Abstract: The widespread use of heavy machinery during harvesting and extraction operations in South African timber plantations has led to concern that soil compaction is causing declines in long-term site productivity and environmental damage. In this paper compaction behaviour is described and compared for a wide range of forestry soils. A description of compaction behaviour was obtained by the use of a simple uni-axial compression technique which enabled the compaction behaviour of typical South African forestry soils to be described and compared. Water-pressure-density (W-P-D) diagrams and semi-log plots of bulk density against applied pressure (compression curves) describe the compaction behaviour of a wide range of forestry soils and provide a means with which to establish the relative importance of applied pressure and water content on the soil compaction process. The range of applied pressures and water contents commonly encountered during timber harvesting and how they effect soil compaction are described by a model utilising applied pressure, water content and initial bulk density as independent variables. The coefficients in the model were related to commonly measured soil physical properties such as clay plus silt percentage or loss-on-ignition (LOI). Soils with between 5 and 10% LOI and between 50 and 70% clay plus silt underwent the greatest increase in compaction as measured by the compression index. Similarly, the role of water content in the compaction process was most important for soils having between 4 and 7% LOI and between 45 and 65% clay plus silt. Inasmuch as local geology affects particle size distribution, clay mineralogy and organic carbon content, it is an effective way of establishing a first approximation of the likely compression behaviour of forestry soils.

Abstract: SUMMARY We investigated the effect of soil compaction and phosphorus (P) application on morphological characteristics of mycorrhizal colonization and growth responses, to determine the reasons for reduced responses observed in our previous work with compacted soil. Growth, phosphorus (P) uptake and intensity of vesicular–arbuscular (VA) mycorrhizal colonization were studied in clover plants (Trifolium subterraneum L.) with and without VA mycorrhizal colonization at two P applications and three levels of soil compaction. Phosphorus was supplied either at constant mass concentration (mg P kg−1 soil) or at constant volume concentration (mg P dm−3 soil). Increasing bulk density of the soil from 1·1 to 1.6 Mg m−3 significantly decreased root length and shoot d. wt, but increased the diameter of both main axes and first order lateral roots regardless of P application. Total P uptake and shoot d. wt of clover plants colonized by Glomus intraradices (Schenck & Smith) were significantly greater than those of non-mycorrhizal plants at all levels of soil compaction and both P applications. However, soil compaction to a bulk density of 1.6 Mg m−3 (penetrometer resistance = 3.5 MPa at a matric potential of − 33 kPa) significantly decreased mycorrhizal growth response. There was no evidence that the increased volume concentration of P at high bulk densities was responsible for the reduced responses. Soil compaction had no significant effect on the fraction of root length containing arbuscules and vesicles, but total root length colonized by arbuscules, vesicles or by any combination of arbuscules, vesicles and intra-radical hyphae significantly decreased as soil compaction was increased. The air-filled porosity of highly compacted soil, which varied from 0.07 to 0.11 over the range of matric potentials encountered (− 33 and − 100 kPa), had no significant effect on the intensity of internal colonization.

Abstract: The relationships between the spatial heterogeneity of maize fields, due to row-cropping and farm machinery traffic, and earthworm abundance were studied in three plots receiving different organic matter treatments: no organic fertilizer, pig slurry and farmyard-manure. In all plots, there was no significant effect of farm machinery traffic although there was a tendancy for earthworms to be less abundant under inter-rows (wheel tracks) than in traffic-free inter-rows. In both the maize field without organic fertilizer and the maize treated with pig slurry, earthworms were primarily located along the maize row. Earthworm abundances were greater within than between rows (16 vs 6 nos 0.1 m−2 in control, 30 vs 15 nos 0.1 m−2 in slurry). In the farmyard-manure treatment, no row effect on the spatial pattern in earthworm numbers was found. However, worm biomass was approximately twice as high under the maize row as under the inter-row. This suggested a greater migration of adults to the maize roots or that juvenile worms grew faster there. Earthworm populations showed spatial variance in life cycle stage with populations under the maize row having proportionally more adults than populations between rows. Soil bulk-density was lower in than between maize rows and lower in maize fields amended with organic matter. Soil bulk-density and earthworm biomass were shown to be negatively correlated (r = −0.92, n = 6). Image analysis of resin-impregnated soil blocks within and between rows showed that the soil under the row was characterized by a higher macroporosity (5.7 vs 0.7%) and also a greater diversity in size and shape of the macropores than occurred between the rows.

