Specific forage sorghum hybrids are equal in quality to corn. Also, grain sorghum – and especially forage sorghum – has more resistance to deer damage than corn.
“Most producers consider corn a premium silage but, in water-limited environments, corn silages lose quality more quickly than forage sorghums. Because of forage sorghums’ drought-tolerant characteristics, they are better able to maintain quality with limited water,” says Jourdan Bell, Ph.D., Texas A&M AgriLife Research.
“Forage sorghum is best adapted to warm regions because of its higher temperature requirements,” says Gregory Roth, Ph.D., Penn State Extension. “Minimum temperature for sorghum growth is about 60 degrees Fahrenheit, and the highest yields occur when mean temperatures during growing season are between 75 and 80 degrees Fahrenheit. However, forage sorghums have a role in nontraditional sorghum-growing areas as well. They been grown successfully in short-season areas of Pennsylvania where 95-day corn is considered full-season.”
“With introduction of brachytic dwarf short-season brown midrib (BMR) forage sorghums, the crop is becoming part of dairy and beef production systems in the Mid-Atlantic region and the state of New York. It’s an economical and stress-tolerant crop best adapted to less-than-ideal soils where corn production is marginal,” Roth says. “It also fits well into later plantings where a winter small-grain silage crop is harvested first and then followed by a forage sorghum.”
Mature height of forage sorghum ranges from 5 to 15 feet depending on the hybrid. Some hybrids are fertile and produce grain yields comparable to grain sorghum, while others are sterile and produce no grain. Forage sorghum usually does not regrow following harvest, which makes it best adapted for a single cut for silage.
“Forage sorghum management and hybrids determine silage value,” Bell says. “There is a vast difference in production and quality between sorghum types and hybrids, so it’s really important to evaluate different sorghums, specifically for silage. These evaluations help producers optimize not only their production in tonnage but also quality of harvest.”
Hybrid selection
Bell’s forage sorghum variety trial, currently in its third year, is a continuation of long-term research conducted at Bushland, Texas, for over 15 years. The Bushland trial includes over 100 different hybrids, including both forage and grain sorghum types. Its large scale provides producers and nutritionists an opportunity to compare forage yield and quality parameters for multiple forage sorghum varieties in the same productive environment.
“As expected, photoperiod-sensitive (PS) types were the higher-yielding forages, but digestibility was lower. Starch contents were also lower in PS hybrids because they did not produce grain, or there was limited grain production,” Bell says. “On average, lignin concentrations were lower in BMR varieties than in non-BMRs. Trial data, however, confirms percent lignin and digestibility vary between individual BMR hybrids. Trial data reflects yield and quality of some forage sorghums can exceed corn.”
“PS hybrids remain in the vegetative stage until day length is less than approximately 12 hours, at which time plants will initiate their reproductive stage and form seedheads about four weeks later. Thus, potential forage yields are higher due to long-season growth, especially if planted early,” says Calvin Trostle with Texas A&M AgriLife Extension. “While producers run the risk of conventional forages going to seed due to delayed harvest, PS-sensitive forage continues to add more leaves instead of producing grain.”
“Forage sorghum varieties that possess the brown midrib trait have brown vascular tissue as a result of reduced lignin content, which improves digestibility. Careful selection of BMR hybrids and timing of harvest are necessary to maximize total digestible nutrients (TDN),” says Joao Vendramini with University of Florida Institute of Food and Agricultural Sciences Extension.
Since sugarcane aphids have become a problem pest on sorghum, Bell infested several different varieties of forage sorghum with different levels of sugarcane aphids to determine their effects on silage quality. Results of these studies will hopefully identify differences in aphid tolerance among the tested varieties.
“Another area of concern for the end user is grain processing,” Bell says. “Often the sorghum berry is not cracked when it is ensiled, which can reduce feed value and carbohydrate availability. Because of this concern, we are also evaluating the ensiling of forage sorghum with and without a cracked berry.”
In hybrid selection, producers should determine their yield goal and the maturity class they need to plant for optimum production. Maturity classes range from early maturing hybrids to PS hybrids with their long-season growth. Optimal hybrid selection is often driven by what the end user wants – just roughage or something with a greater feed value.
Manage to optimize production
“Forage sorghum is most often planted in rows with a corn planter to facilitate harvest, reduce lodging and permit cultivation for weed control. Most planters need sorghum-specific plates or feed cups to handle sorghum seed,” says Trostle. “Air planters may require a special drum or plate. Like corn, forage sorghum yields increase with narrower rows. Delay planting until soil temperatures reach 65 degrees Fahrenheit at 2- to 4-inch soil depth. Set planters to place seed at a depth of three-quarter to 1-and-a-quarter inches.”
Prior to planting, sample the soil for nutrient analysis and fertilize according to the testing lab recommendations. For row plantings, preplant fertilizer requirements are often broadcast and covered with soil by disking. Fertilizer can also be applied at planting in continuous bands 2 to 3 inches to each side and 2 to 3 inches below the seed.
“For drill or broadcast plantings, broadcast the initial fertilizer application and disk it into the soil prior to planting,” recommended Vendramini. “Make sure not to place fertilizer in direct contact with the seed, however. Splitting total fertilizer recommendations equally between ‘at planting’ and one or more additional applications during the growing season increases nutrient-use efficiency and reduces risk of nutrient runoff.
When the crop is produced for silage, apply the second treatment when the sorghum reaches a height of about 12 inches and again at 24 inches if fertilizer requirements are split into three applications.”
Bell says just because forage sorghums are drought-tolerant, it does not necessarily mean you can dismiss irrigation. Forage sorghums managed for optimum production can require three-tenths to four-tenths of an inch of water per day in southern climates.
Forage sorghum responds positively to good silage management practices. Harvest at the right moisture content for the silo, chop uniformly, fill the silos as quickly as possible, and pack the silage well. Sorghum yield and forage quality are maximized at levels between 60 and 72 percent moisture content.
“Ultimately, silage is only as good as the forage and how it was managed,” concludes Bell. 
PHOTO: The 2017 trial at Bushland, Texas, reflects the diversity of sorghums including a grain sorghum check in the foreground. Photo provided by Jourdan Bell.
Robert Fears is a freelance writer based in Georgetown, Texas. Email Robert Fears.
