Effects of plant growth-promoting rhizobacteria on the productivity and nutrition of sugarcane under reduced urea...

The practice of biofertilization enhances the sustainability of sugarcane cultivation. This study evaluated the ability of several bacterial strains to improve sugarcane growth and reduce its dependence on urea. Strains belonging to the genera Gluconacetobacter, Azotobacter, Rhizobium, and Azospirillum were efficient in biological nitrogen fixation, indole-3-acetic acid production, and inorganic phosphorus solubilization. Azotobacter and Gluconacetobacter efficiently solubilized rock phosphate, while Azospirillum was more effective with tricalcium phosphate. Azospirillum brasilense Ab12 showed viability in diluted vinasse, utilizing organic acids. Inoculation with A. brasilense strains Ab12 and Ab16 at 4×10⁸CFU/ml in pre-sprouted cuttings increased productivity in field-transplanted plants without chemical fertilization. The application of Azospirillum improved stem number, stem weight and length, cane yield per hectare, and sucrose content. In addition, it promoted greater tillering and enhanced the uptake of P, S, Fe, and Zn. Bacterial inoculants reduced the need for urea fertilization, showing a complementary effect on plant growth even with the full recommended urea dose. Azospirillum-based biofertilizers allowed the reduction of urea rates, with similar growth observed when using 25-50% of the standard dose. These results demonstrate the potential of A. brasilense as a biofertilizer to reduce dependence on synthetic inputs and improve the nutritional efficiency of sugarcane cultivation.