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Recharged Soil & Robust Yields Require N Top-off

November 15, 2013
By: Davis Michaelsen, Pro Farmer Inputs Monitor Editor

Against earlier speculation, this late planted corn crop is coming in at-or-near bin-busting yields. Early rains were welcome at first, but as the puddles swelled to ponds, concern mounted over the fate of the crop. The weather straightened out just in time and many growers report more consistent yields in-field than last year at the top end of production.DSC 0001

Two things to consider when thinking about fertilizer here. The first is the amount of soil moisture recharge that took place during those early rain events. Heading into spring 2014, soil moisture will be very near normal levels. That raises concerns for nitrogen retention, particularly if this winter produces decent snows and rains are average or above in the spring.

With the soil moisture already topped off -- or nearly so -- the risk of nitrogen loss may be high in areas where fall nitrogen was applied. The University of Nebraska Extension (UNE) says, "Nitrogen is very mobile and easily lost from the soil through leaching and denitrification. A significant quantity of N applied in the fall can be lost throughout the winter and spring, significantly reducing potential plant use."

The other thing to keep in mind is how much nitrogen this large crop is taking with it out of the soil. A fair number of growers were able to rely on carry-over nutrient in the soil this spring in wake of 2012's drought that just will not be there after such an intensive cropping season. UNE notes that a fall application of nitrogen may not be left in the soil by the time spring rolls around and suggests growers consider nitrogen applications targeted more efficiently, where and when corn plants need it.

The U of Nebraska Extension says if you are planning fall N application, consider these factors:

  • Apply anhydrous ammonia because it’s not initially leachable.
     
  • Apply after soil temperatures are below 50°F.
     
  • Because of the potential for N loss, UNL N recommendations for corn are increased by 5% when applied in the fall.
     
  • Fall applications of nitrate (NO3) forms of N are discouraged due to substantial risk of leaching and denitrification.
     
  • Fall N applications are not advisable on sandy or other easily leachable soils, or where ponds or surface drainage is delayed.
     
  • Nitrification inhibitors help reduce the potential for loss through leaching or denitrification, but are less effective with fall than with spring application.

 

A high level of crop offtake at harvest coupled with soils prone to leaching put soil nitrogen at risk for spring. In an effort to combat loss, UNE suggests splitting nitrogen applications with a strong dose in the spring and sidedress during key development phases of the crop's life. Click here for more on fall vs. spring N applications from the University of Nebraska Extension.


 Photo credit: D. Michaelsen, Inputs Monitor

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