As the high cost of nitrogen fertilizer continues to put the squeeze on corn producers, being efficient with the side-dress application becomes even more critical to maintaining profits.
Split applications of nitrogen, says University of Georgia agronomist Glen Harris, are intended to increase the efficiency of nitrogen recovery during the growing season. “We've always said to put out one-fourth to one-third of your corn nitrogen at planting and the remainder at side-dressing. That's a minimum of two split applications,” he says.
And there's increasing interest among growers, he adds, in applying nitrogen through an irrigation pivot. “Research tells us the best system is 25 percent at planting and 22.5 percent at the six, 12 and 18-leaf stage and then the remaining 7.5 percent at tasseling. That's a lot of splits in my opinion, and I'm not sure about it. We have a hard enough time keeping the pivots going, let alone injection pumps and everything else. It's helpful whenever you can split applications when the crop really needs it, during the highest demand period. You can reduce your risk of loss, maybe reduce your total rate, and make a better crop,” says Harris.
Anytime fertilizer prices increase, Harris says he gets calls on fertilizer placement, including banding and timing. “In south Georgia, with our sandy soils and decent rainfall or rainfall plus irrigation, split applications for variable nutrients like nitrogen are critical,” he says.
Applications of nitrogen after pollination are not recommended unless a severe nitrogen deficiency is detected, says Harris.
Applying side-dress nitrogen to corn is not an exact science, even for the most experienced producer, says Charles Mitchell, Auburn University Extension agronomist-soils. But this year, some Alabama growers are planting corn for the first time in many years because of the market, and some may be growing corn for the first time ever.
“High fertilizer prices may have scared some producers into applying absolutely the minimum amount necessary to make a crop,” says Mitchell. “Those who could get poultry broiler litter found it was a less expensive alternative to commercial fertilizers. Regardless of what may have been applied at planting, we are now faced with possibly the most costly, out-of-pocket input of the entire crop, a side-dress nitrogen application.”
The yield of corn, unlike cotton and legumes, is absolutely dependent upon how much nitrogen it takes up, assuming that moisture and other yield factors are optimum, he says.
“A bushel of corn will require an application of 1 to 1.5 pounds of nitrogen. When you harvest corn, you actually remove about 1 pound of nitrogen in each bushel of grain,” he says.
Auburn University's standard nitrogen rate for dryland corn is 120 pounds per acre, notes Mitchell. “Because some producers are capable of making a lot more than 120 bushels per acre, the following comment was added, ‘If yield potential is greater than 120 bushels per acre, apply up to 1.25 pounds of nitrogen per bushel of anticipated yield. Nitrogen should always be applied in split applications with one-fourth to one-half of the total nitrogen applied at or near planting and the remainder as a side-dress.”
For irrigated corn, he adds, the standard nitrogen recommendation goes up to 200 pounds per acre with the following comment: “If yield potential is greater than 200 bushels per acre, apply up to 1.25 pounds of nitrogen per bushel of anticipated yield. Nitrogen should always be applied in split applications with one-fourth to one-half of the total nitrogen applied at or near planting and the remainder as a side-dress.”
The question of how much side-dress nitrogen to apply is particularly relevant if poultry broiler litter was applied preplant, says Mitchell.
“You really need to know the nutrient content of the broiler litter, how much was applied, and when it was applied. If it was applied more than 30 days prior to planting the corn, assume that most of the nitrogen has been lost and you'll still need to apply about one-half to three-fourths of the total nitrogen required by the crop, 60 to 100 pounds of nitrogen per acre depending upon the yield potential of the crop.
“This recommendation is backed by several tests on farmers' fields in north Alabama where poultry litter was used on corn. If litter was applied in the fall or winter, most of the nitrogen was gone by the time the corn reached the V8 stage, and additional nitrogen was needed. If it was applied within 30 days of planting, then enough nitrogen remained in the soil so that the side-dress nitrogen rate could be reduced or eliminated,” he says.
If growers had their litter tested, then they would have a record of total nitrogen applied, says Mitchell.
“Assume that about two-thirds of the total nitrogen applied will be available to the crop this year, if it was applied at or near planting. For example, assume you applied 2 tons of litter per acre at planting. Each ton contained 60-60-40 pound of N-P2O5-K2O. This is about 120 pounds of total nitrogen. If two-thirds will be available (90 pounds per acre), then you can subtract this from the total nitrogen needed to determine how much fertilizer nitrogen to side-dress.
“If you expect to make 120 bushels per acre and planned to apply 150 pounds total nitrogen to your crop (120 bushels multiplied by 1.25 pounds of nitrogen per bushel equals 150 pound of nitrogen), then you'll need to apply 150 minus 90 or 60 pounds of nitrogen as a side-dressing.”
Tissue testing to decide how much nitrogen to apply could take too long, says Mitchell. There is a pre-side-dress soil nitrate test (PSNT) that is used in Tennessee northward, he says, but it has not worked very well in the Deep South. It was marginally successful in predicting the need for side-dress nitrogen in north Alabama but did not work well in the sandy Coastal Plain soils of central and south Alabama, he adds.
“Chlorophyll meters have also been tried with limited success,” says Mitchell. “Growers with an optical sensor, such as a Greenseeker, can apply variable-rate nitrogen on the go. To use this technology, a calibration strip is implemented at planting. During side-dress, the calibration strip is used to determine the optimal nitrogen rate for the field.
“The Greenseeker, which measures NDVI (Normalized Difference Vegetation Index) can then compare the entire field to the reference strip and direct a variable-rate nitrogen application based on those readings. This technology is promising, but it won't help you make decisions this year unless you planned ahead.”
The bottom line, says Mitchell, is that applying side-dress nitrogen to corn in Alabama is not an exact science because growers have to deal with so many soil, weather, field and fertilizer variables. “Extensive research has helped us deal with some of these variables. Careful planning and best management practices always help, but experience is still a good tool to have,” he says.
Mitchell adds that growers should not be “fooled” by fertilizer technology promotions. “In tough and changing times, everyone looks for ways to save money. Growers are no different. Because of the high cost of traditional fertilizers, some companies have jumped at the opportunity to push some new technology fertilizer products and additives with the promise of fertilizer savings. Be careful where you spend your money.
“Remember, if it sounds too good to be true, it probably is. Plants need nutrients in certain amounts. These can be supplied in many different forms, but they still need N-P-K. Traditional fertilizers work, and we know how to use them. Some of the newer, slow-release technology also works, but it hasn't been tried and proven on farms throughout Alabama. Only the producer can decide if he or she can afford the new technology fertilizer products. Be very cautious of new, expensive fertilizer products and use them only on a trial basis.”