A method to predict the soil susceptibility to compaction of surface layers as a function of water content and bulk density

Identifying the vulnerability of soils to compaction damage becomes an increasingly important issue in the planning and execution of farming operations. Soil compaction models are efficient tools for predicting soil compaction due to agricultural field traffic. Most of these models require the knowledge of the stress/strain relationship, as well as the mechanical parameters and their variation with different soil physical properties. Because the soil compaction depends on its water content, bulk density and texture, a good understanding of the relation between them is essential for defining suitable farming strategies according to climatic changes. In this work we propose a new pedotransfer function for 10 French representative soils collected from cultivated fields, a vineyard and forests. We investigate the relationship between soil mechanical properties and easily measurable soil properties as well as water content and bulk density. Confined compression tests were performed on remoulded soils of a large range of textures at different initial bulk densities and water contents. The use of remoulded samples allowed us examining a large range of initial conditions with low variability of measurement. A good linear regression was obtained between soil precompression stress, compression index, initial water content, initial bulk density and soil texture. The higher the clay content, the higher the soil capacity to bear higher stresses at higher initial water content without reaching severe compaction state. The initial water content played an important role in clayey and loamy soils. In contrast, for sandy soils, the mechanical parameters were less dependent of initial water content but more related to the initial bulk density. These pedotransfer functions are expected to hold for soils of surface layers with tillage but further measurements on intact samples are needed to tests their validity. Introduction Soil compaction is one of the major problems for soil degradation in modern agriculture and forestry. Machinery overuse has been found to be the main cause for soil compaction. Due to its persistence, compaction of the subsoil can be seen as a long-term degradation but compaction concerns also surface layers. Compaction adversely affects soil physical fertility, particularly storage and supply of water and nutrients, through decreasing porosity, increasing soil strength and hence soil resistance to root penetration and plant emergence, decreasing soil water infiltration and holding capacity. These adverse effects also reduce fertilization efficiency and crop yield, increase water logging, runoff and soil erosion with undesirable environmental problems (Soane and van Ouwerkerk, 1994). Thus, knowing …