Joel Karlin
DTN Contributing Analyst

USDA personnel are out in the fields tabulating data from field plot surveys and farmer assessments heading into the August 12 crop production report.

For corn, yields are a function of plants per acre, ears per plant, and the weight of each ear.

Ear weights are a function of the number of kernels per ear and the average kernel weight.

The number of kernels per ear is determined during pollination which generally takes place in July, while kernel weights are influenced by the amount of grain fill which generally occurs in August.

Both pollination and grain fill are driven by weather conditions, specifically temperatures and precipitation. On the other hand, plant and ear populations have increased over time with some areas of the Corn Belt now seeing over 30,000 ears per acre.

This graph shows the ear population history in the ten states the USDA uses for the objective yield studies it does in preparation for the monthly crop production reports. Also included is an estimated 2010 ear population using either the six- or eight-year trend.

Iowa and Minnesota continue to have the highest ear populations and this year the ear counts again should be record high as the plants in both states have had plenty of moisture to work with.

Note that with these estimated ear counts, a tentative yield can be calculated using the average five-year ear weights.

(KA)

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