Everything you need to know about cover crops and intercropping practices using cover crops, and implementing nitrate-fixing cover crops.
Intercropping cover crops can serve a variety of purposes. It may meet regulatory requirements, improve agronomic potential, or increase intercropping production value. Sometimes, a few of these objec...
Soybeans are part of the legume family. They are mainly used for animal feed. Like most legumes, they are very beneficial for the next crop because they take in nitrogen from the air and release it in...
Cover crops are highly beneficial for soil health. They uptake and fix nutrients in the soil, which helps reduce leaching, before releasing the nutrients in the spring. In addition, decomposing cover crops reduce weeds and the need for chemical treatments. Finally, cover crops also limit the risks related to adverse climatic conditions:
Cover crops can have certain downsides, such as the cost of planting and destruction, as well as competing with main crops for water and nutrient resources. However, the drawbacks can be outweighed by the many benefits for soil health and lower chemical-input requirements. To maximise the benefits, it is important to choose the right species and varieties of cover crops according to the agronomic needs of the farm and take soil-type and climate into account when deciding on planting methods.
Cover crops have many positive functions that can be divided into four categories: soil protection, water regulation, biodiversity and biomass production. Plant cover can help limit erosion, improve soil structure and fertility, reduce nutrient and pesticide leaching, encourage the development of beneficial fauna and flora, and produce biomass for animal feed or energy production.
To ensure the success of your cover crops, you first need to choose the plants best suited to your farm. It's important to think about the most important agronomic needs for your soil-type and climate. It may be necessary to set priorities. The three most commonly used families are crucifers (or brassicas), grasses (sorghum, rye, moha, ryegrass, etc.) and legumes (clover, alfalfa, field pea and field bean). The success of your cover crop depends not only on the species, but also on the cropping system. Therefore, these 5 tips are recommended:
Cover crops are often used as part of an " intercropping " system. Intercropping means growing plants between two main crops, generally during the winter or summer. Cover crops are sown after the main crop has been harvested and before the next crop is sown. They cover the soil during the intercropping period, preventing erosion and nutrient loss as well as limiting weeds.
In addition, cover crops contribute to improving soil structure and fertility by adding organic matter and boosting biological activity. Cover crops can also be used to fix nitrates in the soil to limit leaching.
The most effective techniques for planting cover crops will depend on the farm. For intercrop seeding, a seed drill with discs or tines is recommended for rapid, even planting. For overseeding in an existing crop, it is advisable to plant early to take advantage of soil moisture, and to plant species that take a long time to develop. It is also possible to bury the seeds lightly. Herbicides are not necessary for controlling weeds and regrowth after the crop has been harvested. Finally, it's important to note that the equipment needed for sowing is generally already available on the farm.
Sowing at the same time as a main crop can have advantages, such as the soil being moist, and the seedbed being prepared. This enables the cover crop to develop and take root well before weeds can develop. However, it can also have disadvantages, such as competition between the cover crop and the main crop, which can hinder the development of them both.
Overseeding an established crop has a number of advantages and disadvantages. Advantages include early planting to take advantage of soil moisture, planting species that take a long time to establish, and limiting the development of weeds and regrowth after the crop has been harvested. What's more, the equipment needed for overseeding generally already exists on the farm.
In terms of the drawbacks of overseeding, it can be difficult to adapt the sowing date and the species, which mustn’t complete too much with the crop or interfere with harvesting. A seedling sown too late in a crop may lack light and fail to develop. In addition, depending on the species, there could be a problem of working-width compatibility with the sprayer tracks.
Examples include legume cover crops such as common vetch, Balansa clover, crimson clover, and Alexandria clover are used in forage systems and interseeding strategies to improve soil health and provide nitrogen. These species may be interseeded into forage maize (corn silage), typically around the V4–V6 growth stage, when corn is tall enough to allow light penetration but not so dense as to shade out the cover crop. While lentils are less common, Austrian winter peas are sometimes used in similar systems. These legumes contribute to nitrogen fixation, erosion control, and forage quality.
Seeding in mulch during harvest or just before means sowing the cover crop as early as possible to get the benefit from the moisture in the mulch produced by shredding and spreading the residues during harvest. This is a difficult technique to put into practice, though, as it requires specific equipment, such as a harvester-mounted system. Furthermore, there may be issues of working-width compatibility with sprayer tracks. The technique is mainly possible with small seeds at low application rates.
Post-harvest seeding, with or without tillage, has advantages and disadvantages. On the one hand, it requires no special equipment, and water loss through evaporation is reduced if a direct seeding method is used. What's more, by using seed drills that have hoppers with compartments and separate distribution systems, it is easy to mix species.
On the other hand, the sowing period often coincides with dryer soils, which can make seed placement difficult because there may be large amounts of residues. In addition, if the soil has been tilled, there may already be regrowth. Mixed cover crops can be used for seeding after harvest.
The species should be chosen to meet the most important agronomic needs for your soil-type and climate, so it is essential to know them and to define the goals of your cover crop. It may be necessary to set priorities. The choice of species must take the cropping system into account. It is also recommended to use complimentary species and varieties as well as mixtures that facilitate plot management. By following these tips, you can make the right choice for your cover crops.
The concept of using nitrogen-fixing cover crops gained traction in the U.S. as part of broader efforts to improve water quality and soil health. These cover crops help reduce nitrate leaching into groundwater and surface water by either fixing atmospheric nitrogen or scavenging residual soil nitrogen. Legumes like hairy vetch are known for their nitrogen-fixing ability, while non-legumes such as cereal rye are effective at capturing leftover soil nitrogen. Although the term “Nitrate-Fixing Intermediate Crop” originated in Europe under the 1991 Nitrate Directive, U.S. farmers commonly refer to these as nitrogen-fixing or nutrient-scavenging cover crops, depending on their function in the rotation.
Green manure is an intermediate crop whose purpose is to supply the following crop with nitrogen, as well as to improve soil structure. Cover crops used as green manures are generally legumes, which can trap atmospheric nitrogen and return it to the soil. Green manure contributes to improving soil fertility and reduces the need for chemical fertilizers.
Other species such as crucifers (white mustard, fodder radish, fodder rape, etc.) can fix mineral nitrogen in the soil, limiting nitrogen leaching. This reduces the C/N ratio, which in turn leads to faster residue mineralization, so that nitrogen is available rapidly for the next crop.
Legumes are known for their capacity to efficiently fix atmospheric nitrogen. This symbiotic nitrogen fixing is a biological process that occurs due to the specific bacteria in the roots of legumes. The capacity of legumes to fix atmospheric nitrogen can be used to improve soil fertility and reduce the need for nitrogen fertilizers.
Cover crops can be terminated or destroyed in different ways, such as shredding, burying or using herbicides. It is important to choose a method in line with the farm's agronomic and environmental objectives. For example, if you want to avoid using herbicides, you can opt for mechanical or natural destruction (by frost). In addition, to prevent competition with the main crop and limit nutrient leaching, the cover crop needs be terminated at the right time. Lastly, the cost of destruction and environmental impacts should also be considered when choosing the method most adapted to your farm.
