This work develops a methodology for estimating supplementary irrigation requirement in tropical and subtropical regions. Irrigations were simulated for February and July through simple water balance technique, based on 21 and 20 years, respectively, of meteorological data from Ribeirão Preto, State of São Paulo, Brazil. In order to attend different situations of crops and soils, five levels of allowable soil water depletion (ASWD) and two crop coefficients (kc) were chosen. For each month, irrigation intervals were annotated and its relative frequency calculated. The results allowed to design graphically the irrigation interval, for each month, as a function of: irrigation depth; crop coefficient; and probability level addopted in a project.
irrigation intervals; irrigation design; water balance