The 2015 Nitrogen Opportunity!?

  • May 15
    Greg Stewart
    The 2015 Nitrogen Opportunity!? By Greg Stewart on May 15, 2015
    Categories: Field Care, Grain Corn

    Year to year changes in N supply

    Over the past three decades, research and extension personnel have been monitoring seasonal fluctuations in nitrogen supply from the soil.  This effort is directed at trying to fine-tune the amount of sidedress N required.  Occasionally, it has been quite clear that the N supply from the soil has moved far enough from normal that significant adjustment to sidedress rates are warranted and are potential profit drivers.  In other years, N supply seems to hang around average values and doesn’t inspire you to make changes from your normal sidedress rates.  

    Is this the year?

    I am of the opinion that 2015 may be shaping up as a year when nitrate supply from the soil could be higher than average; maybe high enough to register some significant reductions in sidedress or topdress N applications.  Soils have warmed up nicely and from the few soil nitrate samples already taken, it appears that mineralization (getting nitrate from organic matter, crop residues, fall manures, etc.) is on the move.  Rainfall has been below normal for the last 30 days, meaning that nitrate that has been accumulated or applied via fertilizer applications has not been lost.  Some of the 30-day weather forecasts indicate that this trend may continue.

    Decision Support

    Making the decision to adjust N rates can take a gut-feel approach - this might be based on rainfall totals, how few days your soils have been saturated, how green the wheat looks where you missed N application or whether your team is still in the playoffs (okay maybe not the last one!).  However, a better approach would be to pull some soil nitrate samples to see what the nitrate levels are like on your fields. The reminders on soil nitrate samples are as follow:

    1. Samples must be from a depth of 30 cm (12 in.).
    2. It is important that all cores in a field be taken to the same depth.
    3. Sampling should occur when corn is 6-12 inches (15 – 30 cm) tall and usually in the May 25 – June 15 window.
    4. Avoid all starter fertilizer bands.
    5. Place soil cores in a clean plastic pail, crushed by hand and well mixed.
    6. Microbial action in the sample can change the nitrate content quickly if it is not handled properly. Chill or freeze samples as soon as possible. For shipping, pack samples with insulating material to keep them cool and send them by courier to ensure quick delivery to the lab.

    OMAFRA has developed new nitrogen rate recommendations based on the soil nitrate reading and the yield expectation for the field or part of the field from where you pulled the sample.  These new recommendations are included in the following table.

    Application Timing

    For those of you who run traditional tractor-drawn sidedress equipment, the decision making is going to come quickly and you may have to pull soil samples before the traditional June 10 window.  For those that have high clearance equipment, you will have a wider window to evaluate what the soil N supply looks like.  But remember that soil nitrate tests taken from corn that is above your knees become increasingly difficult to interpret because of the N taken up by the crop.

    The OMAFRA PSNT test is calibrated based on being able to pull samples from an area that has received zero broadcast N.  If you apply a significant amount of broadcast N upfront, then you can still use the PSNT soil test, but the test may be more of a “threshold guide” rather than a rate recommendation tool. Some of the work done previously indicated that the 36 PPM mark was a good threshold.  That is, if you pull samples in a field that had N applied to it over 30 days ago and the PSNT comes back above 36 PPM nitrate, you should question whether any more nitrogen is needed.

    The Risk

    Many producers feel that after all the investment in getting a good corn crop established, why would we risk shorting the N?!  This is a great point and supports the need to use the tools available to make a good decision.  However, if a $30-40 per acre saving is possible, 2015 would be a good year to get it!  Please feel free to contact me ( or your Maizex representative if you have questions about nitrogen management this season.

    Greg Stewart
    Maizex Seeds Agronomy Lead