Influência de diferentes arranjos agroflorestais com cacau sobre a serapilheira e a fertilidade do solo na Amazônia oriental.

Abstract

The Amazon biome harbors high biodiversity and naturally nutrient-poor soils, whose fertility depends strongly on nutrient cycling driven by litter dynamics. In degraded areas or areas converted to agriculture, secondary forests and agroforestry systems (AFSs) have emerged as sustainable alternatives for reconciling agricultural production with environmental conservation. In Tomé-Açu, Pará State, a municipality characterized by a history of intensive agricultural practices and the expansion of agroforestry systems, understanding how these systems affect soil properties and litter physical attributes is particularly relevant. This study aimed to evaluate litter stock, waterholding capacity (WHC), and soil fertility attributes in four cocoa-based agroforestry systems (AFSs) containing Theobroma cacao L., with different species compositions and ages, compared with a secondary forest (FLO) used as a reference ecosystem. Five plots were established in each ecosystem for litter and soil sampling. Litter was separated into non-woody, woody, and miscellaneous fractions to determine litter stock and water-holding capacity. Samples from the non-woody fraction were also analyzed for macro- and micronutrient contents. In addition, soil samples were collected from each plot at depths of 0–10 and 10–20 cm for chemical analysis. The agroforestry system composed of cocoa and African mahogany (CMa) had the highest total litter stock (12.50 ± 2.48 Mg ha⁻¹), whereas CPMb (cocoa, piquiá, and Brazilian mahogany) had the lowest stock (4.18 ± 1.33 Mg ha⁻¹). For the non-woody fraction, CMa also showed the highest litter stock, with values statistically similar to those observed in FLO. Regarding the woody fraction, FLO showed the highest mean stock (2.95 ± 0.56 Mg ha⁻¹), although it did not differ statistically from CMa and CS (cocoa and rubber tree). The water-holding capacity of the non-woody fraction did not differ among ecosystems. However, for the woody fraction, CPMb showed significantly higher WHC than CMa and CS. For the miscellaneous fraction, FLO showed higher values only than CS. Considering total WHC, FLO (195.88 ± 12.61%) and CPMb (191.41 ± 1.67%) showed the highest values, whereas CS had the lowest (138.82 ± 19.00%). These results indicate that well-managed AFSs can accumulate litter stocks comparable to those found in secondary forests, although water-holding capacity and the relative contribution of litter fractions may vary according to species composition, structural arrangement, and land-use history. Such differences reflect the combined effects of management practices, plant diversity, and the structural characteristics of agroforestry systems. This dissertation reinforces the importance of AFSs as a strategy for restoring ecological functions and improving soil attributes in the Amazon while integrating agricultural production, environmental conservation, and the mitigation of environmental impacts. The indicators evaluated—litter stock, water-holding capacity, and soil fertility—provide relevant information for understanding the functioning and ecological performance of these systems.