Drainage water management techniques are proving to reduce nitrate releases into ditches and streams –- and now researchers and regulators are teaming up to see if the water-quality benefits can be quantified so farmers can earn money by managing their tile drainage water.
An aggressive research program in Ohio aims to expand the scope of nutrient flow research with drainage water management, and create a mathematical model to calculate the impact of drainage-water management on nitrate and phosphorus losses to surface waters.
Controlled drainage –- also called drainage water management –- employs water-control structures at the outlets of tile mains with removable stop logs, or weirs. Growers can set more stop logs in place to raise the water table beneath their fields in the summer when crops can use the extra water, and in the winter to reduce the amount of water and nutrients leaving the field.
Removing stop logs in the spring and fall allows producers to lower the water table to allow for fieldwork, planting and harvest. In short, the system allows growers to actively manage their water table, both in terms of level and timing.
Controlled drainage has caught the eye of U.S. Department of Agriculture officials who are leading the charge to create a national water-quality trading system.
"In the past, tile drains were just a way to get water off the field," notes Carl Lucero, deputy director of the Office of Ecosystem Services and Markets in Washington, D.C. "The advent of drainage-water management allows you to keep water on your land.
"You're not just letting it flush those nutrients out of the system. With great timing, you can manage those nutrients. We're looking at an evolution, a next phase, at how we can optimize the water and nutrients in the system.
"With the whole notion of trading, we've got to be able to know how well they work, to define and measure those conditions with a reasonable level of accuracy."
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To answer those questions, soil scientists and drainage engineers are zeroing in on the relationship between conserving, or holding back, drainage water and reducing the amount of nutrients released into surface waters.
"If we can reduce the outflow from subsurface drainage systems, then we can reduce the nitrate load," says Dr. Larry Brown of The Ohio State University, who has studied drainage water management systems with Dr. Norman Fausey of the U.S. Department of Agriculture-Agricultural Research Service's Soil Drainage Research Unit in Columbus. "What we found out is that the nitrate-load reduction is going to be proportional to the flow reduction on an annual basis.
"Nitrate is a soluble ion, and it moves where water moves. If we can reduce the off-farm flow of drainage water by 30%, then we can reduce the nitrate load by 30%."
One of the priorities of the research Brown and Fausey are conducting -– as well as studies of controlled drainage throughout the Midwest and Southeast -– is finding out where the nitrate is going. Brown says he and Fausey believe some of the nitrate is moving deeper into the soil profile, or moving laterally through the soil.
Brown adds that conserving drainage waters during the nongrowing season may allow more time for the soil to become satiated. That means water fills more of the small pores and cracks in the soil, not just the larger ones.
Once those relationships are solidified and models are perfected to predict the performance of future drainage-water management systems, the process could be accepted into water-quality trading programs like the one being piloted in Ohio's Great Miami River watershed.
That trading program, developed and administered by the Miami Conservancy District (MCD) of Dayton, Ohio, already has 49 projects in various stages of implementation, predicted to reduce nutrient loads in the watershed by 652,000 pounds, according to Dusty Hall, the district's manager of program development. Buyers have paid an average of $1.44 per pound of nutrient reduction, he adds.
Hall says MCD sees tremendous potential in drainage-water management as a tool for farmers interested in selling water-quality credits.
"We can tell you right away that we can essentially cut the discharge in half," Hall says. "That would make it a no-brainer. The problem was that the model we currently use to calculate the commodity –- nutrient reduction –- doesn't address the practice."
The lack of an accepted model for calculating nutrient reduction spurred MCD to team up with the Ohio Department of Natural Resources, The Ohio State University, the USDA-ARS Soil Drainage Research Unit and the Shelby Soil and Water Conservation District (SWCD) to install four drainage water management systems in the Great Miami watershed.
Each control structure will govern water levels beneath 20 to 25 acres of cropland. Those controlled drainage plots are positioned beside free-drainage parcels. In addition to studying nitrate leaving the controlled and free-drainage plots, the group decided to expand the study to include phosphorus, too.
"Primarily in the past, they've been focusing solely on nitrate," notes Jason Bruns, district administrator for the Shelby SWCD in Sydney, Ohio, who is overseeing the installation. "This time, we're adding another search parameter. We're going to pull samples on a biweekly basis during the growing season. We're looking for more concrete information -– especially on phosphorus –- to build a controlled-drainage module into their trading program."
The data will be the basis for a new module of Ohio's Pollution Load Reduction Model –- often called the "spreadsheet model" –- due for release in 2010.
The Ohio Department of Natural Resources is also helping support a drainage-water management study in the northwestern part of the state through the Lake Erie Conservation Reserve Enhancement Program (CREP).
Ohio is also one of five Midwestern states in which university and USDA scientists are observing 20 demonstration sites that put field-scale controlled drainage systems side-by-side with free-flowing tile systems. Those demonstration sites are being coordinated by the Agricultural Drainage Management Coalition, a nonprofit consortium of drainage professionals and researchers based in Owatonna, Minn.
Brown –- like his fellow researchers carefully watching the demonstration sites throughout the Midwest –- is eager to see whether drainage-water management boosts yield. He points out that it's a difficult question to answer.
"After one cropping season, we've had one site, possibly two, that's shown a small percentage yield increase," he says. "There are some studies that haven't, or at least the yield variability is so great we can't tell. We're looking at least at two more summers before we can say with some confidence whether there's an effect on yield."
Data on both the yield effect and the water-quality effect of drainage-water management will have dramatic impacts on the economics of drainage-water management, notes Charlie Schafer of Agri-Drain in Adair, Iowa, president of the Agricultural Drainage Management Coalition.
"What it has to boil down to for a producer is, 'What's in it for me?'" Schafer says. "We've seen yield increases in the field. That's value. When we can quantify water-quality benefits, these projects could receive more cost-share funds under state and federal environmental programs. That's more value.
"And if we can use an accepted model to show that a particular system reduces drainage by, say, 4.5 inches of water per acre, that's a little over 1 million pounds of water. A nitrate level of 20 parts per million in 1 million pounds of water is 20 pounds of nitrate per acre. That 20 pounds of nitrate per acre could be a tradable commodity when more water-quality trading programs are in place."
Boosting the economic benefits of drainage-water management systems could spur the adoption of an important management practice, says John Kessler, deputy chief of soil and water resources for the Ohio Department of Natural Resources in Columbus, Ohio.
He points out that the impact of reducing nutrient loading in Ohio can be felt in the Great Lakes to the north and all the way down to the Gulf of Mexico to the south, where excess nutrients from a variety of sources –- including farms –- contribute to a low-oxygen hypoxic zone that threatens aquatic life. It's a problem growers can help address.
"We want to be a constructive player in nutrient reduction," Kessler says. "For producers who have the right terrain and drainage systems, we see controlled drainage as a practice that could be economically beneficial and can also provide some water-quality improvement.
"It's one tool that will slow the water down and slow the nutrient load down, plus it helps producers have water available when they need it. It's right in there with conservation tillage and buffer strips and other best-management practices. We're looking for these win-wins that benefit the environment and the farms. This seems like one of them."