Assessment of soil compaction using soil shrinkage modelling: Experimental data and perspectives

Soil compaction assessment is an important and difficult issue. In particular, it is difficult to quantify separately the compaction of macro-pores and micro-pores in the soil, and to account for spatial variability in soil properties at field scale. According to recent publications, the measurement and modelling of soil shrinkage curves (ShC) could help to overcome these difficulties. This is discussed in this paper on the basis of a field study. Control and compacted undisturbed samples originating from the surface layer of a cropped field are compared. The methods for measurement and modelling of the ShC are presented. Calculations of the micro-porosity, identified to be the soil plasma-porosity, and of the macro-porosity in the soil samples, at any water content, are described, and the accuracy of the results is discussed. A good agreement between field observation and ShC modelling is observed. The method allows for quantifying the compaction, with distinction between plasma-porosity and macro-porosity compaction. The forming of occluded macro-pores is also detected and quantified. The presented method offers numerous advantages in soil compaction assessment. It is precise, simple and easy to operate. It can be realized on clods of unspecified shape and containing a coarse fraction, and can be calculated for the fine earth fraction without the coarse fraction. The pore systems are quantified at any water content, and the determination covers the full range of pore sizes with quantitative distinction between the plasma-porosity and the macro-porosity compaction. According to previous results, it is possible to remove a certain amount of spatial variability in soil clay content by scaling the shrinkage parameters with clay content. The measurement and modelling of soil ShC is, therefore, a promising tool for soil compaction assessment.