Question of the Week
What information can you provide me on cover crops and crop rotations for organic vegetable production?
Answer: Thank you for your recent request for information from ATTRA, the National Sustainable Agriculture Information Service. I am pleased to provide you with information on cover crops and crop rotations for organic vegetable production.
Cover cropping is another way to minimize off-farm inputs (1). Cover crops are soil-building crops that are not harvested, but are composted or tilled back into the soil. They can be part of a crop rotation, or can be used to prevent soil erosion and improve fertility. When choosing a cover crop you need to make several considerations. There are many ways to use cover crops in a production cycle:
• as a main crop during the primary growing season. Used as a rotational crop, the cover will exclude production of a cash crop.
• as a companion crop, or living mulch, the cover is planted between the rows of the cash crop—for example pumpkins interplanted with white clover.
• as a 'catch' crop for nutrients, planted after harvest of the main crop or between the rows of the cash crop to reduce leaching of nutrients.
• as an off-season crop grown to protect the soil, usually during the winter when there is no main crop—this is not the case in your farm, of course. This is the most common practice in temperate areas.
A rotation plan used in conjunction with cover cropping and compost is an ideal way for a vegetable farmer to increase fertility and organic matter, while minimizing off farm inputs.
In general, many farmers use the season in which the cash crop is produced as a rotation tool. E.g. Spring/ fall crops, winter crops, short season cucurbits, solanaceous crops, etc. Farmers will often plant these “types” of crops in blocks and rotate the entire block each year. E.g. The winter crops of radishes, arugula, lettuce, and beets are planted in block one and rotated to block two next year. This “block” system meshes well with cover cropping, as you can simply have one block in cover crops at any one time. The best way to illustrate this is with some examples. Referenced below is a publication of crop rotation sequences from several diversified vegetable farms titled Managing Crop Rotation Systems. This publication was developed by the New England Small Farm Institute in 2002 as a DACUM from several experienced farmers in the Northeast. As a result of this work, a new book has been published titled Crop Rotations on Organic Farms: A Planning Manual. Information on this book is provided in the Resource section of this letter.
Cover Crops in Annual Rotations
In annual cropping systems, cover crops are often chosen to maximize benefits such as biomass and nitrogen production. However, other factors must also be considered. For example, fitting a cover crop into the sequence of a crop rotation can be difficult. Therefore, fast-growing, drought-tolerant cover crops that require minimal management are preferred. Cover crops with fast germination and good seedling vigor are usually chosen because of their ability to compete with weeds. Also, species with the potential to reduce pest populations should be chosen, while those that harbor diseases or arthropod pests of the cash crops should be avoided.
Common cool-season legumes used as cover crops in annual rotations include vetches, winter pea and bell bean. Because clovers and medics grow slower and compete poorly with weeds and require more management (e.g., mowing), they are used less commonly used in annual rotations. For similar reasons, cereal grains are usually preferred over other grass species, such as bromes, in annual rotations. Sometimes, however, the annual cereal grains can be used as a “nurse crop” for clovers and medics. They are seeded at the same time and the cereal grains are mowed once or twice. This system gives some shelter to the clovers and helps distribute the seed evenly.
In choosing warm- season cover crops, the ability to perform well with minimal irrigation is often of primary consideration. Legume species in this category include cowpea, hyacinth bean and sunn hemp. Typical grass cover crops for warm conditions include sudangrass and sorghum (2).
Please refer to the ATTRA Publication Overview of Cover Crops and Green Manures. This publication outlines some of the cover crops used for the specific purposes as outlined above. Another excellent book is, Managing Cover Crops Profitably, by Greg Bowman, Christopher Shirley and Craig Cramer. It describes several rotation and cover crop scenarios for vegetable farms. The Nordell Farm profile is particularly inspiring for many farmers. Finally, in the document by Vern Grubinger titled “Cover Crops and Green Manures” Grubinger describes the benefits of specific cover crops.
(1) Hinman, Tammy. 2007. ATTRA Case letter on cover crops and crop rotations. Butte, MT: ATTRA.
(2) Ingels, et al. 1993. Selecting the Right Cover Crop Gives Multiple Benefits. California Agriculture 43 (5):43-48.
Sullivan, Preston. 2003. Overview of Cover Crops and Green Manures. ATTRA Publication # IP024.
Bowman, et al. 1998. Managing Cover Crops Profitably. Sustainable Agriculture Network. Handbook Series 3. Pages 36-39.
NESFI. 2002. Guide to the Expert Farmers’ DACUM Chart for “Managing Crop Rotation Systems.” Belchertown, MA: NESFI.
Grubinger, Vern. 2010. Cover Crops and Green Manures. Brattleboro, VT: University of Vermont Extension. Retrieved June 4, 2010.
Greg Bowman, Christopher Shirley, Craig Cramer. 2007. Managing Cover Crops Profitably, 3rd Ed.. Sustainable Agriculture Network.
This book distills findings from published studies and on-farm experience into a user-friendly reference tool for farmers and agricultural educators. You will find detailed information on how to select cover crops to fit your farm, and how to manage them to reap multiple benefits.
Magdoff and van Es. 2000. Building Soils for Better Crops. 3rd Ed.. Sustainable Agriculture Network.
This book provides step-by-step information on soil-improving practices.
Mohler, Charles and Sue Ellen Johnson. 2009. Crop Rotation on Organic Farms. NRAES.
This Planning Manual provides an in-depth review of the applications of crop rotation-including improving soil quality and health, and managing pests, diseases, and weeds.
The above three books are available for purchase through SARE (Sustainable Agriculture Research and Education):
SARE Outreach Publications
PO Box 753
Waldorf, MD 20604-0753
Telephone: (301) 374-9696
Fax: (301) 843-0159
Web site: http://www.sare.org
Kroeck, Seth. 2004. Soil Resiliency and Health: Crop Rotation and Cover Cropping. Northeast Organic farming Association. http://www.nofa.org
This book renders the tool of crop rotation and its close relative, cover cropping, understandable and available for reducing crop pests and disease and building soil's nutrient level, balance and general health.
Cover Crop Seed Suppliers:
Local feed or field crop seed suppliers often carry many different cover crops. The ATTRA web site also contains a database of organic seed suppliers that includes cover crops: http://www.attra.org/attra-pub/organic_seed/
Organic Growers Supply
PO Box 520, Waterville, ME 04903
Call to get a catalog
Johnny's Selected Seeds
955 Benton Avenue
Winslow, Maine 04901
Toll Free: 877-Johnnys (877-564-6697)
Peaceful Valley Farm Supply
P.O. Box 2209
Grass Valley, CA 95945
To place an order, call toll free at 1-888-784-1722.
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