The Des Moines Register

July 7, 2001

Why record nitrates in Raccoon?
The answer to L.D. McMullen's question is Iowa's intensively cropped landscape.

By DENNIS KEENEY

The Raccoon River at its confluence with the Des Moines River in Des Moines established a new record for nitrate-nitrogen (June 7 Des Moines Register). L. D. McMullen, general manager of the Des Moines Water Works, is asking why.

He is right to be concerned. Nitrates in drinking water have been linked to bladder and ovarian cancer in older Iowa women, according to a recent scientifically reviewed study.

The answer to McMullen's question -Iowa's intensively cropped landscape -is clear, yet difficult for many to admit.

The Raccoon River watershed historically has been one of the highest nitrate-yielding watersheds in the United States. (The Iowa River runs a close second.) Why? Because the conditions in the watershed are ideal for high nitrate leaching to the groundwater and on to the streams and finally to the river.

The watershed has high organic matter, fertile soils that supply nitrate even when crops are not growing, much of the land in row crops, cropland, a concentration of animal-confinement units and a preponderance of land drainage by tiles.

Nitrates in the river have been steadily increasing since the mid-1950s. Recent data from Bob Libra of the Iowa Geological and Natural History Survey group in Iowa City has shown a two-to three-fold rise in nitrates in most rivers in Iowa, especially those predominantly draining land in row crops. In fact, he was able to predict fairly closely the nitrate-nitrogen concentration by considering only the percentage of land in row crops.

It appears that "best-management practices" to controlling nitrate leaching from row cropping, while very well-intended, have not yet shown results. The Raccoon River Watershed Project approach -which provides technical assistance to lessen the application of fall fertilizer, to use the late spring soil nitrate test and to apply animal manure to the land at a judicious level - probably has not had the opportunity to reach its full level of achievement. But so far the results have little to show for the effort expended. Why?

Changing agriculture practices is no more simple than changing other human habits and foibles. And we do not realize and appreciate that the nitrates in the river this year may have come from cropping seasons a few years past. The issue is further complicated by weather patterns and perhaps even by shifts in climate caused by global climate change.

Further, we do not have a way to grow our crops without the use of nitrogen, either from the air as practiced by the soybeans, or from the soil (via fertilizer, manure and organic matter) by corn. Instead, we push the soil- plant system harder by increasing the amount of land being cropped, by providing more efficient drainage, and by increasing concentrations of animals.

Minnesota research by Gyles Randall and David Mulla has been very illuminating. They found that tile drains contribute the bulk of the nitrate to surface waters in the Mississippi River basin. They found little difference overall between nitrate loss under corn following soybean or soybean following corn. While nitrate concentrations under continuous corn were about 30 percent higher than under rotated crops, the loss of nitrate was about the same since less drainage occurred with continuous corn. (However, the plots in alfalfa or Conservation Reserve Program grasses lost virtually no nitrate.)

In the Minnesota research, the type of tillage used also did not have an effect on nitrate leaching. Fall application of nitrogen gave about 36 percent higher loss of nitrate than did spring application, and much more nitrate was lost from application of nitrogen fertilizer in excess of crop needs. All of the tools are in place to keep nitrate loss to a minimum, but overall, nitrates still are increasing. Nitrate will leak from any row-crop system. We are deluding ourselves to think otherwise.

There are probably only two alternatives to lower nitrate levels in the Raccoon River on a consistent basis: Move some of the land out of row crops and into a more sustainable perennial agriculture (an agriculture that includes year-around grasses, trees and legumes), and add wetlands and buffer strips. The alternative would be to grow corn at low nitrogen levels and suffer the consequences of uneconomical yields.

The corn-soybean system, like much of intensive Midwest agriculture, is not based on sustainable principles. Either we find policies that shift it to a more sustainable, less polluting system, or we continue to ask why.

DENNIS KEENEY is emeritus professor at Iowa State University in Ames and senior fellow, Institute for Agriculture and Trade Policy, in Minneapolis.