Modeling evapotranspiration of drip irrigated upland cotton from first flower to peak bloom

Abstract

From June 28 to September 27, 1989, precise estimates of daily evapotranspiration (ET) were obtained over drip irrigated Upland cotton at the Maricopa Agricultural Center (MAC) from measurements of latent heat flux by Bowen ratio energy balance (BREB) instrumentation developed at the University of Arizona. Linear prediction models ET1 and ET2 were developed for cotton from hourly daylight BREB ET and Arizona Meteorological Network (AZMET) climate data. Models predict hourly daylight ET for the flowering growth period; daylight totals are increased by 3.3% to account for night evaporation. In 1990 and 1991, ET2 was applied to AZMET climate data and compared to cotton irrigation volumes at MAC. In 1990, irrigation fell 21% below ET2. In 1991, irrigation exceeded ET2 by 6%. Model ET2 form is: ET2 = aKD + bU2 + c, where a, b, and c are constants, KD is incoming solar radiation and U2 is wind speed at 2 meters.