By Benjamin Agyei and Maninder Singh
Corn growth and development are strongly influenced by environmental temperatures. In general, corn develops more rapidly under warmer temperatures and more slowly under cooler conditions. For example, when corn is planted in late April in Michigan, emergence can take up to 18 days. In contrast, corn planted in mid-May typically emerges within a week. The difference in time to emergence is primarily due to normally warmer air and soil temperatures later in the spring season. Temperature also impacts the timing of other key phenological stages such as silking and black layer.
Growing degree days (GDD) is an index used to relate corn growth and development to environmental conditions, typically with observed air or soil temperatures relative to a given temperature threshold at which either growth is known to begin or stops. Using observed temperatures as input, GDD numerically approximate the amount of time an organism spends above (or below) a known threshold temperature.
Corn accumulates a specific number of GDD to reach different growth stages and seed companies use the amount of GDD to reach black layer to assign hybrid maturity rating. GDD can be calculated from either planting to black layer or from emergence to black layer, and seed companies use one of these approaches when assigning GDD ratings to corn hybrids.
When growers select a corn hybrid maturity for their field, they typically rely on relative maturity (RM) ratings assigned by seed companies. However, RM ratings have limitations in accurately reflecting growing season characteristics. First, RM is often misinterpreted as calendar days to maturity, but there is observational evidence to show that corn may require more days in the field to reach black layer and harvest maturity than indicated by its RM rating. Second, RM ratings do not directly account for weather conditions during a given growing season such as temperature and management practices such as planting date.
Source : msu.edu