In additional to being short on bushels, and possibly long on some mold issues, one of the main problems of corn this year will be test weight. Corn kernels will make up a rather light load, compared to typical years with more moisture and a deeper kernel. But when you consider kernel weight, how many kernels will it take to make a bushel, and how fluffy will it be?
The test weight of grain is based on pounds of grain per volume of a bushel. Since elevator offices do not measure an exact bushel, a representative sample is measured in a moisture meter and calculated to determine the weight of a volumetric measurement if it is expanded to that size. Purdue University agronomist Bob Nielsen said US trade in corn is marketed on the basis of a 56 pound bushel, even though 56 pounds would make it US number 1 corn, and 54 pounds make it US grade number 2 yellow corn. It is all based on dry measurement or anything between 15% and 15.5% moisture. Moisture is not part of the grain standard and has not been for a couple decades; however the price is discounted if the moisture is not there.
If the corn comes up short on test weight, then price is discounted for low test weight. Suddenly a semi trailer loaded with—what was thought to be 1,000 bushels-- will only get paid for 956 bushels based on the test weight, if the test weight of the corn was 52 pounds per bushel. If your test weight was 60 pounds per bushel, your deliverable bushel would be 1,071 from the same semi.
Test weight may bolster the number of bushels paid when delivered to the elevator, but did not change the actual number of bushels in the bin. In fact high test weight corn does not have anything to do with yield, nor does low test weight corn. While this year the yield is low along with the test weight, that is more of a coincidence based on Nielsen’s fact sheet. Nielsen says, “Hybrid variability exists for grain test weight, but also does not necessarily correspond to differences in genetic yield potential. Test weight for a given hybrid can vary from field to field or year to year, but does not necessarily correspond to the yield level of an environment.”
Nielsen says there is a common belief that low test weight corn results in lower processor efficiency and quality of products, but that is not consistent. Additionally, he says low test weight corn is believed to be inferior when fed to livestock, but there is no research that supports that. He says whether low test weight corn is inferior to higher test weight is more dependent upon the reason that the corn had a low test weight initially.
He says test weight and moisture have an inverse relationship, and the higher the moisture the lower the test weight. That is because as grain dries, kernel volume shrinks, the kernels are packed closer together, and drier grain is more slick which will also enhance the packing process. He points to the wet harvest year of 2009 and says test weights were lower than would have been expected.
Nielsen also says the 2009 crop had a lower test weight than would have been expected because drought stresses, foliar diseases, and below normal temperatures during September of that year resulted in less than adequate grain fill and dry down. And he said the later developing corn were subject to frost damage that also had an effect on test weight. Additionally, fungal issues can also result in light weight and chaffy grain with lower test weight, and inferior quality grain for livestock feeding.
Test weight of 2012 corn could be lighter than usual because of less than adequate starch filling, but lower test weights do not always parallel the amount of moisture in the grain. Test weight is a function of the weight of a bushel volume, and while the volume may not change, the producer may be paid more or less based on the test weight of the grain than on the volume. Many factors affect test weight, including fungal issues and temperature at drydown.
Source: FarmGate blog