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Notes on corn and soybean yield potentialNotes on corn and soybean yield potential

August 9, 2012

4 Min Read

Editors note: This is a preview to a report that will broadcast on Friday, Aug. 10, at 9:30 a.m. The USDA August Crop Report will be released Friday, and Iowa Corn leaders will respond to the report and provide perspective on the status of their own crops. Stay tuned for an update from Farm Industry News on Friday at www.farmindustrynews.com.

The first yield corn and soybean yield estimates based on pod and kernel counts in the field will be coming out on August 10, said University of Illinois crop sciences professor Emerson Nafziger. Producers, buyers, and sellers will be examining these numbers closely.
In years such as this one, with the crops negatively affected by poor weather, people tend to think that the state or national yield estimates are too high. However, Nafziger says that, while the August 1 estimate and final estimate are usually not the same, there is no foolproof way to improve on the National Agricultural Statistics Service (NASS) numbers.
“NASS carefully chooses a sample of fields in which to make counts, and this sample should be representative,” he said. “In a year like this, with many fields having low or even no yield, it is possible for such random samples to miss the average. But it’s not clear that poor fields would be underrepresented.”
This year’s August corn yield estimate would normally be expected to be more accurate than usual due to this year’s early planting and rapid crop development. “Kernel numbers are more or less fixed, and there is at least some idea of how well the crop canopy is holding up, which indicates how well kernels will fill,” Nafziger said. “This makes it possible to get a little clearer idea of yield prospects.”
With the ongoing stress and the inability of the plants to produce enough sugars to both fill kernels and maintain stalks, standability is going to be an issue in the cornfields that will be harvested for grain. Nafziger said that signs point to this being one of the worst years for lodging seen recently.
“Fields under severe stress did not produce enough sugar to produce the lignin that gives stalks their strength,” he explained. “In fields under stress since kernel set, there may be more lignin, but sugars are moving to the kernels, leaving stalks depleted. Loss of leaf area before maturity will contribute to this.”
Even soybean plants may be subject to lodging this year in areas that have had more rainfall or where the crop was irrigated and the high temperatures have encouraged tall plants. Irrigated soybeans at Urbana are more than a foot taller than non-irrigated ones and are already leaning as pod filling gets underway. Modest lodging may not reduce yields if the leaf area remains exposed and the canopy remains full, but plants that move towards horizontal leaning risk compromising some leaf area and, with it, yield potential.
The yield picture for the soybean crop is less clear than that of the corn crop. “In traveling through some of the driest areas of the state on August 2, I found better growth than I had expected based on what I saw in the same area in mid-July,” said Nafziger.
In one field in southeastern Illinois, plants were about 2 ft. tall, and while leaf area and canopy cover were less than ideal, plants had about a dozen pods, ranging from flat to partly filled. Nafziger estimated that the field could yield 25 bu. per acre if all the pods fill.
“That area received some rainfall since then, and it’s possible that more pods will develop, though how well they fill will depend on getting more rainfall in coming weeks,” he said.
There are some fields in Illinois, however, with soybean plants barely a foot tall, low pod numbers, and a fading canopy color. They are rapidly running out of time to recover even if there is rainfall in the coming weeks.
“The fact that most soybean plants were shortened due to lack of water is probably more of an advantage than a disadvantage,” Nafziger said. “Very tall plants often do not fill pods very well because the lower leaves are shaded. Large plants and leaves also use water faster, so they can dry soils out more quickly.”
He noted, however, that plants that are only a foot tall often do not have much ability to set and fill pods, so neither too tall nor too short is ideal.
Although flowering and pod formation in soybean are ahead of average — 82% of the Illinois crop was setting pods on August 5 compared to the average of 52% — plants in dry areas have had difficulty keeping the pods and starting to fill them.
“Once seeds begin to fill, pods tend to stay on plants, and seeds will often fill out to near normal size,” Nafziger explained. “Stressed plants may abort some of their flat pods to enable the others to fill. It’s possible to have seeds stop filling when they’re very small and end up as ‘BBs’, but this is relatively rare, and it often results from an event like frost or hail that stops photosynthesis quickly after pods start to fill.”

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