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Still have fertilizer to apply? Here are some post-planting options

Agriculture.com Staff 05/14/2010 @ 7:52am

In the mad dash to get all last fall's fieldwork done, then get this year's corn planted, applying fertilizer may have been bumped lower down on your to-do list. Even so, you have a few options to get those nutrients down in time this spring.

Taking into account fertilizer availability, crop protection, potential nutrient loss reduction and cost, University of Illinois Extension soil fertility specialist Fabián Fernández says there are 4 basic plans for application, and he ranks them this way:

  • First choice: Injected anhydrous ammonia or UAN
    Anhydrous ammonia converts quickly to ammonium in the soil and is less prone to loss compared to other sources if weather conditions become too wet after the application.

    Between-row applications keep nitrogen at a safe distance from the crop to avoid injury and also puts nitrogen where the roots will be growing, according to a university report. Applications between rows have become even easier than in the past with real time kinematic (RTK) guidance systems. There is no advantage to applying nitrogen close to the row since roots will grow into the row-middles by around the fourth-leaf stage, Fernández said.

    "Another option to increase speed, reduce horsepower, or both, is to apply N in every other row instead of every row," Fernández says. "Research has shown that there will not be a negative impact on yield by doing this placement because every row will have nitrogen applied on one side or the other."

  • Second and third choices: Broadcast application of solid ammonium-containing fertilizers or broadcast urea with Agrotain
    Surface application of ammonium-containing fertilizers is recommended because these fertilizers are not subject to volatilization, Fernández says in a university report.

    On the other hand, if urea is used, include Agrotain to protect it from volatilization. Since farmers won't be able to incorporate these broadcast applications with tillage after the crop is planted, apply before it rains at least half an inch so the fertilizer gets incorporated into the root zone. To avoid volatilization losses, the sooner it rains the better. Normally little is lost if it rains within 10 days or so from the time of urea application.

    "Broadcast urea applications work fine until the crop is knee-high. However, the sooner it is done, the better. Earlier applications can help reduce canopy injury and increase the chance of a good rain to work the urea into the ground," Fernández says. "While you would likely see some leaf burn with urea applications at the early stages of corn growth, the damage is aesthetic and likely will not result in yield reduction."

  • Fourth choice: Dribble UAN solution between rows
    Dribbling UAN solution is slow, Fernández says. Part of the nitrogen is subject to volatilization, and just like with dry nitrogen fertilizers, it needs a good rain to be incorporated into the root zone.

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