A RE-EVALUATION OF SOME ASPECTS OF THE GROWTH AND MATURATION OF THE CORN (ZEA MAYS, L.) KERNEL (MINNESOTA)

The primary objective of this study was to evaluate the usefulness of the kernel milk-line as a visual indicator of maturity in corn (Zea mays, L.). Five hybrids of varying maturity were grown in the field at St. Paul, Minnesota in 1980 and 1981. Movement of the kernel milk-line was monitored in these hybrids, as was kernel black-layer development, kernel moisture loss, kernel dry-weight accumulation, and calendar-day and growing-degree-day (GDD) accumulation. Four of the hybrids were also defoliated at various stages of kernel maturity to simulate prematurity stress--with the intention of evaluating the usefulness of the milk-line as an aid to making pre-harvest management decisions.;We do not recommend elimination of the black layer and replacing it with the milk-line as a visual indicator of maturity for corn. Rather we suggest watching for, and using, both the kernel black layer and milk disappearance. The two phenomena occurred almost simultaneously under normal conditions, but, depending on the environment, either has occurred in advance of the other. Environmental conditions affecting black-layer development and disappearance of kernel milk, and suggestions for their combined usage for determination of corn maturity, are discussed.;Our findings suggest that the milk-line may be a more useful indicator of corn kernel maturity than other indicators presently being used. The milk-line was always a readily-identifiable feature of maturing corn kernels. Disappearance of kernel milk was coincident with the cessation of kernel dry weight increase (physiological maturity). It was easier to determine the day on which milk was no longer present in kernels than to determine when the placental region was finally black. Also, unlike black-layer formation, the milk-line could be followed in its movement, and was therefore useful in "timing" the maturity process. At the half-milk stage, for example (i.e., when the milk-line was positioned half-way between the kernel tip and the kernel base) kernels had achieved 89% of their final dry weight, contained 40% moisture, and were 2-3 weeks (200 growing degree days) from the optimal date to begin harvest. If plants were completely defoliated at the half-milk stage, the kernels accumulated additional dry matter (apparently via remobilization from the stalk) and achieved 95% of normal dry weight.