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COVER CROP 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
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 fast-starting 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 dislodge soil particles. Sunlight
is used more efficiently because light that passes through the tall
crop is captured by the low-growing crop.
Adding grasses to a fall-seeded legume improves soil coverage over
winter and increases the root mass to stabilize topsoil. A viny
crop like vetch will climb a grass, so it can get more light and
fix more N, or so it can be harvested more easily for seed. A faster-growing
crop serves as a nurse crop for a slow-growing crop, while covering
the ground quickly for erosion control. The possibilities are endless!
Mixtures can complicate management, however. For example:
They
may cost more to seed. Seeding rates for each component of the
mix are usually lower than for sole-crop plantings, but the total
seed cost may still be more.
The
best time to kill one crop may not be the best for another crop,
so a compromise date may be used.
If you
use herbicides, your choices may be limited when you plant a mixture
of legumes and nonlegumes.
Sometimes
you can end up with more residue than your equipment can handle.
The benefits of a mixture will usually outweigh these disadvantages,
but you need to be prepared to manage the mixture carefully to prevent
problems.
Each cover crop chapter gives examples of specific mixtures that
have been tested and work well. Try some of the proven cover crop
mixtures, and create your own tailor-made mixtures. Remember that
adding another crop increases the diversity on your farm, and is
likely to increase the many proven benefits of rotations over monocropping.
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