Determining Nitrogen Rates for Stressed Wheat
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One of the primary determining factors for spring applied nitrogen (N) rate determination is the number of healthy tillers (no disease or insect infestation) per square foot. Personal experience and historical field yield are also important considerations, but a low tillers count means low potential head development. Other factors such as head size and grain weight will influence final yield but these cannot be managed at the time of N application and will be determined by varietal differences and climatic factors we cannot manage.
The first step in N management should be to determine the number of tillers per square foot. One way to do this is to simply make a square frame one foot wide and one foot long. Randomly place the frame within the field and count the number of tillers within the frame within several areas of the field. As an alternative, use the formula below. Remember to count only plants with at least three leaves as a tiller and sample several areas to get an accurate average.
Formula for Tiller Estimation
Tillers per square foot = (tillers per yard of row) × 4 ÷ (row width in inches)
Once the number of tillers is determined, use the chart below as a guide for nitrogen rates.
It should be noted that any N applications is likely to be delayed further based upon the weather outlook over the next weeks and current field conditions. This is not as critical as normal simply because the crop is also delayed about 10 days or so. If continued wet soils delay application past GS 30 but prior to jointing, N applications are likely to burn leaves but still be beneficial. Some yield reduction can be expected simply due to the high demand of N within the plant at this growth stage and the delay in getting the N to the plant.
While the chart provides some guidance regarding fields with some consistency in tillers per square foot, it will not provide much guidance for those with inconsistent plant populations. In this circumstance, personal experience and willingness to accept risks will determine management.
Please consider taking leaf samples for nutrient analysis shortly after N application by submitting leaf tissue to the NCDA & CS Agronomic Division. (Information and forms for tissues testing is available at http://www.ncagr.gov/agronomi/uyrplant.htm). Other nutrients, especially sulfur, manganese and copper have commonly been identified as deficient nutrients of wheat grown within Craven County. Don’t negate the time, effort and good decisions made to determine the correct N rate by limiting yield from a deficiency of some other nutrient! The crop is delayed but still has excellent yield potential. Remember, we can manage nutrient concentration of the wheat. We cannot manage the weather.
Additional information can be found on the NC State Small Grain Web Portal
Jacob Morgan, NC State Extension Agent in Jones County, created a very good video (about 2.5 minutes) showing how to count tillers (using a slightly different method that posted here) at https://www.youtube.com/watch?v=2wZ5_1VgLig
Jacob Morgan, NC State Extension Agent in Jones County, and Chris Jernigan, NCDA & CS Regional Agronomist, posted an excellent video (2 minutes) outlining early season nutrient deficiencies at https://www.youtube.com/watch?v=jsCbC9J-Nj8
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