Abstract: The physical fertility of krasnozems and euchrozems (Red Ferrosols) in Australia has declined substantially as a result of continuous cropping. Much of this decline is associated with reduced levels of soil organic carbon and soil compaction due to vehicle trac when soils are too wet. We examined the impact of kikuyu (Pennisetum clandestinum) and Rhodes grass (Chloris gayana) pasture leys with various management inputs on the regeneration of physical fertility of continuously cropped krasnozems from 2 locations in the South Burnett region of southern Queensland. Pasture leys significantly improved the physical fertility of continuously cropped soils within 2–4 years. The most significant effects were on the creation of improved surface and subsurface macroporosity, and in a reduction in surface crust formation under high energy rain due to improved aggregate stability. Final steady state infiltration rates under well-managed leys increased 4-fold compared with those in continuously cropped soil. Pastures were unable to ameliorate compacted layers below approx. 15 cm, although significant improvements in hydraulic conductivity through these layers (and to depths of at least 70 cm) were made, presumably by creating of continuous biopores. Introduced earthworms improved pasture effectiveness in ameliorating this layer, but only to depths of 20 cm, while deep ripping during the ley phase was the most effective treatment. Kikuyu was the more effective pasture species in overcoming soil physical infertility, particularly in terms of improving aggregate stability under rain. In addition, the ability of kikuyu to resist the compacting influence of cattle trampling during wet weather meant that rainfall infiltration eciency was maintained during the ley phase and management options on returning to cropping were more flexible (e.g. direct drill strategies can be used). However, if pastures were ungrazed, the advantages of kikuyu in soil physical restoration were evident in only 2 years.

Abstract: The simulation of crop - soil systems with a model requires an appropriate description of the root dynamics. An empirical root growth model that simulates root-shoot relations, root distribution and a dynamic response to environmental conditions is presented. The root model extends an existing crop model and links it to a soil model to calculate dry matter accumulation, water and nitrogen dynamics of a wheat crop. Simulated roots are distributed over soil layers according to carbon supply from the shoots by using a 'top down principle'. This principle favours the top layers for root growth by first providing all available carbon to the first layer. Under unfavourable soil conditions in that layer, carbon is given to the next deeper soil layer. This procedure is repeated until a separately calculated rooting depth is reached. At that depth all available carbon is used for root growth regardless of current soil conditions. Under most simulated conditions the 'top down principle ' results in a negative exponential function of a monotone decrease of root distribution with soil depth. However, it can also account for larger root densities deeper in the profile when water or nitrogen deficiency occurs in soil. In addition to soil water and soil nitrogen supply the root model considers soil compaction, aeration and root distribution history for root growth simulation. The new model, consisting of an existing crop and soil model and linked through a new developed root model, was calibrated and tested using two independent field experiments. A sensitivity analysis was carried out by varying parameters, initial soil conditions and hypothetic weather patterns as part of the validation process. Root length density distribution (r2(1:1)=0.65), shoot, grain and total root biomass (r2(1:1)=0.87) were predicted satisfactorily, thus providing a useful tool for specific simulation studies on that site.

Abstract: Selected physical, chemical, and biological characteristics of soils in mechanically damaged North Queensland mangrove forests were examined and compared with undisturbed controls. Soils in nine forests were tested in a factorial sampling programme designed to examine effects of (i) severity of mechanical damage to forests (severely damaged: trees removed and soils disrupted by bulldozing; versus damaged: trees felled no bulldozing; versus controls: trees and soils undisturbed), (ii) soil depth, (iii) forests (10s–100s km apart), and (iv) sites within forests (10s–100s m apart). Characteristics examined were soil compaction, grain size, pH, percent by weight of total C, N, P, K, S, and Fe and the density of crab burrows. Three of the 10 variables examined: total N, total P, and density of crab holes, decreased with mechanical damage to forests. The loss of potentially-limiting nutrients and of an important bioturbator at severely damaged sites suggests the need for further experimental investigation of soil characteristics with respect to natural regeneration and efforts of mangrove restoration.

