Improving fertilizer efficiency has become a necessity rather than an option, says Joe Varco, professor of plant and soil sciences at Mississippi State University.

“It costs money to fertilize, and not only does it cost money, but the EPA is watching what we do,” says Varco. “They’re looking at growers and looking at nitrogen and where it’s going. So we’ve got to improve the efficiency when we put it out.”

Nitrogen represents 35 to 40 percent of the input costs of growing corn in Mississippi, he adds. “Our growers are using 240 pounds or so of nitrogen. What else costs that much and gives you that kind of yield boost. Irrigation or weed control might, but tillage and weed control probably won’t.”

So strategic applications of nitrogen can make a difference, says Varco.

“I like to call it strategic nitrogen fertilization. We begin with the fertilizer source but this also includes availability. It’s easy to say you should be using a certain source, but you might not be able to get it. Price also is very important.

“Another factor is trying to optimize the nitrogen rate. Gone are the days when you can put on that little bit of extra in case you need it. We need to get closer to hitting the ‘bullseye” with the correct rate. That’ll maximize your economic return because that’s really what you want. You’re trying to maximizing outputs relative to inputs, and fertilizer nitrogen is an input. Timing also is important in maximizing inputs, as is placement. In addition, you minimize losses by using stabilizers and inhibitors.”

There are several ways nitrogen can be lost from a system, depending on the source, says Varco. If you use urea and put it on the surface, it can be lost through ammonia volatilization. If you use ammonium nitrate, it can be lost in a heavy rain, especially on sandy soils. On heavier soils, the nitrate form can be nitrified.

“You need to understand your crop’s uptake, and you need to know when to logistically get it in the field in a timely manner. It’s easy for me to tell you need to apply it at V3. But I work with growers in the Mississippi Delta who may have 3,000 to 7,000 acres of corn, and they can’t get it all out in one day, and weather can become a factor. Of course, your fields probably were not planted on the same day, so you’ll want to follow your pattern of planting.”

Varco doesn’t apply preplant nitrogen in his trials. “In our region, I try to get growers not to put out nitrogen preplant. We’ve had growers who started out early, in February or March, with anhydrous ammonia. Some put out a burndown and put some nitrogen in with that. The research we’ve done shows they’re losing 30 to 60 pounds of that nitrogen if that get rainfall prior to planting the crop. That’s expensive.”

He usually puts on out his first split at about V3, and then the second split at V5, V6 or V7.

Nitrogen source and use differs among states

It’s interesting, says Varco, to look at how nitrogen fertilizer source and use differ among states.

“In a major corn-producing state like Illinois, the No. 1 N fertilizer is anhydrous ammonia. They use 600,000 tons of nitrogen in the form of anhydrous ammonia. They also use almost 300,000 tons of nitrogen as N solutions. In Mississippi, we’ve gotten away from anhydrous ammonia, and we now use more N solutions, about 290,000 tons. In Alabama, growers still use ammonium nitrate, at 28,000 tons.”

Anhydrous ammonia, he says, is about 82-percent nitrogen. “UAN – the 32-percent solution used in Mississippi – has 2.24 gallons of water, so 200 pounds of nitrogen per acre is 126 gallons of water per acre. In the U.S. right now, it’s neck and neck each year between anhydrous ammonia and N solutions. The liquids are more convenient. There are hazards associated with anhydrous ammonia, and specialized equipment is required. But there’s new precision equipment that works really well with anhydrous ammonia.”

Turning to prices, Varco says they seem to go down for a year or two and then go up. Given the current of oil per barrel, fertilizer prices should be cheap, but that’s not the case. The U.S. now imports more than 50 percent of its nitrogen fertilizer, he says.

Anhydrous ammonia in 2012 averaged $847 per ton or 52 cents per pound of nitrogen. UAN, at 40 percent, was $400 per ton and 68 cents per pound of nitrogen. Urea averaged $592 per ton at 66 cents per pound of nitrogen. Ammonium nitrate at $544 per ton was 80 cents per pound of nitrogen.

“If you need 100 pounds of nitrogen for cotton, and you choose to use ammonium nitrate over anhydrous ammonia, you’ve docked yourself $28 from the get-go. If you choose ammonium nitrate with corn, with a 200-pound nitrogen requirement, you’ve docked yourself $56 per acre. Anhydrous ammonia is a cheap source of nitrogen.

“We’re switching from cotton to corn in the Mississippi Delta, and the best cotton ground is going to corn. It’s less labor to grow corn, so we’re trading labor costs for the extra 100 pounds of nitrogen.”

Know the rates for your fields

There is an optimum nitrogen rate for your fields, field by field, and your soils, says Varco, and no one can tell you what that is. As a grower, you know better than anyone your field average. “Our studies show that ammonium nitrate is maximizing growth somewhere around 150 to 200 pounds of N. UAN is very efficient, producing almost 200-bushel corn with about 150 pounds. With urea, you need more because of the losses involved. Ammonium nitrate is much better than urea but not as good as UAN. But it is close in its efficiency as long as you don’t get heavy rainfall after applying it on sandy soils.”

Varco recommends about 1 pound of nitrogen per bushel of dryland corn.

“As far as placement for liquids, I’d go 6 to 9 inches from the planted row versus in the middles, about 2 to 3 inches deep. I’ve always recommended a split application as an insurance policy, with 25 to 50 percent at planting and 50 to 75 percent by V7 for corn. Adjust your rates relative to irrigation. My research now is focusing on variable-rate fertilization, and we’re getting real good results with cotton and look to do more in corn with the model we have.”

The use of inhibitors, he says, should be on a case-by case basis. “Are you using no-till, what’s your urea source, are temperatures high, do you have a high-residue situation, what is your placement, is it late in the season? All of these questions and more should be asked before using an inhibitor.”