Bradyrhizobium Inoculant and Nitrogen Fertilization of Texas Soybean.

Inoculants are not applied to a significant portion of Texas soybean production yet N fertilizer applications are somewhat frequent.  When Bradyrhizobium japonicum inoculants are used producers often choose the cheapest inoculant, which are seedbox powders, even though these products are inferior to liquid and granular products.  The objective is to 1) test seedbox powder, granular, and liquid inoculants for nodulation and yield, and 2) measure the effect of added N fertilizer in across three Texas soybean production regions.  Core treatments at each test site included Nitra-Stik ‘S’ seedbox powder and EMD CropBioscience’ ‘Cell-Tech’ liquid inoculant as well as 45 kg N ha^-1 which were applied in RCBD in at three Texas locations:  Gulf Coast, northern Blacklands, and High Plains.  Sites were soil sampled prior to planted to ensure that N levels did not exceed ~25 kg ha^-1.  In-season nodulation was assessed using a minimum of eight plants per plot, and yields were measured.  Nodules counts in general showed a trend toward increased nodulation due to inoculant with liquid materials nodulating slightly more than seedbox powders.  Soybean response in all three regions was inconsistent and not statistically different than unfertilized treatments.  These results suggest that Texas soybean producers should consider ensuring that inoculant is used, but N fertilization is not justified.