[Evaporation of a reference lucerne cultivar for empirical formulas valoration at Montecillo area, Mexico, State]

English. An hectare plot of alfalfa, Medicago sativa, was established in the Hydroscience Center of the Postgraduate College. At the middle of the experimental plot a soil unalterated weighing Lysimeter planted with alfalfa was placed. The Lysimeter, equipped with an electronic load-cell and drainage system was used to measure the reference crop evapotranspiration (Eto) with accuracy. Using metereological information available potential evapotranspiration was calculated using empirical formulas from the literature. Eto was considered as the average of the ten days before each cutting. The correlation between ETo and ETp allowed to calculate calibration coefficients for every one of the empirical formulas. The formulas which consider global radiation data are the best to estimate ETo for this area on a daily basis, and indicates of periods of five and ten days which is the case of the Christiansen-Hargraves formula. It is convenient to continue with this research project to adjust ETo with the information for several years.

Spanish; Castilian. Se establecio un cultivo de alfalfa Medicago sativa, en el Centro de Hidrociencias del Colegio de Postgraduados, con una superficie de una hectarea. En el centro del lote, se instalo un lisimetro de pesada tipo monolitico el cultivo para determinar la evapotranspiracion de referencia (Eto). Con la informacion meteorologica disponible se calculo la evapotranspiracion potencial (ETp), con quince formulas empiricas reportadas en la literatura. La Eto que se considero para los calculos correspondio a la medida de diez dias antes de cada corte del cultivo. La correlacion entre Eto y Etp permitio calcular los coeficientes de calibracion de cada formula empirica estudiada. Las formulas que consideran a la radiacion global en su estructura, son las que mejor estiman Eto, para esta zona a nivel diario, 5 y 10 dias como en el caso de la formula de Christiansen-Hargraves. Se recomienda continuar con esta investigacion para afinar la Eto con informacion de varios anos.