Potencial de azospirillum brasilense como condicionador de solo e promotor do crescimento do sorgo em campo

Abstract

Increasing agricultural production is inevitable to meet the growing global demand for food. However, the combination of climate change and anthropogenic pressures poses a serious threat to food security. The adoption of conservation practices and efficient land management enhances resilience and sustains soil health and ecosystem services. Therefore, the use of microorganisms in the formulation of commercial inoculants offers integrative benefits capable of improving agricultural productivity while promoting the efficient use of chemical fertilizers, thus representing a sustainable strategy. This study aimed to evaluate the potential effects of applying an Azospirillum brasilense isolate on soil fertility, microbial and enzymatic activities, and crop productivity under field conditions. A literature review was conducted to summarize the mechanisms and effects of this bacterial species on plant production. In addition, two field experiments were carried out using an A. brasilense isolate applied to two Red Latosols (medium- and clay-textured soils) within the Brazilian Cerrado biome under sorghum cultivation. The experimental design consisted of randomized blocks in a 2 × 6 factorial arrangement, including two treatments: (i) A. brasilense CCT-7831 and (ii) a control (without microbial inoculation), with six replicates. Statistical analyses were performed using analysis of variance (ANOVA) followed by Scott–Knott’s test (p < 0.05). The evaluated parameters included rhizospheric soil fertility, microbial and biochemical activity assessed through soil microbial respiration (SMR), and the potential activities of arylsulfatase, β-glucosidase, acid phosphatase, fluorescein diacetate (FDA) hydrolysis, microbial biomass carbon (MBC), and the metabolic quotient (qCO₂). Inoculation with A. brasilense reduced sulfur (S) content in sorghum tissues grown in medium-textured soil. Conversely, A. brasilense application enhanced sorghum yield in clay-textured soil. The inoculant decreased soil phosphorus (P) content in clay soil but increased copper (Cu), iron (Fe), and zinc (Zn) levels in medium-textured soil. Application of A. brasilense reduced MBC in medium-textured soil and acid phosphatase activity in clay soil. Inoculation showed positive correlations with MBC, FDA activity, and soil concentrations of S, K, and Cu, while negative correlations were observed with arylsulfatase, β-glucosidase, acid phosphatase, and the contents of B, S, Cu, P, Mo, Fe, and Ca. Although changes in certain variables were detected following the application of A. brasilense, it is necessary to monitor the effects of selected strains used in inoculation and co-inoculation under different soil conditions and seasonal variations to support the sustainable development of environmentally sound management practices that minimize dependence on chemical fertilizers and pesticides.