Evapotranspiration from a Humid-Region Developing Citrus Grove with Grass Cover

Abstract

ABSTRACT EVAPOTRANSPIRATION (ET) of a developing citrus grove in a humid climate in the Flatwoods Land Resource Area was determined by water balance from measured rainfall, irrigation, subsurface drainage, surface runoff, and the change in soil moisture storage. The change in soil moisture storage was estimated from soil moisture characteristic curves and measured water table elevations. Annual ET ranges from 820 to 1280 mm and averaged 1090 mm across all treatments. When soil moisture was not seriously limited the annual ET averaged 1210 mm. Linear regression of ET vs time indicated a significant increase of 13% in ET over the 8 years of the study. This increase was attributed to increasing tree size since the grass understory was maintained to provide similar cover conditions throughout the study. Daily ET rate, averaged by months, ranged from 1.5 mm in January to 5.0 mm in June. Four predictive equations for ET gave good estimates of measured values, but require crop coefficients that are slightly modified from previously published values.