Moisture, nutrient timing big keys

Ah, the goodness of grain sorghum. It's the queen of residue, the royalty of rotation, and a king in a drought.

It also has no aflatoxin problems, a growing number of uses, and changes in farm legislation that sets its value equal to corn.

“It's a good crop,” says Steve Livingston, Texas Extension agronomist at the Corpus Christi Research and Extension Center.

But Livingston recently trekked a bit north of his home turf to discuss the merits and challenges of grain sorghum with Denton County farmers. He said recommendations for the Texas Blacklands would differ from the Gulf Coast but practices used in South Texas provide useful guidelines.

“Grain sorghum produces a lot of residue,” he said. “That makes it a good rotation crop and a good choice for conservation tillage systems. It's also drought-tolerant and will wait on a rain.”

Late-season moisture can cause problems, however. “Sorghum weathering can cause damage when it rains at harvest time,” he said.

An accepted rule of thumb indicates areas that receive more than 26 inches of rainfall a year should plant corn. Anything below 26 inches would do better with grain sorghum. He also noted that distribution of rainfall makes a difference.

Livingston said recommended seeding rates vary according to moisture availability. In low rainfall regimes and 38-inch row spacings, he recommends two to four plants per foot of row. “That's 35,000 to 70,000 seed per acre. I like to plant 50,000 to 70,000.”

For high rainfall areas or under irrigation, again in 38-inch rows, he recommends four to six plants per foot of row, or 75,000 to 100,000 seed per acre. He assumes at least an 80 percent germination rate.

Livingston said the small seed makes grain sorghum vulnerable to at-planting weather problems.

“Small seed mean a small food reserve,” he said. “Seed has a limited period of time that it can remain viable and sprout. It needs to emerge within five to seven days after planting.”

Planting before soil warms adequately could result in skippy, non-uniform stands. “If seed stay in the soil for two weeks without emerging, stand will be weak. We like a Febr. 15 through March 15 planting window in the Gulf Coast,” he said.

“A better gauge across the state will be soil temperature. Don't plant until soil reaches 55 degrees, minimum.”

Livingston said grain sorghum will make a good crop, even with less than ideal moisture conditions.

“The highest yield we've ever recorded was 11,000 pounds per acre. I've seen some 8,000-pound to 9,000-pound yields in the Gulf Coast region, but we've had drought the last few years that restricted production. I was surprised at how well grain sorghum did last year.”

Although moisture demand is far less than for other crops, Livingston said timing plays a critical role.

“Seedling grain sorghum needs little water,” he said. “For the first 30 to 35 days, it establishes a root system. From 45 days to 50 days, it goes into reproductive phase and water is critical.

“We consider precipitation during that time a ‘million dollar rain.’ One inch of water during this stage means 450 pounds to 500 pounds of grain sorghum per acre.”

After 80 days, water demand diminishes, although adequate moisture helps fill out the grain.

Row spacings also influence yield, he said. “We've found that 19-inch rows, with irrigation, produce more than 38-inch rows. In eight out 11 years, the 19-inch rows were better than 38.

“The narrow rows also returned more money than the wider ones. Yield averaged 476 pounds more per acre from 19-inch row spacings.”

Livingston said tillage methods may add to profit potential. “We've shown that conservation tillage systems improve profit on the farm,” he said. “And grain sorghum works extremely well with reduced tillage practices.”

He said rotating with grain sorghum improves yields of subsequent corn or cotton, and hybrid selection takes a bit of study, he said.

Livingston recommended farmers look at more than a year or two of trial data before selecting a new hbrid.

“Established performance over time is important,” he said. Growers should consider yield, consistency, chlorosis tolerance, Sta-Green traits, midge resistance and disease and insect tolerance.

“Taller and later hybrids may yield better, but we mostly have medium varieties.” He does not recommend early-maturing varieties. “They just do not yield high enough.”

Iron chlorosis can be a problem, Livingston said, necessitating applications of copperas, which can be expensive.

