Seed coats are proprietary blends of chemicals commonly applied to agricultural crops and sold as a type of value-added seed. In soybean production these blends often include fungicides, insecticides, and rhizobial inoculum. Over time the ingredients of the seed coat permeate the soil around the seed, potentially altering the soil community and microhabitat characteristics for the developing plant. Seed companies market these blends as a convenient way to protect developing plants from various field challenges and improve yield. To see whether seed coats created an early selection environment which would ultimately increase soybean plant health and fitness, we planted both coated and uncoated seeds of the same soy variety within replicated common garden experiments at four farms across the state of Maryland. We surveyed plants throughout the summer for insect activity, leaf traits, and physiological function. In the fall we harvested all plants in order to assess biomass, yield and seed quality.
Results/Conclusions
We hypothesized that seeds which were coated before planting would grow into plants with lower insect and disease damage and ultimately more root nodulation and higher yield. Early and midsummer surveys found no observable differences between plants which had come from coated and uncoated seeds (p > 0.05 for all metrics). Insect abundance, disease damage, and physiological activity varied among sites but not appreciably between seed coat treatments. Given that hypothesized differences were not observed for functional traits and growth during the season, it is not surprising that we also found no differences in plant biomass, yield, and root nodulation at time of harvest (p > 0.05 for all metrics). The lack of substantial benefit from treated seeds in our results suggests that seed coats may not be having impacts on plant performance and fitness. However, it is worth noting that in different environmental conditions (such as very wet years), seed coats may indeed alter plant fitness. Furthermore, because seed coats may influence the microbial selection environment even if differences are not observed in plant health or yield, future work will investigate the effect of using seed coats on rhizobial community composition.