Abstract: An experimental zero-traffic system was compared with a conventional-traffic system over four seasons in Scotland for both ploughed and direct-drilled winter barley seedbeds. A mouldboard plough was used for primary cultivation in both zero- and conventional-traffic plots in the first season, but a chisel plough was used in the ploughed treatments in subsequent seasons. After mouldboard ploughing in the first season, all wheels of both zero-traffic systems were restricted to permanent wheel tracks and all crops were sown in the bed between them. The crop yield for the ploughed zero-traffic system was never exceeded, although in the second season all yields were similar. Overall mean yield decreased with increasing rainfall in the spring and with decreasing soil permeability to air close to the soil surface. Soil compaction by wheels depressed plant populations under direct drilling in wet autumns, especially below wheel tracks in the direct-drilled conventional traffic system. Compaction also occurred in the absence of traffic under direct drilling. Vertical migration of earthworms was assumed to be responsible for some soil structural improvement at depth and, hence, successful direct drilling for both traffic systems, but after wet seasons crop establishment may also require shallow cultivation prior to drilling. After the fourth harvest, the draught force for primary cultivation averaged 17% more for each conventional-traffic system than for the corresponding zero system.

Abstract: Summary The response of spring barley (Hordeum vulgare, cvs Carnival and Atem), faba beans (Vicia faba, cv. Maris Bead), sugar beet (Beta vulgaris, cv. Monoire), forage maize (Zea mays, cv. Leader), forage peas (Pisum sativum, cv. Poneka) and white turnip (Brassica campestris, cv. Barkant) to topsoil compaction was investigated in a three year trial. Soil compaction was induced by tractor wheeling after crop sowing. Compaction reduced leaf area and dry matter accumulation in all crops in every season. Yield of barley was reduced by 29%, 27% and 40% in 1984, 1986 and 1987 respectively. Yield of maize, peas and turnip decreased by 33%, 14% and 13% in 1986 and 25%, 16% and 19% in 1987. Yields of beans and sugar beet were decreased by 34% and 35% respectively in 1984. Light interception was decreased in all crops in all three years of study but, with the exception of maize in 1987, the efficiency of conversion of radiant energy to dry matter was not significantly affected by soil compaction. It is concluded that reduced dry matter production and yield due to soil compaction was more a consequence of reduced light interception because of restricted leaf area development rather than as a result of an impaired ability of crops to utilise intercepted radiant energy.

Abstract: The climate of the West African Sudan savannah (annual rainfall of 600–900 mm and a monomodal rainy season of 3–4 months) is characterized by frequent long- and short-term droughts. Crop growth in the Alfisols and associated soil groups is further constrained by soil compaction, low soil fertility, high soil temperatures, low soil water retention and available water holding capacity, and low water infiltration rate. Tied ridges, ridges with earthen bunds constructed at right angles to the self-same ridges at intervals of 1–4 m, can alleviate or circumvent the above constraints, and can conserve rainfall received on-site. Water runoff with tied ridging ranges from 0 to 15% of seasonal rainfall, whereas with either open ridging or flat planting 20–45% of seasonal rainfall is lost as runoff. Soil water content is, therefore, greater with tied ridging. Tied ridging also reduces surface bulk density, maintains soil fertility by reducing losses of soil nutrients in surface runoff and improves soil water retention and available water holding capacity. The water infiltration rate in furrows of tied ridged plots is lower than that with flat planting or open ridging. With tied ridging, however, rainwater is retained on site by the ‘ties’, whereas with open ridging or flat planting it is lost as runoff. Tied ridging increases depth of rooting and subsoil root density in maize ( Zea mays ), millet ( Pennisetum americanum ) and cotton ( Gossypium hirsutum ) in both wet and dry years, and in cowpea ( Vigna unguiculata ) in dry years. Root growth of bambara groundnut ( Vigna subterranea ) is unaffected by tied ridging. Cowpea subsoil root growth is not significantly affected by tied ridging in wet years although root proliferation occurs in the topsoil because of the high sensitivity of cowpea to transient waterlogging. Vegetative growth and dry matter production of maize, millet, cotton, bambara groundnut, cowpea, groundnut ( Arachis hypogaea ) and sorghum ( Sorghum bicolor ) are increased by tied ridging in both wet and dry years. Grain yields of maize, millet and sorghum are increased by tied ridging, as is lint production of cotton. Cowpea grain yield is increased only in dry years. Grain yields of bambara groundnut are not significantly affected by tied ridging. Yield responses of groundnut to tied ridges are variable. Growth and yield inhibition may occur in waterlogging-sensitive crops such as cowpea and cotton during wet years. In general, greatest yield and growth increases from tied ridging occur in drought-sensitive cereal crop species and cultivars. Furthermore, strong and positive responses to tied ridges may be obtained consistently over a long period of time only in upland environments where long- and short-term droughts are frequent, soil compaction and temperatures are high, and available water-holding capacity and water infiltration rates are low.

