Cover Crop Terminology – by Dennis Brown

These terms describe the purpose of each category of cover crop. A single species may have more than one function. Before selecting a cover crop or mixture of cover crops, analyze your goals for each field.

This analysis should include

  • a soil test,
  • what are the needs of the next crop such as is it nitrogen needy or nitrogen productive,
  • what are the fertility needs of the field,
  • is it highly erodible land, either from wind or water,
  • could it need organic matter,
  • are there fertility excesses,
  • does the pH need adjusting, etc.?

Then choose cover crops that can make those improve

Cover Crops:

Cover crops are those crops that are planted to provide a cover for the soil. They are grown primarily as a biological soil conservation tool to prevent soil erosion by water and/or wind;and to foster multiple benefits in a farming system. These benefits include but are not limited to: optimization and/or normalization of the fertility profile, improvement of the soil properties such as water-holding capacity, structure and aggregation, rescue lost fertility that has leached away, provide deep root channeling for the next crop, and increased organic matter

Cover crops are typically planted before and after the main designated cash crop in a rotation. Cover crops may be used as a ground cover or mulch, green manure, nurse crop, or a smother crop. The cover crops can be annual, biennial, or perennial species, including legumes, grasses and the brassicas.

Green Manure:

Any crop that is grown and incorporated into the soil while it is green or soon after flowering which can improve the soil, especially with the addition of organic matter plus N, P and K and other elements contained in the plant. The average availability of nitrogen in green-manure material turned under is typically about 50 to 60% of the initial amount as determined by a feed or tissue test. Green manure was once the conventional method of supplying nitrogen and other fertility to crops and was practiced widely before commercial nitrogen fertilizer became available.

Catch Crop:

When cover crops are planted to reduce nutrient leaching they are termed “catch crops”. These are cover crops planted after the cash crop is harvested or after legume plow downs. They are also planted in late summer or early fall to trap nutrients from freshly spread manures. They are grown to take up and hold the nutrients in their tissues or “catch” the nutrients from the soil, especially nitrogen that may otherwise be leached lower in the soil profile and lost below the active crop root zone.

Scavenger Crops:

Farmed soils that have been heavily cropped with shallow-rooted plants such as corn may become deficient in certain micronutrients. Deep-rooted scavenger cover crops such as certain annual ryegrasses, alfalfa, red clover and sweet clover grow roots deep into the subsoil and have the ability to bring soil nutrients from the lower soil profile to the upper layers and also into the scavenger crop’s leaf biomass securing it there for the next crop. The deep-growing root structure additionally helps to break up soil compaction and when these plants die, their decaying roots leave not only organic matter, but also channels in the soil that provide pathways for the roots of the following crop to follow down the profile. Tthese root channels also provide pathways for water to drain from the surface.

Break Crop:

Cash crops attract and harbor particular populations of insect pests including harmful nematodes. Different species of cover crops can be selected in the rotation that do not harbor those pests or actually diminishes their population by interrupting the insects’ life cycle. Reducing pests and disease populations is another one of the best reasons for using cover crops in your rotation.

Nurse Crop:

A nurse crop is one that germinates and emerges quickly, holds the soil with quick cover and root structure and assists the development of a slower maturing crop. Oats, Italian ryegrass and festulolium are common nurse crops used to start a alfalfa/tall fescue hay crop. The oats or nurse crop grasses germinate first, out-compete weeds for available resources and then can be mowed when the legume and slower emerging grass starts to grow.

Smother Crops:

Fast growing crops help control weeds by growing a thick canopy that reduces the amount of sunlight for weed seeds to germinate and grow. Smother crops grow tall at a fast rate or quickly produce broad leaves that shade out lower growing weeds. Including these covers in your rotation, growing double or triple crops in a single season is an effective strategy for weed control. An effective sequence of smother crops is oats in spring, buckwheat or sorghum-Sudan grass in summer and rye, triticale or forage brassicas in the fall. Hairy vetch planted in the fall and overwintering will then act as a spring smother crop smothering early spring weeds. These crops can also produce high quality forage.


The term allelopathy is often used when referring to the weed suppressing attributes of certain cover crops. Allelopathy is “the inhibition of growth in one species of plants by chemicals produced by another species.” It can be any direct or indirect harmful effect produced in one plant through toxic chemicals released in to the environment by another. The magnitude of the detrimental effects depends on the extent of any other stresses, such as environmental conditions or biological factors (e.g. insect or disease pressure) that occur at the same time. Different cover crops have different allelopathic effects, and the activity may be reduced or enhanced by microbial action, oxidation, and other transformations in the soil.

