Determination of actual evapotranspiration and crop coefficients of broad bean (Vicia Faba L.) grown under field conditions in the jordan valley,jordan: Bestimmung der aktuellen evapotranspiration und pflanzenbestandskoeffizienten von bohnen (Vicia Faba L.) unter feldbedingungen im jordantal,jordanien

This study was conducted to determine actual evapotranspiration and crop coefficients at different growth stages of broad bean (Vicia faba L.) grown in an open field in the Jordan Valley, Jordan using a precise and accurate approach. The study involved 30-min fluxes measurements of energy budget components over broad bean crop using a complete setup of an Eddy Correlation (EC) system. The measurements were conducted during the three main crop growth stages namely initial, development, and midseason growth stages following the Food and Agriculture Organization of the United Nations (FAO) crop coefficient model for green harvested broad bean crop. The average crop coefficients during the initial (K_{C ini}), development (K_{C dev}) and midseason (K_{C mid}) growth stages were 0.37, 0.8 and 1.05, respectively. The measured weighted average crop coefficient over the entire growing season K_{C GS} was 9.5% lower than the FAO corresponding value.

Results showed that there was a clear decrease of (bulk) surface resistance (r_s) as crop canopy developed. Daily average r_s values were 855, 337, and 166?s/m for initial, development, and midseason growth stages, respectively. Moreover, r_s was found to be highly correlated to crop height (h_c). A simple linear relation between r_s and h_c with R² of 0.91 was found. This relation will enable future direct determination of crop evapotranspiration (ET_C) using Penman-Monteith equation without the need to calculate both grass reference evapotranspiration (ET_O) and crop coefficient (K_C) values.