Abstract: In this method for achieving optimum, in particular homogeneous, soil compaction, a compaction device (3) acting upon the soil to be compacted, whose oscillations are registered together with those of the soil as a single compaction vibration system by a computing unit (12), is excited by an oscillation-inducing force in such a way that this compaction vibration system oscillates in resonance, or at a frequency (Φ) that exceeds the resonance value by a specified frequency value that is only determined by adjustment stabilities. The value of the oscillation-inducing force, its periodic frequency (Φ), and the phase angle (ζ) to the oscillation of the compaction vibration system are set automatically by the computing unit (12) so that a specified soil rigidity is achieved, taking into account the mass of the compaction device (3) and of the weight pressing on it statically. The compaction device according to the invention can also be used to determine the soil rigidity and/or the soil modulus of elasticity.

Abstract: A programme of laboratory tests was undertaken to identify the volume reduction of a range of granular soils in response to uniform vibration. The purpose of the tests was to quantify the potential compaction settlement of granular soils due to vibrations typical of those experienced when sheet or bearing piles are installed or extracted by vibrodriver. The vibrations in soils within 2–20 m of a vibrodriven pile are well defined as sinusoidal, at the frequency of the vibrodriver, and typically in the range of 1.0g down to 0.02g (whereg=gravitational acceleration). Thein-situ conditions were replicated in the laboratory by vibration of a Rowe cell containing a soil sample. This allowed control of stresses before and during vibration. Tests were conducted on nine granular soils, ranging from uniform Leighton Buzzard sands to a sandy fine-to-medium gravel. Soil samples were prepared at minimum relative density, generally in the saturated state, but also dry and partly saturated. Each sample was consolidated at a selected effective stress of between 10 and 100 kPa. It was then vibrated vertically at increments of controlled acceleration, under conditions of free drainage and maintained confining stress. Reduction in sample thickness was measured continuously. Results showed that even in a small, drained, sample the full volume reduction was reached only after many minutes, although the early response was more rapid. The trends of results showed that: increased surcharge pressure reduced the subsequent vibratory compaction; well-graded soils showed greater compaction than more uniform sands; compaction increased markedly when acceleration exceeded 1 g; saturated soils showed larger compaction than dry and partially saturated soils; compaction was influenced little by frequency, although rate of compaction reduced with frequency increase.

Abstract: A study was conducted on a heavy clay soil to evaluate soil compaction induced by different traffic treatments associated with liquid manure spreader systems. Five spreader weights (from 96 to 218 kN), two running gears (tandem and tridem, i.e., three axles) and two types of tire (conventional low section tire and oversized tire) were combined to obtain six traffic treatments, representative of liquid manure spreading operations in Quebec. Soil dry bulk density ( nb) and cone index (CI) were measured to evaluate compaction. Tire rut depths and the lateral influence zone were also investigated in the study. For a single pass of a spreader, soil compaction was confined to the tilled layer (about 0-250 mm depth) regardless of traffic treatments, and this did not affect emergence rates and yields of soybean under the particular soil and climate conditions that prevailed at the time of the study. Neither tandem nor tridem running gears were found to adequately contain soil compaction within the tilled layer for total spreader weights exceeding 154 kN. The acceptable limitation for a tandem spreader with conventional 21.5L-16.1 tires would be a total load of about 96 kN, resulting in average ground pressures of 150 kPa or less. If medium capacity spreaders are required, oversized tires are recommended for manure spreading on prairies or post-seeding applications on small grain crops. Finally, the recourse to multiple-axle running gears for larger spreaders to maintain or reduce unit load per axle or ground pressure does not result in less soil compaction than lower capacity tandem spreaders with comparable axle loads and ground pressure.

