GROWTH RATES OF MAIZE UNDER FIELD CONDITIONS

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Abstract
Growth curves, obtained by weekly measurements of the dry wts. of 120 plants of each of 4 vars. of maize during the growing seasons of 1938 and 1939, showed that the 4 vars. constituted a single population in their % responses to the weekly complex of environmental conditions. The dry wt. curves were sigmoid, accelerating during the first 40 or 50 days, increasing uniformly for the next 50 or 60 days, and dropping off to maturity at 120-130 days. The data indicate that the growth of corn in the field tends to follow the temp. curve, at least at moderate temps. Weekly increments of dry wt. during a period of 8 weeks when leaf area was approx. constant, were uniform in 1938, but varied significantly in the cooler, wetter season of 1939. The coeff. of correlation, 0.81, between weekly gains and Lehenbauer''s physiol. indices of weekly mean temp. was highly significant for 1939 but not significant for 1938. Poor distribution of rainfall apparently accounted for the failure of the dry-wt. curve to approx. the growth possibilities represented by the temp. index curve in 1938. Data obtained by the use of tensi-ometers suggest that soil moisture became limiting for opt. development whenever the plants were forced to draw heavily on the moisture reserves of the 3d foot of soil.

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