Feeding plants nitrogen fertilizer makes sense, Richard Mulvaney says. But fertilizer, like the food we eat, needs to be used in moderation. Too much is not good, the University of Illinois soil fertility specialist says.

There are four major points to remember about no-till soil fertility, Mulvaney says.

• Synthetic nitrogen fertilizers are an essential part of modern corn production.
• Soil — not the fertilizer — is the main source of nitrogen.
• Good soils have more nitrogen-supplying power. Because of that, they need less nitrogen fertilizer.

Too much nitrogen reduces fertilizer efficiency, cuts profits, promotes the loss of residue carbon and burns up soil organic matter.

Soils differ in how much nitrogen they can supply, and a given soil can change over time depending upon how it’s managed.

“We need a way to measure how much good fertilizer does in feeding the crop,” Mulvaney says. “One way is with the fertilizer nitrogen uptake efficiency parameter.

“Think of this as a mileage meter. It indicates the percentage of fertilizer nitrogen harvested in the grain.”

Nitrogen Efficiency

• To calculate fertilizer nitrogen uptake efficiency:

• Multiply an average content of nitrogen in corn times the difference in yield with and without fertilization.
• Divide that fraction by the pounds of nitrogen applied per acre.
• Multiply that by 100 so you end up with a percentage.

The key to this parameter is the difference in yield, Mulvaney says. The higher the difference in yield, the higher the efficiency. That’s what data from a number of Illinois response…