As corn acres rise, so does the amount of nitrogen Corn Belt farmers use. That's likely to add to the amount of nitrogen runoff that scientists say already finds its way to the Gulf of Mexico and contributes to the 5,000 square mile "dead zone" there.

A new book - From the Corn Belt to the Gulf, written by 25 scientists from around the country - discusses how farmers can make management changes to reduce the amount of nitrogen leaving their land in runoff.

The book concludes that greater precision in fertilizer use, wetlands restoration, production of perennial crops such as switchgrass, and other conservation innovations could significantly reduce low oxygen level in parts of the Gulf of Mexico that threatens ecosystems and commercial fisheries.

"While Corn Belt watersheds account for less than nine percent of the land that drains into the Mississippi, land in these watersheds contribute about one-third of the nitrogen reaching the Gulf," says Don Scavia, a University of Michigan scientist and editor of the book.

An especially large amount of nitrogen comes from five watersheds in three states: the Great Miami River watershed in southwestern Ohio; Upper Illinois River watershed in Illinois; and the Des Moines River, Iowa River and Skunk River watersheds in Iowa.

"Farmers are eager to share the cost of cleaner water, but two out of three farmers are rejected when they offer to improve Mississippi River water quality due to funding shortfalls," sas Scott Faber of Environmental Defense. "Renewal of farm policies in the 2007 Farm Bill is a chance to reward - rather than reject - farmers when they take steps to help rivers like the Mississippi."