GuideCrops
How to estimate your maize yield before harvest
Counting cobs, rows and kernels in a few measured strips gives a useful yield estimate weeks before the combine or the harvest team arrives. Here is the method, the sums and its limits.
Knowing roughly what a maize field will yield before harvest helps you plan bags, storage space, transport and sales. It also tells you early whether you will meet a delivery contract or need to buy in grain for household use. A field estimate will never be exact, but done carefully it is usually close enough to plan with.
When to do it
The count is most reliable once kernels have formed and started to fill, from the dough stage onwards, when you can press a kernel and it is no longer milky. Earlier than that, the kernels at the tip of the cob may still abort, especially if the crop runs into drought. The later you estimate, the more accurate the kernel count, but the less time you have to act on the result.
What the estimate is built from
Maize yield has three parts that multiply together: the number of cobs per hectare, the number of kernels on each cob, and the mass of each kernel. You can count the first two in the field. The third you have to assume, because kernels are still filling.
- Cobs per hectare: count harvestable cobs in a measured length of row.
- Kernels per cob: count the rows of kernels around the cob and the kernels along one row, then multiply.
- Kernel mass: commonly assumed at around 0.25 to 0.35 g per kernel at storage moisture. Use the low end in a dry season or when filling was stressed, and the high end only for a crop that finished with good moisture.
Step by step
- Choose at least five sampling spots that represent the field. Walk well in from the edge and avoid unusually good or bad patches unless they cover a big share of the field.
- At each spot, measure the row length equal to one-thousandth of a hectare. For 0.9 m rows that is 11.1 m; for 0.75 m rows it is 13.3 m; for 1.5 m rows it is 6.7 m.
- Count every cob in that length that you expect to be harvested. Ignore tiny cobs with only a handful of kernels.
- Pick every fifth cob, or at least five cobs per spot, without choosing the best ones. Pull back the husk.
- For each sampled cob, count the number of kernel rows around the cob (it is always an even number, usually 12 to 18) and the number of kernels in one row from base to tip. Do not count small, unfilled kernels at the tip.
- Average the kernels per cob for the spot.
The sum
Cobs per hectare = cobs counted in the strip × 1 000. Yield in kg per hectare = cobs per hectare × kernels per cob × kernel mass in grams ÷ 1 000.
Example: in 11.1 m of 0.9 m rows you count 30 cobs, so there are about 30 000 cobs per hectare. Your sampled cobs average 16 rows of 32 kernels, which is 512 kernels per cob. Assuming 0.3 g per kernel, each cob carries about 154 g of grain. The yield is 30 000 × 154 g ÷ 1 000 = about 4 600 kg, or 4.6 tons per hectare.
| Kernel mass assumed | Grain per cob | Estimated yield |
|---|---|---|
| 0.25 g | 128 g | 3.8 t/ha |
| 0.30 g | 154 g | 4.6 t/ha |
| 0.35 g | 179 g | 5.4 t/ha |
Getting a sensible answer
Work out the yield for each spot separately, then average them. If one spot is wildly different, look at why: was it a low patch, a headland, a place where the planter skipped? If that condition covers a meaningful part of the field, keep it in; if it was an odd corner, you may be over- or under-weighting it.
Treat the answer as a range, not a single figure. A field estimate can easily be about 15 percent off the final weighed yield. The most common reasons are:
- Kernel mass turned out lower than assumed because the crop ran out of water during grain fill.
- Cobs lost after the count, to stalk lodging, birds, rats, theft or ear rots.
- Too few sampling spots, or spots chosen in the best-looking parts of the field.
- Harvest losses from the combine or from cobs left on the ground during hand harvest.
Using the estimate
Once you have a range, multiply it by the planted area to get total production. From that you can work out how many bags or bulk tons to plan for, whether your storage is big enough, and how much you might sell after keeping household and seed needs. If you have a forward contract, the lower end of your range is the safer number to plan deliveries around.
Keep the counts in your field records. Comparing the estimate with the weighed harvest each year helps you learn which kernel mass assumption suits your area and hybrids, and your estimates will get better every season.
Key points
- Estimate from the dough stage onwards, when kernel numbers are settled.
- Count cobs in one-thousandth of a hectare of row at five or more representative spots.
- Kernels per cob = rows × kernels per row; assume a kernel mass range, not one number.
- Expect the estimate to differ from the final yield; plan around the lower end.
This guide gives general information. Conditions differ from farm to farm, so confirm recommendations with your local extension officer, agronomist or veterinarian, and always follow the registered product label.