EVAPOTRANSPIRATION AND ENERGY BALANCE ON AN ALFALFA CROP

Bowen's micrometeorological method of energy balance was used to learn about the accuracy of evapotranspiration estimation during short periods of time and to study energy balance on a crop of alfalfa (Medicago sativa L.) established at the Colegio de Postgraduados in Montecillo, State of Mexico. Lysimeter readings and Bowen's estimates of latent heat fluxes (LE) were compared at hourly intervals for four days. Soil heat fluxes (G) and sensible heat (H) were also calculated. Due to the presence of obstacles around the study area, atmospheric stability conditions required to assume equal turbulent exchange rates for sensible heat (Kh) and vapor water (Kw) were not met; therefore, it was necessary to calculate these rates to correct Bowen's values (β). When β values (assuming Kh=Kw) were compared with corrected values it was found that β fluctuated in the winter from − − − − −129.3 to 63.4 when Kh=Kw and from −0.879 to 2.48 when β was corrected for calculated Kh and Kw. During the summer, β fluctuated from − − − −1.37 to 1.40 when Kh=Kw, and from -0.59 to 0.10 when β was corrected for calculated Kh and Kw. In general, diurnal flux of LE estimated from Bowen's method underestimated lysimeter flux readings due to the advection of sensible heat; which reached values of 92.8 Kw in the summer. Diurnal balance of energy indicated that advection of sensible heat represented slightly more than 40% of the net radiation.