Indicator based assessment of the soil compaction risk at arable sites using the model REPRO

Soil compaction impairs all essential soil functions, which are crucial for the lives of humans, animals, plants and soil organisms. In order to secure the various soil functions, soil compaction must be avoided. One successful method of preventing soil compaction could be based on the precautionary principle, and mathematical modelling might be used to support farmers or consultants when making decisions about husbandry operations. This paper presents a model which calculates an indicator and assesses the risk of soil compaction on arable land based on site-specific data including information on soil, weather and specific husbandry. The first step is to estimate the soil strength in response to soil stress for a topsoil (20 cm) and a subsoil (35 cm) layer. The estimations of these parameters take into account changes in soil moisture throughout the year. Soil strength compared with soil stress is used to calculate the indicator Soil Compaction Index (SCI) for each time the machinery passes over the soil. The results from the separate passes are then integrated for a comprehensive assessment of the risk of soil compaction at farm level. The model was validated in numerous trials. It was found that the calculated SCI was a good reflection of the actual change in soil structure. The model is already being applied on arable farms in Germany. As an example presented in this paper, the calculations for the subsoil at these farms result in low to medium compaction risks.