Introduction
Sorghum-Sudan grass hybrids offer a solution to producing forage dry
matter when an emergency occurs. They are warm season grasses, unlike most
of our forage species which are cool season grasses. Hybrids of Sorghum
and Sudan grass are often used in Ontario. The resulting hybrid may favour
either parent, so be sure to discuss what you want from the hybrid with
your seed sales person. Sorghums are known for being drought resistant.
They are more efficient in water absorption because they have twice as
many secondary roots per unit of primary root as corn and have only half
as much leaf area as corn for evaporation. Their water requirements are
the same as corn but they have the ability to go dormant during extended
drought periods. Growth will begin when the rains come.
Sorghum-Sudan grasses yield slightly lower than corn when harvested for
silage, but they have the advantage that they can be cut 2-3 times during
the season and can also be stored as either chopped silage or wrapped bale
silage, green chopped or pastured. Corn silage produces more tonnes per
hectare but it must be harvested in the fall with specialized forage
harvesting equipment. Sorghum-sudan grasses can also be harvested using a
strip grazing system. They are thus more versatile to harvest than corn.
The availability of harvesting equipment and the immediate need for forage
will help you to decide between Sorghum-Sudan grass and other annual
forages.
There are three very distinct types of forage on the market. These are:
1. Forage sorghum These varieties and hybrids have sweet juicy
stems. They produce less than Sudan grass hybrids and have very slow
regrowth. They have been selected for one-time harvesting. A grain Sorghum
hybrid should be harvested in the soft dough stage for maximum forage
production.
2. Sudan grass This is a fine stemmed and leafy plant with very
quick regrowth. It is best used for pasture or in multiple cut systems. If
used in a one cut system, yields will be less than that of Sorghum. Forage
quality will be high due to low fiber content if cut frequently.
3. Sorghum-Sudan grass hybrids These are the most popular for
use in Ontario. They have larger stems and are less leafy than the Sudan
grass but perform best in our climate.
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CAUTION
Members of the Sorghum family contain dhurrin, a glucoside that breaks
down to release hydrocyanic acid also known as prussic acid. A sudden
disruption of growth such as frost, drought or cutting, causes prussic
acid to be released inside the plant at a more rapid rate. High prussic
acid levels may be lethal to cattle. Prussic acid will breakdown in
one to two weeks, so material made into hay or silage is safe to use. See Nutritional
Concerns and Animal Health Hazards, below.
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Seeding
These warm season grasses must be planted into warm soil, which
generally means delaying planting until the end of May or first of June. A
seeding rate of 15 kg/ha(13.5 lb/ac) should be planted at a depth of 2-3.5
cm (1-1.5 in) in 18-36 cm (7-14 inch) rows. Packing may be required if the
seedbed is dry.
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Fertility
Recommendations for fertilizing corn should be used for the sorghum
family, including the 100-125 kg/ha (90-110 lb/ac) nitrogen applied at
planting. After each cut, 50 kg/ha (45 lb/ac) more nitrogen should be
applied to encourage growth. Sorghum-sudan grasses can grow in a wide pH
range with 5.5-7.5 as the optimum.
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Weed Control
Under good growing conditions the competition from the plants will keep
weeds in check. No herbicides are currently registered for use on these
hybrids.
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Harvesting
The first cut will be ready for harvest about 60 days from planting.
The plants should be over 65 cm (26 inches) in height, and just before
head emergence when cut (usually early August). For a faster recovery of
aftermath growth, leave at least 10 to 18 cm (4-7 inches) of stubble when
harvesting. Optimum growth of these plants occurs under hot, moist
conditions. A second cut should be ready 30-35 days later.
The crop may also be harvested just once, at the hard dough stage, to
get maximum volume in a one cut system. You will sacrifice yield that you
could have captured under a 2 cut system. If this is your goal you should
reconsider corn silage as it would yield more in a one cut system.
At cutting, the crop is about 70-75% moisture and requires wilting
before ensiling. It dries slower than alfalfa. Yield data is limited, but
5- 7.5 tonnes per hectare (2-3 tons /ac) are reported from research and
farm experience. Yields vary with season, moisture and warmth, and are
higher in hot summers than in cool ones.
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Pasture
Sorghum-Sudan grass may be pastured but livestock should not enter
before the plants are 45 cm high. Trampling damage will be very high
unless a strip or rotational grazing system is used. As the plants will
reach this height by mid summer and are drought resistant, this can
provide a source of feed during the summer slump of pastures.
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Feed Quality and Nutritional Value
Sorghum-Sudan grass hybrids fit best in summer feeding programs. They
are thick stemmed and hard to dry for hay but they can supply ample yields
of silage, green chop and pasture when perennial grasses are slowing down
or going dormant. Once Sorghum-Sudan grass begins to head out, the quality
and feeding value drop drastically. It is difficult to meet nutrient
requirements of high production or early lactation milking cows when
Sorghum-Sudan grass is a large part of the forage intake. It is more
suited to rations for dry cows, replacement heifers over 12 months of age,
and beef cows and calves.
As the crop matures, protein content drops rapidly, while fibre levels
increase. This decreases the feed energy value and rumen digestibility.
High NDF1 levels increase the bulkiness of the feed and
dramatically reduce dry matter intake potential. A comparison of nutrient
value of Sorghum-Sudan grass with the more common forages is shown in the
following Table. Sorghum-sudangrass can contain as much protein as mature
alfalfa, but only if harvested at the vegetative stage. Energy levels in
vegetative material are similar to corn and higher than alfalfa.
Sorghum-Sudan grass forage should always be sampled and tested for feed
composition because of the variability in nutrient value.
Forage quality of silages from Sorghum-Sudan grass versus Alfalfa
and Corn
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KARI
I Rothamsted
Research I NARO
I Ministry
of Agriculture, TanzaniaI
Ministrty of Agriculture, Kenya I NALEP I
KAPP
I
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