Kentucky's Soybean Yield Contest's Role in Revising Planting Date Recommendations.

Kentucky’s Soybean Yield Contest was initiated in the 1980s as a way to highlight agronomic practices that resulted in high yielding soybeans.  Beginning around the late 1990s and into the early 2000s, many of the state’s winners were planting soybean earlier than University of Kentucky recommendations.  To further investigate these observations, a four year study was initiated to determine the effect of planting date on soybean yield in Kentucky.  Seven planting dates, which ranged from mid-April to early July, were implemented.  Grain yield was greatest for the mid-April to mid-May plantings.  Beginning in late May significant yield reductions were observed.  This was in contrast to previous recommendations that the optimum planting time for soybeans was early May through early June and the last optimum planting date was defined as June 6.  These results indicate that useful agronomic trends can be gleaned from yield contest entries.