Their findings for the Morrow Plots are confirmed in published literature from field studies that included initial soil organic carbon data. "In numerous publications spanning more than 100 years and a wide variety of cropping and tillage practices," said Boast, "we found consistent evidence of an organic carbon decline for fertilized soils throughout the world and including much of the Corn Belt besides Illinois."
"We don't question the importance of nitrogen fertilizers for crop production," said Ellsworth. "But, excessive application rates cut profits and are bad for soils and the environment. The loss of soil carbon has many adverse consequences for productivity, one of which is to decrease water storage. There are also adverse implications for air and water quality, since carbon dioxide will be released into the air, while excessive nitrogen contributes to the nitrate pollution problem."
Because soils differ in their capacities to supply nitrogen, Khan and his colleagues stress the need for soil testing, ideally on a site-specific basis, as a prerequisite to soil-based nitrogen management that optimizes fertilizer rates.
In comparing USDA data for Iowa and Illinois, the two states that rank highest in corn production, they found that from 1994 to 2001, annual grain yields in Iowa averaged 1.7 billion bushels with 740 thousand tons of nitrogen, as comp
|Contact: Debra Levey Larson|
University of Illinois at Urbana-Champaign