Planting Date, Maturity, and Temperature Effects on Soybean Seed Yield and Composition.

Soybean [Glycine max (L.) Merr.] production has greatly increased in the upper U.S. Midwest over the last decade, but little information exists regarding the interactive effects of environment and spring management decisions on soybean seed yield and composition. Our objective was to assess the effect of four planting dates (PD), four cultivar maturity groups (MG), and ambient temperature between R5 to R8 (T5-8) on soybean seed yield and composition. Field studies were established between 2014 and 2016 at three locations in Wisconsin and one in Minnesota. Across environmental conditions and management decisions, greater seed yield was positively correlated with protein and oil contents but negatively correlated with linoleic, linolenic and sucrose contents. Multivariate data analysis showed positive synergies between early planting (late April to early May) and the longest MG (MG 2) for yield, oil, and oleic acid across the examined region. A MG 2 was the highest yielding and a ~1200 kg ha^-1 yield difference was observed between early and late PDs. These results underline the complexity of the soybean yield-composition relationships. Additionally, the large variability in the responses of constituents to management decisions and temperature variations highlights the importance of a producer knowing the product’s end use (e.g., high yield vs. high protein) and accordingly modifying the growing environment by selecting an appropriate PD and MG for the respective region. To provide more accurate recommendations to a broader range of producers, multi-environment studies are imperative to capture large environmental variability in important soybean production areas across the U.S.