Managing Cover Crops Profitably - Valley Crops Home

Incorporated sorghum-sudangrass residue
reduces N availability to young crops more than
oat residue but less than wheat residue (319).
For suppressing root-knot nematodes in Idaho
potato fields, rapeseed has proven slightly more
effective and more dependable than sorghumsudangrass
hybrids (322).
SEED
Cultivars. When comparing sorghum-sudangrass
cultivars, consider traits such as biomass yield
potential, tillering and regrowth ability, disease
resistance, insect resistance (especially if greenbugs
are a problem) and tolerance to iron deficiency
chlorosis.
If you plan to graze the cover crop, select
sorghum-sudangrass hybrids and related crops
with lower levels of dhurrin, the compound
responsible for prussic acid poisoning. For
maximum weed control, choose types high in
sorgoleone, the root exudate that suppresses
weeds. Sterile cultivars are best where escapes
could be a problem, especially where crossing
with johnsongrass (Sorghum halpense) is
possible.
To extend weed suppressive effects into the
second season, select a cultivar known for weed
suppression and leave roots undisturbed when
the stalks are mowed or grazed (361).
Seed sources. Widely available.
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 often 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. Therefore, if you
need a cover crop to take up excess nutrients
after manure or fertilizer applications, a grass 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.
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
SORGHUM-SUNDANGRASS HYBRIDS 85