Guide to Cover Crops
The concept of covering fallow land with vegetation to reduce erosion and provide biological and structural improvements to the soil has been practiced for centuries. There is evidence that it was used in ancient China and India to enhance their crops; the Romans used it in their vineyards. And, we have heard from youth that Native Americans planted diverse plants together in a form of intercropping of plants which benefited each, calling it “Three Sisters” in which corn, edible beans, and squash were planted together; this process, while not cover cropping per se, made use of the characteristics of each variety coincidentally.
Cover cropping was used and recommended by George Washington and other early commercial farmers who planted clover, grass, and buckwheat in fallow years1; the process was employed by agriculture worldwide until the early 1900s, when industrial chemicals for fertilizing, weed, and pest control (herbicides & pesticides) became broadly available and economically practical.
Unfortunately, this broad application of synthetic compounds intensely stresses the soil’s ability to retain moisture and beneficial organisms. It then became uncommon for farmers to cover their soil in the winter with an unsaleable crop, arguably being one of the triggers of the devastating “dust bowl” in the midwest during the 1930s when millions of acres of land lost topsoil to wind and subsequent storm.
According to many studies, today’s farmers who plant a cover crop do so, among other things, to protect and improve the vitality of their soil by encouraging the growth of beneficial organisms, such as mycorrhizal fungi, which retain a farm’s most important asset – topsoil. We will see below that there are many potential advantages gained by employing cover crops. There are also specific decisions required to achieve a farmer’s objectives including the intended objectives, the types of plants that influence the satisfaction of the objectives, reasonable expectations, timing and duration, possible biological issues, and implementation factors. All of these must be integrated into an understandable and practical strategy.
WHAT ARE COVER CROPS?
A cover crop is a plant that, depending on its species and type, can protect and improve soil health by managing erosion, chemically adding nitrogen and other nutrients, reducing pests and disease, controlling undesirable plants such as weeds, and providing other benefits. They are not, typically, cash crops but are used to maintain vegetation on the soil when income-producing crops are not present.
There are many reasons to plant crops to cover bare land after a cash crop has matured:
- Erosion Control
- Soil Organic Matter (SOM) Amendment
- Nitrogen Fixation
- Nutrient Recycling
- Weed Suppression
- Water Management
- Compaction Management
- Beneficial Insectary
- Nematode Control
- Forage Enhancement
- Quick Growth
- Soil Temperature Moderation
- Cash Crop Yield Stabilization
This is a prodigious list. These facts have been shown in practical applications, both recently and through the ages. For the commercial farmer, the real-world return in both near-term profit and durable revenues with sunk cost investment returns over time are the principal concerns. Farming is a financially risky business and now that several generations of practitioners have grown to understand how to reduce their risks by using commercially available chemicals, there is an antipathy among the community to change their practices.
Later on, we will address some concerns about making the transition to this environmentally friendly method. As with most initiatives, there is good news and slightly less than good news:
While economic profit or loss can be highly variable upon initial use of cover crops – typically 1 to 3 years – the long-term value in land protection and permanent improvement has been shown to be indisputable.
Reducing financial risk for the farmer through soil stabilization and content predictability relative to weather effects is a major consequence of cover crop utilization.
TYPES OF COVER CROPS AND FUNCTIONS
Typically, cover crops are not fallow period cash crops grown for income. They are employed for the specific purpose that they can add to the soil improvement and protection process. Each species used in this application provides one or more complementary factors. The five general categories used worldwide are:
- Grains (harvestable) – these are cover crops that have fruits or seeds of dried, dead grass which can be used as noted in #5.
- Legumes – these are plants that offer a high level of protein and nitrogen-fixing (biologically available) with significant above and below-ground biomass.
- Brassicas – these are plants in the cabbage and mustard family which, generally has deep tap roots and can capture soil nitrogen remaining after a crop harvest.
- Forbs – these are plants without significant woody characteristics above or at the ground level and they typically have deeper roots than grasses.
- Grasses (Poaceae) – for cover crop purposes these are not harvested for their grains but are grown for their above-ground biomass which can be converted to green manure.
