Planning Ahead With Yield Estimates

Late July crop ratings remained steady, with corn rated at 80% good/excellent condition. Daily high temperatures are expected to hold in the 80’s throughout the remainder of grain-fill, with crop maturity expected by the first week of September. Now is the time when yield estimates will be calculated in anticipation of harvest for decision making regarding: delivery and storage, marketing, crop insurance, and cash-flow budgeting. One estimation that is quite useful for speed and efficiency is the Yield Component Method.

The Yield Component Method is based on the idea that one can estimate total grain yield by estimating the various components which attribute to yield: number of ears per acre, number of kernels per ear, and weight per kernel. Fortunately, these are all quite easy to determine in just a few simple steps. For step by step instructions on this method, see below:

Step 1: Determine an estimation site at random in the field. An estimation site should be representative of the field or area within the field. Consider factors like disease pressure, insect pressure, nutrient deficiencies, or lodging when selecting estimation sites.

Step 2: For each estimation site, begin by measuring off a length of a single row equal to 1/1000th acre. For 30 inch rows in corn, the single row length to measured is 17.5 feet. This value will change according to row spacing, so consider this when using custom planters or drills.

Step 3: Count the number of harvestable ears on the plants in the 1/1000th acre of row (17.5 feet).

Step 4: From the row, select 5 harvestable ears and determine the number of kernels per ear.

Step 5: Calculate the average number of kernel per ear for the estimation site by summing the values for all the sampled ears and dividing by the number of ears.

Step 6: To estimate the yield (bushels/acre), multiply the harvestable ear number (Step 3) by the average number of kernels per ear (Step 5) and then dividing that result by a kernel weight “fudge factor”. The fudge factor is used to account for variability in kernel weight, so multiple calculations using different “fudge factor” values (75, 85, and 95) are used to determine a yield range.

For example, say you counted a total of 160 harvestable ears at 5 estimation sites, giving you 32 ears per estimation site. When sampling every 5th ear it was determined that the average number of kernels per ear was 520. Using “fudge factor” values of 75, 85, and 95; the estimated range in yield for that sampled site would (32 x 520) divided by 75 = 221, or divided by 85 = 195, or divided by 95 = 175 bushels per acre.

Remember, this method is used to estimate pre-harvest grain yield and provides only an estimate for decision making purposes; the closer to maturity the crop the estimates are performed, the more accurate they will be. Yield can easily be overestimated in a year with drought conditions during grain fill due to reduced kernel size and weight. Alternatively, yield can be underestimated in a year with excellent conditions during grain fill leading to larger kernel size and weight. Regardless, these estimates can give producers an idea of what to expect and still provide value when done correctly. For questions regarding yield estimate calculations, contact Phillip Alberti, Crop Science Educator with University of Illinois Extension in the College of Agricultural, Consumer, and Environmental Sciences at palberti@illinois.edu, 815-235-4125 or on Twitter (@NorthernILCrops).