“Iron chlorosis turns a plant almost white. The plant can outgrow the problem but it may limit production. We've seen significant increases in grain sorghum yield with proper amounts of zinc and iron.”

Treatment decisions should be based on the value of the crop.

“This condition should be addressed through genetic engineering,” he added. “We need tolerance in a hybrid. Some hybrids currently available are more tolerant than others.”

He cited weathering resistance as another problem research needs to address. Height, lodging score, disease resistance, drought tolerance and greenbug tolerance also beg attention. Glume color could be a factor for grain sorghum produced for food use and for poultry feed.

Livingston said farmers should consider a Sta-Green hybrid on part of their acreage. “These hybrids buy time during a drought,” he said. “After flowering, conventional varieties will rob nutrients from stalks and roots during a drought. The Sta-Green trait will keep the plant functioning three to seven days longer.”

Livingston said in ideal moisture conditions, Sta-Green hybrids “will not perform better than conventional and may be worse. It makes sense to put them on part of the acreage to spread risks.”

Midge-resistant hybrids also make sense. With resistance, damage ranges from zero to 14 percent. Without it, injury goes from zero to 96 percent.

“Midge-resistant varieties usually do not do as well as traditional hybrids that are planted on time, but these are good choices if growers have to plant late.”

He said no “truly midge-resistant hybrids are currently available.”

Proper fertility improves yield potential. In addition to adequate amounts of zinc and iron, nitrogen and phosphorus also boost yield. Livingston recommends two pounds of nitrogen for each 100 pounds of potential yield. “We plan for 5,000 pounds per acre,” he said.

Nutrient application timing plays a critical role, similar to moisture management.

“As a seedling, grain sorghum needs little nitrogen,” Livingston said, “about 2 percent of total need. Rapid growth occurs from 21 days through 40 days and plants need 33 percent of total nitrogen during this stage.

“Beginning at early bloom, about 41 days after planting, and through 60 days, the crop needs 32 percent of the season's nitrogen demand.”

Phosphorus follows a similar pattern: It needs 3 percent during the seedling stage, 0 through 20 days; it needs 23 percent during rapid growth, 21 through 40 days; 33 percent from 41 through 60 days; and during grain fill sorghum needs 32 percent of season nitrogen demand.

The crop also needs micronutrients, including sulfur, magnesium, and calcium.

Weed control is relatively uncomplicated. Livingston recommends a basic pre-plant or pre-emergence herbicide with a residual. “We can use atrazine pre-plant or preemerge but not to seedling sorghum,” he said. “Sorghum should be 6 to 12 inches tall.

He said post-emergence treatments include Permit, Peak, Basagran, Buctril and Roundup Ultra.

Conservation tillage, he said, also aids in weed control. “Unfortunately, we have less than 10 percent of our acreage planted in reduced tillage systems. We want to maintain 30 percent or more residue on the soil surface.”

He said reduced tillage conserves soil moisture. “Every time we cultivate, we lose one inch of moisture.”

Livingston said growers should begin reduced tillage programs just after harvest. “And if we kill a cover crop and other vegetation at least six weeks before we plant the next crop we don't have cutworms. They have nothing to feed on. Crop residue also reduces weed populations.”

He said farmers can find a variety of equipment for conservation tillage. “They need a good planter and a hooded sprayer.”

The reasoning behind conservation tillage, he said, is that farmers “can save a lot of money.”

Livingston said some sorghum farmers use a non-selective herbicide to terminate the crop early to save moisture and nutrients and to aid harvest. He recommends they make certain they have strong stalks and no charcoal rot before they apply the herbicide.

“Also make certain the crop is physiologically mature. Look for the black layer on the seed. After the black layer develops, the crop will not add any more to test weight.”

Livingston said new uses for grain sorghum, including new foods, fibers and ethanol, make the crop more viable than it has been in years.

“We have established planting dates, flexible markets and improved prices,” he said. “Perhaps we can recapture some of the acreage we've lost.”

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