Stability of Soybean Yield and Quality Over a Wide Range of Maturities and Planting Dates in the Midsouth.

The stability of yield is an important factor to consider when deciding what soybean maturity group (MG) to plant in a given environment. Conditions in the Midsouth allow planting soybeans of MGs 3 to 6 during a wide planting window.  The yield stability of 16 soybean cultivars of MG 3.4 to 7.0 was analyzed across eight locations in the Midsouth (30.6 – 36.4°N) with four different planting dates each (from late March to mid-June) during the 2012 growing season. Soybean grain yield, oil and protein seed concentration and seed grade were measured.

The stability analysis of soybean yield revealed a significant effect of the choice of MG. MG 4 cultivars showed a tendency of more stable and higher average yield than the rest of MGs studied. No differences were observed in yield stability within varieties in the same MG. The results indicate that differences in yield stability are mostly explained by differences in growth cycle, and indicate the importance of a good choice of MG or relative MG for the range of latitudes and planting dates in the Midsouth.

Oil and protein concentrations in soybean seed and their stability across the environments studied were significantly affected by the choice of MG and also by the cultivars within a same MG. On average, oil concentration was reduced by 1% from MG 3 to 6. On the other hand, seed protein concentration increased by 0.8% from MG 3 to 6.

Seed grade was highly affected by the location, with US soybean seed grades ranging from N. 1 to 4 in the most northern locations, and soybeans that did not meet the requirements for US soybean seed N.4 in the most southern locations. Within each location, the planting date, choice of MG, and cultivars within MG had a significant effect on soybean grade.