By Jeff Moyer
As mentioned before, cover crops are extremely important to organic no-till. They are the foundation upon which you will base much of your operation from now onward. In fact, as you progress in organic no-till, you’ll become accustomed to thinking of cover crops as your new cash crop.
After you read this chapter, you’ll have a clearer understanding of why it’s important to invest just as much (if not more) time and energy in your cover crops as you might in your cash crops.
Fewer weeds, higher organic matter, soil stability, pest and disease management, increased microbial action, and more nutrients are some of the benefits of cover cropping. In a no-till system we use cover crops somewhat differently, since we do not incorporate them into the soil. Although they still supply many of the same benefits, the cover crops also serve as a mulch, providing a season of weed control.
Even if you use chemical herbicides in your no-till program, cover cropping can be beneficial for all of the same reasons. Cover crops can help boost your soil organic matter, and provide stability and structure while guarding against erosion for the entire growing season. If you take the time to get it right, cover crops will pay back your investment with interest by the end of the season, and for several seasons to come.
The Benefits of Using Cover Crops
Cover crops stabilize soil in a couple of different ways — by increasing infiltration due to top growth of stems and leaves, and through the roots of the cover crop. Roots keep a low profile, but they are an essential part of the equation. The roots of cover crops, especially legumes, encourage beneficial fungi, which extend their hypae through the soil and exude glomalins, which bind the soil together.
Some cover crops have a deep root system and can help relieve compaction caused by tillage, heavy machinery, and working soil in wet weather. For example, forage radishes can be planted in the fall and grow quickly to a depth of 24-36 inches. After they winterkill, they leave holes in the ground that help to aerate the soil. Other subsoil looseners include sorghum-sudangrass and sweet clovers.
Both roots and top growth contribute organic matter to the soil, after rolling terminates them or when tilled into the soil to decompose. A combination of cover crops and compost or farm manure is an excellent choice for building longterm organic matter and providing sufficient seasonal nutrients to the soil. Dale Mutch, of the University of Michigan and Ron Morse of Virginia Tech, two of our partners in the No-Till Plus trials, recommend using fertilizer of some kind for your cover crops. That’s because the stronger your cover crops, the better weed control you’ll have the following season.
Cover crops help to repair a steady decline in organic matter that is very common in agricultural systems in this country and around the world. Nitrogen rich fertilizers and tillage encourage an extremely rapid rate of decay of soil organic matter. Cover crops may contribute to organic matter indirectly — by helping farmers raise a bumper cash crop each year. High yielding crops contribute more crop residue, in the form of roots and aboveground growth which does help to mitigate the damage caused by conventional farming systems.
Microbial growth is stimulated by the addition of organic matter, as well as by the roots of the growing cover crops. Nature wants to have the soil covered with something green and growing year-round. By providing a cover for the soil in the form of cover crops, microorganisms have a continuous habitat and food source.
Microorganisms help keep the soil healthy by suppressing disease organisms, improving soil structure, and digesting organic matter so that nutrients can be used by plants. Simply put, microorganisms are the living part of the soil, and also the part that makes the soil work. Without the continuous breakdown of organic matter performed by soil microorganisms, soil nutrients would be tied up and unavailable to plants.
Stabilizes and Adds Nutrients
Cover crops cover the soil and can prevent excess nitrogen from leaching out of the soil during heavy rains. Cover crops act as a “catch crop” or “trap crop,” holding on to available nutrients in the soil (especially nitrogen). When the cover crop is mature and begins to decompose, these nutrients are released slowly and gradually for use by the cash crop. Rye is particularly good as a catch crop. In addition, legumes used as cover crops can fix nitrogen in special nodules on their roots, in collaboration with Rhizobium bacteria. The nitrogen can be passed on to the next crop you grow, for example sweet corn. Organic farmers depend on legumes in their rotations to provide much of the nitrogen for heavy feeders like corn, broccoli and garlic. In our rotations for organic no-till, we pair legumes with these heavy feeders, building a rotation that will work well long term. The air we breathe is over 70 percent nitrogen. These leguminous plants will pull this nitrogen out of the air and “fix” it in the soil for other plants — our cash crops to use. This will work for both tillage or no-till systems.
Some cover crops are useful in bringing up nutrients from deeper soil layers. Buckwheat, for example, is an excellent scavenger of phosphorus. It has a shallow, fine root system (active in the top 10 inches of soil), producing a weak acid solution that releases nutrients from the soil. Sweet clover, with its deep root system, is adept at accessing nutrients in the subsoil layer and making them available as stems and leaves decompose at the surface of the soil.
Pest and Disease Management
When cover crops are added to an agricultural system, pest and disease management becomes easier. Cover crops add organic matter, which feeds the microbes that can play an important role in disease suppression. Cover crops also encourage beneficial insects by providing a nectar source from their flowers, as well as habitat.
Cultivate a healthy population of microorganisms and you’ll also have less to worry about plant diseases. For example, compost, which has abundant microorganisms, has been proven to suppress populations of harmful microorganisms like Pythium and Rhizoctonia, which cause damping off disease.
In the organic no-till system, the primary function of the cover crop is to serve as a mulch to suppress weeds. Besides acting as a mulch, there are other ways in which cover crops suppress weeds. Covers such as buckwheat are sometimes called “smother crops” because they grow so densely that they outcompete weeds. Others like rye, oats and sorghumsudangrass have an alleopathic effect on weeds — they actually exude compounds from their roots that reduce the seedling growth of weeds.
In terms of soil moisture, cover crops are a double-edged sword. On the one hand, cover crops definitely need water to grow. In a climate with abundant soil moisture, this is not necessarily a disadvantage. In dry climates, however, cover crops may use moisture that would otherwise be used by your cash crop. On the other hand, cover crops can increase and stabilize soil moisture by increasing infiltration, improving soil structure, and increasing soil organic matter. In other words, once killed and left on the surface as in our organic no-till system, any water from rain or dew is held by the mulch and released to the cash crop. Thus, even if you live in an area with low annual rainfall, there are some powerful arguments for cover cropping. Although improved infiltration can be seen during your first cover cropping year, it may be 2-3 years before there is a noticeable difference in soil structure and organic matter.
About the Author:
Jeff Moyer has been working in the field of organic agriculture all of his adult life. Over the past 28 years he has been the farm manager/director for the prestigious Rodale Institute located in Southeastern Pennsylvania. He currently chairs the United States Department of Agriculture’s National Organic Standards Board and serves as an advisor on organic issues to the Secretary of Agriculture. Jeff is also a founding board member of Pennsylvania Certified Organic, a private non-profit certification agency.
Also by Jeff Moyer:
- Organic No-Till Farming
- Be sure to check out our extensive collection of Jeff’s seminars from past conferences!