Cover crops help prevent soil erosion, regulate moisture, attract pollinating insects, facilitate weed and pest control, and serve as mulch or a source of green manure and organic matter, as well as being used for grazing or fodder. Depending on the types of cover crops, they can add or absorb nitrogen.

What Is A Cover Crop?

As the name suggests, these are plants that cover the ground for different causes. Unlike primary species, cover crops  support the secondary needs of the farmer and are not grown for trade or human consumption . They improve soil health, increase yield and feed livestock. However, these plants are not exclusive species. In some situations, cover crops serve as cash crops and can be found on the plate (for example, buckwheat or corn). The case of fall cover crops is different, since these species are used as grass.

Farmers sow cover crops in different seasons, either in fall or late spring/summer, evenly or between rows. Some die from cold and others must be eliminated. It is also possible to plant one species or several at the same time. This last method gives the best results. The most common cover crops are legumes, grasses (fodder grains), brassicas, turnips, radishes, etc.

This practice is highly appreciated in  crop rotation ,  no-till  and organic farming. Smart online tools help make wise decisions.

What Types Of Cover Crops Are There?

Depending on the use options and cover crop characteristics, three main categories are differentiated: grasses, legumes, and broadleaf non-legumes. In most cases, cover crops fulfill several functions at the same time, such as preventing erosion, improving soil quality or grazing, among others.

• Grasses  are annual cereals such as buckwheat, rye, wheat, corn, barley, oats, etc. They grow relatively quickly and leave residue that is easy to manage. Their fibrous root systems are strong and thanks to this they protect against erosion. Regarding nutrients, these cover crops accumulate soil nitrogen from the symbiosis with Azospirillum, but they do not have the property of fixing atmospheric nitrogen.
• Legumes  are famous for nitrogen-enriching, nitrogen-fixing crops. Its primary system helps to avoid the undesirable compaction of the soil when the plants grow. Also, the bigger the crop,  the more nitrogen  it can fix. Some examples of legumes are crimson and white clover, cowpeas, alfalfa, vetch, and broad beans.
• Broadleaf non-leguminous plants  take up nitrogen from the soil, hold it, and produce  green manure . This type of crops usually dies in extreme winter conditions. However, non-leguminous plants used as fall cover crops should be used prior to planting for weed control. This type includes brassicas, fodder radishes, turnips, marigolds, mustards, and others.

Types Of Cover Crops By Season

There is another classification according to the time of planting. Agronomists distinguish fall, winter, spring and summer cover crops. All of them have certain peculiarities in their management, advantages and disadvantages.

Winter Cover Crops

These are cereals planted after the autumn harvests of cash crops. Your goal is  to protect the soil until spring plantings, not to increase yields . How do you make this cover crop? The basic requirements for its growth are sufficient heat in the fall and moisture in the spring. Winter cover crops are used to conserve soil by helping to prevent  soil erosion, they fight weeds, conserve moisture and reduce the leakage of nutrients, but they also consume them. In addition, their seeds require additional costs, can be difficult to dispose of, cause allelopathic effects, and influence the development of the main crop. Plant cover protects against diseases and pathogens, but it can also have the opposite effect.

When planting these cover crop species, farmers must consider their resistance to frost. Cold hardy plants survive the winter, while those sensitive to significant drops in temperature die during the winter.

Summer Cover Crops

As the name suggests, these cover crops are grown in summer between primary species rotations. This practice is applied to  kill weeds, prevent erosion and prepare the land for the next crop . Summer or spring cover crops also serve as fodder for livestock.

With its roots, the soil does not dry out as quickly as in the case of bare soil under the sun’s rays. However, seeds can do poorly in summer due to drought and heat, induce  nitrogen deficiency  (unless they are legumes), require additional residue management, or take longer than expected decay time. , which delays the time to sow the primary fall species.

