Green manuring is an agronomic practice that consists in sowing an herbaceous crop with pure or associated essences, which are then totally buried or chopped.It has the function of fertilising the next crop or the trees planted in the soil sown. The advantages of this technique mainly relate to the fertility of agricultural soils and the reduced use of mineral fertilisers, thanks to the addition of organic matter and nutrients contained in the green manure crop.
In green manure crops, the development of the root system and the burying of plant biomass also bring a large amount of organic substance to the soil, improving its structure and chemical and biological properties in the short term, especially if this practice is repeated over several years with highly developed plant material. Furthermore, in annual rotations autumn-winter green manures have an environmental function since these crops, called ‘cover crops’, cover the soil between one main crop and another, retaining nutrients, and nitrogen in particular, in the layers of soil explored by the plant roots. This makes it possible to reduce the quantity of nitrates carried deep by rainwater.
The use of green manure crops also reduces the phenomenon of surface rainwater runoff, mitigating soil erosion and the dispersion of nutrients, in particular phosphorus, in surface waters. A negative aspect of green manuring is that it requires tillage, and is not suitable for all types of fields. Once the cover crop is buried, it is recommended to apply a very close rotation to avoid the leaching of nitrates into the groundwater. The correct application of green manure also requires shallow tillage to avoid losing the advantages of nitrogen fixation and prevent environmental damage.