Managing Cover Crops Profitably - Valley Crops Home

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.
GRASS/LEGUME MIXTURES EXPAND POSSIBILITIES
Mixtures of two or more cover crops are
often more effective than planting a
single species.Cover crop mixtures offer
the best of both worlds,combining the benefits of
grasses and legumes,or using the different growth
characteristics of several species to fit your needs.
You can use cover crop mixtures to improve:
• Winter survival
• Ground cover
• Use of solar energy
• Biomass and N production
• Weed control
• Duration of active growing period
• Range of beneficial insects attracted
• Tolerance of adverse conditions
• Forage options
• Response to variable soil traits
Possible disadvantages of cover crop mixtures
may include:
• Higher seed cost
• Too much residue
• More complicated management
• Difficult to seed
Crop mixtures can reduce risk in cropping systems
because each crop in the mix may respond
differently to soil, pest and weather conditions. In
forage or grazing systems, for example, a mix of
rye, wheat and barley is more nutritious, can be
grazed over a longer period of time and is less
likely to be devastated by a single disease.
Using drought-tolerant plants in a perennial
mix builds in persistence for dry years. Using a
number of cover crops with “hard seed”that takes
many months to germinate also improves coverage
over a broader range of conditions.
Mixing cultivars of a single species with varied
maturity dates and growth habits maintains optimum
benefits for a longer time. Orchardists in
California mix subclovers to keep weeds at bay
all season. One cultivar comes on early, then dies
back as two later cultivars—one tall and one
short—come on strong. Because they reseed
themselves,the cooperative trio persists year after
year.
Sometimes you don’t know how much N may
be left after cash crop harvest. Do you need a
grass to scavenge leftover N, or a legume to provide
fixed N A grass/legume cover crop mixture
adjusts to the amount of available soil N: If there
is a lot of N, the grass dominates; if there is not
much available soil N, the legume will tend to
dominate a mixture. In either case, you get the
combined benefit of N scavenging by the grass
cover crop and N additions from the legume
cover crop.
Mixing low-growing and taller crops, or faststarting
grasses and slow-developing legumes,
usually provides better erosion control because
more of the ground is covered. The vegetation
intercepts more raindrops before they can dis-
86 MANAGING COVER CROPS PROFITABLY