Main-stem node removal effect on soybean seed yield and composition
Hail injury to soybean [Glycine max L. (Merr.)] is common across the United States. Currently, U.S. hail adjusters use procedures that assume that yield reductions caused by stem cutoff and defoliation or defoliation without stem loss is similar during the vegetative development period. Our hypothesis was that seed yield will be affected by timing of node removal in vegetative soybean and that main-stem node removal will influence seed composition. Research was conducted in Indiana and Iowa from 2003 to 2005 to test if removing 0, 20, 40, 60, 80, or 100% of nodes at V2, V6, or R3 development stages affects seed yield and grain composition. In Indiana, imposing node removal at the V2 stage resulted in 15.9% greater yield than imposing at the V6 stage. In Iowa, imposing node removal at the V2 stage on the average resulted in 24.9 and 46.1% greater seed yield than imposing node removal at the V6 or R3 stages, respectfully. Seed mass was 7.7% greater when comparing the V2 to the V6 node removal timing in Indiana. In Iowa, seed mass decreased 7.0% when 60% of the nodes were removed at V6 and 5.6% when 20% of the nodes were removed at R3. Soybean oil content was only affected by extreme node removal treatments while protein content was unaffected. Our results indicate that the soybean development stage that node removal occurs must be considered when estimating soybean seed yield loss and that an oil content adjustment is not needed to properly compensate growers for economic losses caused by node removal.