Predicting the time of soybean flowering is a critical step for crop management practices, as well as for the development of crop models. The objective of this study was to quantify the effect of photoperiod and of temperature on the duration of the flowering period, and to evaluate the response of a simple linear model for predicting the flowering period of soybean genotypes of different maturation groups within different epochs. The ability of the equation D = a' + b'T + c'F, where a', b' and c' are empirical parameters, and T and F refer to the medium temperature and to the photoperiod between emergence and flowering, was evaluated. Evaluation of the coefficients were carried out through multiple regression analysis combining the data sets from two growing seasons for each genotype (1995/96 and 1996/97) in Passo Fundo, RS, Brazil. Multiple regression analysis showed that the period between emergence and flowering was influenced by temperature and photoperiod. The cultivars under study showed different susceptibilities to each factor, resulting in specific coefficients. The agreement between observed and predicted time of flowering was highly significant for all genotypes (r² higher than 0.77) with standard deviations ranging from 2.4 and 4.8 days.
Glycine max; flowering; environmental factors; sowing date
