Night Temperature Effects on Soybean Phenology

Knowledge of phenological development in crops as a function of environmental variables can be useful in crop improvement and management. Night temperature is an environmental factor affecting soybean [Glycine max (L.) Merr.] phenology. The objective of this experiment was to determine if accumulated heat units can be used to predict stages of reproductive development (SRD) in soybean grown under different night temperatures. Field experiments were conducted at Oregon State University and the University of Minnesota in 1984, 1985, and 1986. Twenty soybean genotypes of Maturity Groups (MG) 000, 00, and 0 of different origins were grown at Corvallis, OR and St. Paul, MN, which have mean minimum night temperatures of approximately 10 and 15 °C, respectively, during the summer months. Mean maximum temperatures for the same period of the year are similar for the two locations (ca. 26 °C). Both locations are at about the same latitude (ca. 45 °N). Dates for all SRD were recorded at both locations and accumulated heat units (using base and maximum temperatures of 6 and 30 °C, respectively) were calculated from emergence to each SRD for all genotypes. Locations were significantly different for heat units requirements for phenological development of soybean within all three MG. Genotypes within each MG were also significantly different. Location by genotype interaction was not significant. However, location by SRD, and genotype by SRD (except within MG 0) interactions were significant, while location by genotype by SRD interaction was not significant. The results indicate that night temperature has a significant effect on soybean phenology, but its relative effect varies at different SRD, and is genotype dependent. The results further suggest that a degree-day model may be adequate to predict SRD in early maturing soybeans with the same adaptation characteristics only when grown at a fixed location for which the coefficients have been developed. Oregon Agric. Exp. Stn. Paper no. 8345.