At which reproductive stage does the black layer form on corn kernels?

The black layer forms on corn kernels during the R6 stage, which is known as physiological maturity. This is a crucial point in corn development as it marks the stage when the kernels have reached their maximum dry weight and are no longer accumulating starch. The formation of the black layer indicates that the kernel has fully matured and is ready for harvest, as it signifies that the plant has ceased all physiological processes related to growth and development in that kernel.

At this stage, the kernels will also start to demonstrate the intended traits for their maturity, such as the hardening of the endosperm and the drying of the moisture content inside the kernel. The black layer itself is a physical barrier that forms at the kernel’s base, marking the transition from the vegetative growth phase to a harvest-ready state. Recognizing this stage is essential for farmers to optimize harvest timing and ensure maximum yield and quality of the corn crop.

Other stages, such as R5 (grain fill), R4 (dough stage), and R3 (milk stage), involve different physiological changes and development but do not signify the complete physiological maturity of the kernel.