Cover Crops

 Crotalaria Cover Crop

What are Cover Crops?

Cover Crops Definition

Cover crops are legumes, grasses, forbs or other plants grown specifically to develop and enhance soil quality and fertility, suppress weeds, control pests and diseases, and help manage soil erosion. They also act as mulch to help retain moisture in the soil.

Cover-cropping is the raising of a crop in the orchard after cultivation (about midsummer) to protect root systems of trees by preventing freezing, thawing and deep freezing of the ground. It also adds to the fertility of soil when used as green manure by turning it under soil in spring.

With improved soil fertility, the physical condition of soil also enhances, ensuring that only crops take up space in your garden, but not weeds. In the south, the considerations are practically identical, except that the contingency of root injury from frost is not weighed. 

There are two classes of cover-crops: the nitrogenous and the non-nitrogenous. Of the former, rye, buckwheat, oats, millet, corn (maize), rape and turnips are principally used. These plants should be sown much later in the season than the clovers, cowpeas or most nitrogenous covers.

Cover crops are valuable where the soil is hard and tough in texture, such as legumes which may be used when an improved physical condition is required. Cover crops are easy to grow, do well in almost all parts of the country and require just basic care.

Cover Crops Benefits

Why should you plant cover crops? Cover crops can benefit both the soil and plants in a myriad ways.

  • Protection from Soil Erosion

Cover crops can help reduce or eliminate water surface run-offs to ensure downstream ecosystems and waterways are protected from erosion. The roots of cover crops help develop soil pores for faster water filtration into the ground. As a result, the crops help in water conservation.

Cover Crop in South Dakota to Prevent Soil Erosion

                Cover Crop in South Dakota to Prevent Soil Erosion

Due to their ability to prevent soil erosion and retain water, cover crops are often referred to as 'living mulches'. In addition to preventing runoffs and soil splashing, cover crops also offer protection from the kind of damage that tends to result from heavy rains.

The root systems of cover crops anchor soil to increase its porosity. As a result, it develops a conducive habitat for soil microorganisms to thrive.

  • Disease Management

Crops used for soil cover reduce fungal and bacterial soil diseases to help break disease cycles. Planting cover crops in soils infested with bacteria and fungi is an effective way of eliminating the disease-borne microorganisms from soil.

  • Act as Green Manure/Improves Soil Fertility

Cover crops are rich in nutrients and can enrich soil for many years. Also known as 'green manure', crops used to cover soil provide as much nutrients as a compost pit or manure does. Organic materials such as residue of crops are placed on the soil surface to form a layer.

Cover crops improve soil fertility. They help manage micronutrients and macronutrients such as nitrogen in soil. Green manure cover crops are grown and plowed before maturity to enhance soil quality and fertility. Since they're covered under the top soil, they also help prevent soil erosion.

Mainly composed of legumes, green manure crops produce nitrogen to benefit the rhizobial bacteria they host. The bacteria converts the nitrogen to ammonium (a form beneficial to plants) in a process known as nitrogen fixation. According to Sustainable Agriculture Research & Education Organization, cover crops increase organic matter in the top soil layers by up to 2.6%.

  • Supports Sustainable Gardening

Most cover crops enhance agroecosystem characteristics and sustainability. They directly impact the crops grown near them while indirectly enhancing nearby natural ecosystems quality.

Environmental, biological, economic, cultural and social factors of a food system, including a gardener's goals and needs influence the type of cover crops to grow.

  • Weed Control

Weeds hamper the growth of crops in gardens and that's where cover crops come in. Cover crops with thick stands can compete well with weeds for food and other growth factors of plants. They terminate the life cycle of growing weeds before they can reproduce.

If placed on the soil surface at the end of their growth cycle, cover crops create a mat that no weed can penetrate to suppress their growth. The cover crop smother effect ensures no light or temperature gets to the weeds beneath for minimal to no growth.

Weeds also fail to get enough space and nutrients to support their growth. With insufficient food in storage, the weeds eventually die. Apart from suppressing weeds physically, preventing seed germination and competition-based suppression, cover crops also use toxins to suppress weeds.

Allelopathy is the process where some cover crops such as mustards, red clover and rye produce toxins to kill the weeds growing around them or simply inhibit the germination of their seeds. According to a study conducted by the Agricultural Research Service, planting patterns and seeding rate of cover crops is an effective way of controlling weeds.

