Smart nitrogen and sweet corn

Smart nitrogen or polymer-coated urea is a suitable nitrogen source for sweet corn and only needs to be applied once. Cost, however, is higher than urea.

Sweet corn is a heavy user of nitrogen. Depending on days to maturity, plant density, soil type, irrigation and other cultural practices, sweet corn can use 150 or more pounds of nitrogen per acre. Applying that much nitrogen to many soils requires careful application management. For most nitrogen fertilizers, if that much was applied all at once there would be significant nutrient loss to leaching, volatilization or both – an economic waste to the producer and potentially damaging to the environment. Therefore, growers use split applications applying a third to half (depending on soil type) of the nitrogen prior to planting and the rest as a sidedress when plants are 18 to 24 inches tall.

Several nitrogen sources are suitable, but the more common ones include ammonium nitrate (33-0-0) and urea (46-0-0) pre-plant and then ammonium nitrate, urea or anhydrous ammonia (82-0-0) as a sidedress. Each is a good source, but each also has limitations. Ammonium nitrate has become fairly heavily regulated due to its potential in making explosives. Urea is quite mobile and volatile and needs to be applied under the correct conditions or much is lost. Finally, ammonia is dangerous to handle and requires specialized application equipment.

“Smart nitrogen” was developed to help solve these limitations. Smart nitrogen is urea covered with a polymer-coating and has a slightly less nitrogen value (42-0-0) than regular urea. The polymer coating slows the rate at which urea is dissolved and therefore released to the soil to eventually be utilized by the plant. Theoretically, one pre-plant application of ESN (Environmentally Smart Nitrogen) should be enough to satisfy the nitrogen requirement for the entire season. To test this on sweet corn, a trial was conducted by Michigan State University Extension at the Southwest Michigan Research and Extension Center in 2015 and tested the following treatments:

  1. 150 pounds as ESN prior to planting.
  2. 25 pounds as urea plus 125 pounds as ESN prior to planting.
  3. 25 pounds as urea plus 100 pounds as ESN prior to planting and 25 pounds as urea as a sidedress when plants were 18 inches tall.
  4. 50 pounds as urea plus 100 pounds as ESN prior to planting.
  5. 50 pounds as urea prior to planting and 100 pounds as urea as a sidedress when plants were 18 inches tall.

Cabo sweet corn (Syngenta Seed Company) was planted 6 inches in the row with rows 30 inches apart. The trial was irrigated as needed and weeds controlled using a combination of Dual and Aatrex. Plant height was measured over time and at harvest the number and quality of ears was determined. After analyzing the data, it was found that all treatments produced similar growth, yield and ear quality.

The benefit of a onetime nutrient application using ESN is labor and equipment savings of the sidedress application. ESN for this trial was $1.16 per pound of nitrogen while urea was $0.80 per pound. A 150 pounds per acre application of ESN cost $174 while urea cost $120, a $54 difference. Labor and equipment costs for a second application are estimated to be between $40 and $50 per acre. So urea is slightly less expensive from the standpoint of product and application. For some producers, there may be a benefit in a “once and done” approach. It is also possible ESN rates lower than 150 pounds per acre may provide a similar performance as 150 pounds per acre regular urea. This is something that will be evaluated in a 2016 trial.

A full report of this trial will be given during the Sweet Corn session Tuesday, Dec. 8, 2015, at the Great Lakes Fruit, Vegetable and Farm Market EXPO. More information can be found at the Great Lakes EXPO website.

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