A Growing Mystery: How Much Fall Nitrogen Is Left?

Posted by on 23 June 2016 | 0 Comments

Many growers across the Corn Belt have already applied all or a portion of their nitrogen for this year’s crop.  Southwest and South Central Iowa experienced,  a warm and wet November-December in connection with an early warmup this spring has led to conversion of the NH4+ molecule to the NO3- molecule making it more available to leach or be denitrified depending on the soil type, texture and drainage profile of your fields. In many cases in Iowa our fall applied NH4+ conversation to N03 is 3 -4 week ahead of 2015.

Testing over the winter in our soils show both Fall applied NH3 with a stabilizer and without are susceptible to high loss based on soil temperatures lingering above 34 degrees for a longer period of time during the winter months and an early warmup this spring. Combined with several heavy rain events over our territory since the beginning of corn planting.

A corn plant only uses about 25% of its total Nitrogen prior to V10 (roughly shoulder high). The remaining 75% is rapidly taken up from V10 – R5. In simpler terms a 200 bushels corn crop only uptakes roughly 55 PPA of nitrogen prior to shoulder high. The remaining 165 PPA of nitrogen is rapidly taken up after the corn reaches shoulder high.  There is extreme high demand for nitrogen later in the season to capture the yield potential you laid down with the planter pass.

So what are the implications?  Right now there could be a significant amount of fall applied N in the nitrate form.  It could also mean that as your crop is moving into the growth phase later in the year where high levels of nitrogen are required, your fields might experience a shortage (conditions in many areas have led to high denitrification or leaching) unless you take some steps to remediate the issue.  What are those steps?

  1. Measure – Use a 360 SOILSCAN machine in-season to measure the conversion and availability of NO3- nitrogen to your crop.  You may discover that your original plan now requires changes in order to reach your maximum yield potential.
  2. Modify – Adjust your plan by understanding the potential remaining demand of the crop and modify your nitrogen application strategy to meet that demand. 
  3. Wait – Let the spring weather play out – flushing rains or mineralization – so you  know as much as possibleare familiar with about the nitrate levels heading into the reproductive stage.
  4. Apply – Utilize technology to apply the needed nitrogen to coincide with the timing in the corn plant’s life that will satisfy the crop needs in order to maximize nitrogen efficiency and the field’s potential.

While each regions’ weather has been different, everyone should be cautious about the nitrogen levels heading into the growing season once the crop is established.  Although many of us have experienced weather conditions that have created a potential issue in our fields, the good news is that there is still a chance to rectify the issue utilizing the measure, modify, wait and apply approach to maximize your results at harvest.