 Cover Crop for Weed Control & Water Retention in Soil

                      Cover Crop for Water Retention & Weed Control

  • Water Conservation & Management

Cover crops improve water infiltration and thus increase aquifers recharging and water storage in soil. They are used as mulch to minimize evaporation and retain water in soil.

They reduce the impact of rainfall on soil while ensuring the amount and rate of water flowing downstream is minimal thereby protecting downstream ecosystems and waterways.

  • Management of Soil Quality

Over time, cover crops create biomass that increases organic matter in soil and thus improved soil quality. With increased organic matter, the structure of soil improves. As a result, the ability of soil to hold more nutrients and water is enhanced.

Soil carbon sequestration also increases, leading to more carbon dioxide being released into the atmosphere. Cover crops also help improve soil pH, salination and balance of microorganisms while reducing contamination of soil, hence increased soil quality.

  • Management of Pests

Trap crops are cover crops used to attract certain pests from value crops after which they're destroyed. Cover crops also support habitat augmentation, a biological control process used to lure natural pest predators.

For instance, Euseius tularensis, a Congdon predator mite is used in Central California to control the citrus thrip pest in citrus orchards.

  • Wildlife and Diversity

Cover crops also help conserve diversity and wildlife as the soil and environment enjoys increased protection.

Categories of Cover Crops

Cover crops are categorized based on their use and application as follows:

  • Catch Crops – Catch crops are grown after harvesting to prevent nutrients from leaching into the ground.
  • Winter Cover Crops – Winter cover crops are grown in late fall or summer to protect soil in winter.
  • Smother Cover Crops – Smother crops are grown to suppress or control weeds.
  • Forage Cover Crops – These are short-rotation cover crops grown for green chops (harvested when immature) or for grazing animals.
  • Green Manure Cover Crops  – These cover crops are grown and plowed into soil before maturity to act as green manure for enhanced soil fertility. They are often used in organic gardening.
  • Living Mulches – These are cover crops inter-planted with main crops during the production season to protect soil and retain water. Living mulches are often used in nurseries and orchards.

Types of Cover Crops

There are many types of cover crops with grasses and legumes being the most commonly used in gardening. The following are major types of cover crops:

  1. Legumes

Legumes are categorized into summer annual, winter annual and biennial and perennial cover crops. Legumes fix nitrogen into soil, control soil erosion, attract beneficial insects and enrich soil with organic matter.

Legume Cover Crop for Nitrogen Fixation and Soil Protection

                      Legume Cover Crop for Nitrogen Fixation

Whereas summer annual legumes are only grown in summer, winter annual legumes are planted in late fall and grown in winter. Summer annual legumes include peas, soybeans and beans. On the other hand, winter annual legumes include crimson clover, Austrian winter field peas, subterranean clover and hairy vetch.

However, field peas and crimson clover only do well in mild frost. Hairy vetch can do well in extreme winter temperatures while Berseem clover grows in hardiness zones 8, 9, 10 and above. Some winter annuals do well in regions with short, cold seasons.

Similarly, summer annuals such as cowpeas can be grown in the south of the U.S as frost easily damages them. White clover, alfafa, red clover and sweet clover make up the biennials and perennials. 

  1. Summer Annual Legumes
  • Soybeans

This legume is grown either as an economic or cover crop. As an economic crop, soybeans are grown for their seeds as they're rich in proteins and oil. However, they lack sufficient nitrogen and residues necessary for use as a cover crop if left to mature.

Therefore, soybeans grown for use as cover crops are left to mature up to the flowering stage. The legumes grow well in fertile soils, but just like cowpeas, they're susceptible to frost damage.

  • Berseem Clover

This clover is an annual summer crop that does well in colder regions. Its ability to grow fast and easily form a dense cover makes it ideal for suppressing weeds. When grazed or mowed, the clover regrows fast. Although it's tolerant to drought, the legume can grow in mild winter climate.

  • Velvet Bean

Also known as mucuna, velvet bean grows best in tropical climates. The annual climbing vine grows many feet high, making it a great weed suppressor. When grown with corn, the velvet bean offers a thick layer of mulch for soil protection and water retention.

