Soil erosion from water compromises soil fertility and can contribute to water pollution. For the sake of a sustainable agricultural sector and in order to protect the environment, it must therefore be reduced.
Soil erosion depends on many factors. Within the SAEDN, the focus lies on the so-called C-factor of the Universal Soil Loss Equation (USLE), which describes the erosion risk caused by management practices. More precisely, the C-factor indicates the relative change in erosion for a particular management practice compared with the erosion of a long-standing bare fallow. The C-factor can take values between 0 and 1, with 0 representing the smallest (100% soil cover, no tillage, good rootability, etc.) and 1 the greatest erosion risk (permanent bare fallow, completely naked soil, fine seedbed).
Normally, the C-factor should be calculated for the entire crop rotation of each plot on a farm. Since the AEI indicators are calculated annually, the simplifying assumption is made that the relative crop shares of a farm reflect its crop rotation. The calculation for each plot is always made from 1 July of the previous year to 30 June of the reporting year, and is based on an area-weighted farm value. For various crops, typical points in time were estimated for six different developmental stages, which are used for the calculation:
- 10% cover
- 50% cover
- 75% cover
For each crop and stage, a typical ‘Soil Loss Ratio (SLR)’ was determined which depends on tillage (e.g. plough, no-till). For the temporal weighting, the erosivity of precipitation events also affects the calculation: the C-factor values are higher in summer, when rainfall erosivity is high, than they are in winter.