An early May storm that soaked Paulding County cleared up nearly a day ago, and the drains buried beneath Terry McClure’s farm fields are doing their job.

The white plastic pipe that funnels water into a ditch along County Road 48 helps keep the 4,000 acres of soft, red winter wheat from becoming a swamp.

Drainage tiles are doing the same thing beneath thousands of fields across the county and state.

But this pipe is different. It is fitted with a tube that sucks a portion of the drain water into a sampling bottle.

A few yards away is another device that samples stormwater that flows along the top of the field toward the same ditch.

For at least the next three years, rainwater runoff from this field and 29 others across Ohio will be collected and tested. They’ll help a team of scientists from Ohio State University and the U.S. Department of Agriculture measure how much phosphorus it contains.

Phosphorus is a byproduct of manure and fertilizers in farm runoff water. It’s the stuff that is finding its way into Ohio lakes, including Lake Erie, Buckeye Lake and Grand Lake St. Marys, where it helps blue-green algae grow into toxic blooms that threaten wildlife and billions of dollars in tourism.

The study could be key to devising plans to reduce phosphorus runoff from farms.Farm groups, including the Ohio Soybean Council, the Ohio Corn & Wheat Growers Association and the Ohio Farm Bureau Federation, have matched a $1 million USDA grant to fund the effort.

“We have a big audience. A lot of people are watching this very closely,” said Kevin King, a hydrologist in the U.S. Department of Agriculture’s Agricultural Research Service. Scientists have long known that farms are a prime source of dissolved phosphorus that winds up in lakes.

Heavy spring rains in 2011 flushed 473 tons of phosphorus down the Maumee River to Lake Erie, according to stream monitors kept by Heidelberg University’s National Center for Water Quality Research.

That summer, a record algae bloom stretched from Toledo to Cleveland. Last year, the bloom was 90 percent smaller because of near-drought conditions that resulted in just 69 tons of phosphorus reaching Lake Erie.

Among the questions that continue to bedevil researchers are how much phosphorus each farm contributes and which methods to keep it out of streams work best. The new study should help.

“It’s pretty important from several respects, not the least of which is there just hasn’t been much of this work done,” said Peter Richards, senior research scientist at Heidelberg.

Elizabeth Dayton, an OSU soil scientist, said she wants to see how different soils and crops affect the amount of phosphorus in runoff.Dayton and King both said they’d like to get samples from fields that grow wheat, corn and soybeans in subsequent growing seasons. Each field is monitored for organic content, soil texture and phosphorus amounts.

Some farmers already use conservation practices to limit fertilizer runoff, including planting grass along ditches to help soak up phosphorus. Others use soil tests and computerized field mapping to try to limit the amount of fertilizers to what the crops require.“What we don’t know is how much (phosphorus) savings come with each practice,” Dayton said.

Samples taken from these types of fields should help determine which is most effective at containing phosphorus, the researchers say.

Farmers who participate in the study will have to supply information about drainage practices, manure and fertilizer applications and when they plant and reap their crops.

McClure said he’s happy to participate.“We need to better understand what our part of the problem is,” he said.One of the ultimate goals of the research is to refine Ohio’s phosphorus risk index, which many farmers use to estimate how much fertilizer or manure they can safely put on fields to help grow crops.

“We’d like to give the farming community not just one thing to do but about five things that would help,” said Jeff Reutter, the director of Ohio State’s Sea Grant Program and Stone Laboratory on Lake Erie. “The one that I promote probably the most is incorporating the phosphorus into the soil rather than simply spreading it on the surface.”

Dayton and King said it will take several years of work to come up with final recommendations and data showing phosphorus concentration in runoff.Until then: “We’ll have a microscope on what’s coming off this field,” Dayton said.