Osmoprotectant in soybean seeds can increase the inoculation and co-inoculation time in pre-sowing

The practice of soybean seed inoculation cannot exceed the 24-hour prior to sowing. The objective of this study was to assess the effects of inoculation and co-inoculation of osmoprotectant soybean seeds, performed at different times of sowing. The experiments were conducted during two crop seasons at "sandy clay loam Acrisol" and "Cfa climate" in Santa Maria, RS, Brazil. The experimental design consisted of completely randomized blocks with four replications. Nine distinct treatments of seeds inoculation were carried out with bacteria of the genus Bradyrhizobium were inoculated alone (conventional inoculation) or combined with Azospirillum brasilense (co-inoculation), associated with the use of osmoprotectants. The components of nodulation, leaf chlorophyll, plant growth and grain yield were evaluated. The number of nodules and pods per plant are the variables most correlated with grain yield. Number of grains per pod, mass of thousand grains, and A, B and total chlorophyll content were not influenced by inoculation, co-inoculation and nitrogen fertilization. All treatments that used osmoprotectant had an increased 30% (in the first year) at average number of nodules in V5 compared to the treatments that did not use it. Co-inoculation provided an increase of 31% and 16% of yield, respectively, compared to the no-inoculation treatment, for the first and second experimental years. Inoculation and co-inoculation when carried out seven days before sowing and associated with the use of the osmoprotector, provides grain yield similar to the inoculation performed at the time of sowing.