Abstract: A procedure is presented that quantifies soil resilience to compressive stress, through elastic deformation or re-expansion after stress removal, with a single numerical index. This was achieved by comparing the three parameter coefficients of static-loaded and rebound compression lines (normal stress range = 0–1.0 MPa) which had been fitted to a non-linear density-stress model equation. The difference between the static-loaded and rebound values of one of these coefficients was significantly correlated to the clay and organic matter contents, the gravimetric moisture content and the initial dry bulk density of the 33 soils sampled as intact cores at field moisture content (coefficients of determination=0.533–0.973, P<0.05). The magnitude of the sample rebound observed varied between 0.018 and 0.075 Mg m−3 at the maximum applied stress of 1.0 MPa. This is likely to be a significant component of the error in prediction inherent in compaction models based on static-loaded compression data. The data further support the segregation of soils into groupings of comparable mechanical behaviour for soil compaction modelling purposes. The implications of these findings for improving soil resilience to compressive stress through soil and crop management are discussed.

Abstract: An axisymmetric linear elastic finite element program was developed to investigate the effect that the two linear elastic parameters, Poisson*s ratio and Young's modulus, had on soil compaction. This program was verified against Boussinesq's linear elastic theory. It was found that increased values of Young's modulus had no effect on the stress state in the soil mass but that strain levels were decreased. Increased values of Poisson's ratio increased the stress state and decreased the strain levels. The interaction of these two parameters point to the need to be able to vary both over the entire stress range.

Abstract: Soil compaction caused by agricultural machinery has become an acknowledged problem in reducing agricultural yields Two modes of vehicular traffic patterns were used: conventional and wideframe tractors The same tires, axle loads, and inflation pressures were used for traction units and implements used Distinct yield reductions caused by soil compaction were noted and statistically quantified for the two-year experiment The absolute yield reductions varied between the two-year records, but the trends and relative effects were the same Use of a wideframe tractor brought an increase in yields as compared to those attained on conventional tractor trafficked plots This yield increase is attributed to the larger non-compacted soil volume found under a wideframe tractor as compared to that under conventional tractor

Abstract: Pigeonpea (Caianus calan) is a perennial crop legume which has demonstrated considerable potential as a new field crop in the sunnier rainfed cropping areas of Australia. On clay soils in south-east Queensland, poor establishment and early growth of pigeonpea was observed on a number of sites despite reasonable seasons and careful management. Shallow compaction layers observed at these sites were implicated as the possible cause of the growth restrictions, however the exact mechanism remained unclear.Experiments were conducted on two clay soils in south-east Queensland to investigate the effect of compaction on the growth of pigeonpea. Field trials were conducted on a vertisol at Dalby (151o17'E 29o9'S) and a coastal oxisol at Redland Bay (153o19'E, 27o37'S). Compaction treatments at both sites consisted of deep cultivation to 25 cm, moderate compaction at 5 cm depth and severe compaction at 5 cm depth. Compaction was achieved by removing 5 cm of the loose top soil and rolling the moist subsoil with a road roller. The effect of these treatments on root growth, water use and shoot growth was investigated over two seasons at both sites under dryland and irrigated conditions. Further investigations were carried out in the glasshouse using large undisturbed cores taken from the treatments at the field sites, and simulating the effects of seasonal variations using different watering regimes. The effect of compaction on soil physical properties and radicle elongation was also investigated using soil packed into small laboratory cores.The response to compaction operated primarily through effects on the amount of water uptake by plants. Water uptake was affected by (1) the ability of the root system to penetrate the high soil strength of the compaction layer, and (2) by the amount of water retained in the profile. The distribution of rainfall and irrigation, the hydraulic properties of the soil and the evaporative demand of the environment influenced the water content of the soil profile which determined plant response.When conditions remained dry after sowing, root growth was restricted by the high soil strength of the compacted layer which reduced water uptake and early shoot growth. The critical period was three to five days after sowing when seedling roots reached the compacted zone. Root growth was reduced by 50% at soil strengths of 1200-1400 kPa and ceased at approximately 4000 kPa. Comparisons between laboratory and field experiments showed that the response of radicles to soil strength in prepacked laboratory cores adequately reflected root growth responses in the field.Under well watered conditions, the soil strength of the compacted layer remained low and compaction improved early growth as a result of the increased water availability in the compacted soil. However, permanently wet conditions reduced the air filled porosity of the surface layers which reduced oxygen availability and root growth.The low hydraulic conductivity of the vertisol reduced the infiltration of rainfall and the storage of water in the subsoil under compacted conditions. Light rain failed to penetrate to the compacted layer due to the high water holding capacity of the soil. However high water contents were retained in the surface layers for some time after heavy rain which reduced soil strength. In comparison, the high hydraulic conductivity of the oxisol resulted in relatively small effects of compaction on infiltration and storage of water. However the soil surface dried rapidly after rain resulting in high levels of soil strength in the compacted layer.Plants were able to compensate for early growth restrictions resulting from compaction when rain or irrigation reduced the dependence on stored subsoil water. Seed yield was unaffected by compaction when rain or irrigation occurred during the critical periods for yield determination at flowering and during pod fill. However when dry conditions persisted, seed yield was reduced by up to 67% on severely compacted plots.This study has demonstrated the key role that water availability plays in the response of plants to soil compaction in dry environments. Significant reductions in plant growth can occur in response to soil compaction. However plant response is difficult to predict due to the influence of rainfall distribution on the soil strength during early stages and the ability of plants to compensate for early growth restrictions. In inland regions of south-east Queensland, periods of dry weather are common and it is likely that the levels of compaction which have been measured at many sites (1.3-1.4 g cm-3 at 0.35 kg kg-1) cause significant growth restrictions in most seasons.

