic conductivity. The results of the graphical and regression analyses were used to identify compaction conditions that yield low hydraulic conductivity, and identify important variables to control during construction of soil liners.

Abstract: The effect of soil mechanical impedance on root growth is discussed on several levels from the apex to the root system. At the individual root level, the balance of pressures on the root apex cannot account for observed reductions in root elongation rate. Furthermore, soil mechanical impedance affects the elongation rate of non-impeded organs, such as leaves or non-impeded roots. A chemical message originating in roots could account for such an effect, probably via changes in cell wall rheological properties in all growing zones of the plant. Changes in carbon allocation could also have a role. At a whole-plant level, indirect effects linked to changes in the plant structure contribute in a major way to the effect of mechanical impedance on root growth. Although only a small proportion of roots of fieldgrown plants are in contact with compact soil, geometrical characteristics of root systems are considerably affected. In particular, root deepening is delayed and roots tend to have a clumped spatial arrangement. Experimental evidence and modelling suggest that this change in root system architecture could cause water stress, even in relatively wet soil, because of an increase in resistance to the soil-root water flux. As a consequence, root water status and water flux decrease, and stomatal conductance is reduced as a consequence of a chemical message originating in the roots. This secondary message is superimposed onto the direct message linked to mechanical impedance. Under some climatic conditions, whole-plant growth rate, carbon allocation and phenologic development can then be significantly affected by a compaction in the ploughed layer, while only small changes can be expected under more favourable conditions.

Abstract: Summary Important indicators of soil aeration status, such as air-filled porosity, air permeability, relative gas diffusion coefficient, soil air composition, oxygen availability (ODR) and redox potential (Eh) are presented. Relationships among these indicators and techniques of measurement are discussed. Field and laboratory experimentation is described. Compaction is shown to restrict aeration and thereby impair crop growth. Examples are given of field experiments, generally involving cereals, with compaction treatments applied either before sowing to simulate unalleviated previous compacton by harvest machinery or during seedbed preparation. Crops, particularly winter crops, are most vulnerable in wet, warm periods shortly after sowing or fertilizer application. Impaired crop growth resulting from compaction is attributed to the interacting effects of poor aeration and mechanical impedance. Poor aeration can also result in gaseous losses of plant-available nitrogen. Experimental evidence of recovery from compaction in undisturbed soils is also presented. Subject areas requiring further research efforts are identified.

Abstract: A method is presented to evaluate the effect of print spacing on the dynamic compaction of loose granular soils. It uses a recently developed wave-equation model together with an approach to predict the lateral extent of soil improvement around the pounder. The procedure to evaluate the effect of print spacing is demonstrated using two examples, which show that the most critical areas are the center of the grid and the middle of the side of the grid where the least improvement of soil is achieved. Three reported case histories of dynamic-compaction projects are analyzed, and the solutions are shown to be in good agreement with those obtained from the field. Two design curves, one for the center of the grid and the other for the middle of the side of the grid, are established. These curves summarize the influence of print spacing on the effectiveness of dynamic compaction in densifying the soil at these two critical locations and are useful for the selection of print spacing in dynamic-compaction projects.

Abstract: Summary Experiments conducted under controlled conditions in greenhouses and observations of tree growth in the field demonstrate that the compaction of soils during forestry operations reduces the rate of establishment of natural regeneration, reduces tree growth for periods spanning at least a decade and can have deleterious effects on tree form. The intensity of compaction is greatest during harvesting, but by judicious choice of harvesting systems, machines and running gear, based on considerations of slope and soil water conditions, the impact on the soil can be reduced. Other options available to reduce the intensity of compaction are the laying of slash beds on the main extraction trails, the grading of terrain into areas suitable for logging during the wet and dry periods of the year, based on soil type and drainage conditions, and, if necessary, the rehabilitation of soils by cultivation or deep ripping and the application of fertilizer.

Abstract: Heavy axle loads of modern agricultural equipment greatly increase the potential for severe soil compaction. Axle loads exceeding 90 kN have been shown to cause compaction considerably below the depth of primary tillage. To evaluate the potential for compaction from heavy axle load traffic in the Pacific Northwest USA, compression characteristics of intact subsoil samples from eight agriculturally important soil series were determined. Clay contents of the soils ranged between 14 and 27%. Compactive stress thresholds (CSTs) of the subsoils, the stress at which irreversible deformation occurs, were determined at varying matric potentials (−30 to −300 kPa) using one-dimensional compression tests and short-duration loading (2-min). CST values for the eight subsoils ranged between 64 and 492 kPa, and increased two- to three-fold between −30 and −300 kPa matric potential. A relationship between CST and clay content did not exist, however, soils with high bulk densities generally had higher CST values than soils with low bulk densities. This implies that structural rather than textural characteristics exert a greater influence on CST under short-duration loading such as wheel traffic. For the range of soil matric potentials which occur during spring tillage in the Pacific Northwest (−30 to −100 kPa), the measured CST values ranged between 64 and 356 kPa. Wheel tractors and other equipment in the region have axle loads exceeding 90 kN and exert surface pressures ranging between 150 and 300 kPa. Since levels of subsoil stress under high axle loads can approach surface-applied pressures, the potential for subsoil compaction in these soils during spring tillage operations is high.