EXAMPLES OF COVER CROPS
The table immediately below shows some of the beneficial and growing characteristics of typical cover crop species. This can be used as a general guide for planning a cover crop; it is recommended that the local agricultural agency be contacted as to the selection of specific species once you have identified your objectives and selected possible species. Mixes of species and varieties are also commonly used to optimize results – at least four (4) is the typical recommendation – and mixing is highly recommended; your objectives and local conditions may dictate how the mix should be formulated. This generic table, drawn from a variety of sources, can provide insight into possible applications of the different types of plants for a cover crop.
The following table gives some general guidance on generic issues such as seeding conditions and methods, soil conditions, some pest resistance, and recommended uses when differing representative cash crops are planned. Again, your local agricultural agent and common local experience in cover crops should be consulted to optimize your choices.
There are many decisions in the process of optimizing your cover crop selection. The practical issues of equipment availability and configuration, seeding schedules, methods of cover crop, termination scheduling before the next season’s cash crop, interactions among plants and plant types, and of course cost and resources, in general, all need to be considered.
The growth requirements characteristics of the component cover crop are also important. And assuming it is a multiple variety seeding care must be taken to assess its potential impact on the following cash crop. There is the possibility of a negative allelopathic reaction among the plants, while there may also be a positive one if a logical mix is created. The following table summarizes some soil requirements, candidate seeding amounts, and possible interactions with a successor crop.
These are common but not the ONLY ones used for cover crops. More varieties can be found in the USDA Library: List of Alternative Crops and Enterprises for Small Farm Diversification | Alternative Farming Systems Information Center| NAL | USDA
The United States Department of Agriculture (USDA) has some general guidance:
“When choosing a cover crop, a farmer might consider a variety of factors, including the cost of the seed, the intended use (e.g., cover only, grazed, or harvested for forage), and how the cover crop fits into the cash crop rotation and anticipated planting and harvest dates, and long-term management goals (e.g., to prevent soil erosion or to improve soil organic matter). Soil and climate, as well as the availability of financial assistance, are also important factors.”
In 2017, approximately one-third of U.S. acres that planted cover crops received a financial incentive payment from either a USDA working lands conservation program or a similar State program. References to those programs are provided below.
BENEFITS OF PLANTING COVER CROPS
So, what really are those benefits that were listed earlier? And why might they matter to improve a farming practice? The following is a description of each benefit listed above; there may be other benefits depending on the specific utilization circumstances.
- Erosion Control – this is the process of reducing the mobility and loss of soil due to the effects of wind and water.
- Soil Organic Matter (SOM) Amendment – this is the process of adding organic matter at different stages of decomposition, the cells and tissues of soil microbes, and beneficial products that the soil microbes synthesize.
- Nitrogen Fixation – because most plants minimally use atmospheric nitrogen, this is a characteristic of certain plant types and supporting microbes to optimally convert the airborne form to compounds that can be utilized in the soil. With the right biology in the soil, nitrogen fixation can happen right around the roots of not just leguminous plants, but most if not all plants. This activity can take place at any time but is enhanced during a season with rain and lightning and is a cyclical process that moves nitrogen to the soil and back to the atmosphere.
- Nutrient Recycling – this is the process that plants and their supporting microbes conduct to move carbon and other nutrients into the soil. There is a carbon recapture cycle similar to the Nitrogen cycle. This enables practitioners to potentially realize cash crop cost savings due to reduced chemical fertilizer requirements. A graphic of the complete carbon cycle can be found here.
- Weed Suppression – a weed is a plant that is not wanted; fast-growing plants in cover crops quickly cover the soil to compete with and deprive weeds of light, water, and nutrients. They may have allelopathic suppression characteristics.
- Water Management – this is the activity by which the cover crops hold and filter water and keep nutrients in the soil to increase the production of the cash crop.
- Compaction Management – cover crops increase soil volume and porosity and reduce its density; some such crops, notably Brassicas, have deep tap roots which can penetrate previously impermeable soil layers.
- Beneficial Insectary – some cover crops attract beneficial insects, which are predatory and parasitic in nature, thus reducing the pest insect population.
