How important is corn test weight? That question is commonly asked as harvest approaches and was addressed by Emerson Nafziger, University of Illinois Extension corn specialist, in the recent Pest Management and Crop Development Bulletin.

Test weight is affected by kernel density, size, and shape as well as by moisture and condition of the seed coat. As producers know, hybrids differ in test weights, and any of the above mentioned factors might affect such differences.

Nafziger has studied the relationship between test weight and yield in corn hybrid trials and never found a strong correlation.

Within the same hybrid, lower or higher test weight is often related to kernel weight, which is often correlated with yield, says Nafziger.

A kernel that does not fill very well with starch has lower endosperm density, thus lower kernel density. This means the kernel has less weight for its volume. This often means a drop in test weight.

An early end to the grain filling process often does mean lower test weight. However, this decrease in test weight may not be proportional to lower yield.

Nafziger notes that test weight is used to take the place of things like kernel density that are hard to measure directly. We can have average test weight and high yields in certain hybrids, but there has been some movement by seed companies away from hybrids with low test weights.

From a practical standpoint, more "bushels" (56-pound units) fit into a bin when test weight is high that when it is low, concludes Nafziger.