At the end of the growth cycle of the corn crop, the bean reseeds to begin a new cycle. According to a study carried out in West Africa, the bean is so rich in nitrogen that it can serve about two corn crops grown one after another (consecutively).

Velvet Bean Cover Crop

                                     Velvet Bean Cover Crop

The beans can be boiled for consumption or used as a substitute for coffee beans.  Crotalaria, Canavalia and Tephrosia are other tropical cover crops left to mature to offer protection to the top soil from erosion and loss of moisture as living mulches.

  • Cowpeas

Believed to have originated from Central Africa, cowpeas is grown in regions with hot climates. The legume's roots grow deep into the ground to find water, making it a drought-resistant cover crop.

Therefore, it's prone to frost damage. Unlike crimson clover, cowpeas can do well in soil with low fertility.

  1. Winter Annual Legumes
  • Field Peas

Field peas is a legume that can be grown as a winter annual or summer annual cover crop in regions experiencing colder climates. The legume is also known as Canadian field peas or Austrian winter peas. Small-grain production systems in dry land have replaced fallow with this legume.

Austrian winter peas do well in cool, humid climates. It produces residue in large volumes of at least 2.5 tons dry matter. Moreover, within every acre of gardening land, field peas can fix a minimum of 100 to 150 pounds of nitrogen in soil.

  • Subterranean Clover

Subterranean clover is a winter annual legume that does well in regions with a warm climate. It does not compete with summer crops because its life cycle ends before the crops are planted. Therefore, there's no need to kill or suppress the legume before planting summer crops.

The legume naturally reseeds, if undisturbed, from mature pods beneath the soil. However, it isn't tolerant to shading and grows low into the soil. Therefore, it cannot be inter-planted with annual summer crops grown in rows.

  • Crimson Clover

 Crimson clover, unlike other legumes, grows well in winter and fall, atop maturing faster. It is grown in the south-eastern regions of the U.S. Although it's winter-hardy, the clover is prone to frost damages. It can be grown as a summer annual legume cover crop in the northern parts of the nation, but not for economic reasons.

Crimson Clover, Winter Pea & Rye Mixes

         Crimson Clover, Winter Pea & Cereal Rye Cover Crop Mixes

Since it fixes a large nitrogen level in soil, the legume can serve two crop-growing seasons. Kentucky Select, Dixie and Chief crimson clover varieties can grow early prior to the onset of winter as they're winter-tolerant. This legume cover crop does well in non-calcareous, well-drained soils with low pH.

  • Hairy Vetch

Hairy vetch is a winter-tolerant legume that does well in regions with hard-freezing temperatures. It is a highly vegetative cover crop that fixes over 100 pounds of nitrogen in every acre of gardening land. Unlike other crops, it releases nitrogen and decomposes faster. Therefore, it's ideal for fast-growing crops with high demand for nitrogen.

  1. Biennials and Perennials Legumes
  • Crown Vetch

Crown vetch is a permanent ground cover and has been used successfully to stabilize road banks. Unlike alfalfa, the legume does well in well-drained soils with low fertility. Its use as a living mulch to provide corn with nitrogen has had limited success.

The legume is used for perennial crop cover due to its slow growth rate. Moreover, herbicides can easily suppress its growth for reduced competition with the main crop.

  • Sweet Clover

Also known as yellow blossom, sweet clover grows fast, is tolerant to winter and has roots that can easily penetrate compact sub-soils. Unlike other cover crops, sweet clover is drought-resistant. It does well in calcium-rich soils with neutral pH. However, it can do well in high-pH (alkaline) soils with low fertility.

Sweet clover can be grown for one to two years as it flowers in the second year when it completes its life cycle. The legume is plowed into soil before it blooms for use as a green manure.

  • Alfalfa

 Alfalfa grows in well-drained, fertile soils with neutral pH. Grown after harvesting of grains, the legume is inter-planted with small grains such as wheat, oats and barley. It is planted in rotation for a certain number of years.

                         Alfalfa Cover Crop

                                           Alfalfa Cover Crop

The Nitro alfalfa variety is not tolerant to winter and dies in extremely cold conditions. Therefore, it's grown as an annual cover crop; nitrogen fixation and vegetative growth after winterkill isn't enough for another growth season. Unlike alfalfa varieties tolerant to winter, Nitro fixes nitrogen to soil into fall.

