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This article in AJ

  1. Vol. 85 No. 4, p. 916-928
     
    Received: Apr 2, 1992
    Published: July, 1993


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doi:10.2134/agronj1993.00021962008500040025x

Energy Exchange and Water Use Efficiency of Field Crops: Validation of a Simulation Model

  1. R. F. Grant ,
  2. P. Rochette and
  3. R. L. Desjardins
  1. Dep. of Soil Science, Univ. of Alberta, Edmonton, AB, Canada T6G 2E3

Abstract

Abstract

Crop canopies exercise some control on the exchange of mass and energy with the atmosphere by regulating their stomatal resistance. A hypothesis is proposed in which regulation of stomatal resistance is controlled jointly by the water status of the canopy and photosynthetic capacities of the leaves in the canopy. This hypothesis was incorporated into an ecosystem simulation model, which was tested against data for mass and energy exchange measured over a growing barley crop at different levels of canopy cover and soil water content. Standard differences (square root of the mean square difference) between simulated and measured hourly values for net radiation, latent heat, and sensible heat over the soil-canopy surface were <50 W m during each date for which comparisons were made, which is within the range of experimental error. The hypothesis allowed title model to simulate diurnal changes in canopy stomatal resistance under changing atmospheric conditions that were consistent with those estimated from flux measurement techniques. These diurnal changes allowed the model to reproduce changing relationships between latent and sensible heat fluxes measured at different canopy covers and soil water contents. The diurnal changes in simulated canopy stomatal resistance also allowed the model to reproduce diurnal changes in soil-canopy net CO2 exchange (SD = 3–4 μmol m−2 s−1) and water use efficiency under changing atmospheric conditions and soil water status. The hypothesis for the regulation of canopy stomatal resistance is simple, and yet allows observed canopy behavior to be reproduced over a wide range of conditions.

CLBRR Contribution no. 92-193.

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