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This article in AJ

  1. Vol. 59 No. 1, p. 41-44
    Received: June 20, 1966

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Diurnal Variation in Growth Rate of Grain Sorghum1

  1. Wendell C. Johnson2



Growth rate of irrigated grain sorghum with moisture not limiting was measured in the field between August 11 and September 4, 1965, near Amarillo, Texas. A growth sensor was used which converted the extension of a grain sorghum leaf from the whorl, or of a head from the boot, into an electrical signal which was continuously recorded on a strip chart recorder.

The minimum growth rate occurred between 7:00 and 9:00 AM on individual days. The growth rate increased rapidly after that and reached a maximum value for the day near noon. The growth rate decreased sharply during a 3- or 4-hr period which began on different days between 4:00 and 7:30 PM and lasted until 8:00 to 10:00 PM. After this evening period of sharp growth rate decline, the growth rate decreased more gradually and paralleled the air temperature decline until the morning growth minimum was reached. (Times stated are Central Standard Time, or true solar time + 50 min.) There was evidence of a double peak in the growth rate curve in the afternoon of a clear day and of a temporary acceleration of growth rate in the early morning when moisture condensed on the foliage.

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