  • White Clover

White clover, unlike other legumes, is less resistant to drought and has low vegetative growth. However, the Dutch white clover is less drought resistant than New Zealand white clovers. Therefore, unlike other legumes, it's used as a living mulch or ground cover for orchards.

The legume doesn't grow tall and is resistant to shading. Moreover, it's often grown with pastures that require intensive management.

  • Red Clover

Red clover is resistant to winter, tolerant to shades and easy to grow. It has a slow growth rate, reducing its competition with the small grains it is inter-planted with. In the northeastern regions of the U.S, the legume is inter-planted with corn.

  1. Grasses

Non-legume cover crops, perennial or annual forage grasses and grass cover crops are also used for soil protection from erosion and loss of moisture. Perennial or annual forage grasses include grasses grown in warm seasons such as Sudan grass or sorghum.

Annual cereals such as wheat, rye, oats and barley make up grass cover crops. On the other hand, non-legume cover crops mostly comprise of grass species; they are used to scavenge nitrogen nutrients from previous crops.

The non-leguminous cover crops grow fast, have extensive root systems and can minimize or even prevent soil erosion. The high residue content of non-legumes means they can add organic matter to soils in large amounts. Moreover, they suppress or control the germination and growth of weeds.

However, the amount of nitrogen available in grasses for following crops significantly reduces if grass is grown to maturity for increased residues. This is attributed to the fact that grasses have low nitrogen percentages or ratio of calcium to nitrogen at maturity.

Manure or fertilizer rich in nitrogen can be added to soil to help remedy the situation. Alternatively, kill the grasses early to prevent the problem from arising. Inter-planting the next crop with grass and legumes can also help increase nitrogen in soil for the next crop.

The following are the type of grasses used as cover crops:

  • Sudan Grass

A hybrid of Sudan and sorghum, as well as Sudan grass are summer annuals with fast growth rates within short time periods. They grow fast to suppress weeds, and if planted with vegetables and strawberries, crops with slow-growth rates, they're grown after the main crop to delay seeding and prevent shading.

Sudan Grass Sorghum Hybrid Cover Crop

                       Sudan Grass Sorghum Hybrid Cover Crop

Sudan grass decomposes in soil to produce toxic substances that suppress organisms living in soil such as parasitic plant nematodes. The grass can be used as forage for livestock and loosens compact soils, doubling its benefits.

  • Oats

Oats are less resistant to cold climates, hence winterkill in varied cold conditions. It's planted in fall or summer to provide dead mulch for weed suppression in spring. It offers quick cover if used with a clover in fall to suppress weeds.

Even after winterkill, the stems of oats conserve moisture and trap snow. In South America, gardeners often use black oat to mulch row crops that aren't tilled.

  • Winter Rye

Also known as grain or cereal rye, winter rye is easy to grow and tolerant to winter. Unlike other rye species and due to its resistance to cold weather and fast rate of germination, it's planted in fall or even winter. Its decomposing residue can suppress weed germination due to its allelopathic chemical effect.

Winter rye has a fast growth rate in spring and fall. It is often used as a catch crop in roll-crimp mulch systems where it's crimped and rolled to enable planting or transplanting of the main crop through the mulch.

  • Annual Rye Grass

If grown early, annual rye grass does well in fall. Due to its extensive rooting system, rye grass adds organic matter in large quantities to soil and prevents soil erosion. Although it's difficult to kill and can become problematic weed, it winterkills in regions with extremely cold climates.

Other Cover Crops

  1. Brassicas

Rapeseed, mustard and forage radish are the types of brassicas used as cover crops. Used in specialty (tree fruits and potatoes) and vegetable crop production, brassicas are rotational or winter cover crops. Although it's grown as a winter crop in some parts of the US (southern and middle areas of the US), rapeseed winterkills.

Forage radish grows fast in fall and late summer for faster nutrient uptake. The diameter of its taproot grows up to 1-2 inches large and at least one foot deep, breaking compact soils so the next crop can grow deeper.

It winterkills and decomposes by spring, improving water infiltration in the soil. Forage radish fosters the growth of the next crop by easing the penetration of roots through soil. Canola, on the other hand, does well in late fall when the climate is cool and humid, and most plants getting into dormancy, ready for winter.

