Comparisons of corn hybrid relative maturities is complexed with flowering dates, black layer timing and harvest moistures. Temperate zone hybrids have mostly shed the day length component affecting time from planting to pollination, as this is mostly determined by accumulation of heat. Earlier hybrids require less heat to reach this stage. After flowering, time to formation of the abscission layer at the base of the kernels and stopping the translocation of carbohydrates into the kernels is about 55 days for all hybrids. Maturity, consequently, as defined by time from planting to completion of grain fill is mostly determined by needed heat from seed germination to formation of tassel and ear shoot meristems.
Grain storage requires moistures close to 15% instead of the 30% when the abscission layer (black layer) forms. Decrease of moisture as the sugar was transported in and starch formed in the developing kernel causing the consistent dropping of percent water down from 85% if the plant remains viable for the 55 days after flowering. Further drying in the field now is through evaporation through the kernel pericarp. Hybrids differ in morphological features affecting this evaporation rate. Husk leaf numbers, length, thickness and tendency to separate after their abscission layers have formed have a great effect on evaporation of water from the kernels. Pericarp thickness also affects loss of water through kernels.
There are several methods used to compare relative maturity of hybrids but practicality demands the comparison made at desirable harvest moistures. That involves the physiology of the young corn plant as it translates heat needed to transform the meristems into forming the male and female reproductive parts. It also involves the morphological structures of ear. The most practical and economic comparison comes when comparing harvest moistures of hybrid growing in same environments such as yield plots.
We probably express relative maturities of hybrids with more definitiveness than we should.
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About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.