- Nematode Control – nematode pests, such as grubs and root-knot worms, infect the roots of and typically colonize only certain plant types; employing a cover crop with the proper selection of species that are either toxic to certain nematodes or can starve them, will minimize the risk of these pests.
- Forage Enhancement – planting crops like clovers and annual ryegrass in your cover crop will provide support for beneficial soil organisms and feed for livestock.
- Quick Growth – in order to achieve other goals in this list the cover crop should be designed to have some varieties of plants that have quick growth, for example: buckwheat, clover, radishes, winter rye, and others.
- Soil Temperature Moderation – cover crops tend to raise soil temperature in winter and reduce it in mid-summer, thus making for more stable and predictable soil temperatures.
- Cash Crop Yield Stabilization – cover crops through their many beneficial effects such as improvements to soil tilth, nutrient content (e.g., nitrogen), temperature moderation, etc., help to provide a consistent soil resource for cash crop predictability enhancement.
REAL-WORLD RESULTS AND USAGE
Farmers often share their experience and knowledge with their farming colleagues. Some ideas, skills, and practice for cover crops and the employment paths they succeeded at follow:
🌎 Farmers often get the advice that they should “start small” when it comes to conservation practices. But Indiana farmer Rick Clark of Clark Land and Cattle is proof that you can do regenerative agriculture at scale. He raises no-till soybeans, and no-till corn, and has had great success planting cover crops on his 7,000-acre farm. What’s more, this is the first year that all his acres will be grown without chemicals as he transitions to organic. He recently recounted his experiences at “One Good Idea” (goodideafarm.org). where he disclosed his cover crop secrets to a massive cost savings of $670,000 a year.
🌎 Brad Lauber of Lauber Seed Farms, which operates regeneratively, hosts a YouTube series of their experiences and success at cover crops. They try different practices yearly to optimize the regeneration and yields from their seed corn planting. A typical episode on cover crops is here: Cover crops, 2 different strategies. What should I do now? – YouTube . He expects his seed corn to produce 270-280 bushels per acre using regenerative practices.
🌎 Since 2006, Matt Griggs and his family at Griggs Farms, LLC has integrated wheat, rye, cover crops, and manure into the farming operation, focusing on high-yield sustainable practices that heal the soil and protect the environment. Check out his YouTube episode on cover crops: Cover Crops and Soil Health!! 5/14/22 – YouTube.
🌎 Despite being the resurgence of a process proven by centuries of agriculture, cover crops are still not broadly utilized today in the commercial farming industry. The United States Department of Agriculture (USDA) which is an advocate for cover crops conducts routine research into the adaptation of various practices. Here, the rate of increase in cover crop agriculture is increasing, but it remains in the 10-15% range of the USDA surveyed fields. The antipathy generated by years of commercial fertilizers, pesticides and herbicides has entrenched the community in mid-20th century practices. The marginal increase in usage makes for restrained optimism about changing to more environmentally sound methods for maintaining soil health and gaining the benefits of more natural and enduring productive farming methods.
POTENTIAL RISKS OF PLANTING COVER CROPS
As with all transitions, there are several approaches and strategies which can be considered. If government financial assistance is utilized, some limitations or criteria may be invoked to qualify.
- Expectations! The overall positive results of cover crop implementation might be a bit obscure. Early benefits such as erosion reduction will be demonstrated quickly; soil health and significant productivity enrichments are likely to take no less than 1 to 3 years and may be somewhat longer.
- A related risk is a long-term adaptability, response, and reception of soil that has been overutilized or damaged by some traditional practices. It has been found that applying a lot of nitrogen fertilizers can definitely disrupt nitrogen cycling communities. If a system is exposed to disruption of nitrogen-cycling microbial communities long enough, it may develop resistance to conservation practices. If this occurs, the improvements will occur but may require protracted efforts.
- Initial yields could be low in years 1-3, although they have been shown under many conditions to improve in the range of 5% to over 70% after 3 years.
- Care must be taken to prevent possible infestation of fungi depending on the selection of plants. Some plants may be hosts to fungi whereas others might actually kill it.
- Accidental allelopathic planting causes cash crop issues.
