Determination of physiological maturity in corn

Ten corn hybrids differing in maturity were planted in the summer of 1978 in order to predict and determine the time of physiological maturity and the rate of moisture loss following maturity. The design of the experiment was a randomized complete block. Observation and measurements of maturity factors included leaf number per plant, dates of tasseling and silking, dates of dead leaf and brown husk formation, dates of kernel denting and of black layer formation, percent moisture of grain and cobs, and the yield of grain.

Leaf number varied from 15 to 19, while tasseling and silking occurred from 55 to 66 and 61 to 69 days after planting. There was a positive correlation between the number of leaves and the number of days from planting to silking. Kernel denting occurred in 109 to 116 days after planting and 40 to 51 days after silking. Black layer formation ranged from 57 to 64 days after silking, and the moisture level at this stage varied from 21.8 to 33.3% in grain and 26.8 to 54.6% in cobs.

Correlation of leaf number and number of days to silking to number of days to black layer after silking was low. However, moisture percentage was negatively correlated to number of days to black layer formation.

The rate of drying (percent moisture loss) was found to be faster in cobs than in the grain but equilibrium was reached in the two at about 19 to 23% among the hybrids. Yields generally varied inversely according to the length of the physiological periods.

Based on the data from maturity factors enunciated earlier on, Princeton SX910, Pioneer brand 3184, Funk G-4507, DeKalb XL72B, Funk G-4525, DeKalb XL80 and FFR707C were classified as early maturing, while Pioneer brand 3147, Funk G-4848 and DeKalb XL394 were late maturing. No single factor measured proved to be an accurate prediction of the date of physiological maturity as indicated by black layer formation. The moisture content of various hybrids at maturity varied by as much as 11% among hybrids.