A team of ISU students and faculty discovered that applying compost before grass seed at road construction sites saves money.

The group is conducting a $189,000 three-year compost study funded by the Iowa Department of Natural Resources and cosponsored by the Iowa Department of Transportation, said Tom Glanville, associate professor of agricultural and biosystems engineering and a project leader for the research.

The DNR, in an attempt to divert waste from landfills, has encouraged home owners and businesses to compost waste materials into a product that can be used to improve soil quality and help plants flourish, he said.

But what to do with the resulting compost becomes the next problem for the state, Glanville said.

“As of today, the state has close to 80 facilities, handling 325,000 to 350,000 tons of organics per year and turning that material into a compost product,” he said. “We have a good thing, but we need to have more markets for it.”

The DOT had its reasons for supporting the project, too, Glanville said.

“Their motivation is to reduce erosion and water-quality impacts following new road construction,” he said. “They have to meet federal erosion control requirements set forth by the Federal Highway Administration.”

Currently, the DOT plants grass seed directly into the compacted subsoil that’s left after road construction or puts down a layer of top soil before seeding. DOT personnel often return to sites to reseed and apply herbicides, Glanville said.

In the summer of 2000, ISU researchers set up research plots at the Highway 18 interchange at I-35 near Mason City, where the DOT recently had completed construction, Glanville said.

After the first summer’s data was analyzed, he said, the researchers found the absorbent compost produces less runoff than the compacted subsoil. This means reduced potential for erosion and water-quality impact. The compost is also a better growth medium than compacted subsoil.

Glanville said the researchers also discovered an unexpected benefit – fewer weeds.

“It turns out that the compost has undergone a heat treatment during the natural composting process,” he said. “That heat tends to kill weed seeds.”

The compost also prohibits most weeds in the subsoil from emerging.

“The weeds have to fight their way up through that blanket before they can begin to compete with the grasses planted,” Glanville said.

The reduction in weeds will reduce the money the DOT needs to spend on herbicide application, he said, giving the department an economic incentive to use the compost.

“Besides the fact it’s a good thing for society, you’re diverting materials from landfills,” Glanville said.

“That’s good. You’re cutting down on erosion. You’re cutting down on runoff. That’s good from a water-quality standpoint. But none of those things pay the bill. Reducing the cost of weed control – that could help pay the bill.”

Jeff Geerts, program planner for the land quality and waste management assistance division of the DNR, said the compost would give Iowa’s food producers a way to dispose of the more than 3 million tons of byproducts that are produced each day.

“So there’s a large potential for expanding compost efforts in the state,” he said. “If we continue to get the results shown in the study so far, we will strongly push for compost to be used in greater amounts by all state agencies.”