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Forage
Forage Extension Program
Warm Season Forages: Sorghum and Sudan Grass
by Dennis Cash and Mike Schuldt,
MSU Extension
"These
"cool season" crops fit well for most
producers, because they can be seeded and harvested
with conventional equipment in normal crop rotations."
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Continued dry conditions throughout Montana have created
severe hay and grass shortages. Depending on winter
and spring precipitation, we could experience continued
forage shortages in 2001. For the past several years,
there has been a significant increase in the production
of small grains, such as hay barley and oats, for annual
hay. These "cool season" crops fit well for
most producers, because they can be seeded and harvested
with conventional equipment in normal crop rotations.
Further, these can be seeded in early spring to capitalize
on spring moisture.
Benefits of Warm Season Crops
Warm season forage crops, including corn, sorghum,
sudangrass, sorghum/sudangrass hybrids, and millets,
have not been widely grown in Montana. However, several
Montana ranchers have experimented with these crops
and gotten good results. These forage crops must be
seeded after soil temperatures are consistently above
60o F. For most years, this is an advantage in Montana,
because by mid- to late May, we have a better idea of
the seasonal moisture situation for perennial pastures
and hay ground. Plus working with later season crops
helps distribute the farming workload. After establishment,
warm season forages can be very productive on dryland.
Compared to our small grain forages, warm season forages
generally have a higher water use efficiency, meaning
they yield more forage per inch of soil moisture. Depending
on moisture, warm season forages can yield 1.5 to 6
tons of dry hay per acre.0
Sudangrass and Sorghum
Sudangrass serves as an excellent pasture or hay crop,
with its 3 to 5' height and slender (<1/2 inch),
leafy stems. These characteristics make it well suited
for pasture, dry hay, or silage. Forage sorghum was
developed from grain sorghum, and this crop is suitable
for silage, but not dry hay production. There are a
number of sorghum/sudangrass hybrids available, which
are very high-yielding and combine the leafiness and
regrowth ability of sudangrass. These hybrids are excellent
for silage or fall pasture, but not dry hay.
Tips for Growing These Crops
First, work with a local reputable seed dealer, as
there are tremendous differences among varieties or
hybrids for adaptation and maturity. Most of these forages
require 60 to 90 days of frost-free weather with soil
temperatures of 65 to 70o F. They generally require
special seeding rates and management. One advantage
of seeding later than small grains is that many annual
weeds will emerge, and can be controlled by light cultivation
or herbicides. However, coming out of a dry spring,
the delay for warm soils can be risky in terms of precipitation
probabilities after seeding.
Seeding Specs
Seeding rates vary from 5 to 35 pounds per acre, depending
on variety (big differences in seed size), method of
seeding, and intended use. For dryland production of
forage sorghum or sorghum/sudangrass in Montana, seed
in wide rows (21 to 28-inch) with 5 to 8 pounds per
acre. Sudangrass can be drilled or broadcast at a seeding
rate of 25 to 30 pounds per acre. Under irrigation,
the seeding rates should be increased to optimize forage
yield and quality. Seeds should be planted 1 to 1.5
inches deep into a firm seedbed.
Fertilizer Needs
With adequate moisture, these crops can be high-yielding,
showing good response to nitrogen (N) fertility. Under
irrigation, with a potential yield of 6 tons of dry
matter per acre, the N recommendation is 100 to 125
pounds N (soil test plus fertilizer) pre-plant incorporated,
then 40 pounds of topdressed N on the regrowth. No current
recommendations have been generated in Montana, but
a good guideline is to supply about 20 pounds of N per
every ton of anticipated yield. Phosphorus and potassium
requirements are similar to those of small grains.
Grazing, Haying, and Silage
Sudangrass is best suited for grazing or hay production.
Sheep can be turned out when the crop is 12 to 14 inches
tall, and cattle when the crop is 18 to 24 inches tall.
Livestock should not graze the crop below about 4 inches
to allow for fast regrowth. For optimum use, fencing
should be used to set up a rotational grazing scheme.
Sudangrass should be cut for hay in the heading stage,
or for silage in the dough stage. Sorghum or sorghum/sudangrass
are best suited for silage or fall grazing. Recently,
several producers successfully made high-quality "baleage"
from sorghum/sudangrass. The crop was cut and round-baled
with net wrap, then individually wrapped in plastic
bale bags while at about 50% moisture. This resulted
in a very palatable and nutritious ensiled feed.
Potential Drawbacks
Aside from the high forage yield of these warm season
crops, they also provide weed and disease control benefits.
One disadvantage may be their deep water removal in
the summer. Other potential drawbacks of these crops
are nitrate and prussic acid toxicities. Many grasses
can have high nitrate accumulations in the early stages
of growth, and particularly during drought stress. Most
MSU Extension Service county agents can provide a nitrate
"QuikTest" on a representative sample of the
crop prior to it being cut or grazed. Prussic acid (hydrocyanic
acid, HCN) can accumulate in these crops from the breakdown
of glucosides. The forage sorghums and sorghum/sudangrass
hybrids tend to have higher incidences of prussic acid
toxicity, and these should either be ensiled or NOT
grazed until after a killing frost. There are commercial
laboratories that can analyze for prussic acid concentrations,
but sampling and timeliness are critical.
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