Excess Heat During Season Can Hold Down Yields

Even irrigation can't offset all effects of stressful summer.

The Corn Illustrated high-yield plots didn't reach Dave Nanda's goal, but he's still amazed how well they performed considering the season that unfolded and the area where the plots were located.

The goal for the plots was to reach 325 bushels per acre. Nanda, a long-time plant breeder and now president of Bird Seeds, Tiffin, Ohio, reports that the top-yielding six-row, field-size strip in the replicated plot wound up around 235 bushels per acre. Moisture corrections will be made before final numbers are released soon. The plots were located near Edinburgh in south-central Indiana.

"These aren't flat, black, high-organic matter soils," Nanda says. "So we knew we had a challenge going into the project." The soils consist of about three feet of silt loam (medium-textured) soil over gravel. The gravel is so rich for those wanting to mine it that a gravel company actually owns the land. Jim Facemire, a local farmer, operates the land and is the cooperator for the Corn Illustrated project.

Organic matter is only about 1.5 to 2.0 %, Nanda observes. That's based on long-term soil testing Facemire has completed in the field over the years. The field is relatively flat to very gently rolling, and reasonably uniform. However, there are still some differences in the make-up of the soil from one side of the plot area to the other.

The high-yield portion of the plot was irrigated all season, as needed. Then a third of the plot was irrigated after pollination. The final third was never irrigated. Yield differences as high as 160 bushels per acre or more were recorded on the same six rows of most six-row strips, running from the irrigated to non-irrigated areas.

"It's difficult to reach very high yields on these types of soils," Nanda says. It's not like shooting for top yield son dark, black, rich organic-matter soils, where good artificial or natural drainage helps keep soils from being too wet."

These soils are prone to the opposite problem- drought. And this year tested the limits, with scanty rainfall all season. The biggest rain Facemire recorded during the grown season was just over 1 inch, in the third week of June.

The other factor holding back yields, even on irrigated ground, was heat, Nanda believes.
Indianapolis, some 30 miles away, recorded more than double the number of 90 degree days this summer, at 37. Temperature is a rather constant variable across areas, and temperatures at Facemire's weather station, provided by Spectrum Technologies, Plainfield, Ill., tended to run a degree or two warmer than Indianapolis/

"Nighttime temperatures that stay too high and don't cool off affect plants," Nanda says. "That can result in somewhat lower yield."

Others have observed that irrigated corn doesn't always do as well as expected on very warm years. With today's advanced hybrids, yields are still historically good. What's not known is how high yields could have been here without so many hot days, especially in the latter half of the season.

"I really believe we might have hit 300 bushels per acre, even in this moisture-stress year and with these soils, without so much heat," Nanda concludes.

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