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This article in AJ

  1. Vol. 61 No. 4, p. 539-542
    Received: Nov 29, 1968

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Diurnal Variation in Growth Rate of Irrigated Winter Wheat1

  1. Wendell C. Johnson2



During the 2-week period before heading, a continuous growth record of irrigated winter wheat (Triticum aestivum) was obtained using a growth sensor attached to a leaf emerging from the whorl and a strip chart recorder. The growth rate was typically the greatest in the afternoon, with a maximum point usually occurring around sunset. The minimum growth rate usually occurred at the time of the minimum temperature, which on days without moisture condensation was around sunrise. The normal decrease in growth rate at night was arrested, or there was an increase in growth rate, when an increase in temperature or humidity occurred.

A continuous growth record of a plant was obtained during a 6-day period that included a cold front passage followed by a late freeze and several days of subnormal temperatures. The temperature below which growth ceased was in the range 1 to 1.5C. On the day with the coldest morning, minimum temperature −0.5C (31F), considerable growth was made in the afternoon when the temperature rose to 23.5C (74F).

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