Abstract: Summary In Central and Eastern Europe, due to the recent increase in field traffic, soil compaction has become one of the major factors affecting crop production. The variations in crop response to soil compaction associated with crop type, soil characteristics and weather conditions, are reviewed. The importance of soil water in influencing soil comparability and crop response to soil compaction is illustrated. The influence of fertilization on crop response to soil compaction and the response of plant roots are briefly discussed.

Abstract: Forest harvesting removes nutrients in biomass and, along with site preparation operations, may remove or displace nutrients contained in logging slash and the forest floor. Considerable soil disturbance may also occur resulting in nutrient loss and often soil compaction. Sites vary in their resilience to disturbance, depending not only on inherent site factors, including climate and soil properties (i.e., site quality), but also on the intensity of the forestry operation and site conditions at the time of disturbance.

Abstract: Compaction of soil is a detrimental result of heavy human use of a site. The destruction of the associated vegetation is an accompanying feature. Soil compaction com- monly causes reduced water infiltration, loss of pore space and increased soil density, decreased waterholding capacity, reduced aeration, increased mechanical impedance to root growth with concomittant decrease in nutrient uptake, and reduction in soil microorganism activity. Amelioration of soil compaction under existing vegetative cover, especially trees, is difficult without some injury to the root systems. Some standard methods of surface soil aeration exist that can be applied to turf and some tree areas, but amelioration of compacted subsoils is very difficult in most cases. For existing trees and their root systems, radial trenching appears to be a promising technique for compaction amelioration.

Abstract: Summary Soil compaction has been estimated to be responsible for the degradation of an area of 83 million ha world-wide, of which 33 million ha lies in Europe and 18 million ha in Africa. Soil compaction problems are of economic importance in the production of a wide range of crops throughout the world. Current research on this subject is leading to a greater understanding of the soil/machine/crop/weather interactions, which strongly influence the incidence and severity of these problems. Modifications to vehicles, their running gear and their management systems, have been shown to offer opportunities to reduce greatly the incidence of compaction problems. However, as yet the commercial uptake of these techniques is at a rudimentary level. There is a pressing need to adopt a more rigorous approach to the conduct of basic research and to extend the use and validation of models to predict soil, crop, environmental and economic responses to different systems of machinery management for a range of crops, soils and weather conditions.

Abstract: Summary An increasingly large amount of wheel traffic, from a variety of machines and transporters, is necessary for management and harvesting of grass and legume forage species. The soil compaction problem in perennial forage crop production has been recognised in both farming practice and in a number of research activities. Research has shown that any significant deterioration in soil conditions brought about by wheel traffic leads to impaired crop performance and yield, particularly if the traffic is imposed on wet soil or if the soil remains relatively wet during the main period of crop growth. The influence of traffic on land in forage cropping and the subsequent effects on yield, can be moderated by use of alternative machinery or traffic management systems. These alternatives are discussed, together with techniques for improvement of over-compacted grassland. Research has indicated that measures taken to avoid compaction are more likely to be beneficial than most ameliorative operations.

Abstract: The effects of different axle loads on the yields of silage maize were compared on sandy soils at four locations in the Netherlands over the period 1983–1986. The same traffic intensity resulted in changes in bulk density, cone resistance and crop reactions in several types of sandy soil. Depending on the soil profile and weather conditions during the growing season, the heavy axle loads reduced yields by up to 38%. Average yield reductions were 15% with an axle load of 10 Mg and 4% with an axle load of 5 Mg. It is estimated that traffic-induced soil compaction reduces the total production of Dutch silage maize by 7%.

Abstract: Summary Soil compaction concerns are increasing in the temperate region of North America. Increased size and weight of field equipment, plus changes in farming patterns to a predominate row-crop culture, are contributing to this problem. Soils in the region are annually subjected to a freezing and thawing cycle plus several wetting and drying cycles. However, these natural forces do not necessarily ameliorate soil structural changes resultant from compaction. Yield decreases from soil compaction have been identified for all investigated crops grown in the region, but responses have been variable and in some cases difficult to assess, although compaction problems are magnified when combined with other plant stress situations. Soil compaction effects have been identified by increased bulk density, higher soil strength and reduced pore volumes, which in turn exert a negative influence on soil aeration, root exploration, and water and nutrient uptake. Crop responses to compaction are strongly influenced by soil texture and soil water content at the time of load application. However, crop responses are not always negative, as they are also a function of growing season precipitation. Subsoil compaction, which is mainly due to high axle loads, is causing increasingly serious concerns about future productivity. Subsoil compaction is long-lasting and difficult to correct. In the temperate region of North America, efforts to reduce soil compaction have been limited and compaction will remain a production problem until changes in farm practices are made.

