Temperature and cultivar effects on soybean seed oil and protein concentrations

The soybean [Glycine max (L.) Merr.] industry is interested in cultivar and climate effects on seed composition. These factors may underlie the known geographic variation in seed protein and oil concentrations. Regression ana lyses were used to test hypotheses of the effect of temperature and cultiva r on oil and protein concentrations of soybean seed using a large data set from the U.S.A. Soybean Uniform Tests. The data set included 20 cultivars r epresenting 10 maturity groups across 60 locations (latitude 29.4 to 47.5 d egrees N) for a total of 1863 cultivar by location by year observations. Te mperature was determined for each observation as the average daily mean tem perature from predicted first pod (first pod at least 5 mm long), using the SOYGRO phenology model, to observed maturity. The mean temperature ranged from 14.6 to 28.7 degrees C among the observations. Linear, quadratic, and linear plateau regression models of oil and protein concentrations vs, temp erature were evaluated. The quadratic model gave the best-adjusted R-2 Valu es for oil and protein with temperature, of 0.239 and 0.003, respectively. The analyses showed that the oil concentration increased with increasing te mperature and approached a maximum at a mean temperature of 28 degrees C. U naccounted variation in the protein concentration may be from other factors such as photoperiod, water stress, or high temperatures during seed fill. Protein plus oil had a linear relationship with temperature (adjusted parti al R-2 = 0.183). These data document the contribution of climate and cultiv ar to geographic variability of oil and protein concentrations in the Unite d States.