Abstract: Wetland vegetation developed in the crater of Mount Usu, northern Japan, soon after the 1977-1978 eruptions which destroyed the vegetation. The cover of each species was meas- ured in 1994 in 118 50 cm x 50 cm plots situated in transects and related to environmental factors (elevation, water depth, soil texture, soil compaction, soil organic matter, and soil pH) to clarify vegetation development. Five vegetation types were recognized dominated by Eleocharis kamtschatica, Equisetum arvense, Lythrum salicaria, Juncusfauriensis and Phragmites australis respectively. Sedge/grass marsh and reed swamp dominated deep-water sites; willow swamp and wet meadow vegetation characterized shallow-water sites, indicating that vegetation zonation developed soon after the eruption. Since those wetland plants were derived neither from seed banks nor from vegetative propagules, they had to immigrate from out- side the summit areas. However, except for willows, most species lack the ability for long-distance dispersal. Late suc- cessional species, such as P. australis established in the early stages of the primary succession. The water depth varied by 27.5 cm among the plots. Coarse soil particles accumulated, and pH (5.22 - 6.55) was low on the elevated sites. Organic matter ranged from 2.8 % to 19.1 %, and was high on the elevated sites. Water depth was responsible for the establish- ment of large-scale vegetation patterns, while edaphic factors, i.e. soil compaction, pH, and organic matter, were determi- nants of small-scale vegetation patterns. Among the edaphic factors, soil compaction appeared to have a strong influence on vegetation development.

Abstract: Livestock production in the Great Plains has experienced major changes over the past 30 years (GPAC, 1995). Beef feedlots of 50,000 head and greater are now common, and the number and size of concentrated animal feeding operations for dairy, swine and poultry has also increased. Vertical integration of animal production with increasingly larger concentrations of livestock increases production efficiency. Consequently, the trend toward larger and more concentrated production units is likely to continue. Unfortunately, an animal waste disposal problem and a great potential for groundwater contamination is associated with this trend (Elliot et al. 1973; Schepers et al. 1993). The livestock industry tends to develop near grain producing areas which are often centered along river basins utilized for surface irrigation. Because soils in the western U.S. are typically low in organic matter, a reasonable remedy is to recycle the nutrients in manures by application to cropland. Reported benefits include increases in soil organic matter, soil nutrient availability, soil permeability and water holding capacity, and reduced soil compaction (Tiarks et al. 1974; Herron and Erhart 1965; Olsen et al. 1970). However, water quality can also be negatively impacted by excessive application rates, poor timing, and mismanagement (GPAC 1995; Liebhardt …

Abstract: Variation in dry-matter yield at second harvests was studied in a long-term comparison of wheel traffic systems and soil compaction in grassland for silage in Scotland. Yields were obtained from compacted soil subjected to conventional traffic (C), from less compacted soil in a reduced ground-pressure traffic system (R) and from non-compacted soil in a zero-traffic system (Z). Relationships between the ratios of second-harvest yields, C2/Z2 and C2/R2, and a number of soil, rainfall and crop parameters were tested by correlation analysis. The yield ratios increased significantly with the number of days after mowing before 2 mm of rain fell in 1 d (r= 0·923*** and 0·715*, for C2/Z2 and C2/R2 respectively), and C2/Z2, but not C2/R2, decreased with increasing amount of rainfall in the 14 d after first mowing (r= 0·787*). It was concluded that yield from compacted soil was greater than that from non-compacted soil because the former depended less on rainfall in the weeks after first mowing. The degree of soil compaction in the reduced ground-pressure traffic system, although maintaining first-harvest yield benefit, reduced the risk of significantly diminished yield at second harvest in dry summers.

