When you select a cover crop, you should consider
continued interest in others, such as buckwheat. Some
the soil conditions, climate, and what you want to
of the most important cover crops are discussed below.
accomplish by answering these questions:
• Is the main purpose to add available nitrogen to the
Legumes
soil, or to scavenge nutrients and prevent loss from
Leguminous crops are often very good cover crops.
the system? (Legumes add N; other cover crops take
Summer annual legumes, usually grown only during
up available soil N.)
the summer, include soybeans, peas, and beans. Winter
• Do you want your cover crop to provide large
annual legumes that are normally planted in the fall
amounts of organic residue?
and counted on to overwinter include Austrian winter
• Do you plan to use the cover crop as a surface mulch,
field peas, crimson clover, hairy vetch, and subterra-
or incorporate it into the soil?
nean clover. Some, like crimson clover and field peas,
• Is erosion control in the late fall and early spring
can overwinter only in regions with mild frost. Berseem
your primary objective?
clover will overwinter only in hardiness zones 8 and
• Is the soil very acidic and infertile, with low avail-
above. Hairy vetch is able to withstand fairly severe
ability of nutrients?
winter weather. Biennials and perennials include red
• Does the soil have a compaction problem? (Some
clover, white clover, sweet clover, and alfalfa. Crops
species, such as sudan grass, sweet clover, and
usually used as winter annuals can sometimes be grown
forage radish, are especially good for alleviating
as summer annuals in cold, short-season regions. Also,
compaction.)
summer annuals that are easily damaged by frost, such
• Is weed suppression your main goal? (Some species
as cowpeas, can be grown as a winter annual in the deep
establish rapidly and vigorously, while some also
southern United States.
chemically inhibit weed seed germination.)
One of the main reasons for selecting legumes
• Which species are best for your climate? (Some
as cover crops is their ability to fix nitrogen from the
species are more winter-hardy than others.)
atmosphere and add it to the soil. Legumes that produce
• Will the climate and water-holding properties of
a substantial amount of growth, such as hairy vetch and
your soil cause a cover crop to use so much water
crimson clover, may supply over 100 pounds of nitrogen
that it harms the following crop?
per acre to the next crop. Legumes such as field peas, big-
• Are root diseases or plant-parasitic nematodes prob-
flower vetch, and red clover usually supply only 30 to 80
lems that you need to address? (Winter [cereal] rye,
pounds of available nitrogen. Legumes also provide other
for example, has been found to suppress a number of
benefits, including attracting beneficial insects, helping
nematodes in various cropping systems.)
control erosion, and adding organic matter to soils.
In most cases, there are multiple objectives and
Inoculation. If you grow a legume as a cover crop,
multiple choices for cover crops.
don’t forget to inoculate seeds with the correct nitrogen-
fixing bacteria. Different types of rhizobial bacteria are
TYPES OF cOVER cROPS
specific to certain crops. There are different strains for
Many types of plants can be used as cover crops.
alfalfa, clovers, soybeans, beans, peas, vetch, and cow-
Legumes and grasses (including cereals) are the most
peas. Unless you’ve recently grown a legume from the
extensively used, but there is increasing interest in
same general group you are currently planting, inoculate
brassicas (such as rape, mustard, and forage radish) and
the seeds with the appropriate commercial rhizobial
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Building SoilS for Better CropS: SuStainaBle Soil ManageMent