An intermediate culture is a crop grown between two main crops (wheat, beet, etc.) to prevent the soil from remaining bare during the winter. Two types of intermediate crops exist:
- Nitrate-fixing intermediate crops: The purpose of nitrate-fixing intermediate crops is to capture nitrogen that remains in a field to prevent pollution of waterways. These crops are re-incorporated into the soil to feed the next crop.
- Intermediate culture with energetic purpose: Those crops are also used to trap nitrates but are mostly grown to produce maximum biomass in order to be harvested and used in biomethanisation or bioheat plants.
As nitrate-fixing intermediate crops are generally destroyed, crop yields are not important. The most commonly used species are mustard, phacelia, ryegrass and oats.
For intermediate culture with energetic purpose, it is necessary to produce a maximum of biomass in a short time, with a good energy potential as it can be the case of pure or mixed oats, barley, Italian ryegrass or even nyger plant.
Intermediate culture captures surplus nitrogen in the soil, which prevents nitrogen from being washed away and polluting waterways. If water contains too much nitrogen, it can be non-potable and risks causing hypoxia (lack of oxygen) in bodies of water, encouraging the proliferation of algae (phenomenon of eutrophication).
Intermediate cropping also has other advantages, including maintaining soil cover for better water infiltration without soil erosion, improving the soil structure and adding organic matter to the soil.