Abstract: Tests were conducted in Coastal Plain soils for three years to determine proper fall primary tillage for a system that supports interseeding soybean into standing wheat. The residual effects of various tillage systems and controlled traffic on soybean yield, crop response, and hardpan formation were determined. Use of a Paratill greatly reduced soil compaction, especially in the E horizon. For each tillage system, there were no significant differences in cone index values measured two and eight months after tillage in non-traffic rows. A good correlation between average soil cone index in the E horizon and soybean root length was demonstrated. Deep tillage significantly increased wheat and soybean yields. Interseeded soybean consistently yielded more than double-cropped soybean planted after wheat harvest at irrigated and non-irrigated locations. Due to controlled traffic patterns associated with the interseeding system, only one deep tillage operation before small grain seeding is required for the wheat/soybean double-cropping system. The residual effect of deep tillage operations will extend for one additional year when interseeding is practiced in costal plain soils.

Abstract: Root development in alfalfa (Medicago satire L.) is dependent of many factors including the soil environment which is influenced by crop management procedures. Soil compaction, which is unavoidable under current management procedures, can have a detrimental effect on root development. The purpose of this field experiment was to compare the effects of controlled and conventional traffic management on alfalfa fine root growth in a Wasco sandy loam (coarse-loamy, mixed, nonacid thermic Typic Torriorthent). No wheel traffic and traffic only before planting were compared to two conventional systems that varied in the amount of traffic applied during crop production. Twenty months after planting, there was a significant decrease in fine root density (FRD) from single passes of traffic after each harvest down to a 0.45-m depth while several passes after each harvest significantly decreased FRD down to 1.8-m depth. Regardless of treatment, root density was greatest in the upper 0.1 m of soil decreasing to 1.8 m in the first summer. By the second summer FRD showed bimodal distribution with significantly fewer roots at 0.3 to 0.6 m compared to layers above and below this depth. Seasonally there was a significantly higher root density during the winter than the summer in the upper 0.3 m of soil. The results of this study shows that alfalfa fine roots more thoroughly exploit the soil volume in the absence of wheel traffic and that compaction from traffic diminished root growth to different depths depending on its intensity.

Abstract: This study provides an overview of the adaptation of direct-drilling systems on sandy loam soils under the cool boreal, humid to perhumid soil climate of Prince Edward Island in Atlantic Canada, where the growing season is relatively short (May–October). Direct drilling can overcome the constraints of limited field workdays for seeding of spring cereals, owing to wet soil conditions in early May, or the integration of planting date with optimum soil temperatures for silage corn (Zea mays L.). However, the advantage of timeliness may be offset under sequential direct drilling for these crops, owing to a combination of reduced macroporosity at the soil surface and increased percentage of water-filled pore space, especially in soils with levels of organic carbon below 2% (w/w). In contrast, the presence of standing-crop residue, in pasture-renovation studies, allowed sequential or regular direct drilling of various forage species to occur with no adverse effect on soil structure. Use of direct drilling for spring cereals and silage corn on a rotational basis allowed intermittent soil loosening to prevent increasing surface soil compaction. Overall, direct drilling on perhumid, sandy loam soils proved successful when soil surface compaction was alleviated or circumvented.

