Effect of soil surface wetness and air temperature on transpiration in wheat [Triticum aestivum] field covered sparsely by vegetation
2009
Fukumoto, M.(National Inst. for Rural Engineering, Tsukuba, Ibaraki (Japan)) | Hirota, T.
We constructed a detailed heat balance model for a sparse canopy, which allowed the interaction of heat flux between soil and vegetation, and set the values of various parameters for the model based on observation data, obtained from a wheat field covered sparsely by vegetation (plant height, 0.52 m; leaf area index, 1.2) between 1100 and 1400 h on July 12-14. Using this model, we examined the effect of soil surface wetness (volumetric soil moisture in the top 2 cm layer theta, 13.7% or 22.3 %) and air temperature (23degC or 27degC) on transpiration from vegetation under a given condition (solar radiation, 850 W/square m; atmospheric radiation, 350 W/square m; specific humidity, 0.013 kg/kg). As a result, it was found that transpiration increased 1.41-1.46 times as air temperature rose by 4degC under the same condition of soil surface wetness, and increased 1.14-1.17 times as soil surface changed from wet (theta, 22.3%) to dry (theta, 13.7%) condition at the same air temperature. The ratio of transpiration to evapotranspiration was 0.42-0.49 when the soil surface was wet, and 0.71-0.75 when the soil surface was dry.
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