Abundance of earthworms in Nigerian ecological zones: implications for sustaining fertilizer-free soil fertility

Abstract

The abundance of earthworms in the ecological zones in Nigeria has been determined and the possibility of earthworm functions replacing both mechanized land preparation and organic fertilizers discussed. The most abundant earthworms, comprising 62 % of the population, were the advantageous solid-wormcast makers. Mixed Leguminous Wooded Savanna had the highest earthworm density (1.50 million worms/ha), while Wooded Savanna had the lowest (0.23 million worms/ha). Coastal Forest and Mangrove (0.51 t/ha) had the highest earthworm biomass and Afziela Savanna/Semi-Deciduous Forest (0.03 t/ha) had the least. A new soil impact index (SIINDEX) is introduced, which simultaneously incorporates both earthworm biomass and density. The highest SIINDEX was from Mixed Leguminous Wooded Savanna (0.72) and the lowest from Afziella Savanna/Semi-Deciduous Forest (0.11). Forests with SIINDEX less than 0.2 should be regarded as endangered, because their earthworm functions are too low to accomplish significant leaf-litter breakdown and recycling. We suggest that if the illegal annual bush burning is prevented, the soil surface will be naturally mulched, earthworms protected, and by their function in the soil, the need for soil mechanization and fertilization could be replaced by earthworms to produce natural foods.

Keywords: Annelida, Oligochaeta, leaf litter breakdown, soil fauna, SIINDEX