Relationships between soil morpho-chemical parameters and earthworm community attributes in tropical agro-ecosystems in the Centre-West region of Cote d'Ivoire, Africa

This study was carried out to investigate the relationship between earthworm trophic groups and soil morphology and chemical attributes, and moreover, to determine which of these attributes would be most significant in explaining the distribution of earthworm communities in agro-ecosystems in the Centre-West region of Cote d'Ivoire. Earthworms' soil morphology and soil samples were studied in three agro-ecosystems: 20-year-old cocoa plantations, 5-year-old mixed cocoa plantations and mixed crop-fields. The semi-deciduous forests near the agro-ecosystems were also sampled and considered as control plots. Earthworm global densities varied on average between 53.9 +/- 7.9 and 86.0 +/- 19.0 individuals m(-2) and biomass between 16.5 +/- 3.1 and 20.6 +/- 4.1 g m(-2) under these ecosystems. Path analysis produced a significant model: soil morphology and chemical attributes under different agro-ecosystems affected the density and biomass of earthworm trophic groups, and these attributes are potential regulators of the fauna communities. The morphological components related to dead leaves (r(2) = 0.73, P < 0.05) and fine woods quantities (r(2) = 0.71, P < 0.05) are most decisive for detritivore abundances, whereas geophageous mesohumic abundances were positively affected by soil organic carbon (r(2) = 0.79, P < 0.05) and N (r(2) = 0.84, P < 0.05) and geophageous polyhumic abundances were positively affected only by soil N (r(2) = 0.63, P < 0.05). In agro-ecosystems the relationship between soil conditions and earthworm communities varied between earthworm trophic groups, so detritivores were more affected by litter quantity, whereas shallow geophageous populations were guided by soil organic matter.