Growth Dynamic Factors Explaining Yield Improvement in New Versus Old Soybean Cultivars

Reasons for genetic yield improvement in soybean (Glycine max [L.] Merr.) during cultivar development are not clearly understood. Since greater yield in new vs. old cultivars is largely regulated by final vegetative total dry matter (VTDM[R7]) and/or production efficiencies for node, pod, and seed yield components ([yield component no.]/ VTDM[R7] [no. g−1]), our objective was to clarify the importance of these two factors for yield improvement in 18 public southern cultivars released between 1953 and 1999. The study was done near Baton Rouge, Louisiana, during 2007 and 2008, with a validation study in 2009. Yield increases were affected by increased production efficiencies for nodes, reproductive nodes (node bearing at least one viable pod), pods, and seeds (R2 = 0.42–0.47), but not VTDM(R7). Increased yield component production efficiencies resulted in greater harvest index (HI; R2 = 0.55–0.73), which in turn, resulted in greater yield (R2 = 0.42). We concluded that a major factor contributing to yield increases between old and new cultivars was increased yield component production efficiency.