Effect of planting date on measured growth intervals for a set of genetically diverse maize hybrids
Delayed planting is known to affect the thermal and calendar day requirements of corn hybrids. There are conflicting reports in the literature as to whether the thermal intervals to certain growth stages are increased or decreased by delayed planting. A study of 12 maize hybrids was conducted in 1994 and 1995. These hybrids were characterized for: 1) thermal time requirements to growth stages, 2) grain moisture at black layer, 3) GDD accumulation patterns based genetic backgrounds, and 4) explore the effect of delayed planting on these hybrids as related to thermal time requirements. Field experiments were established at five locations in 1994 and three locations in 1995 within the central, eastern and northern corn belts. Twelve hybrids were planted in a randomized complete block arranged in a split plot layout. Main plot was planting date, and hybrid maturity comprised the sub-plot. A 14-21 day interval between planting dates was desired. Thermal time requirements for growth stages were documented using the NOAA formula. Over years, the calendar day interval to both silking and black layer was reduced by 11 days, with the interval between planting dates averaging 18 days. Thus, the grain fill period was constant from a calendar day standpoint, and yet required 80 fewer GDD's when planting was delayed. Growing degree day requirements to silking and black layer were reduced by 31 and 110 GDD'S, respectively. Hybrids required 10 fewer calendar days and 93 fewer GDD's to reach 25% moisture. Black layer moisture increased due to delayed planting by an average of 1.1% over years. Calendar days to black layer were reduced by delayed planting in 1994, and more so by the warm, dry early Fall in 1995. Days to 25% moisture responded to year effect much the same as days to black layer. GDD reductions per day of delayed planting were highest in 1995, indicating that more adjustment occurred in that year environment. Black layer moisture was relatively independent of location, hybrid and year, although moisture levels generally were elevated for delayed plantings. Average BL moistures due to delayed planting ranged from .6% higher in 1994 to 1.8% higher in 1995.
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