- Poor crop sequence planning causes pest spread – insects and disease – happening as a result of using successor plants that may be susceptible to pests harbored in the cover crop. Crop rotation helps to minimize this problem.
- Added costs and possible delays: seeds, seeding, cover crop termination, and other activities which were not required in the traditional practice will likely occur. Costs may be offset by the benefits. Delays can come as a result of inadequate planning or unusual weather. (Cover crop termination can be problematic and will be discussed below.)
COMMON COVER CROP MISCONCEPTIONS
THEY DON’T WORK HERE
“If you want cover crops to work, they will work for you,” says Myron Sylling, a southeastern Minnesota corn and soybean producer who farms with his brother Mikal near the Iowa border. “But you can’t just try something. If you do, it probably won’t work.”
He notes that negative stories often include glaring examples of doing things the wrong way, such as planting the wrong species after harvest.
“We don’t want anyone to make that kind of mistake,” he says. “It’s why we share the mistakes we’ve made and the problems we’ve encountered. Cover crops will work if you are willing to adapt.”
THEY ENCOURAGE PESTS
Cover crops, properly selected, can be shown to reduce pest issues of all kinds: insects, nematodes, and harmful bacteria. They smother weeds or reduce them with allelopathic processes.
THEY DEPRIVE WATER AND NUTRIENTS FOR CASH CROPS
Once a cover crop has been established the resulting increase in SOM, reduction in compaction and overall improvement in soil consistency will cause more effective moisture retention. Rather than extracting critical nutrients, the cover crop will sequester nitrogen and carbon to enhance fertility.
THEY CAUSE PROBLEMS WITH SOIL TEMPERATURE
Existing users of cover crops and researchers have demonstrated in multiple trials that cover crops tend to make the ground warmer in winter and cooler in summer than deeply tilled soil. It has also been shown that cover crops tend to stabilize temperatures possibly due to microbial action and the increase in SOM, creating a kind of insulation against temperature change.
COVER CROP INCENTIVES
There are government programs that help to save costs by using these conservation program funding where possible. As noted above, initiating the use of cover crops requires a period of education and front-loaded costs; these programs, at the Federal, State, and, sometimes County and
Non-Governmental Organization (NGO) levels, assist farmers to transition with lower financial risk. Federal programs are available in all states. Some of the programs include:
- USDA NRCS Environmental Quality Incentives Program (EQIP)
- USDA NRCS Conservation Stewardship Program (CSP)
- Periodic special incentive and disaster relief programs
- Possibly others – check with the USDA local office
The USDA programs tend to be fixed cost-share and each state has been assigned standard rates for individual species and multiple species cover crops
Example State Specific:
State Cost Share, and watershed-specific assistance programs, for example in Maryland:
The Maryland Cover Crop Program is funded by the Chesapeake Bay Restoration Fund and the Chesapeake and Atlantic Coastal Bays Trust Fund. See your soil conservation district representative or contract for details.
The following graphic identifies the states which have existing state-sponsored cover crop incentive programs (Note: the USDA programs are often administered by the state agriculture agent.) The structure of each differs somewhat from state to state, and even within a state, there may be multiple programs with differing criteria. While this graphic identifies states with existent programs, pending legislation in several states will either enhance or initiate support for cover crops. You should contact your state government’s agricultural and environmental departments to enquire about these programs.
Dark Green: —– State sponsored/funded program
Green: ———— New or emerging State program
Light Green:—– Only administration of Federal (USDA) programs
While these programs usually are cost-share and don’t fully cover the costs of implementing a cover crop, they help farmers in the implementation phase as they are finding what works best on their farm and as they start to experience the soil health benefits of this practice. Pending legislation in several states will either enhance or initiate support for cover crops.
HOW TO START UTILIZING COVER CROPS
1. Share the idea! Contact your local agricultural agents – Federal, State, and Local. Contact your seed and equipment suppliers. Collaborate with other cover crop experienced farmers in your area.
(If there are none, then the governmental agency operatives should be able to help or contact Kiss The Ground. Take a look at the various YouTube and other media that experienced farmers have produced on cover crops.)
