The study was performed using phenological observation of field experiments carried out during three years (1977/78, 1978/79 and 1979/80), for four soybean cultivars in three localities. The proposed model to estimate crop yield was based on the reduction of the potential productivity when soil water content decreases below a critical value or when the surplus was above the potential evapotranspiration for a given period, in a manner that: YEst = (YPOT) x (FThe) x (FDef) x (FSur), where: YEst = estimated yield; YPot = potential yield for a defined locality, being a function of the cultivar and technology; FThe = thermal factor, to express the degree of crop development (accumulated degree days); FDef = effect of water deficit in the soil on crop yield; FSur = effect of water surplus on crop yield. A comparison between the observed and estimated yield was highly satisfactory with determination coefficient (R²) ranging from 0.76 to 0.87 for all cultivars.
agrometeorological model; Glycine max (L.) Merrill; potential yield