The justification for the low pH values that prevailed in the areas, possibly due to the material of origin of the crystalline rocks (argilite and sandstone) and corroborated with low levels of basic cations (Latossolos Amazon) (Souza et al. 2018). Corroborating with the natural condition of acid Amazonian soils (Nascimento et al. 2019). Os baixos níveis das bases trocáveis (K+, Ca+ 2 and Mg+ 2), mainly in degraded areas, erosion and leaching cause the loss of bases (De Souza Braz et al. 2013; Souza et al. 2018), as a result of the greater degree of soil degradation, differing in a certain way from environments with insertion of the tree component and longer recovery time and isolation of the degrading agent (cow).
The suppression of vegetation for the establishment of pastures (DP) causes negative changes in the soil physical properties (Lavelle et al. 2014; Celentano et al. 2017), and increased by cow trampling during (De Souza Braz et al. 2013; Byrnes et al. 2018), that justifies the higher BD and lower TP values compared to values (APP-6) with Degraded pasture (DP).
The results obtained in Fig. 2 elucidate that the difference in groups I and II are caused by the improvement in soil fertility, justified by the greater increments of exchangeable cations (K+, Ca+ 2 and Mg+ 2). Chauhan et al. (2018); Krainovic et al. (2020)d rez-Flores et al. (2018) stated that the litter deposition, such as the accumulation of leaves, flowers, fruits, branches of various tree species, contributes positively to increase the content of these elements in the soil. With an increase in exchangeable bases, consequently, the sum of bases (SB) and cation exchange capacity (CEC) showed an increase in the values of APP-6, differing statistically from other areas.
In group IIa, the active acidity (pH) was determinant in the grouping, providing a reduction in fertility by reducing exchangeable cations (K+, Ca+ 2 and Mg+ 2), and lower OC content. As the APP-6 areas have a longer recovery time, there is a greater diversity of tree species in these areas, causing an increase in the contribution of organic carbon to the soil. In this way, it provides greater production of organic matter and carbon sequestration in the soil (Chaves et al. 2020b).
For group IIb, there was a greater increase in soil density and lower total porosity in the soil, especially in degraded pasture areas. The justification is the result of intense trampling of cattle, arising from inadequate management practices (Byrnes et al. 2018; Antonio et al. 2019; Lai and Kumar 2020). In addition to presenting lower values of organic carbon and P content, negatively impacting soil fertility in these areas.
In PC1, it is possible to observe that the attributes that provided the highest correlation coefficients were in ascending order of importance: P content (0.89), CEC (0.89), SB (0.88), Ca (0.83), K (0.82), OC (0.79), H + Al (0.77), Mg (0.75), BD (-0.74) e TP (0.69) (Table 2 and Fig. 3). These results are explained by the longer recovery time in the APP-6 area, which provided better soil fertility compared to the other areas.
It is noteworthy that the first hypothesis is validated by the results obtained in the PCA (Fig. 4), as it shows that areas with longer recovery time have better chemical and physical soil attributes. For PC2, the order of importance was as follows: pH value (0.95) and Al content (-0.80), corroborating with base removal situation, low available P and loss of organic carbon in degraded areas (Table 2 and Fig. 4).
Amazonian soils are naturally low in exchangeable phosphorus (Quesada et al. 2011). One of the main causes of this unavailability is the precipitation with Al and Fe ions, the region's soils have high levels of these ions (Gama-Rodrigues et al. 2014). However, the present study the APP-6 area provided high P content in the soil. Possibly, the diversification in tree composition allowed the movement of P through the interaction between roots at different depths of the soil (Chaves et al. 2020b).
It is notorious that the loss of native vegetation cover, the land use change (LUC) and incorrect soil management cause degradation, resulting in lower soil quality (Rojas et al. 2016). Thus, the removal of exchangeable cations from K+, Ca+ 2 and Mg+ 2 is justifiable in degraded areas, due to the factors mentioned above. Thus, he noticed that APPD and DP provided lower values compared to APP-6. Even APP-3 did not differ from degraded areas, due to the shorter recovery time, it is not possible to have a greater contribution of litter that improves the chemical and physical attributes of this area.
The BD variables were verified, inversely, the OC, TP and other soil chemical variables, except for Al + 3 and pH, according to PCA (Fig. 4). The greater input of OC changes the soil structure, leading to an increase in soil porosity (Lopes et al. 2020), and reducing the bulk density of the soil (Zacharias and Wessolek 2007). The contribution of litter and the production of fine roots of different trees species provides a direct effect on nutrient cycling and on the microbial community (Scheibe et al. 2015). Thus, the increase in organic carbon improves the physical attributes of the soil, and consequently contributes to the increase in soil fertility.
The changes observed in the chemical and physical attributes of the soils, show that the pasture is degraded by the absence of replacement of correctives and fertilizers, consequently there is a reduction in the bases (K, Ca and Mg) and lower P contents, as well as the APPD area, possibly there is low fertility due to the absence of nutrient replacement, in addition to soil compaction, due to the low carbon content in these areas.