2. Review your crop planning, including the years before this and the upcoming ones. Some practitioners have used a cover crop as a ‘bonus’ cash crop; however, the incentive programs typically encourage mixed variety cover crops.
3. Create a plan for, optimally, a mixed cover crop that can be integrated into whichever other practices you follow on your land. Plan for any equipment requirements and develop the mechanical strategies which make sense for your application. Review possible double uses for equipment, such as modifying your seeder to include vertical tilling. Consider transitioning your tractor fleet to lighter equipment and turf-like or floatable tires to reduce compaction. Consider the adaptation of drone technology to reduce equipment time on the field.
4. You probably keep detailed records of your farming activities. Add cover crops into those records so that you will be able to correlate the effects on your other activities. Share your successes and learning with others.
As with all transitions, there are several approaches and strategies which can be considered. If government financial assistance is utilized, some limitations or criteria may be invoked to qualify.
A potentially major issue, raised above in the Risk Section, is how the cover crop is killed prior to seeding the following cash crop. This can be problematic when the environmental sound “No-Till” practice is employed. As with most farming, there are several ways to accomplish the cover crop kill, some of which are environmentally undesirable – chemical herbicides. The preferred methods are mechanical, meaning some added work. Some methods do not work well with cover crops with a relatively tall growth habit, such as grasses. And it has been established that, for a cover crop area to be made suitable for the following crop, the kill should be close to 100%. Some strategies are only about 80% effective on their own (e.g., roller crimping), but they can be supplemented, adding work. However, strategies to accomplish multiple objectives on one pass have also been developed and one such strategy is shown in the picture below.
The overall strategies are:
- Cutting very short using a disc or flail mower
- For tall-growing cover crops: use as forage and cut or roller crimp at 12”
- Using a front-mounted roller-crimper and towing a drill or other seeder.
- Follow the cover crop termination with “flaming”. This propane-fueled process has been shown to be very effective.
WHY USE COVER CROPS?
Cover crops are a key tool for farmland soil protection and regeneration. Like most farming practices it is not a simple matter of selecting and seeding. Optimal cover crop practice means understanding and matching the crop investment and function with each specific set of conditions and objectives. Improvements in soil health will result, but significantly palpable results may require maturation of the process over one to three years. Reduced negative effects on the soil, such as erosion, extreme temperature variation, lowered fertility, and others will disappear quickly. Net economic benefits through improved soil condition, enhanced beneficial organisms, reduced chemical fertilizers, herbicides, and pesticides with stable or increased cash crop yields will incrementally materialize.
Cover crops are one element of a comprehensive effort to regenerate farmland. Kiss The Ground is a 501(c)3 that provides information & inspiration – through media, policy, education, and policy – to farmers, government officials, and the general public on regenerative practices.
Together, we can do this!
Bergtold, J., Ramsey, S., Maddy, L., & Williams, J. (2019). A review of economic considerations for cover crops as a conservation practice. Renewable Agriculture and Food Systems, 34(1), 62-76. doi:10.1017/S1742170517000278
Groff, S. (2015). The past, present, and future of the cover crop industry. Journal of Soil and Water Conservation, 70 (6) 130A-133A; DOI: https://doi.org/10.2489/jswc.70.6.130A
Munyon JW, Bheemanahalli R, Walne CH, Raja Reddy K. (2021) Developing functional relationships between temperature and cover crop species vegetative growth and development. Agronomy Journal. 2021;113:1−16. https://doi.org/10.1002/agj2.20537
Myers, R. (2019). Cover Crop Programs and Incentives Landscape Assessment (pp. 1–18). AGree, Economic + Environmental Risk Coalition
Wallander, S., Smith, D, Bowman, G., Classen, R. (2021) Cover Crop Trends, Programs, and Practices in the United States, USDA Economic Research Service, February.
ABOUT THE AUTHOR
An organic farming practitioner for many years, Joseph J. Kranz, PhD joined the Kiss The Ground community in 2018, and became a certified soil advocate for regenerative farming practices. Previously, he adapted the Native American “Three Sisters” companion and cover crop planting concepts as an avocation on a 20-plus acre New England farm. His experience as a scientist and decision-making researcher is now focused on improving our climate and earth.