DDG Prove a Helpful Herbicide

WASHINGTON - Jun 18/07 - SNS -- Distiller's dried grains (DDGs) left over from creating ethanol could be helpful in reducing herbicide requirements and boost yields of crops such as tomato and turfgrass, say USDA researchers,

Currently, the U.S. Midwest generates 10 million tons of DDGs annually, selling it for between U.S. $85 and $110 a ton for use in livestock feed.

Steven F. Vaughn, a plant physiologist with ARS's National Center for Agricultural Utilization Research (NCAUR) in Peoria, Illinois, notes that DDGs worked best when incorporated into the soil and left to decompose for a few months.

"DDG mulch applied in this manner promoted Kentucky bluegrass growth while inhibiting seed germination of annual bluegrass—which is considered a weed," he says.

Similarly, Vaughn applied DDGs to Roma tomato plots in November 2005, at rates of 1, 2, and 3 kilograms per square meter, and transplanted the crop in early May. At the end of September, the yield was 226 pounds of tomatoes from plots treated with the lowest rate of DDGs and 149 from control plots, which received no DDGs. Nitrogen, phosphorus, and other nutrients from the decomposing mulch probably contributed to much of that yield increase. At the higher DDG rates, however, plants grew large but did not yield as much fruit as the low-DDG plants did. That's a symptom of too much nitrogen, Vaughn points out.

"Weed-seed inhibition is a bit more complicated," adds Mark A. Berhow, an NCAUR chemist. Using various analytical methods, he's trying to identify, measure, and monitor the yearly fluctuations of DDG chemicals that may have inhibited germination in crabgrass, chickweed, annual rye, and other weeds studied.

So why wasn't growth of the tomato plants inhibited? One possibility may be that they were planted in the treated plots as seedlings rather than as seed, which may be more sensitive to the mulch, Berhow says.

The situation was a bit different for potted ornamentals. Transplanted plugs of rose, coreopsis, and garden phlox benefited from the DDG mulch's suppression of chickweed and other weeds—but only when it was applied to the soil's surface. "When mixed into potting soils, DDGs were toxic to the ornamentals," reports Rick A. Boydston, an agronomist with ARS's Vegetable and Forage Crops Research Laboratory, Prosser, Washington.

Besides weed inhibition, Berhow is examining DDGs for phytosterols (added to some margarines), lecithin, and other health-promoting substances. Antioxidants are of particular interest for their ability to neutralize cell-damaging molecules called "free radicals."

NCAUR chemist Rogers E. Harry-O'kuru is examining processing methods for removing economically important materials from the DDGs, such as phytosterols and oil (DDGs are about 10% corn oil by weight), which can be made into biodiesel.

Vaughn, meanwhile, plans on expanding the turfgrass studies. He'll also try the mulch with Swiss chard, a relative of beets whose leaves may flourish with the added nitrogen.

ARS has applied for a patent on the mulch and is negotiating terms for the scientists to collaborate with an Illinois-based turfgrass company.