Iowa farmer Tim Smith reduced the nitrates in his tile drain water by 29% compared to the stream levels it drains into.

Already known for being very conservative with his nitrogen rates (0.8 lb./bu. of yield goal) and using BMPs, he was surprised that his 2011 tile nitrate benchmark readings were higher than the stream’s nitrate content. “The first year I enrolled in the Mississippi River Basin Initiative (MRBI) program, my farm’s tile water had higher nitrates than the stream where it drained,” he says.

“My daughter lives near Des Moines and drinks water downstream from my tile lines’ discharge. I was shocked to think that what I thought were sound agronomic practices like ridge-till, N application rates below 150 pounds per acre and MRTN nitrogen calculations were contributing to poor water quality for her and others,” Smith says. MRBI is a USDA-NRCS program in targeted watersheds to reduce agricultural impacts on the Gulf of Mexico dead zone.

Smith jumped into action in 2011, adopted strip-till, flew on cereal-rye cover crops, delayed his fall nitrogen applications to spring and sidedress, installed a bioreactor on some fields, and enrolled in the Mississippi River Basin Initiative (MRBI) offered to Boone River watershed farmers. “Water-nitrate level reductions are possible with proven practices, without reducing yields,” he says.

He also uses a cornstalk nitrate test and V10 leaf tissue test to assess in-plant N levels during and after the growing season. “You need to do these test for 5 years to develop a feel for what you did,” Smith says.

After implementing these practices, peak nitrate levels in Smith’s tile outlets were half those in Eagle Creek, based on 2012 and 2013 tests (see bar chart). The cereal rye is particularly effective in reducing water nitrates because it “nabs them when crops aren’t there to use them,” says Bruce Voigts, MRBI coordinator for the Boone River Watershed that surrounds Smith’s 850 acres.

 “Cover crops improve soil structure and stabilize yields in challenging weather. And they sequester a lot of nutrients that would otherwise leave the farm,” Smith says. “Cereal rye grows when it’s as cold as 38 degrees, so I see it in March.”

“Later in the year, it releases at least 30 pounds of N per acre later, based on actual dry-matter nitrate measurements that MRBI took from my cover crops. People ask me what it costs to seed a cover crop ($25/acre), and I ask them what it costs them not to plant one, in lost nutrients and eroded soil. A study by Iowa State Economist Mike Duffy figured you lost $10-15 per acre per year in soil loss alone in our county here.” When you add to that losses in land quality, water quality and fertilizer, the state average is $340 per acre, although each situation is different.”