Variations in soil biological and physicochemical properties of reclaimed artisanal mining sites under cocoa cultivation in Ghana across different reclamation ages

The artisanal small-scale mining contributes one-third of Ghana’s gold production; however, it has become a major driver of land degradation and pollution, which affects soil suitability for cocoa production. We assessed the soil physicochemical and microbial properties of cocoa established on reclaimed land. Six cocoa farms were established after 5 years (F1) and 10 years (F2) of reclamation, and Control Farms (CF) as references were selected in the moist semi-deciduous forest zone of Ghana. A total of 18 farms were selected and four quadrants (10 m × 10 m) laid per farm with five soil samples (0–15 cm depth) collected per quadrant. The soil physicochemical properties, microbial community composition, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP) were determined. The results showed that the bulk density of the CF and F2 were similar (1.62 g/cm3) whilst F1 had 2.00 g/cm3. Mercury in F1 (2.21 mg/kg) was higher than CF (1.07 mg/kg) but copper concentration showed a reverse pattern. The CF had higher MBC (205.2 mg/kg), MBN (133.6 mg/kg), and MBP (3.19 mg/kg) than F1 and F2. CF and F1 contained Aspergillus niger and Trichoderma species, respectively. Providencia spp and Salmonella tphyi were present only in F1 and F2, whereas Klebsiella pneumonia and Enterobacter aerogenes were present only in CF. In conclusion, cocoa established on older (>10 years) reclaimed or unmined lands could benefit from improved soil physicochemical properties and health compared to recently reclaimed lands (after 5 years). These findings have implications for SDGs 3 (environmental and public health) and 15 (biodiversity protection).