Saúde do solo em sistemas de produção de palma de óleo na Amazônia oriental.

Abstract

Agroforestry systems (AFS) are generally recognized for enhancing soil health and increasing soil carbon (C) stocks. In the Amazon region, AFS with oil palm have been cultivated as a productive strategy and for the recovery of degraded areas. In the first chapter, we evaluated two AFS with oil palm that differ in species diversity: higher diversity (AFS-B) and lower diversity (AFS-A). A regenerating forest (FOR) was used as a reference. In the 0-10, 10-20, and 20-30 cm soil layers, we evaluated chemical indicators: active acidity (pH), calcium (Ca), magnesium (Mg), potassium (K), phosphorus (P), aluminum (Al); (b) physical indicators: soil density (SD) and aggregate stability (AGG); and (c) biological indicators: permanganate oxidizable carbon (POXC), particulate organic carbon (POC), total soil organic carbon content and stock (SOC), and root stock (ROOT). The values of the biological indicators in the 0-10 cm layer, especially the C indicators, were higher in the AFS than in the forest, and we found the same pattern for the chemical indicators. The physical indicators did not show a specific variation pattern; AGG was higher in the forest than in the AFS across the soil profile, and density was higher in AFS-B and FOR compared to AFS-A in the 20-30 cm layer. Therefore, AFS with oil palm improve the chemical and biological health of the soil, especially in the more superficial layers, but do not improve the physical health of the soil compared to the forest. In the second chapter, we evaluated the activity of the enzymes βglucosidase (Beta) and arylsulfatase (Aryl), POXC, microbial respiration (MR), soil organic matter (SOM), and SOC in three ground cover systems (AFS with oil palm, oil palm monoculture, and forest) and in the management zones (MZ) of the oil palm production systems (pathway - CAR, area around the oil palm crown - ACP, leaf pile - PIL, and diversified strip - DIV). We found higher levels of these soil health indicators in the AFS compared to the forest and monoculture; and superior levels in PIL, intermediate in DIV and ACP, and lower in CAR. Our results for SOC, Beta, Aryl, and POXC indicate that AFS promote better soil health compared to monoculture and forest. These indicators show that MZ with higher C input (PIL, DIV, and WED) improve soil health. In general, Beta, Aryl, POXC, and SOC were more sensitive than MR and SOM to differentiate the ground cover systems and MZ. In the third chapter, we evaluated the increase of POXC and SOC between 2018 and 2022 in AFS, monoculture, and forest, and in MZ. Our results for POXC and SOC show that AFS present a greater short-term increase in soil health compared to monoculture. Regarding the MZ, the zones of the AFS 19 showed an increase in POXC and SOC, unlike the monoculture, where the soil health of the MZ did not change or decreased. Overall, POXC was more sensitive in identifying differences in soil health increments in the ground cover systems and MZ. The combination of organic fertilization with species diversity in AFS was the main factor responsible for the short-term increase in soil health in this system compared to monoculture. Despite the positive results for AFS, further research is needed to evaluate long-term changes in soil health in these cropping systems, given that the oil palm planting cycle lasts approximately 25 years. However, our results suggest that cultivating oil palm in AFS can be a more sustainable alternative to monoculture and has great potential to enhance soil health.