Organic residues stimulate β-glucosidase in severely degraded soils

Soil biological activity is highly sensitive to management changes, such as the enzyme β-glucosidase and basal respiration, and can be used as indicators of soil quality and recovery. This study aimed to assess the health of the soil in a severely degraded area under-recovery, comparing it with a conserved Cerrado area. The experimental area is located on land that was used as a borrow site for constructing the Ilha Solteira Hydroelectric Power Station, from which soil was removed between 01 and 12 m deep. To restore it, mechanization (M) was carried out to break up the surface sealing, as well as the addition of organic compost (C), seeds of native species (S), Stylosanthes spp. (E), sheep residue (R) and branches on the surface (G), in a total of 12 treatments, arranged in 5 × 5 m (25 m²) plots, with 4 replications in randomized blocks. After 6 years from the beginning of the interventions, the soil was collected in the 0 to 0.10 m layer, the samples were dried, sieved and the organic matter content was determined, subsequently converted into organic carbon, basal respiration, and β-glucosidase activity. Data from the recovering area was compared to the conserved Cerrado (Dunnett's test p < 0.05) and between treatments in the recovering area (Scott-Knott test p < 0.05). Compared to the conserved Cerrado area, among the three variables analyzed, only the most complete treatment (MCSERG), which received all the interventions, showed β-glucosidase activity statistically similar to that of the reference area (33.88 ± 6.79 and 34.82 ± 6.15 μg p-nitrophenol g-¹ soil h-¹, respectively). The other variables - basal respiration (6.00 ± 1.56 and 47.14 ± 13.88 C-CO₂ kg-¹ soil h-¹) and organic carbon (7.54 ± 1.29 and 14.79 ± 7.99 g kg-¹) remained lower than the Cerrado area. Among the treatments applied in the recovery area, the MCSERG showed the best performance, with β-glucosidase values ten times higher, basal respiration three times higher, and organic carbon content twice as high as those observed in the control treatment (no intervention). These results show the positive effect of the addition of twigs and organic residue on the biological activity of the soil. It is concluded that the joint application of these conditioning agents contributes significantly to the recovery of microbial activity in degraded soils, with the surface incorporation of leaf litter and sheep residue being a promising strategy for improving soil health.