By CELESTE BAUMGARTNER
Ohio Correspondent

URBANA, Ill. — The most heavily tile-drained areas of North America are the largest sources of nitrate to the Gulf of Mexico, leading to seasonal hypoxia, said a study by scientists from the Uni-versity of Illinois and Cornell University.

In the summer the dead zone caused by hypoxia spanned more than 7,000 square miles. There is increasing pressure from the U.S. EPA to do something about that, said Mark David, a UoI biogeochemist who has been studying the issue since 1993.

“Drain tiles allow the water, especially in the late winter and spring, to drain out of the soils, but nitrate is not held very well in soils,” he said. “When the water drains out if there’s nitrate, it is easily moved with the water. That helps to move the nitrate from the field into a nearby ditch and then into a river.”

Ideally there wouldn’t be much nitrate in the soil then, but fall fertilization worsens the situation, David said. There are no roots in the soil at the time. Corn doesn’t start taking nitrogen until June.
“So, anytime we have big rain events in March, April and May we can move large amounts of nitrate,” David said.

Farmers are not to blame, he opined. They are using the same amount of nitrogen as they were 30 years ago and getting much higher corn yields. The agricultural system is just “very leaky.”
Solutions are varied and some are expensive, David said. Wetlands installed at the end of a tile line can remove nitrate by holding back the water and letting natural processes remove it. A two-acre wetland would be needed for a 40-acre field – and wetlands cost a fair amount to build. “A number of bioreactors have been built in Illinois and Iowa,” David said. “The simplest version of that is a trench at the end of the tile line filled with wood chips. The wood chips remove the nitrates by de-nitrification and it becomes anaerobic and goes back to the atmosphere.

“When wood chips get really decomposing, that is perfect for removing nitrate, so it doesn’t take that long. In a wetland it takes longer because (de-nitrification) is occurring in the sediment at the bottom.”

Establishing more involved cropping systems are a possible partial solution, he said. The use of cover crops would bind any nutrients until the following year. Biofuel is another approach. Miscanthus and switchgrass are efficient at removing nutrients and once established, they can be harvested for 10 years.

Yet, making a serious difference in nutrient loss from agriculture will take big changes and big money, David said.

“Right now we give farmers every incentive to produce the highest yield. Our payment system is geared to producing – you are paid on yield,” he said. “The National Resources Conservation Service has some incentive for various conservation programs, but they are very small programs compared to the commodity program.”

Farmers will need to be paid for something other than yield, David said; they would need to be paid for a range of practices that are known to reduce nitrate loss.

“It’s not a simple problem when you have watersheds across the Corn Belt that are 80-95 percent in corn and soybeans,” David said. “To really reduce nutrient loss, it can’t be one farm here and there; it is going to take a major effort. The question is, who is going to pay for that?”