David says that ripping out all of the drainage tiles is not a viable option. “Creating wetlands and reservoirs such as Lake Shelbyville can remove nitrate by holding the water back and letting natural processes remove it, but that’s not a solution. It’s expensive and we can’t flood everyone’s land to stop nitrate. That’s not going to happen.”

“The problem is correctable but will take a concerted effort to change the outcome, with some of the solutions expensive. Installing small wetlands or bioreactors at the end of tile lines that remove nitrates before they flow into the ditch do work, but would cost thousands of dollars per drain. Who’s going to pay for that?” David says.

Cover crops can hold the nutrients so they are available in the spring, and are reasonably cheap, David says, but can increase the farmer’s risk for the following crop. “So if a farmer plants a cover crop and his neighbor doesn’t, he may be at a disadvantage.”

David believes that the system can be improved by focusing conservation efforts on the areas of the country that are contributing the most nitrate loss and establish an incentive program for farmers to utilize one or more practices known to reduce nitrate losses from tile lines.

Encouraging farmers to apply the right amount of N in the spring rather than the fall (or to sidedress), establishing a more complex cropping system which incorporates cover crops or even biofuel crops such as miscanthus or switchgrass when there are markets and installing end-of-pipe solutions such as controlled drainage, bioreactors or wetlands are some of the efforts David suggests would help reduce nitrate loss.

“Until we change the payment system beyond our focus on yield alone, we’re not going to make much progress in reducing nitrate losses. We also haven’t developed voluntary programs that really address nitrate loss from tiles, and we need to provide more incentive and cost-share funding to producers. We may also need regulation. We could say to producers, ‘If you buy fertilizer, you’ve got to do one of these five things,’” he says. “There’s no one solution.”

Dennis McKenna of the Illinois Department of Agriculture says “David’s work is an important contribution in helping producers and policy makers identify the most critical areas. Hopefully this information will be used to develop a focused national and state effort to reduce nutrient losses to surface water.”

Sources of Nitrate Yields in the Mississippi River Basin was published in the September-October 2010 issue of the Journal of Environmental Quality.

This research was funded by the National Science Foundation Biocomplexity in the Environment/Coupled Natural-Human Cycles Program. Authors in addition to David were Greg McIsaac from the University of Illinois and Laurie Drinkwater from Cornell University.