Forage Sorghum Options

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are best used for single or multiplehay cuttings and grazing.

Growth, yields, and pestmanagementSorghums are coarse, fast-grow-

ing, warm-weather grasses that canprovide feed in mid-summer whenmany other types of forage are slowerto develop. Stems are erect and solidand reach from 2 to 12 ft in height.

Buds that form near the crown de-velop into grain-producing tillers.

Sorghums are best suited towarm, fertile soils; cool, wet soilslimit their growth. The crop toleratesdrought fairly well though adequatefertility and soil moisture maximize

yields. Sorghum becomes dormantin the absence of adequate water,but it does not wilt readily. Growthresumes when moisture conditionsimprove.

Soil fertility requirements aresomewhat similar to those of u


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corn at the same yield goals; al-though sorghums are usually moreefficient in their use of phosphorusand potassium.

Following are some recommendeduses based on the Forage SorghumSilage Production GuideWesternProductionby Marsalis and Bean:

Forage sorghums are best har-vested as silage. Forage sorghumscan range anywhere from 6 to 14 ftin height. The feed value of sorghumsilage per acre is about 90% thatof corn silage. On more produc-tive soils, with favorable moistureand fertility, corn is a better silagecrop, producing comparable yieldsand higher feed value than foragesorghums and sorghum-sudangrasshybrids

Grain sorghum hybrids were de-veloped for grain production andtend to make good quality silage;however, silage yield will be less thanwhat can be obtained with foragesorghums. In some cases, producersof dairy silage will sometimes prefera high-grain hybrid rather than tallertypes with higher stover content.

Sorghum-sudangrass hybrids are across between sorghum andsudangrass and are characterized byrelatively small-diameter stems, hightillering capacity, rapid re-growthpotential, and low grain yield.Sorghum-sudangrass hybrids can

produce good quality silage, butare best suited for grazing or hay

production.

New developmentsThe introduction of

some new traits inthe past few

years isexpand-

ing the use of forage sorghums.These new developments include theintroductions of brown midrib for-age sorghums, photoperiod-sensitive

sorghums, and brachytic dwarf sor-ghums.

Brown midrib sorghumsThe brown midrib gene is linked

to a reduction of lignin content inthe plant. Lignin is a non-digestiblecomponent of the cell walls that lim-its forage fiber digestion. New brownmidrib hybrids have shown an 18.9%average increase in feed value com-pared with conventional types.

Before the release of the brownmidribs, sorghums have been knownfor their good heat tolerance, waterefficiency, and ability to producegood volumes of forage in a short pe-riod of time, says Ricky Rice, foragesorghum specialist with Advanta US.They were used extensively in thesouthern United States, but as youmoved north, they were basicallyused as a rescue crop. The reasonwas because the forage quality couldnot match that provided by cornsilage, alfalfa hay, or cool-seasongrasses.

However, with the introduc-tion of the brown midribs that allchanged. This trait dramatically low-ered the lignin content and improvedthe nutritional quality.

The trait provides a premium sum-mer annual hybrid with the sameagronomic characteristics that arefound in a conventional sorghum-sudangrasses hybrid such as good

hay quality, heavy pasturing, superiordrought tolerance, and adaptability.

Photoperiod-sensitivesorghums

Delaying flowering in sorghumsand sorghum-sudangrasses willalso delay the decline in quality ofthe vegetative portion of the plant.

uSorghum with the brachytic dwarf trait.Photo courtesy of Advanta US (www.advantaus.com).


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Selected maturity genes have beenused to produce hybrid forages thatare extremely photoperiod sensi-tive and do not flower until verylate in the growing season. Some ofthese photoperiod-sensitive variet-ies, including forage sorghums andsorghum-sudangrass hybrids, arecommercially available. The delayedflowering slows the decline in foragequality associated with floral initia-

tion and provides flexibility in har-vest management for producers.The addition of the photoperiod-

sensitive trait has really helped in theagronomic management of sorghumsand sorghum-sudangrass hybrids,Rice says. The plant no longer isdependent on how many days it hasbeen growing or how many heatunits it has acquired. It will changefrom vegetative to reproductive whenthe day length gets to a certain pe-riod.

So what that did was, especiallyin sudangrass hybrids, give growers awide window when the crop can beharvested and still maintain qualityover a long period of time.

Varieties with the photoperiod-sensitive trait combined with thebrown midrib trait were introducedaround 2001, so this allowed thecombination of improved nutritionquality with more versatility in ag-ronomic practices, according to Rice.

Brachytic dwarf sorghumsBrachytic dwarf genes in sorghum

control height and produce a type ofdwarfism known as brachytic dwarf-ism, which reduces the length of theinternodes without affecting otheragronomic plant characteristics, suchas leaf number, leaf size, maturity, oryield/biomass production.

The brachytic dwarf sorghums pro-duce comparable tonnage to tallerhybrids by producing more leavesand more tillers. Sorghums with thistrait have very high leaf-to-stalk ra-tios, prolific tillering, superior stand-ability, and comparable tonnage tonormal-height sorghums.

