August 28, 2012
2012 U.S. Corn Crop Highly Variable, Yield Estimates Difficult
As illustrated by the recent crop tours, the key word this year for the corn crop is variability. Not only the variability between fields but also within a field as well. This variability is going to make it very difficult to come up with an accurate yield estimate before the corn crop is completely harvested.
Teams from NASS are already in the field conducting surveys for the September Crop Report. For this report they will count the ears and weigh them as well if the corn is close enough to maturity. Even so, there will still be some aspects of the crop that they will not be able to completely determine for this report such as the final test weights, the harvest loss, and the seed quality.
Test weights - For the most advanced corn, they will have a good idea about the test weights when they collect and weigh their field samples, but the test weights are yet to be fully determined for the later maturing corn. Additionally, the farmers who participate in the survey probably do not know what the final test weights will be for their crop unless they have already harvested their corn. Test weights this year will certainly be lighter than normal so therefore any model that uses average test weight will probably be overestimating the final corn yield.
Harvest loss - Harvest losses this year will also be greater than normal. Generally, 0.5 to 1% of the corn is lost during the harvesting process, but in the drought ravaged fields, the losses could be much greater this year. The farmers need to adjust their header and thrashing drum in their combine to a closer tolerance in an attempt to harvest as much grain as possible from the many small "nubbin" ears. In doing so, they also run the risk of cracking and damaging some of the healthy kernels resulting in what are called "fines", or broken pieces of kernels. These fines can be blown out the back of the combine or be removed during the grain handling process. If there are an increased number of fines, then there will be less total production.
An additional source of increased harvest loss is the fragile nature of the drought impacted corn crop. These plants have weaker stalks, roots, and ear shanks than in a typical year and are more subject to ear droppage, stalk breakage, and lodging. All of these factors could result in lower overall corn yields. NASS will not be able to determine the final harvest loss until the fields where there plots are located are harvested by the farmer. Once the field is harvested, they will go back into the field and determine how many kernels were left on the ground. Very few of these harvest loss surveys will be completed in time for the September Crop Report.
The bottom line for harvest loss is that it will probably be much greater than in a normal year. This year it is possible that the harvest losses could reach 3-4-5% or more in the drought impacted fields.
Grain quality - Poor grain quality could also be a factor this year. In the droughty areas, the corn kernels this year are probably less able to resist fungal infections. The worst thing for this corn crop would be a prolonged period of heavy wet weather before harvest. Not only would the wind and rain cause additional stalk breakage, lodging, and ear droppage, it would also expose the crop to additional fungal infections resulting in even lower grain quality. The lower grain quality could also mean that more corn would need to be fed to livestock to achieve the same weight grain compared to high quality corn.