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Angie Peltier

Angie Peltier
Former Extension Educator, Commercial Agriculture

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Hill and Furrow

Current topics about crop production in Western Illinois, including field crops research at the NWIARDC in Monmouth.
Figure. Marty Johnson (L) and Brian Mansfield (R)counting kernels at the NWIARDC.
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Planting date and corn yield

In my commute back and forth to the office along Highway 164 this spring, I was able to see when people's corn and then soybean crops began emerging from the soil. Many people were able to take advantage of this spring's warm temperatures and dry soil conditions to get into their fields earlier than in years past. Others waited a little bit longer to plant.

Watching the corn crop develop over the growing season, it seemed that the earlier the corn was planted, the better it was doing. Earlier planted corn may have been able to take advantage of subsurface soil moisture to grow strong, deep roots and better withstand the sustained drought conditions than later planted corn.

We see this scenario playing out in the yields of the NWIARDC corn planting date study. To estimate yields, we used the method detailed in Dr. Emerson Nafziger's July 27th Bulletin article, "Estimating yield in stressed corn". Briefly, we counted the number of ears in 17 feet, 5 inches of row (with 30 inch rows, this is 1/1000th of an acre) in two rows of each plot and found the average number of ears. We then picked three representative ears from each plot as ear size was relatively constant (if your ears vary in size, you may want to pick more ears from which to estimate yield). We then counted kernels per ear by multiplying the number of rows by the number of kernels within a row (Figure). We then divided the total number of kernels in 1/1000th of an acre (average kernel number per ear x number of ears) by the estimated number of kernels per bushel at harvest.

Dr. Nafziger explains how the average number of kernels per bushel you use to estimate yields may vary depending upon both when you take your yield estimate (he took his July 27th) and crop stress:

To estimate yield, divide the number of kernels in 1/1000 of an acre by the number (in thousands) of kernels expected to be in a bushel at maturity. In recent years we have been using the number 80 (thousand) kernels per bushel, which under good conditions is reasonable. But this number can range from less than 60 to more than 120, and it's almost impossible to guess what it might be at maturity for a particular field when we do not know how long stress will last.

For our estimates, we decided to be conservative, so as to not over estimate yield, and chose to divide by 100 (100,000 kernels per bushel).

Estimated yields ranged from between 187 and 134 bu/A, with the highest estimated yield in the March 30th planted corn (Figure). Corn planted on May 10th had the lowest estimated yield, 134 bu/A, and very heavy kernel abortion (Figure). Peak pollen shed takes place over a narrow window of time (3-4 days). Perhaps pollination of the May 10th planted corn took place during a period of particularly stressful conditions.

Drive-by yield estimates will tend to overestimate yields because ear size on end row plants tends to be significantly larger than those competing for light within the field. Although yields are likely to be down significantly from years past (Figure 1), early planted corn in some areas of Western Illinois still has the potential to beat the 2011 state-wide average of 157 bu/A.

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