Soil Cover

Mean soil cover comprises a spatial and temporal component. Spatial soil cover changes, for example, through the growth of crops, reaching almost 100% before harvest. Temporally distinctive changes in the degree of soil cover are found when the seedlings become visible at the surface, but also after ploughing. A high degree of soil cover has several positive effects: for starters, it reduces nutrient leaching and soil erosion, and favours biodiversity.

A soil-cover figure of less than 30% is viewed as critical for nutrient loss and erosion. Soil cover over a specific time period can be given in so-called ‘soil cover days’ (SCDs). The number of SCDs is calculated by adding up the daily soil-cover values (between 0% and 100%) over the time period considered. Thus, 1 SCD can mean that a plot is 100% covered for one day, or 50% covered for two days.

In the context of the SAEDN, soil cover is calculated as a spatially and temporally weighted average for each farm, with both crop-residue cover and living-vegetation cover being taken into account (Büchi et al. 2016).

Crop-Residue / Vegetation Cover

Crop-Residue Cover

To calculate crop-residue cover, information is needed on initial soil coverage by residues directly after the harvest, the rate of decomposition of the crop residues (decomposition coefficient), and tillage methods.

Soil cover directly after harvest and the incorporation rate (as a function of tillage measures) were both determined from values from the US literature, and in the latter case were adapted for Swiss machinery. Crop-residue decomposition is taken into account with the following function

where  represents the initial soil cover and SC the soil cover after the time  ias a function of the decomposition coefficient .

Vegetation Cover

Grassland cover is almost always 100%, which is why the calculation focuses on soil cover in arable crops. The daily soil cover depends on the growth of the arable crops. Using the STICS model, the growth of numerous crops was calculated for tens of thousands of scenarios with different sowing dates, soil depths/textures and climatic regions. All in all, 27 years (1982–2009) were simulated using daily-resolved weather data. With the leaf-area index (leaf area per soil area; LAI) calculated by STICS, soil cover was calculated using the formula

Where K is the crop-specific extinction coefficient (figures adopted from STICS). For tuber and root crops as well as late-ripening cereal crops, fixed harvest dates were set, whilst the harvest times for the other crops were calculated by STICS.

The scenarios calculated with STICS serve as a reference table: For the SAEDN data, those values whose input variables most closely correspond to those in the reference table are taken for soil cover. Here, the median over the 27 simulation years is applied, in order to avoid random annual fluctuations.

Contact

Publication

Integrating simulation data from a crop model in the development of an agri-environmental indicator for soil cover in Switzerland.

Büchi L., Valsangiacomo A., Burel E., Charles R.
European Journal of Agronomy, online, (18 November), 2015, 1-11.