Rhizobia and other plant growth‐promoting rhizobacteria (PGPR) have been broadly used as inoculants in agriculture, resulting in morphofunctional improvements in roots and grain yield. This study was carried out during two cropping seasons under field and greenhouse conditions in Brazil to verify the effects of inoculation of two soybean cultivars with PGPR and secondary microbial metabolites (SMMs) on root activity and nodulation, plant development, and grain yield. Inoculation and co‐inoculation treatments consisted of Bradyrhizobium japonicum strain SEMIA 5079 and B. diazoefficiens strain SEMIA 5080 inoculated together, in combination with Bacillus subtilis strain QST 713, Azospirillum brasilense strains Ab‐V5 and Ab‐V6, and SMMs extracted from B. diazoefficiens strain USDA 110 and Rhizobium tropici strain CIAT 889. Root systems were evaluated by direct (optical reading) and indirect (rubidium nitrate application, 85RbNO3) methods. Increases of up to 1.6% in root diameter (0.01‐ to 0.5‐mm class), 28.5% in length, 19.7% in root volume, 17.8% in root surface area, 29% in the number of nodules, 27.2% in nodule dry weight, 13.5% in root dry weight, and 3.8% in shoot dry weight. Greater exploration and activity within and between rows following inoculation at up to 40 and 10 cm in depth, respectively, were observed in plants co‐inoculated with the standard inoculation (only Bradyrhizobium spp.) + SMMs + A. brasilense, resulting in a yield increase of 485 kg ha−1. The results emphasize the biotechnological potential of using secondary metabolites of rhizobia with inoculants containing rhizobia and PGPR to improve the growth and soybean yield in tropical conditions.

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The use of plant growth-promoting bacteria combined with Integrated Agricultural Production Systems (IAPS) has resulted in productivity increases in the Brazilian Cerrado region. Thus, the objective was to evaluate the effect of inoculating or not inoculating Azospirillum brasilense on corn and palisade grass seeds (Urochloa brizantha cv. Marandu) on growth, yield components, and dry matter yield of the aerial part and grains in an Oxisol cropped in ICLS and under a no-tillage system for 12 years in an irrigated area. The experimental design was a randomized block design with four replications. The treatments were composed of corn (monoculture) with inoculated seed, corn (monoculture) without inoculated seed, corn + palisade grass (intercropping) without inoculation, corn + palisade grass (intercropping) with inoculation in both seeds, corn + palisade grass (intercropping) with inoculation of corn seeds, and corn + palisade grass (intercropping) with inoculation of grass seeds. At the end of each production cycle, the yield and components of corn, corn straw biomass, and dry matter of palisade grass were evaluated. Considering the optimal conditions of soil provided by liming and fertilization at sowing and nitrogen applied in topdressing, the application of A. brasilense in corn seeds did not show its potential. Intercropped systems inoculated or not with A. brasilense on corn seeds increase grain yield, dry matter production of grass, and nutrient accumulation in the straw, providing greater sustainability to the Cerrado no-tillage system.

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