Abstract: A mechanistic dynamic model (Verberne et al. 1990) was used to simulate mineralization of white-clover materials in a loam (25% clay) and a sandy loam soil (5% clay). I tested the model‘s ability to simulate the observed temporal patterns and to take account of altered physical protection as affected by soil compaction or spatial residue distribution. With default parameter values, the model greatly overestimated net N mineralization. The model was very sensitive to changes in the C/N ratio of the microbial biomass. Reducing this value from 8.0 to 6.0 improved the model performance. Nevertheless, initial N mineralization was appreciably overestimated. Two hypotheses may explain the discrepancies: (1) the C/N ratio of the microbial biomass is initially low (3–4) and gradually increases because of a succession from bacterial- to fungal-dominated biomass (H1); (2) the C/N ratio of the substrates first attacked by microorganisms, i.e. water-soluble components such as sugars and free amino acids, is higher than the average value (6.0) assumed for the readily decomposable fraction (H2). Conceptually, this fraction originally included N-containing polymers (proteins and nucleic acids), which in large part are water insoluble and probably attacked somewhat later than the monomers. Modification of the model, either by implementing a dynamic C/N ratio of the biomass and the effect of faunal grazing or by increasing the C/N ratio of the easily decomposable fraction, improved the model performance substantially. The two hypotheses need to be tested experimentally. The model adequately simulated measured effects of spatial residue distribution and soil compaction on N mineralization after adjustment or parameter values regulating physical protection of microbial biomass and metabolites. Moreover, there was a good agreement between simulated and measured microbial biomass N in the two soils.

Abstract: The engineering properties of compacted soils are of primary importance in fill performance. However, for economic reasons, the achievement of a given relative compaction and compaction water content has become an end in itself for field compaction control. Although the profession has developed an understanding of the relationships between properties and compaction density/water content, it has become routine practice to use some combination of precedence and code rather than desired material properties to establish compaction specifications. Because of the heavy emphasis placed on relative compaction, it is extremely important that geotechnical practitioners and earthwork contractors recognize the deviations in field density that can occur as a result of typical differences in the compaction processes and in the methods of compaction control encountered. Variations in both the field density and the laboratory-determined reference maximum dry density arise from numerous sources. A corresponding spatial variability of relative compaction should therefore be anticipated. This paper provides a comprehensive evaluation of potential problems in compaction control and addresses the sources of field variability in relative compaction.

Abstract: Orchard floor treatments of total weed control with herbicides, disking, mowing, grass control only with herbicides, and no control of vegetation were maintained in a 3 x 3-m area underneath young pecan [Carya illinoinensis (Wangehn.) K. Koch] trees. Soil compaction in treated areas was compared to heavily trafficked row middles. Mean cone index (CI) readings obtained from a cone penetrometer for the heavily trafficked areas were higher, indicating greater compaction than all other treatments in the 4.7- to 11.8-cm soil depth range. Heavily trafficked areas had severe compaction (>2.0 MPa) at the 9.5-to 22.9-cm soil depths. Mowed plots had similar CI readings at 14.2- to 54.3-cm depth as those heavily trafficked. The mowed areas had severe compaction at the 14.2- to 22.9-cm depth range. Grass control only with herbicides and plots with no control of vegetation had low CI throughout the soil profile. Disking, grass control, and no control treatments had similar effects, except at the 4.7-cm depth, where disking reduced compaction. An orchard floor management practice that minimized traffic near young trees, but also reduced weed competition, appears to be the best choice.

Abstract: A highly compacted soil layer was detected in an amaranth field in Tulyehualco, Mexico. The purpose of the present work was to analyze the effect of soil compaction on the crop of amaranth. Two plots with superficial (S) (10-15 cm) and intermediate (I) (20-25 cm) levels of compaction were compared. Several crop physiology parameters were studied and soil resistance was measured with a digital penetrometer. The cone Index values of both compacted soil layers were > 3 MPa. Amaranth plants from the S plot had 46% smaller leaf area (p<0.01) and were 12% shorter (p<0.01) than those from the I plot. The grain yield was significantly higher in plants from I compared to plants from S (68 vs 38 g/plant, p< 0.03). Concerning the root growth, the main roots of plants from S were 34% shorter than those from I (p<0.01). The adventitious roots emerging from the stem base were very prolific in both plots (non statistical differences were appreciated). Adventitious roots were 4-4.8 times longer than main of plants from either plot. In summary, our results show that the depth of compacted soil layer has a direct effect on the amaranth crop. Superficial soil compaction rendered short plants with lower grain yield whereas intermediate compaction resulted in taller plants with higher grain yield.

Abstract: A theoretical model was suggested and equations of motion derived. A computer program was developed to solve the resulting system of equations. Agreement between calculated and experimental results is not quite satisfactory. Reasons for discrepancy are discussed and suggestions for further investigation are given.