Grain sorghum provides one of the best residue crops for Texas farmers working with conservation tillage systems.

“Next to small grains, sorghum provides the most soil protection of any row crop grown in Texas,” says Steve Livingston, Texas Extension economist at Corpus Christi.

But the amount of residue grain sorghum produces, as well as potential yield, varies significantly with planting date,” Livingston said during a presentation at the recent Conservation Systems Cotton and Rice Conference in Houston.

He said if growers do their best with hybrid selection, weed control, and tillage, date of planting becomes the next most critical decision growers make to increase profitability.

Livingston conducted a three-year research effort at Corpus Christi to determine the effect planting dates have on grain sorghum yield.

“Planting date is often the most neglected aspect of establishing a stand,” Livingston said.

In his study, he planted to moisture in 38-inch row beds and planted at weekly intervals, beginning as early as late January and extending into May.

“Using conventional production practices, we managed all planting dates equally,” he said.

In 2002, Livingston had adequate moisture at planting, from January through April. “But we received no rainfall until July. The entire crop was made without the benefit of rainfall or irrigation.”

Seed yields ranged from 1,566 pounds per acre for the Jan. 31 planting date to 3,999 pounds per acre for a Feb. 20 planting.

“Subsequent yields decreased linearly with later planting dates to a low of 1,613 pounds per acre for a March 28 planting date,” he said. “After the Feb. 20 peak planting date, yields decreased by 68 pounds per day delay in planting, with no additional rainfall. Seed numbers increased from 4,000 to 6,200 per 100 grams during the same days of delay through March 28.”

In 2003, the planting season began dry, similar to the way it started the year before. “However, we received 3.5 inches of rain from June 5 to June 15, which affected some later plantings significantly. Grain yields were decreasing at 291 pounds an acre per week before the rain.”

Trend reverses

After rainfall, that trend turned with a 743 pounds per acre yield increase with rain occurring two weeks post flowering. Rain received one week post flowering and at flowering provided 2,211 pounds per acre and 2,900 pounds per acre, respectively. Rain at one week pre-flowering resulted in 1,930 pounds per acre.

“Every inch of rainfall, when received in significant amounts at the following growth stages may be valued as follows:

  • Two weeks post flowering: 212 pounds per acre.

  • One week post flowering: 632 pounds per acre.

  • At flowering initiation: 829 pounds per acre.

  • One week pre-flowering: 552 pounds per acre.

“Rainfall received at bloom stage is of greatest benefit to sorghum when it needs rain. Peak water demand is at boot and bloom growth stages, when the plant needs as much as 2.7 inches a week. Larger plants and higher yields result from prime planting dates.”

Livingston said the 2004 season had adequate rainfall through 11 weekly planting dates from Feb. 23 through May 6. “Planting dates provided seed yields that decreased in a linear fashion, from 5,822 pounds per acre on Feb. 23 to 3,227 pounds per acre on May 6, a loss of 36 pounds for every day planting was delayed.”

Livingston said higher late-season nighttime temperatures contribute to yield losses in later planting dates.

“Increased plant residues provide greater protection to the soil,” Livingston said. “Water conserved from increased residue also “contributes to increased seed production.”