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Northern Illinois Agriculture

University of Illinois Extension
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Harvest dates?

Posted by Russel Higgins - Corn

As we near September our 2014 corn and soybean crop appear to be are taking a leisurely trip to maturity. This is in part due to July and the majority of August's below normal temperatures coupled with a delayed planting for most northern Illinois farmers. Utilizing the Illinois State Water Survey Water and Atmospheric Resources monitoring program and inputting May 1st as a planting date with DeKalb as a weather collection site (coincidentally, that data is collected on site at the Northern Illinois Agronomy Research Center) we have reached 2066 base 50 growing degree units (GDU'S) in northern Illinois as of August 27th. We are only 66 GDU's behind the 11 year average. The cooler weather has not necessarily been a bad thing for our corn crop. The weather pattern extends the time required for the plant to reach maturity and can provide additional days dedicated to grain fill. I would be interested in hearing from some of our area farmers, but most of the northern Illinois corn fields I have been in over the last week are in in early to mid-dough stage (R4), with a few fields starting to reach dent stage (R5). Kernel moisture is approximately 70 (R4) and 60% (R5) in these respective stages. Research from Purdue University suggests that corn in the dough stage requires approximately 36 days to reach physiological maturity. This number can be decreased or increased by above or below average temperatures. Allowing several more days for additional drying from the physiological maturity moisture of 30%, it seems likely that very few corn acres will be harvested in northern Illinois prior to October 1st.

Many of the corn fields I have visited have areas that are goose necked to some degree, a result of substantial wind events that have crossed the state. It will be well worth a farmer's time to check the standability of different hybrids and schedule harvest accordingly, starting with those most likely to lodge. Because the total number of kernels have been set on the corn ear at this stage, those visiting fields can make preliminary yield estimates.

  • In the field, measure off a length of row equal to 1/1000th acre. For 30-inch rows, this equals 17.4 feet. Row length equal to 1/1000th of an acre = 43560/(row spacing/12)/1000
  • Count and record the number of ears on the plants in the 1/1000th acre of row that you deem harvestable.
  • Collect at least three (or more) predetermined ears. For example, grab the fifth, 10th and 15th ear. The more ears you choose the greater the reliability you will likely have on your estimated yield.
  • Record the number of complete kernel rows per ear and average number of kernels per row. Multiplying the row number by average kernels peer row then multiply each ear's row number by its number of kernels per row to calculate the total number of kernels for each ear. Calculate the average number of kernels per ear by summing the values for all the sampled ears and dividing by the number of ears.
  • Estimate the yield for each site by multiplying the ear number by the average number of kernels per ear and, this is where it can get a little subjective; some suggest dividing that result by 90 (approximately 90,000 kernels in a bushel of corn). Under excellent growing conditions with very good kernel fill this may underestimate final yield and you may want to divide the number of kernels by 75-85.


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