The three-field system is a form of ecological farming designed to maintain soil health. A specific succession of various crops grown on the same field is designed to make the best use of the soil and avoid an unbalanced reduction in nutrients. Depending on their effects on the soil, crops are classified as humus enhancers (cereals, e. g. grains) or humus consumers (oleiferous and tuber crops, e. g. linseed, sunflowers or potatoes).
Green manure crops are integrated into the crop rotation to enrich the land with nutrients and activate life in the soil, with plants such as leguminous plants (lucerne, lupines). For three years these crops are planted on three, roughly equally sized agricultural fields and the same sequence repeated (grain - oleiferous/tuberous crop – green manure crop). The sequence is fixed and cannot be arbitrarily changed.