STRAIGHT FROM THE HORSES MOUTH

Duane A. Lienemann
UNL Extension Educator

     There will be some of our dryland producers and even pivot irrigators that have suffering corners that are going to be making a decision on corn fields and what to do with the deteriorating condition of the crop.  Some producers are trying to figure out what kind of yield may be out there or how much corn may be available for quality silage or perhaps for grazing if that opportunity exists. I have been fielding questions lately on how to find out approximately how much corn may be out in the field or what the potential yield may be considering the array of conditions, ear development and of course pollination.  I think this week it may be good to go over a couple of ways to determine this.  We will start with a simple method and then look at something a little more complicated. 
     The simplest and for sure the least accurate method is to select an ear or ears that represent the average ear size in the field. Simply count the number of kernels per ear and multiply by 0.300 to get a very rough yield estimate. To determine number of corn kernels per ear, multiply number of rows on an ear by number of kernels in a row. Do not count kernels near the tip that are less than half the size of kernels midway up the ear. For example: You count 12 rows per ear and 50 kernels per row to equal 600 kernels per ear - 600 x 0.300 = 180 bushels/acre. For a quick and easy method for a rough estimate, this will do the trick, but please note that drought conditions could affect the accuracy or reliability.
     UNL Extension suggests a proven method to get a more accurate yield potential assessment of drought effected corn that is standing in the fields by following these steps: 1) To estimate potential yield in standing corn, measure a distance equal to 1/1000 acre in one row and count the number of plants that will produce an ear. Repeat this in several areas of the field. The length measured will depend on row spacing (for 30 inch rows measure 17 ft & 5 in, for 38 in rows measure 13 ft & 9 in, and for 40 inch rows measure 13 ft & 1 in, respectively). Multiplying the measured value by 1000 will result in the number of plants per acre that will produce an ear. 2) Take an ear at random from each of these areas and count the number of rows of kernels and the number of kernels per row on each ear. Average the number of rows per ear and the number of kernels per row. 3) Multiply the average number of rows by the average number of kernels per row to get the kernels per ear. 4) The kernels per ear multiplied by the ears per acre results in the kernels per acre. 5) There are about 90,000 kernels per bushel in normal corn. Drought-stressed corn may have 110,000 kernels per bushel. Dividing the kernels per acre by 110,000 results in the estimated yield of most drought stressed corn.
     For example: A dryland field of corn under moisture stress during pollination and kernel fill has 20,000 plants per acre with ears that pollinated but have “tipped back” to an average of only 22 kernels per row. There is an average of 14.1 rows of kernels per ear. The estimated grain yield (assuming enough moisture is received for photosynthesis to occur and transport of starch into the grain) would be 56 bushels per acre (20,000 x 22 x 14.1 / 110,000 = 56 bu/ac).
     Here are some tips to help the accuracy of this method. a) Do not sample nubbins or obviously odd ears, unless they fairly represent the sample area. b) If row number changes from butt to tip (e.g., pinched ears due to stress), estimate an average row number for the ear. c) Don't count the extreme butt or tip kernels, but rather begin and end where you perceive there are complete "rings" of kernels around the cob. d) Do not count aborted kernels and if kernel numbers are uneven among the rows of an ear, estimate an average value for kernel number per row.
     Remember that this method for estimating pre-harvest grain yield in corn indeed provides only an estimate. Since kernel size and weight will vary depending on hybrid and environment, this yield estimator should only be used to determine “ballpark” grain yields. Yield will be overestimated in a year with poor grain fill conditions (e.g., low kernel size and weight from a drought year) and underestimated in a year with excellent grain fill conditions (e.g., larger kernel size and weight from non-stress grain fill periods). Recognize that this method for estimating corn grain yield is probably only accurate within plus or minus 15-30 bushels of the actual yield. Of course the more ears you sample within a field, the more accurately you will "capture" the variability of yield throughout the field. For the mathematically challenged an online yield calculator can be found on the internet by going to: www.conservfs.com/ProdServ/AgCalc/Calc1.html or www.pioneer.com/home/site/us/agronomy/tools/corn-yield-estimator .  You can also get an app for mobile devices.
     If the corn was successfully pollinated and will produce grain, harvesting grain may be the best alternative. The combine may need several adjustments to accommodate the smaller ear size and lighter test weight grain. Test weight is one of the factors that determines market grade. Drought stress during grain fill can result in light test weight grain, resulting in lower grain grade and considerable price dock at the elevator. Nonetheless, light test weight corn usually makes good animal feed, often having 90 to 100 percent of the feed value of normal corn. It can be a bargain for the feeder, provided the corn does not contain mold toxins.  If you decide to harvest the drought-affected corn via direct grazing or mechanically harvesting the corn as forage, check the labels of all chemicals that were applied. Be sure all pesticides (herbicides and insecticides) applied to the crop are cleared for forage and the minimum harvest interval has been met. You may also want to check for nitrate levels. Also check with the USDA Farm Service Agency to maintain compliance with USDA farm program provisions and crop insurance requirements before harvesting corn as forage. 

The preceding information comes from the research and personal observations of the writer which may or may not reflect the views of UNL or UNL Extension. For more further information on these or other topics contact D. A. Lienemann, UNL Extension Educator for Webster County in Red Cloud, (402) 746-3417 or email to: dlienemann2@unl.edu or go to the website at: http://www.webster.unl.edu/home