Evaluation of Soybean Inoculant Products and Techniques to Address Soybean Nodulation Problems In Kansas.

With increasing soybean acreage across Kansas, more nodulation issues have been encountered in “new”” soybean fields. In all reported cases, producers claim to have properly applied inoculant to the seed before planting. The objective of this study was to determine how to improve consistency of soybean nodulation and production, especially on new soybean ground. Two inoculant products from three companies using single rates, double rates, and product combinations were applied to soybean seed. Seed was inoculated according to company protocol and planted within approximately a week of inoculation. Field experiments were set up in a randomized complete block design with four replications at six sites. Sites differed in soybean cropping history, with previous soybean crops occurring from 2 to 40+ years before the experimental year. Evaluations included stand, nodule assessments, plant dry matter weight, plant nitrogen content, yield, and grain quality. Two nitrogen application treatments to untreated plots at the V4 growth stage also were included but were not found to significantly influence soybean yield. A liquid + additive inoculant product consistently ranked in the top groupings for nodule assessments on the sites without recent soybean history. The untreated check consistently ranked in the lowest groupings where there were significant treatment differences. Dry powdered inoculants requiring water hydration for seed application proved to generally rank lowest in all locations in comparison to other inoculant products. There was not a consistent response to higher rates or inoculant combinations over single rates.  Hot and dry summer conditions likely reduced yields, making detection of treatment differences more difficult. Although there were early season nodule differences in new soybean ground, these did not carry through to harvest yield differences.