If you haven't seen the January issue of Indiana Prairie Farmer yet, it should arrive soon. If you have seen it, from the cover story to the last story, Market Outlook, the tone is the same. Hot weather affected the 2010 corn crop, and USDA underestimated the effect in its beginning estimates.
Arlan Suderman, a Farm Progress market analyst, makes it clear in these stories that the 2010 season was one of those unusual seasons where assuming normal weather conditions for the rest of the season after initial crop estimates doesn't work. That's because the temperature stayed hot, and it was dry. The key was nighttime temperatures, which were especially high in late July and much of August across a good chunk of the Corn Belt.
Nighttime temperatures that are above normal tend to cause the plant to continue respiring, expending energy from products made during photosynthesis during daylight hours that would otherwise wind up as starch in the kernel, adding to kernel weight and yield.
Bob Nielsen, Purdue corn specialist, says other factors also likely contributed to USDA's initial estimate being too high, including the jump diseases got on corn due to the weather in many areas. When diseases like gray leaf spot get a head start and conditions remain favorable, they can do serious damage, and cause plants to shut down early. Once the black layer forms, the plant can no longer put starch, or extra dry matter weight, into the kernels.
The result of all of this is that when USDA issues its final crop report in one week, on January 12, in Washington, D.C., Suderman expects that if the trend established in other years similar to this one holds true, the estimate may be slightly lower once again. He doesn't expect a large drop, but he does expect USDA to adjust the final number for corn yield per acre for 2010 lower by some amount.
That's what's happened in other summers where heat, especially with high nighttime temperatures, was a dominant factor. The largest drop USDA has ever made from initial August crop estimates for corn to final crop yield for corn is just over 12 bushels per acre. So far, the drop for the 2010 crop from the August estimate based on late July and early August findings to the last estimate issued is just over 10 bushels per acre.