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Rain delays create nitrogen application challenges

Cars are getting up and floating away in Yazoo City, Mississippi.

Flooding in the streets like this is one off-farm symptom of the heavy rains that have socked parts of the mid- and deep South in the last few days. Yazoo City saw seven inches of rain on Wednesday, according to agronomist Jack Bridgers. While he says much of the area's countryside missed the "big rains," the 1 1/2 to 2 inches was enough to make it tough to get into the field. And, that comes at a critical time for applying fertilizer, leaving many farmers looking to alternative ways to get it on when the corn crop needs it.

"The corn crop looks really good. The older corn has started to tassel, and the younger corn is growing off really well," says Bridgers, a field representative for Jimmy Sanders Seed, Inc., in nearby Tchula, Mississippi. "We had to fly on an application of fertilizer in some small acreage because we were wet and the corn was getting to big to go through with a ground rig."

Farmers are doing what they can to get nitrogen applied to their corn, even under conditions that are right now keeping wheels out of the field. The issue's growing in seriousness with each day the corn is allowed to grow and it becomes more difficult for normal ground application rigs to get into the field.

"Rainfall and/or other limitations compounded by wet weather during this spring have delayed nitrogen fertilizer applications for some corn growers, making side-dressing no longer possible," says Mississippi State University Extension agronomist Erick Larson. "The crop is now too tall to permit ground equipment passage. Thus, these growers must generally apply their remaining nitrogen by airplane or high-clearance applicator."

Timing is the most important thing with applying nitrogen now that it's past the ideal application window, Larson says. Even if conditions aren't ideal, it's better to get the N on now than to wait and risk a deficiency later on.

"We do not suggest applying nitrogen fertilizer when soils are completely saturated, flooded or ponded, because anaerobic conditions stunt crop growth/response and promote nitrogen loss," he says. "However, you do not have to wait for the soil surface to completely dry or crust before application if the crop is nitrogen deficient, particularly if there is a high likelihood of subsequent rainfall and the soil is well-drained.

"Prolonged nitrogen deficiency during rapid vegetative stages, which is when nitrogen demand is highest, is going to reduce corn grain yield potential considerably."

But, keep a close eye on your corn before pulling the trigger on an application, Larson adds. "If the crop is dark green, then you have slightly more latitude to wait for 'ideal' application conditions."

If using a higher-clearance ground or aerial applicator to put on your N, be wary of what fertilizer granules can do to growing corn. If allowed to fall into the leaf whorls or stick to leaves themselves, granular N can cause burning. This is why, Larson says, it's important to watch application rates closely and try to put the N down when it's as dry as possible.

"Broadcast application should be limited to 100 to 150 pounds of granular nitrogen fertilizer material per acre on corn more than three feet tall. Avoid fertilizer application when leaves are wet with dew or rain because moisture encourages fertilizer granules to stick to leaves and promote burn," he says. "When topdressing nitrogen later than normal, you should be able to use more conservative fertilizer rates than normal. Plants should use the nitrogen very efficiently since they are already rapidly using nitrogen during late vegetative stages.

"If the crop has been deficient for long, normal yields are no longer likely, so full rates are not necessary," Larson adds.

Cars are getting up and floating away in Yazoo City, Mississippi.

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