J.J.H. van den Akker

Introduction to the special issue on experiences with the impact and prevention of subsoil compaction in the European Union

Abstract The papers in this special issue present results of the European Union (EU) concerted action “Experiences with the impact of subsoil compaction on soil crop growth and environment and ways to prevent subsoil compaction”. The results and conclusions of earlier research on subsoil compaction are memorized and it is emphasized that the conclusions are still sound: high axle load traffic on soils of high moisture content causes deep and persistent subsoil compaction. The concerted action on subsoil compaction in the EU and an almost identical concerted action on subsoil compaction in central and eastern Europe are briefly introduced. This special issue presents a selection of papers of the concluding workshop of the concerted action on subsoil compaction in the EU. It includes three papers on modeling the impact of subsoil compaction on crop growth, water availability to plants and environmental aspects; three papers on modeling of subsoil compaction by heavy machinery; four papers on measurement of soil mechanical and physical properties in relation to subsoil compaction and four papers on methods to determine the risk of subsoil compaction and to identify prevention strategies. The trends in agriculture in relation to subsoil compaction are discussed. A positive trend is that policy makers in the EU and worldwide recognize soil as a vital and largely non-renewable resource increasingly under pressure. A negative trend is that wheel loads in agriculture are still increasing causing severe damage to subsoils. The conclusion is that European subsoils are more threatened than ever in history. Manufactures, agricultural engineers and soil scientists should collaborate and research should be initiated to solve this problem and find solutions. Subsoil compaction should be made recognized by all people involved from farmer to policy maker. Therefore an assessment of the existence and seriousness of subsoil compaction throughout Europe should be initiated.

Subsoil compaction caused by heavy sugarbeet harvesters in southern Sweden; II. soil displacement during wheeling and model computations of compaction

Traffic with high wheel loads in combination with high inflation pressure implies a risk for subsoil compaction, but effects will depend on the soil strength. Soil displacement during traffic with a heavy sugarbeet harvester (total load approximately 35 Mg on two axles) was determined at 0.3, 0.5 and 0.7 m depths during harvesting in the autumn. Measurements were made on one occasion on a clay loam (Eutric Cambisol) and a sand (Haplic Arenosol), and at different water contents on a sandy clay loam (Eutric Cambisol). Soil mechanical properties (precompression stress and shear strength) were determined for each traffic occasion. Field measurements were also compared with model computations of soil compaction, based on calculation of soil stresses and on the mechanical properties measured. On the sandy clay loam in the driest condition, displacement occurred only at 0.3 m depth, while it was registered down to 0.7 m depth in the wettest condition, when soil moisture was around field capacity. On the clay loam and the sand there was displacement down to 0.5 and 0.7 m depth, respectively. Model predictions of compaction correlated well with the depth to which displacement was measured in the field. One important task in subsoil compaction research is to define methods to determine soil mechanical properties that are easy to use and that still make it possible to predict compaction. The results clearly demonstrate that heavy sugarbeet harvesters may cause compaction to more than 0.5 m depth during normal field conditions in the autumn, with soil water content as the most decisive factor.

Prediction of aspects of soil-wheel systems

Abstract A simple formula is given which predicts maximum stress-depth relationships under wheels from vertical wheel load and the tyre inflation pressure. Predictions were compared with stress measurements at a depth of 30 cm under a wide range of vehicles, for zero rut depth, non-significant horizontal wheel force, and soil top layers overlaying more rigid subsoil. A very wide diagonal rubber tyre and a very wide radial polyurethane tyre were compared with respect to their contact stress distributions. Stress measurements at a depth of 15 cm showed that the former tyre produced higher peak stresses. If values of soil cohesion and angle of internal friction are available, the model SOCOMO can predict size and location of plastic regions in soil under tyres. If only specific types of field traffic and given pieces of land are considered, it is possible to measure useful relationships between soil water content at traffic event and traffic-induced change of any soil physical property.

Impact of traffic-induced compaction of sandy soils on the yield of silage maize in The Netherlands

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%.

Land use change impacts on floods at the catchment scale : Challenges and opportunities for future research

Abstract Research gaps in understanding flood changes at the catchment scale caused by changes in forest management, agricultural practices, artificial drainage, and terracing are identified. Potential strategies in addressing these gaps are proposed, such as complex systems approaches to link processes across time scales, long‐term experiments on physical‐chemical‐biological process interactions, and a focus on connectivity and patterns across spatial scales. It is suggested that these strategies will stimulate new research that coherently addresses the issues across hydrology, soil and agricultural sciences, forest engineering, forest ecology, and geomorphology.

