Planting time and variety effects on biomass, harvest index, and yield of irrigated soybean in mid-Southern United States

Soybean [Glycine max (L.) Merr.] biomass and grain yield has increased over the past several decades in the mid-southern United States. This is attributable to technological advances and improved management strategies. However, a better understanding of biomass accumulation and partitioning is needed to improve our knowledge base of varietal growth habits relative to yield, planting date, and harvest index (HI). Field experiments within a split plot arrangement in a randomized complete block design were established in 2017 and 2018 in Stoneville, MS. The study aimed to evaluate the effect of early (late-April or mid-May) and late (late-May) planting on biomass, HI, and yield amongst eight soybean varieties. Soybean total biomass accumulation was collected at multiple development stages, including V4, R2, mid R5, mid R6, and R8, and partitioned into senesced leaves, pods, and seeds. Overall, the planting date had no effect on yield, HI, and biomass accumulation at any of the growth stages. Yet, the interaction between planting date and variety significantly affected biomass accumulation at the mid R5 stage. Contrarily, the variety selection significantly affected yield, HI, and biomass accumulation at all growth stages except mid R6. The total biomass accumulation at R8 was greatest for Asgrow 46X6, Asgrow 4632, Terral 4857X, Terral 48A76, and Credenz 4748, when pooled over planting dates. Averaged across two planting dates, the greatest yield was produced by Terral 48A76, Asgrow 4632, and Asgrow 46X6. Furthermore, averaged across site-years, HI was greatest for Asgrow 4632 and Terral 48A76. Based on the results of this study, evaluating soybean HI rather than overall biomass accumulation may be more beneficial for variety selection decisions.