Black layer of grain

Corn is beginning to be harvested around North Florida this week. Most all of the corn planted in the area has reached “black layer” or physiological maturity. This is where a black layer develops at the tip of the kernels, where they attach to the cob. Some farmers have started harvesting and drying grain, while others are waiting for air drying to remove additional moisture. In the recent hot dry weather, we see corn lose 3/4 to 1% of grain moisture per day by air drying. Warm temperatures and low humidity favor rapid drying of grain. Post-maturity grain moisture loss occurs only by evaporation from the grain. Moisture is lost through the pericarp, or outermost layer of the kernel wall. There is no loss of moisture from the grain back into the plant. At the onset of kernel black layer, the connection between the grain and plant is broken. Following this development there is no additional movement of water or nutrients.