Soggy Soils Could Mean Big N Losses This Spring

High corn prices, saturated soils put spotlight on nitrogen fertilizer application this year.

For the second year in a row, farmers in Iowa and many parts of the Midwest are heading into a soggy planting season. Many are facing saturated soils that could leave corn short on both nitrogen and yield in 2008. That's despite the fact that they applied, or are planning to apply, nitrogen at rates that typically are adequate to produce a bin-busting crop.

The possibility that soil moisture conditions could cause large nitrogen losses is especially daunting with corn futures prices above $5 per bushel and nitrogen so high priced this spring. Nitrogen that's purchased this spring and applied in season is expected to cost 60 cents or more a pound, says Tracy Blackmer, research director for the Iowa Soybean Association's On-Farm Network.

"There is so much money being invested in the crop and the crop is so valuable, that growers need to devise strategies to counteract what could be a challenging year for supplying adequate nitrogen to their corn crop," he says. "I have been getting lots of calls from farmers who are concerned about nitrogen losses. Many of them applied anhydrous ammonia last fall because it was relatively cheap compared to other forms."

Is fall-applied anhydrous still in fields?

What advice is Blackmer giving to those farmers? He says you should be prepared to make in-season sidedress nitrogen applications if it looks like the crop will come up short on nitrogen this year. Why wait to sidedress the N? Why not apply your nitrogen at planting time? Additional nitrogen applied at planting could be wasted if weather and soil conditions are conducive to large N losses this spring, he notes.

Based on ISA On-Farm Network research across the state the past several years, he suggests sidedressing 50 pounds per acre of additional nitrogen to your corn crop if rainfall is more than 13 inches from March through May.

Another alternative to this "sidedress-no sidedress" approach is to use an optical sensor system to customize the nitrogen application rate, says Blackmer. Optical sensing technology, which is relatively new on the market, assesses actual crop needs and applies the appropriate additional fertilizer rate in a single field pass.

What trials with GreenSeeker show

The On-Farm Network tested the GreenSeeker optical sensing and variable-rate application system in 2007, when many Iowa farmers also faced saturated soil conditions that short-changed the crop on nitrogen. The six-sensor GreenSeeker RT200 unit, which is mounted on a sidedress nitrogen applicator, uses infrared and near-infrared light to assess plant biomass and health as the rig moves across the field. The nitrogen fertilizer application rate is adjusted on the go, depending on the sensors' assessment of the crop's yield potential.

"The research showed that GreenSeeker detected nitrogen stress in the corn plants and applied the amount of nitrogen needed to alleviate that stress," he says. "The amount it applied provided an economic yield response to the extra nitrogen. The sensors, as the applicator moves through the field, can detect early on which plants in the field are stressed. Often, by the time you can look at the plants and visually see with your own eyes that additional nitrogen is needed, it's too late."

The ISA On-Farm Network's 2007 stalk testing program, which tests cornstalks for nitrate content in the early fall, confirmed that above-average rainfall can reduce corn yield because of the nitrogen loss.

Follow up with fall cornstalk nitrate test

"More than 30% of the fields we tested in the fall with the cornstalk nitrate test were low on nitrogen," says Blackmer. "Growers were horrified by what they saw from aerial imagery and the stalk tests. They lost money because they didn't have enough N for their crop. That really hurts when corn is worth $5 per bushel. Growers have to do what they can to protect this high-value yield. And that includes better management of their nitrogen input."

In the long term, optical-sensing technology such as GreenSeeker could be the solution to managing nitrogen. "It makes more sense to monitor the plant to determine how much N you need than presuming you know how much the crop needs ahead of time," says Blackmer. "Because of the complex factors affecting nitrogen availability, it just isn't realistic to assume that you know how much nitrogen the crop will need ahead of time."

The ISA On-Farm Network plans to conduct additional research with GreenSeeker technology in 2008. The research is being conducted with support from GreenSeeker manufacturer NTech Industries, Inc., along with its distributor, Redball, LLC. They are providing the On-Farm Network with a six-sensor GreenSeeker RT200 unit.

For more information on the ISA On-Farm Network, visit More information on GreenSeeker is available at

TAGS: Soybean
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