## 4 Discussion
### Phosphorus Fractions and Soil Health  
Phosphorus concentration in the soil can increase either through mineral fertilization, which immediately supplies the nutrient to the crop, or organically, where P only becomes available after microbial activity mineralizes SOM, releasing inorganic phosphate ions (available P) [49]. Therefore, areas with a higher volume of organic material and SOM naturally have higher levels of labile P, which aligns with the results obtained in this study. In the non-inoculated area, where there was greater dry matter production (Table 23), the labile P fraction in the soil was 32.5% higher (Table 19). Plants absorb only the P present in soil solution, where its ionic forms include H2 PO4\({}^{-}\), HPO4\({}^{2-}\), and PO4\({}^{3-}\), with the first form predominating in Brazilian soils due to their low pH [9]. The greater the nutrient availability, the higher the plant absorption. In areas inoculated with _A. brasilense_, due to the increased root volume, nutrient uptake and temporary immobilization in plant biomass are also higher, explaining the lower labile P content in the inoculated areas of this study. The response of phosphorus fractions to residual fertilization was also distinct between inoculated and non-inoculated plots. In Figure 9, exponential increases in both labile and moderately labile P were observed in non-inoculated areas, suggesting a more efficient release of bioavailable phosphorus under conventional management. Similarly, Figure 10 shows an increase in inorganic phosphorus (Pi), indicating that phosphorus applied in earlier cycles may persist in forms accessible to plants under no-tillage conditions. These results reinforce the importance of understanding P dynamics under biological interventions. The mineralization of organic P into inorganic P is related to microbial and plant enzymes involved in this cycling process, which act on SOM. However, there is a dynamic interplay between microbial mineralization and the immobilization of P (P from microbial biomass), making microorganisms both a source and, at times, a sink for rapidly cycling P [49]. This effect can be observed in the relationship between higher \(\upbeta\)-glucosidase and arylsulfatase enzyme activity (Table 20) in non-inoculated areas due to the greater volume of dry matter (Table 23), resulting in higher labile P content in non-inoculated areas and the breakdown of the labile, moderately labile (Figure 9), and inorganic P (Figure 10) fractions. This indicates that a higher dry matter volume leads to greater enzymatic activity, enhancing the availability of the aforementioned P fractions. Meanwhile, in inoculatedplots, which exhibited greater stability, enzymatic activity was lower and had no effect on the existing P fractionation from prior organic material degradation. Microbial biomass P (P-mic) constitutes a highly variable fraction of soil organic P, representing, on average, 1 to 10% of total P and 2 to 24% of organic P. Many forms of organic P found in the soil, such as phospholipids and nucleic acids, originate from microbial sources [50]. However, even though P-mic is not readily available to plants, it serves as a dynamic reservoir of P in tropical soils due to its role in the accelerated decomposition of soil organic matter (SOM). Thus, the poorer the system is in available P, the greater the dependence on organic forms, particularly P stored in microbial biomass, which absorbs and immobilizes P from the soil solution and gradually releases it [51]. Highlighting the importance of SOM for the uniformity of crop production in the rotation studied, in areas with non-inoculated crops (_A. brasilense_), better soil exploration and, consequently, higher P uptake were driven by the greater input of organic material, which provided adequate nutrient supply for plant development (details in Figures 10 and 11). In contrast, in inoculated areas, due to the hormonal effect of _A.