The harvest day for the tests should be soon enough after the earliest hybrids mature so that a meaningful range of moisture differences exists between the early and late hybrids. Black layer formation is a precise indication of physiological maturity. This is discussed in NebGuide G76-301, How to Tell Corn, Sorghum Maturity . The moisture content of hybrids may differ markedly at physiological maturity. Rate of drydown.
Hybrids lose kernel moisture at different rates in the field.
Rapid drydown after physiological maturity is desirable to permit earlier harvest, reduce drying costs, and reduce field losses. Consistently high harvestable yield is the most important characteristic to be considered. Hybrids of the same maturity may differ widely in yield. Yield is the overall measure of how well the hybrid is adapted and how well it may respond to favorable weather and good management. Measured yields under a farmer's own conditions over three or four years will reflect the hybrid's ability to produce under specific soil, climatic and management conditions.