Evaluation of Soybean (Glycine max) Yield Potential Following Sub-Optimal Plant 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 yield reduction. 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 yield impact following various levels of reduced soybean populations.

Experiments were conducted in 2019 at the R.R. Foil Plant Science Research Center near Starkville, MS. Indeterminate, maturity group IV and determinate, maturity group V Roundup Ready 2 Xtend (RR2X) soybean were blended with LibertyLink (LL) soybean to achieve seeding rates that could be reduced by specific percentages using chemical removal methods. Treatments consisted of initial seeding rates targeting 130,000 seeds per acre and were planted at three different planting dates: late-April, mid-May, and late-May. Blended percentages of the seeding rate were as follows: 100% RR2X & 0% LL, 80% RR2X & 20% LL, 60% RR2X & 40% LL, 40% RR2X & 60% LL, and 20% RR2X & 80% LL. Glyphosate was applied to eliminate the LL variety, leaving the initial RR2X population.

Preliminary results confirm that soybean planted in late-April has the greatest yield potential, regardless of growth habit. Furthermore, as population is reduced by 60% of the intended population, yield potential also declines. Future research should be conducted to fully evaluate soybean yield response to population reductions based on soybean planting date and growth habit.