Some examples of allelopathic cover crops include:

  • Peas, lentils, vetches – Beta-(3-isoxazolinonyl) alanine: released as root exudates. Suppressing lambs quarter, yellow foxtail, Yellow nutsedge and pitted morning glory.
  • Buckwheat – A compound called diethyl phthalate is produced by buckwheat and is responsible for weed suppression. This weed-suppressing compound is mainly in the stem rather than the shoots, so it is likely to be most active by suppressing weeds after the buckwheat is harvested. It was especially active on pigweed, and not particularly effective on plants in the mustard family.
  • Cereal Rye and small grains including triticale- produce several compounds that inhibit crops and weeds. The most active compounds are two hydroxamic acids and their breakdown products.
  • Crimson Clover – has been shown to suppress pitted morning glory, wild mustard and Italian ryegrass.
  • Sorghum-Sudan grass – releases sorgoleone through the root exudates. sorgoleone interferes with photosynthesis of neighboring plants and crops that follow the sorghum.

To overcome the effects of allelopathy, light tillage or a heavy application of liquid manure will stop allelopathic effects. Many farmers use the allelopathy to their advantage to stop weeds from growing in between harvesting the small grains and before the next crop

Selecting A Cover Crop – by Dennis Brown

Cover crops can be a key soil improvement resource for conventional and organic growers alike. Here is an introduction to the role and selection of cover crops for farming systems. There are cover crops to fit almost every type of cropping system.

For Certified Organic agriculture, according to the USDA National Organic Program Standards “the producer is required to implement a crop rotation, including but not limited to sod, cover crops, green manure crops, and catch crops.”

Many types of plants can be grown as cover crops. There are two broad general categories of cover crops – non-leguminous and leguminous. The leguminous cover crops fix and add nitrogen to the soil. Non-leguminous cover crops are users of N and hold it until either incorporated or fed ass forage. Non legumes are often preferred on erosive soils. Each plant type has advantages over the other and differs in its area of adaptability.

In choosing a cover crop for soil improvement, first identify the purpose or the primary function of the cover crop based on the needs of your system. Use the list below to identify the primary function(s) of the cover crop:

Provide nitrogen – Growing legume cover crops is one of the most important tools to increase soil fertility. The main benefit of using a legume as a green manure is that the legumes fix nitrogen from the atmosphere and convert it into a form that is available to other plants. Choose legumes that are adapted to your area. Legumes (peas, vetches, clovers, beans and alfalfas) grow in a symbiotic relationship with soil dwelling bacteria (rhizobia). The bacteria take gaseous nitrogen from the air trapped in the soil and convert or “fix” this nitrogen into a form that the plant can use, in exchange the plant provides carbohydrates to the rhizobial bacteria. Legumes vary from one another in the percent of nitrogen they contain on a dry matter basis. Legumes contain nitrogen in both their top growth and in their roots. A high percentage of the biologically fixed nitrogen is in the top growth, so it is important to manage them to let them grow long enough to produce their full high potential amount of biomass.. The residues of these crops can contribute substantial nitrogen (75 to over 150 units of N) to following crops.

Increase soil organic matter – By improving the soil biological activity, cover crops can conserve or increase soil organic matter if they are managed to grow long enough to produce a high amount of biomass. A major benefit from green manures is the addition of carbon compounds in the form of organic matter to the soil. Over time, soil organic matter is decreased through tillage and biological activity. Adding crop residues back to the soil also helps maintain soil organic matter. Complex soil structure is built by the addition of organic matter. In no-till systems where there is limited incorporation of plant residues, cover crops are important key to building soil organic matter. The roots will physically penetrate the soil and release carbon compound root exudates in the soil at varying depths as the roots grow deeper. When these cover crops are terminated their dying root biomass becomes incorporated organic matter at various depths. Obviously, a plant with large root biomass will do this job the best. With summer annuals like the sorghum family, harvesting the forage at least once drives the roots deeper into the soil. With cool season grasses, each harvest causes the roots to shed about half their biomass and it regrows as the leaves regrow.

