Also avoid broadcasting UAN solution in no-till corn, because there's a high risk of losing N to the air and tying up N in the residue, Scharf says. Missouri research has shown a 25-bu./acre yield loss from that practice. Injecting UAN is more efficient, he says.

CONSIDER SIDEDRESSING N
“Sidedressing supplies the N at a time when there is maximum need,” lowering the potential for leaching, says George Rehm, retired University of Minnesota soil scientist. The maximum N-uptake rate by corn occurs when the plants are about knee-high to shoulder-high. On sandy soils and irrigated corn, Rehm recommends split sidedress.

Trials in southern Minnesota from 1998 to 2006 showed no yield penalty for sidedressing N, Rehm says. “Lower yields with sidedressing are almost always associated with late application,” Illinois' Hoeft says. He recommends starting “as soon as you can see the row.”

SKIP ROWS
Save money by sidedressing N in a skip-row pattern, with the injector knives running down every other row, Hoeft says. University of Illinois studies in 1999 and 2000 found no yield penalty from the practice.

Skip-row sidedressing cuts fuel and power costs, and allows you to use a smaller tractor, Hoeft says. And the injector positions can be adjusted to avoid applying anhydrous ammonia in wheel tracks, where it's harder to get a good closing seal. “Be sure to set up the applicator correctly,” Hoeft says, “with every hose the same length.”

EVEN UP APPLICATION
“I'm seeing a lot of trouble with uneven application,” Missouri's Peter Scharf says. “I take a lot of aerial photos in areas that have been very wet, causing N loss, and what I see are streaks in two-thirds of the fields that have N-deficiency symptoms. These streaks indicate uneven applications.”

Potential for uneven N application is highest for spinner spreaders that broadcast ammonium nitrate or urea, followed by anhydrous ammonia and boom-type spreaders that broadcast ammonium nitrate or urea, he says. Broadcast or injected UAN solution has the lowest potential for uneven application.

Spinner spreaders should be regularly checked and adjusted, Scharf notes. Wear on parts, humidity and poor-quality fertilizer all cause uneven application.

On anhydrous ammonia applicators, older manifolds often distribute ammonia to the knives unevenly, Scharf says. “When an older manifold is used, the most important management practice is to randomize the hoses. This means that a row getting a low rate is more likely to be next to a row getting a high rate, which will minimize yield loss.”

On boom-type spreaders, Scharf says, check the distribution pattern at least once a year for hot spots with higher output.

KILL WEEDS EARLY
You might be surprised to know exactly how much N large weeds steal. In 2006 and 2007 trials at the University of Wisconsin, Laboski found that “when weed control was postponed until weeds were 12 in. tall, an extra 100 lbs. N/acre was needed to achieve the same yield as preemergent control. An additional 40 lbs. N/acre was needed when weeds were controlled at a 4-in. height.”

COMPARE COLOR
Plant color sensors can help you gauge N deficiency and fine-tune in-season fertilization. “I think this is the wave of the future,” Scharf says.

Chlorophyll meters, aerial images and other sensing instruments measure leaf color late in the vegetative growth period, when N stress is expressed through reduced leaf greenness. The measurements must be compared to an adequately fertilized reference strip in the field. You'll need a reference strip for every field and every variety.

Nitrogen-deficiency sensing can be used as early as V-6 until pollination, Scharf says. If N deficiency is detected, apply supplemental N as soon as possible — and before silk emergence — says Dan Walters, University of Nebraska fertility expert says. You'll need high-clearance application equipment or irrigation systems equipped for fertigation.

“This is still a developing technology,” says Iowa's Sawyer. “I see it as a good tool to assess N deficiency when things don't go right and there is considerable uncertainty about N losses and additional N application needs,” as in 2008's wet spring conditions.

“There's a lot of interest in this from irrigators,” Mengel of Kansas adds. “We really like it for wheat and sorghum. It's just getting started in corn.”

TAKE ADVANTAGE OF N CREDITS
Account for N contributions from residual nitrate, manure and previous legume crops, such as alfalfa, says Walters. Also credit the N supplied by phosphorus fertilizers that were applied in the spring, he says.

And remember, Camberato adds, that “corn grown in rotation with soybeans requires less N, and the more expensive N gets, the more valuable that rotation is.”

In Iowa, for example, “research over many years has shown that the N rate needed for corn rotated with soybeans is 50 lbs. N/acre less than continuous corn,” says Sawyer.

GIVE YOURSELF A REPORT CARD
Keep good records, Walters says, and use this information to evaluate your N management. One benchmark he suggests is looking at how much corn you produce per pound of N fertilizer. Nationally, the ratio is 1 lb. N/bu. of corn, down from 1.3 lbs. in the late 1970s, he says.