Every year around the milk or “roasting ear” stage, we begin to wonder how good the corn crop is going to be. This especially holds true in years that corn yields are looking really good.
There are several yield prediction methods. The most popular is the yield component method, which can be used well ahead of harvest. This method can be used beginning at the roasting ear or milk (R3) stage of kernel development. Under normal conditions, the kernel milk stage occurs about 18 to 22 days after pollination. Estimates made earlier than the R3 stage could overestimate yield if stress occurs causing kernel abortion.
The yield component method was first described by the University of Illinois. It is based on or includes ears per acre, number of kernel rows per ear, number of kernels per row, and weight per kernel. The first three yield components (ear number, kernel rows, kernels per row) are easily measured in the field.
However, final weight per kernel cannot be measured until the grain has reached harvest moisture. Therefore, an average value for kernel weight is used in the yield estimation equation. Kernel weight will vary depending on growing conditions for a particular field or year. The original equation used 90,000 kernels to equal a bushel of corn or 56 pounds. However, kernel size has increased as hybrids have improved over the years. Currently, 75,000 kernels per bushel is used if growing conditions were excellent during the season.
Also, issues with non-uniform plant populations and low spots across the field could impact the accuracy of your yield estimation. For more accurate estimations in non-uniform fields, take more samples throughout the field.
See pdf for more details.
The LSU AgCenter and the LSU College of Agriculture