Abstract: Controlled infestation with eggs of western corn rootworms, Diabrotica virgifera virgifera LeConte, was used in a 2-yr study on the effects of wheel traffic-induced soil compaction on corn rootworm establishment, survival, and larval injury to the roots of maize, Zea mays L. Root injury ratings and cumulative emergence of adults of western corn rootworms, as taken from emergence cages, were lowest in plots where eggs had been infested into compacted interrows. Measurements of soil bulk density, air-filled porosity, and air permeability were taken on core samples to characterize soil physical properties in relation to soil compaction. Lowest rootworm survival and injury coincided with higher bulk density, lower air-filled porosity, and lower air permeability values characteristic of soil from the compacted interrow plots. Survival and establishment of western corn rootworm larvae were associated with greater soil pore continuity in uncompacted plots. Soil compaction induced by controlled wheel traffic may have potential as a management strategy for reducing larval corn rootworm movement into strip intercropped maize adjacent to areas previously planted to maize and rotated into a crop that is not a host for corn rootworms.

Abstract: Publisher Summary This chapter reviews the existing knowledge about improving rice yields per unit quantity of rainwater available. Nearly one-third of the world's lowland rice is rain fed; however, rain-fed rice comprises only one-fifth of the global rice produced. Insufficient or excess water is the major constraint in the production of rain-fed lowland rice. Coupled with this are problems of poor agronomic practices followed by farmers, socioeconomic constraints, and lack of technology suited to rain-fed lowlands. There are two aspects of increasing the efficiency of rainwater use under rain-fed situations: raising the yield of the rain-fed crop when rainfall is normal and preventing yield loss when rainfall is inadequate and drought occurs frequently. The technology for improving the efficiency of rainwater use in rain-fed lowlands aims at increasing in situ rainwater interception, soil infiltrability, and profile water storage; decreasing nonproductive water losses, such as percolation and seepage; collecting runoff water for providing supplementary irrigation at critical growth stages, if needed; and properly managing rice crops for efficient utilization of conserved soil moisture. These objectives can be achieved by proper soil, water, and crop management techniques and the chapter reviews some of the findings, possibilities, and challenges that are significant. Subsurface soil compaction before planting rice appears to be a practical way to decrease percolation losses and to improve profile water storage in coarse-textured soils. Water harvesting is an important component of rain-fed technology. Rainwater stored in suitable reservoirs can provide supplemental irrigation to rice during prolonged dry spells. The adoption of suitable agronomic practices is equally important in increasing the efficiency of rainwater use in growing rain-fed lowland rice. These include selection of crop variety, time of planting, plant populations, crop geometry, efficient fertilizer use, weed control, and insect control.

Abstract: The effects of reservoir tillage on runoff and water quality were studied under two levels of soil compaction in the production of cotton A wide frame tractive vehicle was used during plot establishment and during all farm operations to provide the desired soil compactions LEPA (Low Energy Precision Application) irrigation was used to apply supplemental water as required Runoff quantity was monitored with flumes and runoff samples were taken using Coshocton-type runoff samplers Thirteen runoff events were monitored and analyzed over a two-year period for the replicated, four-treatment study Reservoir tillage decreased runoff and total discharges of organic nitrogen and phosphate Differences in concentrations of water quality parameters (total solids, ammonium, total kjeldahl nitrogen, nitrate, phosphate, and COD) were not statistically significant Although not statistically different, total runoff and total discharge of water quality parameters (except phosphate) were lower for the low compacted treatments compared to the high compacted treatments

Abstract: Summary There is concern about compaction of soils by wheeled agricultural equipment, and especially by equipment with high axle loads. Tracked vehicles have been and continue to be used to some extent in crop production. Development of rubber-belt tracks has removed many of the disadvantages of steel tracks relative to rubber tires. This has caused renewed interest in tracked equipment. Loading of the soil by trafficking with wheeled or tracked equipment is a complex dynamic process that is not well understood. Evaluation of the stresses applied to the soil by traffic with wheels and tracks and of the resulting soil compaction, shows that tracked vehicles can be used to reduce compaction, which tends to improve crop emergence, growth and yield. Effective management of field traffic with equipment used in crop production requires an improved understanding of the mechanics of soil loading by wheels and tracks.