Abstract: Suitability of a winged point for sowing to improve early growth of wheat crops using direct drilling on a hardsetting soil in Cowra, New South Wales, Australia was evaluated. Soil physical conditions, including bulk density, shear strength, water content, water potential and porosity close to the seedlings, were monitored. Comparisons were made between the winged point and the conventional combine point. Results indicate that on a compacted soil (bulk density = 1.7 Mg m −3 ), use of the winged point encouraged downward growth of roots. Sowing with the winged point doubled the root length density in the 25–50 mm layer below seed level compared with that of the combine point 18 days after sowing. Bulk density and shear strength measurements did not explain this difference. However, analysis of epoxy-resin-impregnated seedbeds revealed the presence of more large voids (> 4 m) at 50- and 75-mm depths in the plots sown with the winged points. These large voids were in the form of fracture planes possibly created by the wing. Sowing with a combine point caused compaction, especially on a previously loosened soil (bulk density = 1.4 Mg m −3 ), and this was found to restrict downward growth of roots.

Abstract: Field observations indicated that combines can cause soil compaction. Front axle loads of today's highest-capacity combines can be as high as 18 Mg (40,000 lb) with ground pressures exceeding 100 kPa (15 psi). Statistical results indicated that the header and grain tank are dominant factors affecting axle loads. A grading system was developed to rank combine configurations on cost, operation, performance, service, and compaction. Two altematives might be feasible compared to a mid-capacity, standard combine: a combine with full-length tracks, and a combine/ grain cart with weight distributed on three axles. Today's largest standard combines need four axles to have acceptable axle loads and ground pressures.

Abstract: The increase in the size of broadacre machinery in recent times has raised questions regarding the extent to which wheel traffic is damaging the soil and depressing crop yield. Paddock trials have been established on Roseworthy College Farm using a self propelled prototype gantry to demonstrate controlled traffic cropping and investigate any soil or crop responses by both amelioration of the existing compacted soil layer (deep ripping) and removing wheel traffic from crop zone. The barley crop grown in the first year of the trial highlighted some management problems associated with controlled traffic farming. Measurements were taken of soil penetrometer resistance, soil moisture content, crop biomass yield and grain yield. Crop biomass measurements were inconclusive however penetrometer measurements showed marked differences between treatments. Grain yields showed little response to deep ripping in the wheeled treatments but a significant increase where both the compacted layer and wheel traffic were removed.

Abstract: A field experiment was conducted for three consecutive years on a Ste. Rosalie clay soil to assess the effect of compaction, tillage and no tillage on the yield of silage corn. Plant growth parameters, crop yields, soil bulk densities, and moisture retention characteristics were measured in the experiment. Crop responses varied with seasonal rainfall and soil physical properties changes caused by different treatments. In a season of normal rainfall distribution, the performance of zero-tilled plots was far superior to those of compacted plots and tilled plots. In a relatively wet season, the air-filled volume between 0.15 and 0.30 m depth was extremely low (0 to 2%) and may have impeded root development. The amount of water available for plant use was highly correlated with crop yield in the first and third years but not in the second.

Abstract: An in situ densification probe that employs the novel technique of simultaneous vibration and dewatering has been developed by Phoenix Engineering Ltd. to compact deep, loose, granular soils. It is believed that pumping water out of the soil during the densification process offers improved densification capability over systems operating with vibration alone. An independent study was undertaken by the In-Situ Testing Group at the University of British Columbia to evaluate the performance of the Phoenix system.A field testing programme was conducted at a site in Vancouver where hydraulic sand fill overlies a natural silt and then medium Fraser River sand. Characterization of the site and evaluation of the densification treatment process were achieved using in situ tests. Changes to soil parameters due to densification treatment were examined, taking into account the modification of stresses brought about by the vibro-drainage process. The study investigated the degree of densification achieved, the value of...

Abstract: Problems of landscape and resource protection resulting from the intensification of land-use can be mastered only by intersectoral planning and a land management considering (landscape-)ecological principles right from the beginning. In the district of Leipzig ecological studies in the '80ies have focussed on: 1. Determination of the regional pattern of atmospheric immissions; 2. Registration of heavy metals in soil and vegetation; 3. Soil compaction, soil erosion; 4. Study of stress indicators in the aeration zone and in the top-most aquifer in order to examine barrier effects in the percolation process.