Evaluating different soil compaction measurement techniques: simplicity versus Complexity

The problem of soil compaction in agricultural fields through trampling, drying and wetting processes, and tillage is well known in the Netherlands. It leads to a change in soil structure which impacts soil properties and processes. Consequently, crop yields will reduce causing financial losses to farmers. Therefore, there is a need for cost-effective soil compaction measurement techniques. However, soil compaction cannot be directly assessed by a specific measurement technique. Therefore, a reliable proxy is needed allowing to identify and quantify soil compaction. For this, a field experiment was set up involving 31 persons and four contemporary methods were tested for the estimation of in-situ soil bulk density 1) core sampling, 2) the ‘knife method’, 3) Penetrologger, 4) RhoC.
In this field experiment various sources of error were accounted for using basic statistical analysis, including the uncertainties in the measurement equipment, human error or small-scale variability. Results show that the Penetrologger was capable to identify the start of the compacted layer but was not capable to estimate the depth of the layer and was prone to ‘human’ error. Therefore, the Penetrologger was deemed the least suitable method. Considering the simplicity of the knife method it performed very well, even inexperienced people were able to identify the start of soil compaction. Yet it remains a qualitative and more uncertain method, due to its subjectivity of the human’s perception of changes in bulk density and soil strength. The RhoC was the best alternative method compared to the core samples to quantify bulk density.