Evaluation of soybean inoculant products and techniques to address soybean nodulation problems in Kansas

Nitrogen fixation by Bradyrhizobium japonicum in soybean [Glycine max] is highly beneficial in soybean crop production. Nodulation issues have been encountered on fields new to growing soybeans in recent years in Kansas. The purpose of this research was to evaluate soybean nodulation performance under various situations and seed handling practices in order to educate producers on how to achieve reliable nodulation consistency in the field. The objectives of the study were to: 1) compare inoculant products using single and double rates and in combination with one another on fields with varying soybean history; 2) determine if there was a negative interaction between inoculant products and common seed treatments; and 3) discover the influence of inoculated seed storage conditions before planting on the rhizobia’s ability to successfully nodulate soybean roots. Field experiments were conducted on diverse Kansas sites in 2011 and 2012. Inoculant treatment and seed treatment interaction trials had ten and seven experimental sites respectively. Inoculated seed storage conditions were evaluated in a greenhouse experiment during the spring of 2013. All studies used a randomized complete block design with four replications. The Novozymes inoculant products generally provided superior nodulation performance over other company products in the study where soybean had not been in recent rotation with an average increase of 167% in nodule number verses the control. The combination of dry and liquid inoculant products provided a significant increase in root nodule number at five of the environments out of recent rotation with a 76% increase over single inoculant rates. Although there were early season nodulation differences between treatments in new soybean ground, these did not carry through to seed yield differences in the majority of research sites. Hot and dry summer conditions reduced yields, making detection of treatment differences difficult. There were no negative effects on nodulation performance with any of the seed treatments. Although soybean seed yield was 634 kg ha[superscript]-[superscript]1 greater for the Novozyme combination treatment compared to the check at one location in 2011, the control yielded as well or better than all other treatment/inoculant combinations, implying that yield differences were likely not related to inoculant treatments. At other sites, yield was not influenced by seed treatment and inoculant combinations. Results indicate that seed treatment formulations did not significantly impact bacterial inoculant product performance, soybean nodulation, or yield. Storage conditions had no effect on nodulation performance in the greenhouse study, likely due to survival of Bradyrhizobium japonicum in the heat-treated growth medium.