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This article in AJ

  1. Vol. 75 No. 2, p. 281-286
     
    Received: Dec 24, 1981


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doi:10.2134/agronj1983.00021962007500020028x

Field Evaluation of a Water Relations Model for Soybean. 11. Diurnal Fluctuations1

  1. J. W. Jones,
  2. B. Zur and
  3. K. J. Boote2

Abstract

Abstract

A field study was conducted on soybeans (Glycine max L. Merr. cv. Williams) growing in Arredondo fine sand, a member of the hypothermic, coated family of Typic Quartzipsamments to determine the effects of drying cycles on plant water relations for comparison with results predicted by a dynamic model. Two different drying cycle treatments were imposed on different plots during late vegetative development and mid-to-late pod fill stages and well irrigated plots were maintained for comparison. Every other day during each drying cycle, hourly measurements of leaf water potential, canopy carbon exchange rate (CER), and canopy transpiration were measured on dry and wet plots. During the initial phases of the drying cycles leaf water potential, transpiration, and CER followed diurnal cycles closely related to radiation flux. This response lasted for 9 and 5 days during the first and second drying cycles, respectively, when crop water deficits reached critical levels causing leaf water potentials of − 1.4 and − 1.7 MPa. After these critical time periods, midday leaf water potentials became relatively stable with time whereas transpiration and CER decreased such that diurnal fluctuations disappeared. The model was successful in simulating diurnal patterns of these variables for the crop exposed to the two drying cycles.

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