Determination of Optimal Seeding Rates for Soybean (Glycine max) Replant Situations in Mississippi.

Throughout the planting portion of the growing season, there are many uncontrolled variables that have the potential to contribute to suboptimal soybean populations ultimately resulting in reduced soybean yields. This experiment was conducted during 2016 and 2017 in Starkville and Stoneville, MS, as well as Brooksville, MS in 2017 to determine the optimal replant seeding rate for various levels of reduced soybean populations. Indeterminate, maturity group IV Roundup Ready (RR) and LibertyLink (LL) varieties were blended to achieve seeding rates that could be reduced by specific percentages using herbicide removal methods. This experiment consisted of 25 treatments where initial seeding rates targeted 321,100 seeds per hectare and blended percentages of the seeding rate were as follows: 100% RR & 0% LL, 75% RR & 25% LL, 50% RR & 50% LL, 25% RR & 75% LL, and 0% RR& 100% LL. Glyphosate was applied across the entire experiment at the V1 growth stage in order to eliminate the LL variety, leaving the initial RR population. Replanting occurred 14 days after the application of glyphosate at reseeding percentages of 100%, 75%, 50%, 25%, and 0% using the RR variety.

The combination of soybean stand removal and replant resulted in significant differences among soybean yield, as well as, node and plant heights. Soybean yield for the treatment of 0/0% removal/replant was greater than that of the 100/100% removal/replant, likely a function of delayed planting date. No soybean yield difference was observed for treatments of 50/50% removal/replant and 0/0% removal/replant. When 75% of the initial population was removed, soybean yield was maximized by replanting at least 75% in the existing stand. These data suggest replanting 50% of the initial population, if a reduced soybean stand of 50% exists, however, no replant is recommended when soybean stands are reduced by 25% or less.