An Iowa State University report shows applying nitrogen fertilizer at certain levels to corn and soybeans helps maintain carbon in the soil, bringing a range of environmental and production benefits.

ISU agronomy professor Michael Castellano co-authored the study and says there’s long been disagreement among scientists and farmers over fertilizer’s impact on the soil.

“A lot of folks are under the impression that nitrogen fertilizer, particularly anhydrous ammonia, may be bad for soil health, it may degrade the carbon and the organic matter in our soil,” Castellano says. “We found just the opposite in our studies across the state, all the way from northwest Iowa to southeast Iowa.”

Researchers collected soil samples from the four ISU research farms at Sutherland, Ames, Chariton and Crawfordsville in 1999 and 2000 and then again 15 years later after each site received regimented applications of nitrogen fertilizer.

“We observed that nitrogen fertilizer was in fact very important for maintaining and improving soil health,” Castellano says. “The reason why it maintained or improved soil health is because it’s critical to increase the production of crop residues in the soil.”

The test compared soil health for various levels of fertilizer applications — be it too low, too high or at optimum levels.

“We think by looking at the range in nitrogen fertilizers, we really cleared up this uncertainty about whether nitrogen fertilizer is good or bad for soil health,” Castellano says. “We found that it’s good right up until that optimum level but beyond that, there’s just no improvement to be seen from adding more.”

Funding for the study came from the U.S. Department of Agriculture’s National Institute for Food and Agriculture.

See the full report here.

Reporting by Pat Powers, KQWC, Webster City