Improve the nutrient availability in the soil – Nutrient availability is improved because the cover crop plant roots release 80% of the sugars that the plant produces into the soil to feed the soil microorganisms that build soil and in turn mineralize, recycle and release nutrients to the next crop. When incorporated into the soil, cover crop biomass is decomposed by soil bacteria and fungi. Through this process of biological decomposition the soil nutrients are recycled. Look for high biomass –producing cover crops. In addition, increased plant residues associated with cover crops in a system improve the soil environment for certain beneficial organisms. Organisms such as earthworms, insects and microorganisms can improve soil quality and increase nutrient availability by quickly decomposing organic matter and plant residues.

As a summer cover crop, consider sorghum-Sudan grass hybrids. Fall-planted winter annuals, such as cereal rye and triticale plus certain deep-rooted annual ryegrasses work well. The legumes which produce much biomass include hairy vetch, alfalfa, medium red clover, ladino white clover, field peas, sweet clover and crimson clover. Mixes of legumes and cereal crops can be used as well.

Scavenge nutrients – Soluble plant-available nutrients, especially nitrogen, are left in the soil after the cash crop has been harvested. Over the winter, bare soil is prone to losses of nutrients both into the air by volatilization and to water by leaching or by erosion. Growing a cover crop will reduce those loses by taking up the nutrients into their own tissue. The nutrients in cover crops are not always directly available to plants. The soil microbes decompose the cover crop residues, taking up some of the nutrients and releasing the rest to the soil environment. When the plants and the soil microbes decompose, the nutrients contained in them become available for the next growing crop in the rotation like a slow-release fertilizer. Legumes and grasses have symbiotic relationships with fungi that produce mycorrhizal hyphae (fungus roots) which branch through the soil and can help the plant scavenge nutrients (e.g. phosphorous). These fungi must be in association with a living root to survive. By having legumes, brassicas and/or grass cover crops growing after the cash crop, these microbial –plant root relationships can be maintained throughout the rotation to help foster further nutrient scavenging and cycling.

Examples of crops used for this purpose are annual clovers, specially-bred daikon radishes whose roots tend to grow straight down and penetrate 25 to 35 inches into the soil and certain annual ryegrasses which grow down even further (40 to 60 inches buy the next spring.

Prevent soil erosion and runoff – Cover crops can protect soil from raindrop impact and wind. . Choose species that grow rapidly and cover the soil surface quickly. Most of the same crops that are used for nutrient scavengers also provide good soil cover. The cover protects the soil from direct raindrop impact and also impeding the velocity of rainwater flowing across the soil surface and thus reducing erosion potential, also covering the soil surface from direct wind gusts.

Improve soil structure – Increasing the soil organic matter with cover crops as previously mentioned improves the soil structure. As plant residues degrade, the soil microbes feeding on them release compounds into the soil. These compounds are gums, waxes and other exudates that have “glue-like” properties which cement soil particles together to form stable soil aggregates. Soil components aggregated together result in improved soil structure and tilth. Grasses have mycorrhizae associations as do legumes, however, grasses are characterized by dense masses of fibrous roots that improve the soil structure by exuding polysaccharides (sugars). The polysaccharides stimulate soil microorganisms which in turn exude gums that aggregate soil particles. Aggregates contribute to greater soil permeability, soil porosity, aeration, water infiltration and holding capacity, cat-ion exchange capacity, ease of crop emergence and root growth. Added organic matter also alleviates compaction by reducing the bulk density of the soil.

Improve drainage and alleviate compaction – Deep-rooted plants can help break through compacted layers in the soil such as a hard pan, or as it is sometimes known, plow pan. This will improve drainage. The penetrating roots of the cover crops make channels through which soil water can move after the root system decomposes. Species to consider are certain annual ryegrasses, sweet clovers and brassicas. These winter cover crops with large tap roots or massive root systems can help to alleviate some of the effects of soil compaction by penetrating the compacted layer when the soil is wet and relatively soft during the winter.

Provide mulch to conserve soil moisture:– Choose cover crops with a combination of high above-ground biomass and moderate or high carbon/nitrogen ratios. The microbes that decompose crop residues use carbon as an energy source and nitrogen to build tissue. If residues have a C/N ratio higher than 25:1, the microbes will need to gather N from the surrounding environment to do their work. Generally speaking, the higher the C/N ratio of the cover crop residue, the more slowly decomposition will occur and the longer the residue will serve as both a moisture conserving and weed-suppressing mat. The small grain cover crops are well suited for this. Most legume residues with higher nitrogen content will decompose more rapidly and be less effective as mulch. Mature rye and triticale can be effectively used as weed suppressing mulches when rolled down which also conserves soil moisture evaporation by keeping the soil covered.

