The composition of the soil solution provides crucial information on the condition of the forest ecosystem. It indicates which nutrients are available for plants and serves as a key indicator of the forest's nutritional status.

The composition of the soil solution varies depending on soil type and environmental influences. It reflects the soil's pH value, mineralogical composition, and external substance inputs. Weather conditions cause fluctuations in the soil solution. Temperature and soil moisture affect the balance between the soil solution and solid phase, leading to dilution or concentration processes. Biological processes, such as the activity of soil organisms or the uptake of nutrients by plants, can also influence the composition of the soil solution.

To sample the soil solution, suction lysimeters are installed at different soil depths on the surfaces. By applying a vacuum, the soil solution is sucked through the suction lysimeter and a sample is collected. The chemical composition of the sample solution is analyzed in the laboratory.

At this time, the app is only available in German.

The app allows users to display the concentration of various substances in the soil solution and compare values at different depths. It can show the concentration of total nitrogen, N-NO₃, N-NH₄, S-SO₄, aluminum, dissolved carbon, and pH value. For example, it can illustrate that the concentration of nitrogen and carbon in the soil solution is higher in the topsoil compared to greater soil depths.

All displayed values represent annual averages (dashed line) or the corresponding medians (solid line). The concentrations of substances in the soil solution can cover a very wide range. Therefore, the y-axis is logarithmically scaled.

It is possible to compare values from up to three different depths. The respective depth range is selected using the corresponding sliders. The depths at which samples are taken differ between the Level II sites. When different depths are selected, values from different sites might be compared. If multiple depths are available for an area for the selected depth range, these are shown individually in the "per site" view. The "per site" view also allows users to assess how many individual values contribute to the overall median or average. For example, only ten sampling points are available for depths below two meters.