Frequently used in large-scale farming, the perennial plant cover is a plant cover that remains in place for more than a year on a field and that successively plays the role of intercrop and cover-crop throughout the rotation. The establishment of the main crop and its harvest must therefore preserve the perennial plant cover. In comparison with a conventional cover crop, perennial covers reduce interventions related to sowing and cover destruction.

It presents various interests:

• limits the development of weeds by allowing the soil to be covered all year round;
• improves soil structure by limiting settlement, as well as erosion in winter and during heavy spring rains;
• limits nitrogen leaching, thus improving water quality;
• promotes soil’s biological activity as well as the biodiversity that allows biological regulation of certain pests. The spread of diseases is also slowed down;
• in the form of a legume, it can be used to fix atmospheric nitrogen and to relocate it into the soil thanks to the dead parts of the cover.

Choice of perennial cover species and variety is crucial because the cover must be competitive for weeds but harmless for cash crops. It must therefore be very thick to prevent weed development, as well as relatively low, with shallow rooting, and water efficient, in order to limit competition for light, nitrogen and water with cash crops. For instance, birdsfoot trefoil, white clover and cultivated alfalfa can be used. This competition must be controlled over time by intervening on the perennial cover in order to limit its growth without killing it, with the aim of optimizing yields.

Perennial plant cover is thus part of an agroecological approach by ensuring the sustainability of soils and promoting the biological regulation of pests and diseases, thus limiting the use of pesticides