Comparison of stresses, compactions and increase of penetration resistances caused by a low ground pressure tyre and a normal tyre

Abstract The direct effect of wheel load on soil was measured as part of a research project on perspectives of a low ground pressure farming system, using two trailer tyres with inflation pressures of 80 and 240 kPa and two loosened topsoil layers with a thickness of 0.35 and 0.55 m. The wheel load was 32 kN for all the tests. The stresses were measured at the topsoil-subsoil interface using five pressure cells in a section perpendicular to the driving direction. Deformations and compactions were measured by photographing a vertical point grid positioned in the soil profile perpendicular to the direction of wheel passage. The penetration resistances were measured in three cross-sections, before, directly after and 6 days after wheel loading. Although the stresses measured beneath the low pressure tyres were higher than expected, the deformations and compactions were considerably reduced. The peak penetration resistances caused by a low pressure tyre and a normal tyre were almost equal; however, in the case of the low pressure tyre the area involved was much smaller. Low pressure tyres would seem to be a good option in the prevention of soil degradation by excessive compactions and deformations.

A subsoil compaction database: its development, structure and content

Abstract A database which holds results of field and laboratory experiments on the impact of subsoil compaction on physical and mechanical soil parameters and on crop yields and environmental impact is being developed within the EU sponsored concerted action (CA) project “Experiences with the impact of subsoil compaction on soil, crop growth and environment and ways to prevent subsoil compaction”. The database accumulates and can provide all available data from the participants of the European Union countries, and is compatible with the European Soil Database and other related databases. More than 600 sets of data (Excel workbooks) from participants from the European Union, plus Poland, Switzerland and Norway are included in the database. Through a similar EU sponsored CA, Eastern European countries are expected to deliver 260 sets of data thus bringing the total number of Excel workbooks to approximately 860. In total, the database will contain approximately 13,500 data spreadsheets. The objective of the database is to collect data on subsoil compaction, to store it in a structured format and to make it available for analysis and use. Thereby it will enable elucidation of the impact of subsoil compaction on soil properties, crop yields and environment and evaluate the vulnerability of soils to compaction.

A sensitive method to measure and visualize deformation and compaction of the subsoil with a photographed point grid

Abstract Owing to heavy wheel loads the subsoil increasingly compacts, and measurement of subsoil compaction with the generally applied undisturbed volume sampling techniques is not sensitive enough. This, together with the need to know which deformations occur during compaction, is the reason for developing a new sensitive method to measure and visualize compaction and deformation in the subsoil. A vertical point grid, positioned into the soil profile perpendicular to the driving direction, was photographed before and after wheel passage. Through monoplatting, a photogrammetric technique, the position of the grid points was measured and their displacements calculated. Volume changes dur to compaction were found by computing the volumes between four grid points before and after wheel passage. Changes in dry-bulk density as low as 1% could be measured.

Quantification of C and N stocks in grassland topsoils in a Dutch region dominated by dairy farming

Estimates on soil organic carbon (SOC) and nitrogen (N) stocks in soils cannot be directly calculated from routine soil analyses, since these often lack measurements on soil bulk density (Bd). Hence, flexible pedotransfer functions are required that allow the calculation of SOC stocks from gravimetrically determined SOC contents. The present paper aimed to: (1) quantify SOC and N stocks in grassland topsoils for a Northern Dutch region dominated by dairy farming and (2) analyse the relationships between SOC and bulk density at the field level. As estimates of SOC and N stocks are potentially affected by soil compaction, the combined measurements on soil bulk density and soil organic matter (SOM) were also evaluated with respect to critical limits for soil compaction using soil density (Sd) for sandy soils and packing density (Pd) for clay soils. The SOC and Bd measurements were done in the upper 0·1–0·2 m of grasslands at 18 dairy farms, distributed across sandy, clay and peat soils. Both farm data and grassland management data were collected. Non-linear regressions were used to analyse relationships between Bd and SOM. Significant non-linear relationships were found between gravimetric SOC contents and bulk density for the 0–0·1 m layer (R2=0·80) and the 0·1–0·2 m layer (R2=0·86). None of the fields on sandy soils or clay soils indicated signs for limited rooting in the topsoil although some fields appear to approach the critical limit for compaction for the 0·1–0·2 m layer. Stocks of SOC in the top 0·2 m at farm level were highest in the peat soils (21·7 kg/m2) and lowest in the sandy soils (9·0 kg/m2). Similarly, N stocks were highest for farms on peat soil (1·30 kg/m2) and lowest for farms on sandy soil (0·60 kg/m2). For the sandy soils, the mean SOC stock was significantly higher in fields with shallow groundwater tables.