Grain sorghum is second only to cotton in acres planted on the High Plains, and greater demand for grain sorghum for export and ethanol production has stimulated an acreage increase. USDA figures show 2006 High Plains gain sorghum acreage was 250,000; in 2007 it was 850,000.
“If the demand for grain sorghum for feedstocks in ethanol plants increases as expected, grain sorghum acreage will increase, particularly if the price for the grain continues to rise,” said Calvin Trostle, extension agronomist, Texas AgriLife Extension Service, Lubbock.
“Whether or not the producer increases acreage, he may benefit financially by updating crop management: hybrid selection, planting date, planting rate, irrigation, fertilization, and weed and insect control,” Trostle said.
Hybrid selection should be based primarily on potential yield and anticipated planting date. “Full-season hybrids generally have the highest yield potential. However, they may not be the best choice for economic returns because additional inputs such as water and fertilizer are required,” Trostle said. “Too-long maturity can outstrip limited water.”
Grain sorghum hybrids come in five relative maturity groups based on the number of days from planting until one-half the plants have flowers: early, about 58 days; medium-early, 59 to 63; medium, 64 to 68; medium-long, 69 to 73; long (full season), more than 74. Once flowering begins, hybrids need about 35 days to reach maturity.
Planting dates for grain sorghum on the High Plains range from late April to early July.
“Knowing maturity range is a key to effective sorghum management strategies,” Trostle said. “A targeted planting date coupled with a specific hybrid maturity can enable a producer to ensure dryland flowering occurs outside of the hottest period, around July 5 to August 15. For example, medium-early hybrid planted by May 1 can be expected to flower in 66 days or so and thus avoid flowering during the ‘hot’ period. Furthermore, when sharing irrigation water with another crop, either early or late sorghum planting dates, coupled with appropriate hybrid maturity, will enable a producer to minimize the overlap of peak irrigation requirements with a ‘shared’ crop such as cotton.
“A conservative first planting date for grain sorghum is when the 10-day average minimum soil temperature at the 4-inch depth is 65 F. However, farmers may consider planting when the 5-day-average minimum at the 2-inch depth reaches 60 F. Local forecasts should always be checked to ensure cold fronts that could significantly lower the soil temperatures are not expected,” Trostle said. Soil temperatures are available at http://txhighplainset.tamu.edu/.
“Explaining the value of reduced sorghum seeding rates remains my most frequently discussed sorghum topic with producers in the High Plains,” Trostle said. “Too many fields are still planted too thick.
“Seeding rate recommendations in the region start with a base of 32,000 seeds dropped per acre for a dryland field with excellent soil moisture. That seeding rate is then adjusted down for dry conditions and no irrigation, or upwards to reflect irrigation,” Trostle said.
“For limited irrigation of 6 to 8 inches, Extension generally recommends acre seeding rates of 50,000 to 55,000 if soil moisture is high, but only 40,000 to 45,000 seeds per acre for poor soil moisture conditions. Extension doesn't recommend seeding rates past 80,000 seeds per acre even for the highest yield potentials.”
For a spreadsheet that helps align seeding rates to soil moisture at planting as well as projected irrigation, producers may contact Trostle for a copy of a seeding rate calculator for the High Plains. Call 806-746-6101, or email firstname.lastname@example.org.
“It takes 6 to 8 inches of available water to get a typical grain sorghum crop from emergence to grain production. For low-population, dryland grain sorghum the requirement may be only 5 inches. Once grain formation begins, yield response is about 350 to 450 pounds of grain per inch of water,” Trostle said.
“Critical irrigation (or rain) times are at growing point differentiation, and especially at boot stage. Maintaining irrigation from heading to the milk stage during grain fill is also important. Soil water deficits at any of these times will lower potential yields.
“Most producers don't realize that at about 30 to 35 days after germination the growing point begins differentiation to determine the maximum number of spikelets, and seeds per spikelet in the head. This is critically important to yield potential, and minimizing moisture stress during this time can set a significantly higher yield potential,” Trostle said.
“The rule of thumb for nitrogen fertilizer is 2 pounds of nitrogen for every 100 pounds of yield goal, whether for irrigated or dryland crops,” Trostle said. “However, the producer should have a realistic goal as adding nitrogen above what the plant needs will not increase yields. Phosphorus needs are about 0.35 to 0.40 pounds per 100 pounds of yield goal.”
Many herbicides are available to control weeds in sorghum, but most have limitations such as rotation restrictions, pre/post timing, or require safened seed, etc. For a current list of labeled sorghum herbicides visit http://lubbock.tamu.edu/sorghum.
Though numerous insects are present in grain sorghum only a few regularly present a threat to grain production, according to Brant Baugh, Texas AgriLife Extension Service IPM agent, Lubbock County. “These insects include greenbugs, yellow sugarcane aphids, Banks grass mites, and sorghum headworms.” Other insects such as wireworms, fall army worm, or sorghum midge occasionally cause problems.” In 2007 sorghum midge caused damage on numerous later planted fields though it was the first time we had problems with midge in recent memory,” Baugh said.
Extension released the updated “Managing Insect and Mite Pests of Texas Grain Sorghum” in 2007. The new edition includes color photos and revised economic thresholds as well as information to guide producers in whether to apply seed insecticide treatments. The document is available through county Extension offices or for viewing/downloading on the Web at http://lubbock.tamu.edu/ipm/AgWeb/.