Evaluation of Replant Methods for Maximizing Yield in Suboptimal Soybean (Glycine max) Populations.

Throughout the planting portion of the growing season, there are many uncontrolled variables that have the potential to contribute to suboptimal soybean populations that may ultimately result in reduced soybean yields.  The soybean planting window in Mississippi typically begins in late-March when environmental conditions tend to be less favorable for achieving maximum stand potential. This experiment was conducted to determine the optimal replant seeding rate for various levels of reduced soybean populations. 

This experiment was conducted during 2016 in Starkville and Stoneville, MS.  Indeterminate, maturity group IV Roundup Ready 2 Xtend (RR2X) and LibertyLink (LL) varieties were blended to achieve seeding rates that could be reduced by specific percentages using chemical removal methods. Treatments consisted of initial seeding rates targeting 321,100 seeds per hectare with blended percentages of the seeding rate as follows: 100% RR2X & 0% LL, 75% RR2X & 25% LL, 50% RR2X & 50% LL, 25% RR2X & 75% LL, and 0% RR2X & 100% LL. Glyphosate was applied to eliminate the LL variety, leaving the initial RR2X population. Replanting occurred at reseeding percentages of 100%, 75%, 50%, 25%, and 0% using the RR2X variety. Data collection consisted of final node count, final plant height and yield. 

The interaction between soybean stand removal and replant resulted in lower soybean yield when 75% or more of soybean plants were removed. Plant heights in treatments receiving 100% removal and 50, 75 and 100% replant were greater when compared to 0% removal/replant with this height difference likely being attributed to the change in planting date. Final node count indicated no difference among treatments other than the 100% removal followed by 0% replant. These data suggest that replanting into a reduced stand of soybean is only beneficial for improving yield potential when 75% or more of the initial stand is lost.