Crop coefficient for irrigated beans derived using three reference evaporation methods

Reference evapotranspiration (Eo), together with the crop coefficient (kc), allows to generate crop curves of water consumption to manage irrigation for several crops. However, Eo estimates using different methods has led to quite distinct results. In this work a comparison is made of Eo estimates by Penman-Monteith, Class A evaporation pan and measured water consumption of grass to generate crop curves corrected by leaf area to manage irrigation of a field of beans, in Campinas, São Paulo, Brazil, during the period of September to November 1994. The water consumption of the grass and of the bean plants was measured using compensation lysimeters, under which condition the relations between basal crop coefficient (kcb) and beans leaf area index (L) were developed for each Eo method. The relations obtained were all statistically significant and correct well the differences in water use of a field of irrigated beans sown in population densities of 14 and 28 plants m−2, as it was evaluated by a field water balance. The best crop curves, for both irrigated population treatments, was obtained based on the Penman-Monteith method, followed by the Class A method and by the grass compensation lysimeter. It was also verified that reliable estimates of Eo could be obtained for an interval of at least 5 and 7 days, respectively, for grass compensation lysimeter and Class A evaporation pan.