Meteorological data and yields of 'Valência' orange trees from orchards located in Matão (lat.: 21o35'S; long.: 48o25'W; alt. 551 m), State of São Paulo, Brazil, were evaluated with an agrometeorological model. The relative impact of the water stress ratio (ETa/ETp) was determined for three different stages of growth. The best agreement between observed and estimated data was the ratios that form a multiplicative model for estimating orange yield using field data. These ratios were weighted by applying crop stage dependent exponents or sensitivity coefficients. An analysis of the sensitivity coefficients shows that this model gives higher weight to the water relations during flowering and beginning of the fruit set, which occur in this region in October-November, with R2 higher than 0.70 and d-index of agreement of 0.87.
orange; water balance; growth stage; crop yield-modeling; climate-yield relation
