American Agriculturist - June 2007
Hay & Forage Management
20
Try BMR sorghum-sudan grass
Field
Notes
By Bill Pardee
RY it! You may like it! So say dairy
farmers who have grown brown
midrib sorghum-sudangrass.
In fact, they found it to be a quickgrowing, high-quality summer forage —
one that can be planted as late as June in
New York state. As a late-planted crop, it
can match late-planted corn in tonnage
and produce a high-quality silage crop.
And it’s cheaper to grow than corn!
Sorghum-sudangrasses aren’t new, of
course. Since older versions produced
low-quality silage, they were never
widely used for lactating cows.
But new BMR types are gaining attention. Plants with the BMR gene develop
less lignin fiber than traditional sorghums, making them more digestible.
T
High points to check out
Here’s a quick wrap-up from Cornell scientists Tom Kilcer, Quirine Ketterings
and Jerry Cherney:
■ Plant BMR sorghum-sudangrass in
late May through June, even into early
July. Manage it intensively to get top
yield and quality. Suggested seeding
rates are 65 to 70 pounds per acre.
Key Points
■ BMR sorghum-sudangrass can match
late-planted corn silage tonnage.
■ Without insecticide or herbicide, it’s much
cheaper than corn.
■ For top feed quality, it must be cut when
36 to 40 inches tall.
■ It grows best on good corn soils,
but does well on droughty soils, even
heavy clay soils. However, it’ll do poorly
in wet soils or during prolonged spells
of cool, wet weather.
■ Nitrogen is important for building
protein and yield. Tests show profitable
response from 100 to 150 pounds of N,
before planting and after each cut.
Manure is an excellent N source.
Work in a good pre-plant spread, then
apply manure after each cutting.
Newly cut sorghum-sudan fields
are great for summer spreading. The
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ground usually is firm, and the crop responds quickly.
■ Apply potassium and phosphorus
as you would for corn silage (by soil
tests). Fertilize it as you would a highperformance forage grass.
■ Weed control is rarely a problem
in this fast-growing crop. Seeds start
quickly in June soils and soon crowd
out weeds.
■ Insecticides aren’t needed either.
Corn insects don’t bother it.
■ Drought tolerance is another
strength of this crop. Sorghum-sudans
may slow their growth in a dry spell, but
a good shower will start them growing
again.
■ Mow when growth is 36 to 40
inches tall. You should be able to get
three cuttings from May sowings, two
from June plantings and at least one
from early July seedings.
Note the 36- to 40-inch cutting height.
Don’t delay mowing beyond that to get
more growth. Feeding quality declines
as the crop matures, just as with any
other grass crop.
■ Protein content, at 15% to 16%,
has surpassed corn silage in tests, running almost twice that for June-planted
corn silage. This may reduce the need
for off-farm protein purchases.
■ High fiber digestibility is a strong
point of BMR sorghum-sudangrass.
Cornell tests have shown the digest-
ible neutral detergent fiber of this BMR
grass to be about 70% — compared to
52% to 53% for corn silage and alfalfa.
So cows ruminate more energy from the
grass. And they eat more of it, since it
digests quickly. Energy content may be
lower than corn silage, so you may need
to add starch sources to the ration.
■ For harvest, mow as you would
haylage, laying the crop down in wide
swaths. Use your conditioner to crack
stems for faster wilting. Chop when
moisture hits the 65% to 70% range.
The trade-offs
Note the usual warnings about sorghum-sudans, particularly for pasture.
New sorghum growth contains a chemical (dhurrin), which can convert to poisonous prussic acid in the animal’s gut.
Prussic acid breaks down in the silo,
so it’s not a problem in properly fermented silage from any harvest. But it
can cause problems for cattle grazing
new regrowth after cutting or after a
frost.
Don’t graze green forage until it’s 24
to 30 inches tall. Let frozen plants dry
completely before feeding. If you’re in
doubt, ensile the crop and let it ferment.
Then it’ll be safe.
Do not graze horses on any form
of sorghum or sorghum-sudan. These
crops can cause cystitis syndrome, a
serious condition in horses.
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