A technique for controlling the soil moisture potential in the root zone of transpiring plants was developed. The method uses the principles of unsaturated flow through a porous media to develop the desired moisture potential. In the case of non-steady state transpiration, the maximum possible fluctuation in the soil moisture potential can be determined by the techniques presented.
Two implicit leaf temperature prediction equations were derived from the energy balance approach. The equations define sensible and latent heat transfer from a plant population as a two step process:
- Transfer between the plant leaf and the canopy bulk air and
- Transfer between the canopy bulk air and the atmosphere.
Boundary layer concepts were applied to leaf heat transfer in both equations. Turbulent atmospheric transfer by free and forced convection were considered.
Measurements of leaf temperature and wind velocity, temperature and humidity profiles for a cucumber plot were taken during ten tests. Richardson numbers to classify atmospheric stability were determined. The neutral wind velocity profile parameters, roughness height and zero displacement height were determined by a computerized least squares technique using data from the ten tests. Calculated Richardson's numbers indicated transfer by free convection. Comparison of predicted and measured leaf temperatures revealed the forced convection prediction equations considerably over estimated leaf temperature while the free convection predictions was much more accurate.
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The work upon which this report is based was supported in part by funds provided by the United States Department of the Interior, Office of Water Resources Research, as authorized under the Water Resources Research Act of 1964.
Haan, Charles T.; Barfield, Billy J.; and Edling, Robert, "Part I - Controlling the Soil Moisture Environment of Transpiring Plants, Part II - Prediction of Leaf Temperature Under Natural Atmospheric Conditions" (1970). KWRRI Research Reports. 162.