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Synopsis Ten hybrids and 10 inbreds were planted on 5 different dates in 1956 and their maturities, based on silking dates, were calculated in heat units by 15 different methods. The present method of calculating degree days, daily mean minus 50° F., was improved by correcting for temperatures below the minimum for growth, 50° F., and above the optimum for growth, 86° F. The number of heat units required for silking, designated as effective degrees, remained relatively constant for crops with different planting dates, while calendar days varied widely.
Gilmore et al. (Wed,) studied this question.