Cover crops are defined as crops used to protect agricultural soils because it can maintain or improve soil fertility and productivity without direct costs for fertilizer, especially regarding legumes because they can fix their own nitrogen from the atmosphere.
Actually, there are several reasons to apply cover crop into land. It may be used:
1) As a green manure “plow-down” crop to increase soil organic matter, stimulate soil
biological activity or improve soil physical characteristics;
2) To catch or keep valuable nutrients;
3) To protect the soil from erosion;
4) To interrupt pest and disease cycles;
5) To kill weeds;
6) To provide an additional food source for pollinators like honey bees.
Depending on Carbon/Nitrogen ratio and types of crop materials (young and fresh, or mature and fibrous), benefits are different when incorporated into the soil. Young and fresh soil amendment with a low C/N ratio will produce little organic matter but will significantly
provide stimulation of soil biological activity (food for soil micro-organisms in the area
located near the roots). On the opposite, mature and fibrous crop materials with high C/N ratio will increase stable soil organic matter.
Depending on soil characteristics and the result expected, producers have to decide which type of cover crop to use. Actually, properties of various crop material residues have direct influence on soil structure following two reasons:
a) Mature cover crops decompose slowly and generate humus (long-lived organic
b) The outcome of young cover crops enhances mineralization due to biological
Moreover, it should enhance soil stability and soil porosity (due to the improvement of soil
aggregation following to the action of earthworms); water retention and erosion protection
will be definitely provided in the end.
In general, the best strategy is to work with several crops that have complementary root
patterns for green manuring, in accordance with your soil characteristics. By planting a
mixture of cover crops you will get all the advantages from each green manure crop. There are actually three big groups of cover crops to be used: deep rooted crops like oilseed radish, forage crops (or grasses) like oats, rye, and legumes like vetches, alfalfa, clovers. Additionally, a fourth cover crop useful for honey bees can be mix with the others, like Phacelia. Benefits of using cover crops are also providing ability to catch, preserve or extract nutrients (available or not) from soil horizons, bringing them to the roots of vines. Depending on the crops to grow and environmental conditions, cover crops are generally planted few months before harvest (beginning of summer) and they have to be worked into the soil in the beginning of spring.
There are other very interesting effects by doing green manuring. Incorporation of cover crops well selected is able to:
- Reduce pathogenic infection from insects, nematodes or other organisms, by acting
on the pest life cycle;
- keep under control weeds growing due to the huge competition with the cover crops.
In terms of costs, it is not free since cover crops have to be seeded and incorporated or mowed into the soil.
Moreover, they are non-harvested crops, so they don’t have monetary value. In fact, their benefits promote the soil on the long-term effects and, in turn, lead to improved vine growth, to reduce the risks of pests out-breaks, to enhance natural resistance of vine plants, and then, finally, to increase the overall sustainability of the vineyard.