Farmers could be restricted in their use of nitrogen if public anxiety accelerates.
Nitrogen has exceeded health standards in some drinking water supplies and has been linked to hypoxia in the Gulf of Mexico. Farmers are taking most of the heat.
"Nitrogen is a natural-occurring material found in soil organic matter and human and animal waste, as well as in fertilizer," notes University of Minnesota soil scientist Gyles Randall.
"Therefore, trying to regulate its use as a fertilizer would be complex. However, if the public shows growing concern, we could see restrictions. Farmers might be required to file nutrient management plans as is now done along areas of the East Coast."
Randall says such plans could include phosphorus and other elements along with nitrogen.
He notes that there could be timing restrictions, such as no fall application of N, or application only after a certain date in the fall. That's the case in Europe.
What can farmers do to head off restrictions?
"The first step is to get past the denial stage and recognize that agriculture does have an impact on the amount of nitrogen in both drinking water and streams," says Randall.
"We have tended to apply too much 'insurance' nitrogen and that extra is what gets us in trouble. We need to take full credit for the nitrogen supplied by manure, by soybeans and other legumes, and by that put on with herbicides."
Following a dry year, when less N is taken up by crops, Randall recommends a soil nitrate test to determine carryover, especially when corn follows corn.
"That test won't work in wet years in the more humid areas, but it should be effective in dry years," he explains.
Crop consultants are implementing various measures that make nitrogen use more efficient and economical.
Phil Cochran of Cochran Agronomics, Paris, IL, recommends that application rates be based on soil type, tillage method, N material used and application timing. He says credits for manure and/or legumes usually make up part of that N.
His clients rarely apply more than 160 lbs/acre N as fertilizer. Often, it's less. Yet yields are excellent for the soil types and locations.
In spring, Cochran takes a presidedress soil nitrate test to decide whether any sidedress is needed. In fall, to monitor N sufficiency, he takes a stalk nitrate test to determine if plants received too much or too little N.
"I emphasize that the organic matter in the soil produces part of a crop's nitrogen needs," Cochran points out.
"It's roughly 20 lbs of N for each percent of organic matter, but tends to self-adjust based on growing conditions. If conditions are good, the soil releases more N, and vice versa."
At Greencastle, IN, Mel Nicholson, Nicholson Consulting, monitors N three times during the year. He does a spring soil nitrate test on fields receiving manure or sludge, an ear-leaf tissue test at tasseling on all cornfields, and a stalk nitrate test in fall. The leaf and stalk tests help determine the next year's rates.
"Where manure has been applied, fields may need anywhere from no additional N to nearly a full rate," Nicholson reports. "Other fields usually require 135 to 160 lbs/acre."
Nicholson adjusts rates based on time of application. Lowest rates are with sidedressing, which he says is the most efficient timing.