Assessing the Yield Potential of this Year's Wheat Crop

estimating yields, crop yield, crop yield formula

Submitted by Craig Askim, Extension Agent/Agriculture and Natural Resources

At this time of the year, producers, agricultural lenders and other people ask me, how good is the wheat crop this year? While this can be hard to determine until it is actually in the bin, the article below explains a formula process you can use to estimate yields.

Estimating yield using a formula that is based on yield components can also give your insight into how environmental and management factors are influencing crop yield this season. The formula I like to use for predicting yield can be applied soon after the crop has headed. Most of the early-planted crop is now in this stage. The three components that contribute to yield in wheat are the number of spikes per area, the number of kernels per spike and kernel weight. Kernel weight can vary by variety and the environment and cannot be accurately ascertained until maturity. This is one of the reasons that estimating yield is just that, an estimate with the potential of some level of variance from the actual. The formula described below uses a historic average for kernel weight to allow for an estimation prior to maturity and harvest. That value and other conversion factors are incorporated into the value “0.142” included in the numerator. Since small differences in the numbers used in this formula can results in large differences in the estimated yield, multiple samples taken from representative areas of the field will help improve the accuracy of the estimate.

Bushels/acre = (spikes per 3 ft. of row X spikelet’s per spike X kernels per spikelet X 0.142

Row spacing in inches

Directions for obtaining the values for this formula:

1. Count the number of spikes in a three-foot length of row (taking an average of several counts improves the estimate). Do not count small heads that will not significantly contribute to yield. If the crop was planted with an air seeder in bands or as paired rows, count the spikes from the entire width of the band or both rows in the pair.
2. Count the number of spikelet is in six or more randomly selected spikes. Omit the top and bottom spikelet is as they contribute little to the overall yield. Spikelets are the primary branches on the spike.
3. The number of kernels per spikelet can be determined by hand threshing the head and counting the kernels and then dividing that number by the number of spikelets. Previous experience, however, has shown that 2.3 kernels per spikelet gives a more accurate yield estimate, unless the crop has been stressed, then 2.1 kernels per spikelet should be used.
4. If not known, determine the row spacing by measure the distance between several rows or bands of wheat. Most double disc drills are set at 6, 7, or 8 inch row spacing. The width of air-seeded bands can vary. To determine the row spacing of the bands, measure the distance between the edges of one band to the same edge of the adjacent band.

Example:

(64 spikes in three foot row X 14.3 spikelet’s per spike X 2.3 kernels per spike X 0.142)/ (7 inch row spacing) = 43 bu./acre

Source: Joel Ransom, NDSU Small Grains Cropping Systems Specialists

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