The right timing and the right choice of  farm crops  are the keys to success, as benefits can easily turn into disadvantages when things go wrong. Farmers have to face this challenge, creating productivity maps. Through a comparative analysis, the optimal timing and crop species can be chosen.

Cover Crops And Grazing

Farm owners can enjoy additional benefits with cover crops over grazing livestock. These species have general advantages and are also used as animal feed. In addition, grazing cover crops allow farmers to create a natural outdoor environment for breeding, which is important in organic farming. Grazing also provides manure on pastures, saves forage costs, and facilitates removal before planting of the main crop. This practice is especially beneficial in late fall, winter, and early spring, due to the lack of fresh, juicy ground cover.

Typical cover crops for grazing  are cereals and legumes such as ryegrass, wheat, sorghum, millet, oats, triticale, barley, downy vetch, red and white clover, pennies, egyptian bean, field pea, cowpea, alfalfa and broad beans, among others.

Benefits of Cover Crops

Cover crops have several positive effects for agriculture.

Soil Health And Fertility

Cover crop roots help prevent erosion caused by water and wind. Some species can make nutrients easily ingestible for other crops. By planting cover crops between rows, farmers get a mulch as part of  integrated weed management . Also, flowering plants between rows attract pollinators. Deep and shallow rooted cover crops penetrate the soil at different levels, addressing compaction and improving aeration.

Nitrogen Enrichment

Its concentration increases with legumes and decreases with non-legumes. Legumes are known as nitrogen-producing cover crops. However, they do not take up and convert gaseous molecular nitrogen from the air by themselves.

Nitrogen-fixing cover crops are in symbiosis with the mediators in their roots: soil-dwelling Rhizobium bacteria (formerly defined as agrobacterium). In turn, the bacteria obtain carbohydrates from the legumes. The nutrient is mostly released when nitrogen-fixing cover crops or bacteria die and rot. Rhizobium also decreases plant root diseases, but the  Rhizobium radiobacter group  causes infections in humans.

Another biological alternative to convert atmospheric nitrogen into soil nitrogen is carried out with the non-symbiotic cyanobacteria family. If not, nitrogen is made ingestible to plants in the process of chemical synthesis.

Humidity control

Cover crops can soak up excess water after winter rains, improve water infiltration (as well as  soil aeration ) with their roots, and store moisture for future commercial plants.

Farmers have to check soil moisture at two levels: at the top surface (up to 5 cm) and the root zone.

Selection And Management Of Cover Crops

The choice of crop for planting depends on its  type  and  sequence . For example, legumes are beneficial for nitrogen supply for downstream commercial species. Consequently, farmers should not plant these cover crops when nitrogen levels become saturated.

One study calculated that nitrogen uptake in maize silage increased after field peas and decreased after rye up to  40 kg/ha in both cases compared to fallow.

Another aspect to take into account is  the time required for the correct decomposition of cover crops . For example, buckwheat residues decompose faster than barley or sorghum residues.

Cover Crop Management 

The  vegetation indices  of plant development. For example, the NDVI  helps to check the general condition of the vegetation and to distinguish the most critical areas (to detect the urgency in irrigation or fertilizers, for example). The MSAVI allows to control the seedlings, since it does not penetrate deeply into the soil. NDRE monitors nitrogen content through chlorophyll activity and helps apply fertilizers where needed, as well as detect plant degradation.

The historical data on the vegetation allows to elaborate maps of productivity that allow to reduce the costs of planting and fertilization. Thanks to the information on the phenological phases, farm owners can schedule field activities, since certain operations, such as spraying and fertilization, must be carried out in a certain growth phase.

Meteorological records of the past allow us to foresee extreme winters or summers. Weather forecasting allows farmers to efficiently plan field activities such as herbicide end-of-use, as some of them require dry weather while others need rainfall to react.

Thus, farmers decide when to plant cover crops, how to treat them and when to finish them, as well as keep track of field operations. Farmers can monitor the overall process of plant development, density and health. Reliable information encourages smart farming decisions.