Estimating yield before harvest
A yield estimate a few weeks before harvest helps with marketing, storage and logistics. The yield component method, published by many university extension services, counts ears and kernels in a small sample area and converts them to bushels per acre.
The formula
Bushels per acre = ears in 1/1,000 acre × kernel rows per ear × kernels per row ÷ kernel weight factor
- For 30 in rows, 17 ft 5 in of row equals 1/1,000 acre. For 36 in rows, use 14 ft 6 in; for 20 in rows, 26 ft 2 in.
- The kernel weight factor is the number of kernels per bushel in thousands. The standard is 90, or about 90,000 kernels per bushel. Use 80 for large, heavy kernels in a good year and 100 or more for small kernels after drought stress.
Example
32 harvestable ears in 17 ft 5 in of row, with 16 rows of 30 kernels:
- 32 × 16 × 30 = 15,360 kernels per 1/1,000 acre;
- 15,360 ÷ 90 ≈ 171 bu/acre, about 10.7 t/ha;
- on 160 acres: about 27,300 bu.
How to sample
- Choose at least 5 representative spots across the field, not just the best area near the road.
- Count every ear that will be harvested in the measured row length.
- Pick every fifth ear, or at least 5 ears, and count the kernel rows and the kernels along one row, ignoring the aborted tip kernels.
- Average the counts and run the formula for each spot.
When to estimate
The method works best from the dough to dent stage (R4 to R5), when the kernel count is set. Before that, kernels can still abort; after that, the kernel weight becomes the main unknown.
Accuracy
Expect results within about ±20% of the final yield. The biggest source of error is the kernel weight factor, which depends on grain fill weather. A late season drought or early frost lowers kernel weight and the real yield; good weather does the opposite.
Other crops
- Soybeans: plants per acre × pods per plant × beans per pod ÷ seeds per pound ÷ 60.
- Wheat and other small grains: heads per square foot × kernels per head × kernel weight, counted in several 1 ft² frames.
Combine the estimate with the grain shrink calculator to see the dry bushels you will sell.