Brachytic dwarf hybrids haveshortened internodes, Rice explains.The height of the plant is greatly

reduced, but the same number ofnodes exists as in normal hybrids.This helps with problems associatedwith lodging, and also the shorterinternodes are not harvested too low,allowing good regrowth after grazingor cutting.

Herbicide resistanceAccording to Rice, herbicide-

resistant grain sorghums could beavailable by 2012 or 2013. Heavy

weed infestations can reduce grainsorghum yields by up to 50%.

Kansas State researchers havedeveloped a herbicide-resistantgrain sorghum line that is tolerantto acetolactate synthaseinhibitorherbicides, Rice says. This trait willgive growers another managementtechnique to help control weeds andincrease yield.

Kansas State is working with sev-eral seed companies in developingthe acetolactate synthase (ALS)resistant sorghum. The researchersare also working with the USEPAsMinor Use Pesticides program toregister the use of Steadfast herbicide(DuPont) on ALS-resistant sorghum.

In addition to herbicide resistance,a variety of improved biotech andconventional forage sorghum traitsare being developed. u


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These include:

X cold tolerance: a conven-tional trait that could lowersorghums tolerance to coldsoils by 10F or more. Thismeans sorghum can be plantedearlier, in 50F soils, and therange of grain sorghum can be ex-panded throughout the Corn Belt;

X salt tolerance: this trait will ex-pand the range of lands availablefor crop production and reducerequirements for fresh water;

X nitrogen use efficiency: al-though sorghum already requiresless nitrogen than corn, an in-crease in its nitrogen use efficien-cy will increase its usefulness; and

X drought tolerance: although sor-ghum is already a drought-tolerantcrop, this trait will provide addi-tional drought tolerance beyondthe current 30 to 50% less waterthat sorghum currently requirescompared with corn and othercrops.

Pest managementSorghums are hardy plants but

can be attacked by several pests andcurrently lack good weed controlmethods beyond cultivation. Sudan-grass and sorghum-sudangrass hy-

brids planted in a well-prepared,warm seedbed germinate andgrow rapidly and can com-

pete well with most annualweeds. Weeds can be con-trolled with cultivation if

the crop is planted inrows 20 inches or more

wide.Forage

sorghumsare at-

tacked

by wireworms, seed beetles, cut-worms, aphids, sorghum midge,chinch bugs, spider mites, army-worms, and earworms. Some ofthese pests can be controlled withinsecticide seed treatments in theplanter box. However, most of theseinsects do not normally occur insufficient populations to warrantcontrol in the Midwest.

ToxicityAccording to the Forage Sorghum

Silage Production GuideWesternProductionby Marsalis and Bean,sorghums have the potential to bevery toxic to animals. Two concernsthat producers should be aware ofare hydrocyanic/prussic acid poi-soning and nitrate toxicity.

Sorghum plants, particularlyyoung plants, contain an alkaloidthat releases hydrocyanic, or prus-

sic, acid when hydrolyzed. This canbe toxic to livestock. Young plants,branches in the leaf axils of injuredplants, and new shoots from thecrown at the soil surface containmore than twice as much acid asthe mature leaves of normal plants.When the crop is cut and field-cured or is ensiled, and the hydro-cyanic acid degrades (two to threeweeks after ensiling), the danger isgreatly reduced. Sudangrasses con-tain less than half as much hydrocy-anic acid as most sorghums.

In addition, during periods ofplant stress such as drought, sor-ghums tend to accumulate nitrates,which can poison livestock. If re-tarded crop growth is observed,analyze the forage for excessivenitrates before feeding it. In the caseof high nitrate levels, the storage

should be ensiled or combined withother feeds low in nitrate to reduceoverall daily nitrate intake.

Another concern is that ensilingforage sorghum with a high nitrateconcentration can produce nitrogendioxide (NO2), which is toxic to hu-mans and animals. For this reason,care should be taken when a silagepit or bag is first opened when highnitrate levels are suspected. If nitrate

concentration in forage sorghum isan issue, add 8 lb of sodium metabi-sulfite per ton of fresh material toreduce the risk of NO2formation.

Forage sorghums can be a betteroption than corn in some environ-ments. The drought hardiness offorage sorghums and their greatlyreduced use of water comparedwith corn make them an excellentforage or silage plant in semi-aridproduction areas. Recent develop-ments such as the brown midrib

and brachytic dwarf traits and oth-ers coming in the seed pipelineare expanding and improving theproduction possibilities for foragesorghums.X

The information in this article wasbased on Forage Sorghum SilageProduction GuideWestern Produc-tion, by Mark A. Marsalis, extensionagronomist, New Mexico State Uni-versity Agricultural Science Centerat Clovis, and Brent Bean, extensionagronomist, Texas AgriLife Researchand Extension Center at Amarillo.

Available online at www.sorghumcheckoff.com/userfiles/WesternForageGuide_FINAL.pdf. The Sor-

ghum Checkoff Program offers avariety of production guides basedon region. For more information, seewww.sorghumcheckoff.com.

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Forage Sorghum Options