Amazonian syntropic agroforestry systems: impacts on soil health after mineral extraction

Sand mining severely degrades soils in Eastern Amazonia, affecting soil multifunctionality and ecosystem services, creating significant challenges for environmental restoration. This study assessed the effects of syntropic agroforestry systems of different ages on soil health in areas degraded by sand extraction in Santa Bárbara do Pará, Brazil. Soil chemical, physical, and biological indicators were measured in a 20-year-old secondary forest and three syntropic agroforestry systems (AGF2, AGF4, AGF5) at depths of 0–5, 5–10, 10–20, and 20–40 cm. Tukey's test was applied to assess significant differences, followed by integration into a Soil Health Index (SHI) using principal component analysis (PCA). SHI values varied across systems and depths. At 5–10 cm, AGF4 (0.67) had the highest SHI, followed by AGF2 (0.62) and AGF5 (0.61), while SF had the lowest (0.51). At 10–20 cm, AGF4 (0.70) also showed the highest value, followed by AGF2 (0.62). In the 20–40 cm layer, AGF4 (0.69) remained the highest, with AGF2 (0.61) and AGF5 (0.59) following. The overall SHI for the 0–40 cm depth ranged from 0.52 to 0.69, with AGF4 (0.69) showing the highest value. Syntropic agroforestry systems present a promising approach for restoring degraded Amazonian soils, supporting both ecosystem restoration and agricultural production. These systems contribute to global sustainability goals, particularly SDG 2 (food security) and SDG 13 (climate change mitigation).