Guide to Cover Crops

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.

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.

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.

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.

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.

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. 

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.

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: 

Federal: 

• • 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. 

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.

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!