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Book: Field Soil Water Regime
Published by: Soil Science Society of America



  1.  p. 57-76
    SSSA Special Publication 5.
    Field Soil Water Regime

    R.R. Bruce (ed.)

    ISBN: 978-0-89118-900-8


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Experiments in Predicting Evapotranspiration by Simulation With a Soil-Plant-Atmosphere Model (SPAM)1

  1. E. R. Lemon,
  2. D. W. Stewart,
  3. R. W. Shawcroft and
  4. S. E. Jensen2


From extensive field study, we have introduced a comprehensive mathematical model that acts like a plant community. It is based upon the conservation of energy. Our understanding and deficiencies have been gauged by testing model forecasts of local climate and community processes against real world experience with a simple system—a corn field (Zea mays L.). Microclimate prediction is biologically good enough, but reveals inadequacies of understanding airflow fluid dynamics within the vegetation stand. The inability to measure or predict the degree of wetness of the soil surface hampers correct forecast of evaporation. Probably the most difficult problem to resolve is the biological one of predicting how leaf pores (stomates) open and shut under drouth stress, thus affecting both evaporation and photosynthesis in leaves. Additional serious problems will arise in the future modeling of nonuniform or more complex systems especially in forecasting the distribution of wind, momentum, and radiation within the foliage stand.

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Copyright © 1973. Copyright © 1973 by the Soil Science Society of America, Inc., 5585 Guilford Rd., Madison, WI 53711 USA