No-Till for Organic Farmers: Recent progress has been made in organic no-till and killed mulch no-till systems using a crimper/roller that is mounted to the front of a tractor to roll down and mechanically kill fall-planted small grains or hairy vetch cover crops in the spring. With the front-mounted roller the process is a time and energy saver being a one-pass system of roll and plant. A no-till planter or no-till trans-planter can be used to cut through the mat of rolled-down cover crop and then seed or transplant into it. Winter annual cover crops are used to cover the soil and recycle nutrients from fall through early spring and then rolled and into a weed-suppressing killed cover crop mat to no-till plant into. The rolled down cover crop deters weed emergence by the formation of the physical barrier of the cover crop residue, in addition, light transmittance to the soil surface declines with increasing residue biomass. Many weeds require light to activate a germination process prior to emergence. Reducing the amount of light reaching the soil surface by the residue is an important factor inhibiting weed germination. Early weed suppression provided by the cover crop residue will permit crops to become established before weeds.

Byron Seeds’ Involvement In Cover Crops – by Samuel Fisher

Byron Seeds started in the early 1990’s because we could not find the quality grass varieties we needed for our farms. We started out with mostly forages and then soon got involved with cover crops on a small scale.

Research on our farm has been pretty extensive since the beginning. From 1999 through 2007 we tried a lot of different crops broadcast into corn and since we have done some very successful cover crops in rotations. Since 2007, Byron Seeds has been involved in quite a lot of research for cover crops with agronomists and farmers who share our passion for the future of farming.

At Byron Seeds, we see ourselves as an education-based company. We started an early spring Cover Crop Field Day this year involving famers and NRCS folks and we look forward to continuing this effort. In addition, we do seminars, winter meetings and newsletter in order to help spread our message. Since we are an independent seed company, we can constantly look for new and improved varieties from anywhere in the world. In fact, that is one of our key strengths. We strive every day to make sure the seed we sell is the most viable and best value for the farmer.

Here is an example of how we view cover crops fitting into our organization: Let’s say you’ve just bought a new piece of equipment, like maybe a tractor. You’d want to protect your investment by working it according to specs and following a proper maintenance program. You’d know that, if you took good care of it and didn’t work it too hard, normal wear would allow it to last for years. But, what if the more you worked it, the better it got. That using it hard was taking care of it . . . improving it, not wearing it out. That constant work was actually part of the maintenance program. In fact, the more you used it, the more its power and performance were improved and the more years of service were added to its life?

Sounds too good to be true doesn’t it. Nothing in life works that way, material investments always seem to depreciate in value and decrease in productivity. But wait, there is one exception. Soil is just like that, the more you have something growing in it, the more you improve its quality and productivity. The bad news is that modern farming is incredibly hard on soil. The typical corn\soybean rotation we follow year after year is kicking the life and productivity out of our soil, ever notice how it takes more inputs to maintain yield?

The good news is cover crops can reverse the damage of modern farming, improving soil quality and performance. Like a finely tuned tractor, rejuvenated soils can make you money. That’s why cover crops are so important, something green and growing year round. “But” you say, “Cover crops are a pain and don’t fit into my rotation. Besides all that, my neighbor tried them and had an 800 acre disaster.” You’re right. All that you just said is true. Cover crops are an important tool in our sustainable farming toolbox, but the whole cover crop program has been set back in recent years by wanna-a-be seed peddlers jumping in to the cover crop market trying to make a fast buck without any knowledge or experience. There have been a lot of expensive disasters as a result of following unsound advice.

But, what if there was a company that could make cover crops an easy success for you. They did the groundwork so that you could have maximum effect with minimal involvement on your part? Byron Seeds has a cover crop program that will be tailor-made for you. We have consultants that can do an on-farm prescription of the cover crop or crops that best suits your unique operation. If need be, we can custom blend a mix that will optimize your soil improvement program. We understand your unique situation, we’re farmers too. Even more, we have connections with the people that can fly the seed on if needed at just the right time to maximize success. So what does it take on your part? Give us a call and talk to us. We’d be pleased to give you a hand in rebuilding your soil. Let our experience help you make cover crops be a success on your farm.