Water Loss from a Sorghum Field and Stomatal Control
1968
Van Bavel, C. H. M. | Ehrler, W. L.
Measurements of temperature and diffusion resistance of leaves and of micrometeorological factors in a wellwatered sorghum field during June in central Arizona show that the stomata regulate transpiration only during the periods of darkness and low light. This was concluded from a comparison of the values for the canopy resistance as derived from direct measurement on leaves and as calculated from the environmental data. This finding predicts that, during the main part of the daylight period, neither an increase in number or aperture of stomata nor a wetting of the entire foliage would increase the evaporative flux. The action of the sorghum plant is then like that of a wick. We also found that, in a hot and dry environment, the sorghum foliage will constantly be several degrees cooler than the ambient air, even in the middle of the day when radiant energy input is large. Finally, the energy equivalent of the evaporative flux exceeded the net radiant flux significantly at all times, and by 80% over a 24-hour period. All three findings are at variance with common generalizations concerning the energetics and mechanics of crop transpiration. However, we recognize that our findings cannot be generalized to include other crop plants without specific studies.
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