Some brassica cover crops such as canola can suppress pets thriving in soil such as plant-parasitic nematodes and root pathogens, rendering them biofumigants. However, they give inconsistent results.

Moreover, they don't foster mycorrhizae (helps with inoculation) in the next crops because they don't develop associations with the fungi. However, brassicas are excellent rotational cover crops.

  1. Buckwheat

Buckwheat winterkills and does well in soils with low fertility. It grows fast and flowers in six weeks. It can be grown more than once a year in different climatic regions. One month after planting, the buckwheat can grow to a minimum of 2 feet tall. Due to its fast growth rate, it competes with weeds, suppressing their growth.

           Buckwheat Cover Crop

                                      Buckwheat Cover Crop

Buckwheat also hampers the growth of certain important root pathogens such as Rhizoctonia and Thielaviopsis species. Although it doesn't disperse its seeds widely, it reseeds into weeds.  Therefore, it's tilled or mowed at the flowering stage to prevent reseeding.

Legume Inoculation

Legume seeds must be inoculated with the right nitrogen-fixing bacteria. The rhizobial bacteria vary depending on the type of cover crop to be planted. Cover crops seeds and bacteria are mixed with milk or water to ensure the latter sticks onto the seeds; this is done just before planting.

Selection of Cover Crops

Timing of planting and harvesting, the equipment and tools required for gardening, the pros and cons of specific cover crops, the expected end result and cropping system in use are factors that govern the selection of the right type of cover crop.

The question of what cover-crops to use is best determined by an examination of the character of the soil, and the condition of the orchard trees. If the trees are growing slowly on mellow and friable soil, it will probably be advisable to use a nitrogenous cover-crop.

If, on the other hand, the trees are making a luxuriant growth, and the soil is of the heavy order, a member 0! The non-nitrogenous group should be tried.

Characteristics of Cover Crops

Cover crops have the following characteristics:

  • High seedling vigor
  • Tolerance or resistance to adverse weather conditions such as drought and frost
  • Fast seed germination and emergence
  • Easy weed suppression
  • More competitive than other plants such as weeds
  • Require minimal care and management
  • Cost-effective to establish

Cover Crop Mixes

Cover Crop Mixes

                                 Cover Crop Mixes

Different cover crop seeds can be mixed to come up with a cover crop solution to maximize output and protection for various crops.

Cover Crops for Gardens/Soil Cover

Cucumber Garden with Soil Cover for Weed Suppression

       Cucumber Garden with Soil Cover for Weed Suppression

Are you looking for cover crops for your home garden? There are artificial soil covers used in place of cover crops that you can easily buy to suppress weeds in your garden. Soil covers such as the Green Valley Supply Fabric Weed Barrier are cost-effective and can easily be re-used, making them ideal for home gardeners.

Placing Soil Cover in a Garden

                  Placing Soil Cover in a Garden

 What's the Right Cover Crop Population Per Acre?

In apple growing sections where the soil is mellow, red clover does well. A mixture of crimson clover and oats is used in peach sections in Michigan with success; 12 quarts of the former to 3 pecks of the latter per acre are sown about the middle of August.

The Geneva Experiment Station recommends a mixture of 56 bushels of buckwheat to 1 bushel of field peas per acre for clay soils.

  1. Non-nitrogenous ll. Rye, two bushels per acre. b. Buckwheat, ‘/, 1 bushel per acre. c. Outs, 2% bushels per acre.
    1 Corn, broadcast 1 bushel per acre. 0. Rape or turnips, 3 pounds per acre.
  2. 2. Nitr0genous— a. Crimson clover, 16 pounds per acre.
    11. Red clover, 14 bushels per acre. 1: Sand vetch, 1% bushels per acre. d. Soybeans, 2 bushels per acre. e. Cowpeas, 2 bushels per acre. I. Field peas, 1% bushels per acre.
  3. 3. Mixtures of Nos. 1 and 2
    a. Buckwheat, 1% bushels per acre. Field Peas, 1 bushel per acre. II. Crimson clover, 12 pounds per acre. Oats, three peeks per acre. c. Oats, 1 bushel per acre. Votch, 1 bushel per acre.
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