Predicting corn yield before harvest offers growers a practical tool for early planning and marketing decisions. This projection is achieved through the yield component method, often called the pre-harvest yield check. It involves measuring specific plant characteristics in the field to generate an estimate of bushels per acre. This technique provides insight into the potential productivity of a cornfield, relying on field measurements rather than final weight, making it a powerful forecasting tool.
Counting Ears to Determine Population Density
The first step in developing an accurate yield projection is determining the harvestable ear count per unit area. This requires establishing the population density by selecting multiple spots, typically five to ten, that represent the overall field condition. To standardize the measurement, a segment of row equal to 1/1000th of an acre is measured at each location.
For example, in a field with 30-inch row spacing, 1/1000th of an acre is represented by 17 feet and 5 inches of row. This linear distance changes based on the row width; a 20-inch row requires 26 feet and 2 inches, while a 36-inch row needs 14 feet and 6 inches of measurement. Within this measured segment, only ears that appear fully developed and capable of being harvested should be counted.
Counting multiple locations and calculating the average ear count per 1/1000th of an acre provides a statistically sound representation of the field’s population density. This average ear count serves as the first variable in the final yield formula.
Estimating Kernel Count Per Ear
Once the population density is established, the next step involves quantifying the average kernel production per ear. This is achieved by randomly selecting a set of ears, such as three from each of the previously measured sample areas, to ensure a representative average. Two specific measurements are taken from each sampled ear to estimate its kernel volume.
The first measurement is the number of kernel rows that circle the ear, which is always an even number due to the paired development of spikelets on the cob. The second measurement is the length, in inches, of the ear that is covered by fully developed kernels. This length measurement should exclude the tip where kernels may not have fully pollinated or developed, focusing only on the filled portion.
To estimate the total number of kernels on a single ear, the average number of kernel rows is multiplied by the average measured length. This product provides the estimated kernel count per ear, assuming a consistent kernel depth and filling across the sampled ears. The resulting figure is averaged across all sampled ears to provide the second variable for the final calculation.
Assembling the Final Yield Calculation
With the ear count and the estimated kernels per ear now calculated, these variables are combined to project the final yield. The complete formula is structured as follows: (Ear Count per 1/1000th Acre) multiplied by (Estimated Kernels per Ear) and then divided by a standard conversion factor. This conversion factor, the final component of the equation, translates the total estimated kernels into bushels of corn.
The standard value used is 90,000 kernels per bushel, representing an assumed average kernel weight and size across various hybrids and environmental conditions. This constant is the primary assumption of the method and the most significant source of potential error. Dividing the total estimated kernels by 90,000 converts the raw count into a practical, marketable yield projection in bushels per acre.
For instance, if an average of 30 ears were counted in the 1/1000th acre segments, and the average ear contained 500 kernels, the calculation would be 30 multiplied by 500, resulting in 15,000. Dividing this 15,000 figure by the standard 90,000 conversion factor yields an estimated 166.67 bushels per acre. The use of 1/1000th acre segments allows the result from the initial multiplication to be quickly scaled up to a per-acre estimate before the final division.
Factors That Influence Estimate Accuracy
While the yield component method provides a strong estimate, its accuracy is subject to several biological and environmental variables. The most significant variable is the standard 90,000 kernels per bushel conversion factor, which is merely an average.
If the corn hybrid produces smaller than average kernels due to drought stress or high population density, the conversion factor could be closer to 100,000, meaning the final yield will be lower than the estimate. Conversely, a field with large, heavy kernels might require a factor closer to 80,000, making the actual yield higher than projected.
The timing of the estimate also affects reliability, as the calculation is best performed after the “milk line” has moved halfway down the kernel, indicating that the grain fill period is mostly complete. Furthermore, the estimate does not account for potential losses between measurement and final harvest. Factors such as insect feeding, stalk lodging, or disease development can reduce the amount of grain collected, leading to an overestimation of the final yield.