Scientists looking for new uses of ethanol byproducts have discovered that distillers dried grains (DDGs) have potential as an environmentally friendly herbicide or as a fertilizer, or perhaps both.
DDGs are produced when corn is converted into ethanol. In the Midwest, ethanol producers generate about 10 million tons of DDGs annually, according to the U.S. Department of Agriculture. Farmers buy most of it for about $80 a ton and feed it to cows and other ruminants, but the increasing production of ethanol might create a DDG surplus.
Dr. Rick Boydston, agronomist with the USDA’s Agricultural Research Service in Prosser, Washington, has been testing DDGs for weed control in ornamental plants, including roses, coreopsis, and perennial phlox. He found that when DDGs were incorporated into the soil, they killed the plants as well as the weeds, but when they were applied only to the soil surface, they controlled weeds without harming the ornamentals. The weeds used in his experiments were annual bluegrass and chickweed.
Boydston said scientists don’t yet know what is causing the herbicidal effect. The DDGs might increase microbial activity in the soil or release toxins, carbon dioxide, or other compounds. When large amounts are applied, the temperature of the soil increases. For weed control, DDGs need to be applied at a rate of about two tons per acre, he said.
Dr. Steve Vaughn, horticulturist with the Agricultural Research Service in Peoria, Illinois, said the product does appear to inhibit dicot weeds, but the herbicidal effect may be temporary. After a time, DDGs appear to provide nutritional benefits and promote plant growth.
"I am much more interested in the fertilizer aspect," he said.
For his tests, Vaughn has been modifying the DDGs. Other value-added products, such as phytosterols, which are used in margarines to lower cholesterol absorption, can be extracted along with a considerable amount of oil that is left. The resulting product does not have the objectionable fermented odor that DDGs have, and it does not go rancid, but it still has potential as a fertilizer, with an NPK rating of 6-2-1.
When he applied it to Roma tomatoes, the treated plots produced 52 percent more tomatoes than the untreated. In tests with turf, Vaughn compared the DDG extract with urea. After three months, the urea plot looked as if it had never been fertilized, but grass in the DDG plot was greener and had more growth, he reported.
Vaughn believes there could be a big potential market for DDGs as a fertilizer for high-value crops, and that it would be a higher value use for DDGs than animal feed. DDGs have microbial activity and, if left wet for a time, can develop mycotoxins that are harmful to animals but not to plants. The oil content also may be high for animals.
A DDG-derived fertilizer could be used in organic production as long as it could be verified that the corn had not been genetically modified, he said.
Boydston said he’s going to test DDGs as a nutrient source in potatoes in Washington State this year. The DDGs will be applied before the potatoes are planted, to allow the herbicidal effect to wear off.
He has not tested the material on tree fruits but has noticed that DDGs also have a temporary acidifying effect. He wonders if they could be used as a weed-suppressing mulch for blueberries, which grow best in acidic soil.
Whether DDGs would be economically feasible would depend on how close the farm was to an ethanol plant and how effective the DDGs might be on a broad spectrum of weeds, he noted. The product is bulky and would be expensive to haul.
Boydston said a new plant has opened in Hermiston, Oregon, to convert corn into ethanol, but it produces wet distillers grains, which are fed directly to cattle.
He expects that DDGs might have the most potential in organic agriculture, because organic growers are used to using bulky, low-nitrogen sources and applying them in large quantities. However, if there are local sources of DDGs and the price of commercial fertilizers increases, they might have some appeal to growers.
"It would depend on the price, and you’d have to haul this stuff and spread it, and it’s pretty bulky," he said, "But if conventional fertilizers get outrageous, maybe it could be used in that situation, too."
Although there’s been a major push to produce ethanol from corn as an alternative fuel, Vaughn noted that it is not an efficient process. It requires one unit of energy to produce 1.3 units of energy in the form of ethanol. Producing biodiesel from white mustard is far more energy efficient in terms of the energy that goes in and comes out. For every unit of energy used in its production, 3.5 units are generated.
Seed meal, a byproduct of converting mustard into biodiesel, is also being studied as a herbicide and gives good suppression of weeds, Boydston said. White mustard is mainly grown as a condiment, but if the seed meal had a high enough value, it might be more feasible as a crop for oil production.