In-situ partitioning of evaporation and transpiration components using a portable evapotranspiration dome-A case study in Tall Fescue (Festuca arundinacea)

Understanding the components of water consumption of a crop or pasture through evapotranspiration is important for improving water management. In this study the FAO dual crop coefficient methodology has been used in conjunction with a portable evapotranspiration chamber in-situ, to quantify the basal crop (K_cb ) and soil evaporation (K_e ) coefficients of a pasture as a function of leaf area index and a widely used spectro-optical reflectance index, NDVI. To facilitate the measurement of soil evaporation component, small segments of the green biomass of a target pasture canopy, Tall Fescue (Festuca arundinacea var. Dovey) were allowed to rapidly senesce by applying a commercial herbicide while preserving the soil moisture and canopy structure. The ratio between the transpiration and evapotranspiration components (K_cb/K_c) increased from 0.03 to 0.46 for zero to highest available vegetation cover (LAI from 0 to 4.22). A significant linear relationship was observed between K_cb and NDVI (R² = 0.88) suggesting the possibility of using the latter, for example through remote sensing technologies, to determine the former.