By growing a green cover after the main crop, nitrogen leaching is prevented. White mustard has a fixation of 75 – 95 kg nitrogen per hectare in light soils; in the slightly heavier soils this varies from 120 to 160 kg nitrogen per hectare. Fodder radish has an even greater potential for nitrogen fixation above ground of 90 to 120 kg nitrogen per hectare on the lighter soils; on the heavier soils this is 200 to 240 kg per hectare.
White mustard, fodder radish, Italian and Westerwold ryegrass can be sown after an early potato crop (grown for either consumption or seed). After maize and late potatoes, grasses, winter rye and winter vetches can still be sown. In the following year, N fertilization must take into account the N released from the green cover. If not, the N fertilization will not be saved, burning can damage the crop and the chance of N leaching increases. Of all the green cover crops, grass is the best to limit N leaching, because it absorbs nitrogen both before and after the winter. The total aboveground N uptake by the grass is slightly lower than with mustard, because grass grows less quickly than mustard.