|
General Information on Cover Crops
By Dale R. Mutch Kellogg, Biological Station, Land and Water Program
and MSU IPM Program
This article was first printed in the July/Aug 2008 issue of the Organic Broadcaster, published by the Midwest Organic and Sustainable Education Service
Cover crops are a key component to sustainable agriculture. The cover crop/IPM program at Michigan State University/W. K. Kellogg Biological Station (MSU/KBS) in Hickory Corners, Michigan provides research and demonstrations on cover crops in several farming systems. Early research/demonstrations primarily focused on incorporating cover crops into field crop (corn, soybean, wheat and alfalfa) systems. MSU/KBS has sandy loam soils. In the last four years, we have expanded into cherries, tomatoes, cucumbers, sugar beets, summer squash, zucchini and pumpkins.
Cover crops serve many beneficial purposes for organic farmers. They are especially important for maintaining and improving soil quality. Some other benefits from using cover crops include nitrogen management and weed suppression.
Nitrogen management
Cover crops can either provide nitrogen for future crops or recycle nitrogen. Good legume cover crops for nitrogen production are red clover, hairy vetch, crimson clover and cowpea.
Red clover can be frost seeded into small grains such as spelt, wheat or cereal rye in March. A 12 lb/A rate will often provide you with over 100 lbs. of N/A the next season.
Hairy vetch, a winter annual cover crop, seeded at 30 to 40 lbs/A in August can provide over 100 lbs/A of nitrogen. Hairy vetch can be bulk seeded with shallow incorporation or drilled. It fits best when you are growing a short season crop such as green beans, cucumbers, pickles or small grains. Note: hairy vetch will often re-grow the next season due to hard seed coats.
Crimson clover is an annual red clover that will winter kill during cold winters (2002-03) or survive the winter if it is mild. If winter killed, crimson clover will produce about 30 to 40 lbs/A of nitrogen. This can be doubled when it survives the winter. Seed crimson clover at 15 lbs/A following a short season such as described above. It can be killed rather easily with tillage.
Cowpea is a cover crop we are trying to fit into Michigan farming systems. It is a summer cover crop that will winter kill in Michigan. We have been seeding it at 60 to 80 lbs/A. We do not have enough data yet on the nitrogen produced by cowpea. Potato leafhopper has been an insect problem on cowpea and can stunt its growth. Cowpea should be seeded when there is no risk of frost and when the soils have warmed up. Since it winter kills, no tillage is needed to control it in the spring.
Legume cover crops, as described above, are primarily used to provide nitrogen for next year’s crop. Crops such as sweet corn, field corn, leafy vegetables, peppers, tomatoes, etc. will all benefit from legume cover crops grown the prior season.
Sometimes we want to recycle nitrogen to decrease nitrate leaching and runoff from our fields. These cover crops are referred to as non-legumes. They are characterized by being fast growing cover crops. Good recycling nitrogen cover crops are oats, cereal rye, wheat, spelts, buckwheat, oilseed radish and oriental mustard.
Oats seeded in August at 1.5 to 2.0 bushels/A can recycle about 20 to 30 lbs. N/A. We like to seed oats after a legume crop was grown. Oats establish fast and the roots take up the nitrogen rather than the nitrogen leaching.
Small grains such as spelt, wheat or cereal rye can be seeded late into the fall (October). These cover crops will recycle more nitrogen in the spring versus fall. If they are being used as a cover crop and you are not harvesting the seed, they should be tilled when they reach 10-15 inches tall.
Oilseed radish will winter kill. You should seed it in August after a short season crop. It will produce a large root and can recycle up to 40 lbs. of N/A.
Buckwheat is a rapid growing cover crop, but is very susceptible to frost and cold temperatures. It is a summer cover crop and should be planted at a 50 to 60 lbs/A rate. It is very good at extracting phosphorus from the soil.
Weed suppression
Cover crops can improve your ability to manage weeds.
Oilseed radish seeded at 20 lbs/A in August can reduce weed populations while providing excellent ground cover. Oilseed radish will winterkill in the fall after hard frosts. The cover crop program at MSU/KBS is testing four different cultivars of oilseed radish for influence on weeds, disease and nematodes. Oilseed radish seed is expensive.
Oats seeded at 1.5 to 2 bu/A in late August for lower Michigan will provide excellent cover, however, will not provide as good of weed control as oilseed radish. If you are further north you want to seed in early to mid August. Oats are susceptible to winter killing so early growth in the fall is important. In the spring, fall-seeded oat ground will be very mellow and easy to work. Oats are inexpensive and easier to find than oilseed radish.
Red clover can be effective in reducing weeds. Even though it is a perennial, it acts like a biennial and typically succumbs to disease pressure in its second year. Red clover influences weeds more after it has been established. You can clip and mow red clover and it will re-grow so mowing can help you to reduce weeds in your red clover seeding. The cost of red clover varies, however, it generally costs more than oats and less than oilseed radish. Red clover is a legume and it will produce substantial nitrogen as well as reduce weeds. Red clover is most effective when it is frost seeded into small grains in March.
Cereal rye is a great cover crop for weed control. Cereal rye produces allelochemicals (naturally produced compounds) that control and suppress weeds. Rye can be seeded late fall (October) and still provide excellent cover. Since it is a winter annual, rye will grow very rapid in the spring. Therefore, it must be controlled in the spring or it can grow up to four feet tall. We recommend controlling it with tillage when it is between eight and 15 inches tall. Cereal rye variety “Wheeler” is known to have allelochemicals and it costs more than other rye varieties.
Buckwheat is a rapid growth cover crop. It needs to be seeded after the risk of frost is over and soil temperatures are warm in the spring. Buckwheat needs to be controlled with tillage at flowering to avoid seed production and becoming a weed. It has a hard seed coat and will often re-germinate where it has been planted. Seed cost for buckwheat is reasonable.
Hairy vetch is a legume cover crop that can be seeded in August. It is a winter annual plant that will produce a lot of biomass in the spring. It is also a very good cover crop for nitrogen production. It will compete well with weeds as long as it gets established before the weeds do. It will survive most winters in Michigan. Hairy vetch should be controlled with tillage before it blossoms in the spring. Hairy vetch has a hard seed coat and can become a weed itself in fields where it was planted. Hairy vetch seed is expensive.
Crimson clover is an annual clover and a legume. It will establish easier and grow faster than red clover. Therefore, it is better for weed control when seeded in August versus red clover. In Michigan’s southern counties, crimson clover will survive most winters. Crimson clover produces nitrogen, but not as much as red clover or hairy vetch. Seed cost for crimson clover is about the same as red clover. Crimson clover is easier to control with tillage than red clover or hairy vetch.
Cover crops are an important component for our farming systems. For more information about cover crops, please check our web page at www.kbs.msu.edu/extension/covercrops.
Selected reading
-Cover crop choices for Michigan. MSU Extension bulletin E-2884. Order E2884.
-Cover crop choices for Michigan Vegetables. MSU Extension bulletin E-2896. Order 2896.
-Managing cover crops profitably. 2nd edition. Sustainable Agriculture Network Handbook Series. Order.
|
