Using flame cultivation to control weeds could make producing organic soybeans a profitable venture for those Southern growers willing to invest the extra time and money in this value-added market. That's the conclusion of an ongoing study at the Delta Research and Extension Center in Stoneville, Miss.

It's more complicated, more labor-intensive, and more expensive per acre, but with organic soybeans bringing from $7 per bushel for split and damaged beans to $22 per bushel for high-quality soybeans, the reward may justify a few risks.

“Organically grown soybeans can be produced economically in the Mississippi Delta, especially if early planting is used in conjunction with flame cultivation, says Dan Poston, a weed scientist at the Delta Research and Extension Center. “I certainly wouldn't use this system unless it was economically motivated. In addition, I don't expect this system to take over any large acreage, but it could represent a profitable niche market for some producers.”

The obvious advantage to organic soybean production, aided by flame cultivation, is the potential for higher net returns per acre. On the other hand, this production system is complex, expensive, dangerous, and extremely labor intensive if hand weeding is used to supplement flaming.

To see just how economical this production system would be for Delta soybean growers, Poston is field-testing the economics of a transition from traditional soybean production to organic production over time in a worst-case weed control scenario using flame cultivation for weed control.

His research plots are infested with annual morningglory, hemp sesbania, prickly sida, sicklepod, and annual grasses such as barnyardgrass.

What he's found is a system that shows potential; it could find a fit on some Southern acres. In his tests, however, the silty-clay loam soil commonly used for soybean production didn't fare as well as silt loam soils did under this production system. The silt loam soils were far less cloddy than soils that have traditionally been used for soybean production, and tillage, bed preparation and drainage were much easier in the silt loam fields, Poston reports.

In his study, Poston compared systems using no weed control, flame cultivation, conventional cultivation, and a Roundup Ready weed control system. Precision parallel and cross flamers were used in flame-cultivated plots. The parallel flame cultivator is used prior to soybeans reaching 12 inches tall, and shoots a flame parallel to the soybean rows, while a shield protects the soybean plant. In comparison, the precision cross flamer is used after soybeans reach 12 inches tall, and is similar to a layby rig with burners oriented perpendicular to the soybean row to shoot flames up under the soybean plants.

Weed control with flame cultivation alone in all of the tests ranged from 75 to 93 percent, and was equal to the best treatments except in the case of pigweed. Soybean yields in April-planted tests on silt-loam soils ranged from 63 to 65 bushels per acre, and were similar in all treated plots.

“Weed control with flame cultivation was generally higher than the level of control achieved with cultivation only, and all weed management treatments improved soybean yield compared to the untreated test plot. Annual morningglories and annual grasses were the weeds most difficult to control with flame cultivation. Annual grass control also tends to be more of a problem in later-planted soybeans,” Poston says. “Although morningglory was difficult to control in one study with flame cultivation, the level of control achieved was similar to the level provided by the Roundup Ready weed control system. In addition, the level of sicklepod control with flame cultivation was 93 percent, compared to 83 percent with a conventional herbicide system supplemented with cultivation.”

Flame cultivation is more costly than conventional cultivation. Operating at three miles per hour, it costs $21.44 per acre for the precision parallel flame cultivator treatments and $39.81 per acre for the precision cross flame treatments. The cost of conventional cultivation is estimated at less than $7 per acre.

“Higher labor and tractor costs were estimated for flame cultivation than for conventional cultivation because of the added time needed to fill up propane tanks and adjust equipment in the field,” Poston says.

“Operating flamers at 4 miles per hour can reduce the cost of operation. At this speed, the cost of operation is estimated at $15.65 and $29.58 per acre for parallel and cross flamers, respectively. However with some weed species, increasing speed may reduce weed control or require multiple trips across the field.”

Effects of planting date

Planting organic soybeans in April will increase yield potential, but it will also increase weed control costs, according to Poston's research.

He says, “Early production system soybeans have the opportunity to establish a competitive advantage over several summer annual weeds, especially annual grasses and to begin to shade the row middles before many summer annual weeds become established.

“In contrast, summer annual weeds emerged simultaneously with the crop in May-planted studies, and labor to remove these weeds was extremely costly.”

Because planting in early April allows the soybeans to emerge before many summer annual weeds, the crop can gain a competitive edge over the weeds. In comparison, planting organic soybeans in May allowed the weeds to more readily establish a competitive advantage over the crop, making it more difficult to achieve broad-spectrum weed control with flame cultivation, Poston says.

“Soybean vegetative growth and canopy closure occur much faster with May planting dates than with April planting dates. Because the May-planted soybeans grew faster, fewer flame cultivator trips were required in May-planted soybeans, than in April-planted soybeans,” he says.

According to Poston's research, season-long weed management costs using flame cultivation alone were $126 per acre for April-planted soybeans and $83 per acre for May-planted soybeans. However, soybean yields were 11 bushels per acre higher on average for the April plantings than for May plantings.

“With May plantings, the extra level of weed control provided by flame cultivation compared to conventional cultivation is more valuable, making flame cultivation the more efficacious and profitable system for these later-planted soybeans grown for the organic market,” he says. “Assuming an estimated selling price of at least $12 per bushel for the organically grown soybeans and an average selling price of $6.56 for the non-organic soybeans, net returns with flame cultivation could greatly exceed net returns from other soybean production systems.”

Poston's flame cultivation studies, as well as flame weed control research in cotton, are being underwritten by the Propane Education and Research Council, which believes that by 2010 the agricultural industry will recognize propane as a preferred energy source.