## 4 Discussion
### Soil Biological Indicators
These factors also influence microbial biomass carbon (MBC) [61]. Due to the large amount of dry matter in the overall experimental area (Table 23), SOM content in the 0.00-0.10 m soil layer remained at intermediate levels, averaging 28 g dm\({}^{-3}\) (Table 13). Consequently, TOC and MBC stabilized in the experimental plots (Table 21). The association between MRA and MBC allowed for the calculation of the metabolic quotient (qCO\({}_{2}\)), which is the ratio of MRA per unit of MBC over time. This metric estimates microbial substrate use efficiency and serves as a sensitive stress indicator when MBC is affected. Both tools are crucial for understanding transformations and losses in the soil organic compartments [17]. By analyzing MRA along with other soil quality indicators (Table 21), it was observed that MRA was higher in plots that did not receive _A. brasilense_ inoculation. This suggests a system with greater CO\({}_{2}\) loss due to increased microbial activity. However, as MBC and TOC remained stable between inoculated and non-inoculated areas, and the metabolic quotient decreased in the inoculated area, this indicated lower CO\({}_{2}\) loss. This is an interesting outcome for nutrient cycling and carbon sequestration processes in the soil. These microbial dynamics also help explain the observed changes in soil nutrient availability. In the inoculated areas, both enzymatic activity (\(\beta\)-glucosidase and arylsulfatase) and microbial respiration (MRA) were significantly lower, suggesting reduced microbial metabolic activity. This may have limited the mineralization of organic residues, consequently reducing the release of key nutrients such as phosphorus, calcium, and magnesium into the soil. At the same time, the inoculated plots showed a greater accumulation of organic carbon in stable fractions, indicating that microbial communities may direct resources toward carbon stabilization rather than nutrient cycling. Therefore, microbial activity data provide a valuable framework for understanding the nutrient dynamics observed in this long-term conservationist system. The physical fractionation of soil organic matter, analyzed in this study as particulate organic carbon (POC), mineral-associated organic carbon (MOC), and total organic carbon (TOC), contributes to understanding its dynamics under conservation management systems [62]. In the present study, TOC levels increased with soil depth, differing from the findings of studies on organic production systems with different crop rotations within a year, where TOC levels decreased at greater soil depths [62]. However, in this study, high TOC levels in deeper layers could be explained by the long-term no-tillage system, which enabled greater organic material accumulation, resulting in higher carbon levels throughout the soil profile. Inoculating various crops with the bacterium _Azospirillum brasilense_ enhances root biomass production due to its hormonal stimulation [63]. This explains the higher values observed for TOC, MOC, and POC in this study. With greater root volume, more root-derived organic matter was left in the soil after each cultivation cycle. This also accounts for the higher TOC and MOC levels in deeper layers, as organic matter at the surface decomposed rapidly due to edaphoclimatic conditions. When anthropogenic alterations occur in a native ecosystem, carbon inputs become lower than outputs or soil organic matter decomposition rates accelerate, leading to a reduction in soil carbon stocks [64]. Consequently, the increase in POC and MOC fractions observed in inoculated areas, along with higher TOC levels under greater residual phosphorus doses, indicates a better balance between SOM input and decomposition.