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Relationships Among Black Layer Formation, Grain Moisture Percentage, and Heat Unit Accumulation in Corn¹

Two field experiments were conducted near Guelph, Ontario in both 1969 and 1970 with the objectives of (i) studying the relationship between grain moisture percentage and black layer development and (ii) examining the effect of environment on the length of the interval from planting or silking to black layer formation in corn (Zea mays L.). The first experiment involved 10 adapted commercial hybrids planted in early May at a plant population of 70,000 plants/ha. The second study concerned three commercial hybrids that were planted at a plant population of 55,000 plants/ha on each of four dates in 1969 (May 14 and 23, and June 5 and 13) and four dates in 1970 (May 6 and 20, and June 1 and 8). For both experiments records or measurements were taken of the date of 50% silking, 50% black layer, grain moisture percentage at 50% black layer, and final yield. Weather records were used to compute the number of accumulated heat units, by either the Ontario Corn Heat Unit (OCHU) or the 10- to 30-C Growing Degree Day (GDDHU) systems, from planting or midsilking to 50% black layer.

Among adapted hybrids planted in May percent grain moisture at black layer varied from 30 to 37. For two hybrids planted on June 13, 1969 and June 8, 1970, black layers developed "prematurely" at a grain moisture of 39 to 42%. This premature black layer formation was an apparent consequence of cool weather during the week prior to black layer development.

Delayed planting resulted in a decrease in number of days from planting to midsilking, and an increase in number of days from mid-silking to maturity (50% black black layer). Delayed planting resulted in an increased number of accumulated heat units from planting to midsilking, and a decreased heat unit accumulation from midsilking to maturity, by either the OCHU or GDDHU system. As a result, the number of accumulated heat units from planting to maturity was only slightly reduced by delayed planting date. The two systems were of comparable precision and were superior to number-of-days per se in characterizing the length of the interval from planting to midsilking, but not from midsilking to maturity.

Because of its ease of detection, black layer development can serve as a useful end-point for characterizing corn hybrids as to their relative maturity and their adaptability to various localities. Present results suggest that there are significant problems, however, in the wide-scale use of black layer development for this purpose.

Key Words: Hybrid • Silking

² Assistant Professor, Department of Crop Science, University of Guelph, Guelph, Ontario, Canada.

Received for publication September 3, 1971.