Soybean Nodule Inhibition and Root Growth As Influenced By Nitrogen Source and Nitrogen Rate.

Greenhouse studies were conducted in Stoneville, MS in 2016 to evaluate the influence of supplemental N fertilizer on nodule formation and root growth of soybean (Glycine max (L.) Merr.).  Greater below ground biomass was observed on silt-loam soils versus below ground biomass on clay soils directly correlating to all other root parameters.  N fertilizers additions resulted in approximately 19% below ground biomass reduction across soil textures when compared to soybean receiving no N (0 kg N ha ^-1).  However, soybean above ground biomass was observed to have no response to N fertilizer additions.  Soybean receiving N fertilization were observed to exhibit a decrease across all belowground experimental parameters when compared to soybean receiving no N (0 kg N ha ^-1).  N fertilizers additions were observed to result in a 52% decrease in mean number of nodules present.  N fertilizers utilizing ESN as the N source observed to exhibit a greater number of nodules than that of urea+NBPT as the N source.  Overall, N fertilizer additions negatively impacted root growth and nodulation resulting in a decrease across all experimental below ground parameters.