Fundamentally Speaking
Joel Karlin DTN Contributing Analyst

Friday 07/18/14

IL July Temps vs. Corn Ear Weight

Though prices have stabilized over the past week, corn futures have posted substantial losses over the past two months based on growing expectations of a monster crop to be harvested this fall.

Current U.S. crop ratings as of mid-July are the best since 1999 and the fourth highest ever for that date.

The state of Illinois in particular is seen in stellar shape with 81% of their corn crop either in good or excellent condition.

This state along with much of the Midwest has enjoyed well below normal temperatures for the first half of July providing a huge boost to corn as it moves through its critical yield sensitive pollination period.

It is thought that cool July temperatures in addition to adequate moisture supplies are beneficial to the corn plant and are positively correlated with final yields.

This chart is a scatterplot of average Illinois temperatures in degrees Fahrenheit vs. the average derived corn ear weight in pounds.

The data points representing the years 1990 to 2013 reflects a distribution where lower average July temperatures in Illinois are usually associated with larger or heavier corn ear weights and vice-versa.

The R squared figure indicates that July temperatures explain about 50% of the variability in corn ear weights.

The average Illinois July temperature is 75.5 degrees but through the first half of the month, readings have been about three degrees below this average.

This would equate to 72.5 degrees and plugging that into the equation would result in an average Illinois corn ear weight of 0.3505 pounds.

We have also tracked the number of corn ears per acre in Illinois over the past number of years and based on a 23 year trend, the expected number of corn ears per acre in Illinois for this year is 29,611.

Taking this ear per acre figure and multiplying by the average derived corn ear weight of 0.3505 pounds and dividing by 56 pounds per bushel resulted in a calculated Illinois acre is yield of 185.3 bushels per acre (bpa).

This would top the 2004 record of 180, a year when the average July temperature was also a cool 72.8 degrees.

One of the coolest Illinois July's in recent memory was in 2009 and that was the case through much of the Midwest contributing to the all-time high national corn yield set that season at 164.7 bpa.

Even though the 70.3 degree Illinois reading that year was the coolest July ever, the states' corn yield that year was a very good though not record 174 bpa suggesting other factors are at play besides July temperatures.

Rainfall is also important and the data labels showing Illinois July precipitation in inches show that dry years also tend to depress ear weights and vice-versa.

(KA)

Posted at 7:22AM CDT 07/18/14
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