Características morfométricas e trocas gasosas da soja coinoculada com bactérias promotoras de crescimento vegetal e aplicação de bioestimulantes

Abstract

Soybean (Glycine max [L.] Merrill) plays a strategic role in Brazilian agriculture, standing out as the main export crop and a key source of vegetable protein and oil. Given the projected global increase of up to 110% in soybean demand by 2050, challenges such as climate variability, dependence on imported fertilizers, and physiological stability of plants call for sustainable alternatives to optimize the crop's metabolic efficiency. Among these strategies, the use of plant growth-promoting bacteria (PGPB) and foliar-applied biostimulants is noteworthy, as they influence morphophysiological development and enhance plant resilience. This study aimed to evaluate the effects of coinoculation with different PGPB strains and foliar application of biostimulants on soybean biometric, physiological, and reproductive characteristics. The first field experiment, conducted with the cultivar 64I61RSF IPRO, involved inoculation with Bradyrhizobium japonicum combined with co-inoculation of Azospirillum brasilense, Pseudomonas fluorescens, and Bacillus spp. Variables assessed included plant height, stem diameter, dry mass of leaves, stem, and roots, leaf area, number of nodules, SPAD index, and gas exchange. Co-inoculated treatments showed superior performance in vegetative and physiological traits compared to the control. A. brasilense promoted a higher root-toshoot ratio, while Bacillus positively influenced stomatal conductance, internal CO₂ concentration, and water use efficiency. The second experiment, conducted under protected conditions using the cultivar M5947, evaluated the interaction between A. brasilense co-inoculation and foliar application of biostimulants: plant growth regulator, silicon, and amino acids. Variables included biometric characteristics, SPAD index, gas exchange, and yield components. The combination of plant growth regulator and A. brasilense resulted in the highest values for leaf area, total dry mass, and photosynthetic efficiency. Silicon increased root density and provided greater physiological stability, while amino acids enhanced leaf density and biomass accumulation in leaves. However, these physiological effects were not reflected in significant improvements in reproductive components. The results indicate that co-inoculation with PGPB, especially A. brasilense, combined with biostimulant application, constitutes a promising strategy to enhance soybean physiological efficiency, promoting greater vegetative growth and beneficial responses under different cultivation conditions. These practices have the potential to contribute to more efficient and sustainable agricultural systems, with reduced reliance on chemical inputs and increased yield stability.