Abstract: SYNOPSIS World-wide literature has clearly documented the fact that soil compaction caused by wheel traffic has a negative effect on future site productivity. In spite of this evidence there remains a difference of opinion within the forestry community calling for more emphasis to be placed upon compaction research. Penetrometer soil strength is an experimental method currently being used to quantify the effects of wheeled movement on soil. The penetrometer soil-strength measurement is a fast, effective way of measuring the resistance the soil offers to potential root growth. The sandy soils of Zululand are susceptible to compaction and it has become increasingly important to determine its long-term effects on site productivity. This study on a Mondi Forest plantation attempts to identify and quantify the potential damages caused by wheeled traffic. Results show that harvesting planning and operations in future will have to consider the implications of compaction and plan and operate accordingly.

Abstract: Nursery production of hardwood seedlings and cuttings is different than the production of pine seedlings in several important ways. Hardwoods need approximately twice as much water and significantly more of most nutrients, especially nitrogen and calcium. Hardwoods are generally produced from open-pollinated, wild seed. This results in large within-seed source variability in seedling size and vigor. Seed orchard seed has tended to reduce this variability some and to increase the average seedling size. Hardwoods are particularly sensitive to soil physical properties. Soil compaction, which results in high soil bulk-density, is very deleterious. This is due to impeded root growth and impaired gas and water movement in the soil. Some hardwoods are ectomycorrhizal, some are endomycorrhizal, and a few can be either or both. Most hardwoods must be grown at a much lower seedbed density than most pines. When this fact is coupled with higher irrigation and fertilization costs per acre, the cost per seedling becomes much higher for hardwoods than pines.

Abstract: Summary Where a soil has already been compacted, or where there is a risk that it will be compacted, it is essential to know how the condition can be alleviated or overcome. By using the right equipment and by not subjecting soft surfaces to high axle loads, compaction can be avoided. Where the soil is already compacted, the wise and sympathetic use of an excavator can assist in bringing the soils into a condition where it can support vegetation—grow shrubs and trees. This paper describes and discusses the use of mechanical equipment to improve the condition of soils which have been affected by construction practices.

Abstract: Conventional and zero traffic systems were mole ploughed and effects on soil physical properties were compared. Draught of the plough operating at 550 mm depth was measured while it was winched across plots having a 5-year history of different traffic regimes. Results showed that the draught was reduced by about 18% on non-trafficked compared with conventionally-trafficked soil. Cone resistance measurements, 1 month before and 3 months after mole ploughing, confirmed that the non-trafficked soil had significantly less strength to a depth of about 400 mm. Bulk density measured at 75 and 175 mm depth 1 month before mole ploughing indicated a similar trend, but clod and bulk densities at 125 mm and 350 mm depth 3 months later, failed to show any consistent differences between treatments.

Abstract: 振動式締固め機械の振動挙動の変化から地盤の締固め度を計測する手法の確立を目指し, 起振機の振動挙動と地盤剛性との関係, ならびにこれに及ぼす振動条件の影響について数値計算により考察を行い, この結果をもとに振動条件によらず地盤剛性を評価することのできる計測手法の提案を行った. さらにこの手法の適用性を小型の起振機を用いた室内実験ならびに大型のタンパを用いた現場実験により検討した.

Abstract: Soil compaction has been the subject of intense research in recent years, but the mechanisms involved in the compaction process remain poorly understood. The objective of this study was to characterize these mechanisms for a Kamouraska clay (Orthic Humic Gleysol) using beds of aggregates (1–2 mm and 2–3.4 mm) compressed into a uniaxial compression device. Changes in structural void ratio were monitored as a function of aggregate size, applied load and soil water content. Measurements of tensile strength and shrinkage were also made on the larger aggregates (2–3.4 mm) to investigate the involvement of the structural units in the soil compaction process. Aggregate size had little effect on the shape of the compression curves. Compression of the aggregate beds was mainly a function of applied load and water content. The compaction sensitivity threshold was about 0.20–0.22 g g−1 at compression loads of less than 200 kPa. This threshold water content corresponds to the air entry point and to the upper limit of...

Abstract: As part of an investigation of factors limiting nodulation in the field, cultivars of common bean were grown in a sandy loam soil that had been either deep tilled (DT) to reduce compaction or repeatedly rolled by a golf cart or by a tractor followed by a golf cart. In 1991 and 1992, the tractor-rolling treatment was replaced by a conventional tillage system. Nineteen cultivars were grown in 1990; 10, in 1991; and 4, in 1992. In general, soil compaction decreased plant growth and yield but had no adverse effect on numbers or weights of nodules per plant. In 1990, nodule numbers and weights were increased by compaction in the first sample, 35 d after planting. In a combined analysis of the four cultivars common to all 3 yr, nodule weight as a fraction of total plant weight was increased by compaction. Thus, compaction had a more severe effect on overall plant growth than on nodulation per se. Numbers and weights of nodules differed among the cultivars, but they all responded similarly to compaction. Cultiva...