Laboratory analysis method (electro-ultrafiltration) for the examination of soil substrates for their nutrients available to plants. All main nutrients and trace elements including nitrogen (in the form of ammonium and nitrate, as well as organically bound nitrogen) can be recorded. Soil samples are taken from 0 to 60 centimetres of the soil before the beginning of vegetation (February to March). The subsequent chemical determination of the water-soluble elements and compounds, as well as their concentration, is carried out using standard analysis from the extraction solution (atomic spectroscopy or spectrophotometry). The extraction of the nutrients is carried out in a unit specially developed for this process using heating and electricity. In a first step (fraction), the directly available nutrient fraction is determined at 30 °Celsius, 200 volts and 15 milliamperes, and in a second step the potentially available nutrient fraction (stock) is determined at 80 °Celsius, 400 volts and 150 milliamperes. Depending on the nutrient, the two results are presented either individually, as a sum or in relation to each other. The analysis serves as a basis for the required fertilisation. See also under Bonitur and Nmin method.