Soybean Response to Stand Reduction and Defoliation¹

Abstract ‘Beeson’ soybeans ( Giyeine max (L.) Merr.) were treated at a vegetative (V7) and a reproductive (R3) stage of development to determine how soybeans respond to two important components of hail damage‐stand reduction and defoliation. This information is used by the crop hail industry to construct crop loss charts. Treatments consisted of 0, 25, and 50% levels of stand reduction and defoliation in all combinations at both growth stages. Defoliation was accomplished by removing designated percentage of each leaflet with a hand shears. Stand reduction alone reduced seed yield a maximum of 17% while defoliation alone reduced seed yield a maximum of 6%. The largest yield reduction (23%) occurred when the 50% stand reduction and 50% defoliation treatment was imposed during the reproductive stage. Plant height at maturity and lodging were reduced slightly by both defoliation and stand reduction treatments with stand reduction causing the most change in these parameters. More pods and heavier seed were produced on plants remaining after stands were reduced. Defoliation during the reproductive stage reduced seed yield, number of pods per plant, and lodging more than similar treatments applied at the vegetative stage. Number of seeds per pod was not significantly influenced by the treatments. From the data we concluded that low levels of defoliation removed leaf tissue which contributed little to seed production, and the soybean community was able to compensate for plants removed from the population. Most of the compensation was due to an increase in number of pods per plant.