Pasture canopy temperature under cloudy humid conditions

Abstract The temperature of a forage canopy, which is determined primarily by climate conditions and plant water status, is an important regulator of the forage's physiological processes. Canopy temperature measurements are widely taken as an indicator of plant-water status under arid, sunny conditions. This study was conducted to determine the canopy temperature response of orchardgrass ( Dactylis glomerata L.) to the high humidity and variable radiation levels of Appalachia. Average hourly climate parameters were measured along with average hourly canopy temperature and daily evapotranspiration from a monolith lysimeter at the North Appalachian Experimental Watersehd at Coshocton, Ohio, from Day 110 through 183 of 1989. The responses during a reference spring with plentiful rainfall indicate that canopy temperature decreased 2.1°C for a 1 kPa increase in vapor pressure deficit and increased 0.6°C for each 100 W m −2 increase in net radiation. The levels of average hourly wind during this period had no significant effect on canopy temperature. Aerodynamic and canopy resistances calculated from canopy temperature responses to vapor pressure deficit and net radiation were consistent except at net radiation levels below 100 W m −2 . Reductions in canopy height by a half, as a result of lodging, had no pronounced effect on evapotranspiration or canopy temperature. The response of canopy temperature to changes in climate conditions was as reliably determined under cloudy humid conditions as under sunny conditions.

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