Earlier planting increases yield, decreases plant height, and decreases lodging in the farmers’ fields. The earlier of two plantings may decrease plant height and stalk breakage even when both plantings emerge at the same date. Things are going on under ground. Cooler temperatures during early development shorten internodes.
Seed coat integrity (to keep disease and fungi out) is important to cold test germination. Damage to the seed coat (by the seed company) during harvesting and conditioning reduces cold test germination. Seed from larger kernels may be more susceptible to damage because their seed coats (female tissue) have been stretched thinner. Flat kernels protect the germ face (embryo) more than round shaped kernels.
Angle of secondary root growth is a heritable trait, but corn roots grow only where environmental conditions permit. Seed bed temperatures warm from the surface down. Cooler soil temperatures promote more horizontal secondary root growth, thus reducing early root lodging.
Seedling vigor is important. During the first 4-6 weeks of the growing season, seedling vigor is the farmer’s basis for hybrid comparison. It affects sales! Also, fast early growth increases leaf canopy for photosynthesis during longer days. The greatest quantity and best quality of sunlight is on June 21st (the summer solstice in the northern hemisphere). Seedling vigor scores are an estimate of green mass. Robust seedlings are advantageous over thin, grassy looking seedlings, because they have more leaf area for photosynthesis.