The Energy Budget at the Earth'S Surface: Preliminary Wind Tunnel Studies of the Photosynthesis and Transpiration of Forage Stands

摘要

Vegetative stands of alfalfa and orchardgrass, grown in flats in a glasshouse, were investigated in a small wind tunnel. The windspeed parameters of the crop surfaces were determined at low radiation intensity at each of two windspeeds; and the rates of net photosynthesis and evapotranspiration were measured at the two windspeeds at each of three radiation intensities. The roughness length (zo) increased with windspeed and was greater in orchardgrass. Rate of net photosynthesis, but not evapotranspiration, also increased with windspeed. In consequence, water-use was most efficient under the highest wind regime. The rate of net photosynthesis increased to the intermediate radiation intensity, whereas evapotranspiration increased and water-use efficiency decreased to the highest radiation regime. The work indicated that a small wind tunnel of the type described would be useful for further studies of the photosynthesis and transpiration of forage stands. (Author)