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OVERVIEW OF LEGUME COVER
CROPS
Commonly used legume cover crops include:
 Winter
annuals, such as crimson clover, hairy vetch, field peas, subterranean
clover and many others
Perennials
like red clover, white clover and some medics
Biennials
such as sweetclover
Summer
annuals (in colder climates, the winter annuals are often grown
in the summer)
Legume cover crops are used to:
Fix
atmospheric nitrogen (N) for use by subsequent crops
Reduce
or prevent erosion
Produce
biomass and add organic matter to the soil
Attract
beneficial insects
Legumes vary widely in their ability to prevent erosion, suppress
weeds and add organic matter to the soil. In general, legume cover
crops do not scavenge N as well as grasses. If you need a cover
crop to take up excess nutrients after manure or fertilizer applications,
a grass, a brassica or a mixture is usually a better choice.
Winter-annual legumes, while established in the fall, usually produce
most of their biomass and N in spring. Winter-annual legumes must
be planted earlier than cereal crops in order to survive the winter
in many regions. Depending on your climate, spring management of
legumes will often involve balancing early planting of the cash
crop with waiting to allow more biomass and N production by the
legume.
Perennial or biennial legumes can fit many different niches, as
described in greater detail in the individual sections for those
cover crops. Sometimes grown for a short period between cash crops,
these forage crops also can be used for more than one year and often
are harvested for feed during this time. They can be established
along with—or overseeded into—other crops such as wheat
or oats, then be left to grow after cash crop harvest and used as
a forage. Here they are functioning more as a rotation crop than
a cover crop, but as such provide many benefits including erosion
and weed control, organic matter and N production. They also can
break weed, disease and insect cycles.
Summer-annual use of legume crops includes, in colder climates,
the use of the winter-annual crops listed above, as well as warm-season
legumes such as cowpeas. Grown as summer annuals, these crops produce
N and provide ground cover for weed and erosion control, as well
as other benefits of growing cover crops. Establishment and management
varies widely depending on climate, cropping system and the legume
itself. These topics will be covered in the individual sections
for each legume.
Legumes are generally lower in carbon and higher in nitrogen than
grasses. This lower C:N ratio results in faster breakdown of legume
residues. Therefore, the N and other nutrients contained in legume
residues are usually released faster than from grasses. Weed control
by legume residues may not last as long as for an equivalent amount
of grass residue. Legumes do not increase soil organic matter as
much as grasses.
Mixtures of legume and grass cover crops combine the benefits of
both, including biomass production, N scavenging and additions to
the system, as well as weed and erosion control. Some cover crop
mixtures are described in the individual cover crop sections.
Top | Grass/Legume
Mixtures
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