Earthworm Casts for Improving Soil Biological Quality in Daloa, Côte d’Ivoire

Aims: Intensive agriculture in sub-Saharan Africa, particularly Côte d’Ivoire, degrades soils through physical and biological erosion, reducing their productive capacity. This study explores sustainable fertilization using earthworm casts to enhance soil fertility. Methodology: Four localities of the city of Daloa (Côte d’Ivoire), namely the neighborhoods “Abattoir”, “Tazibouo Université”, “Tagoura” and “Soleil” were investigated on February 2025. In each neighborhood study site, two composite samples (earthworm casts and surrounding soil) were collected, for all sites, eight composite samples. Analyses focused on (i) the fungal and bacterial diversity of the casts and soil and (ii) the effect of different quantities of these casts on the physicochemical characteristics and biomass of the soil. For the latter, varying amounts of earthworm casts were mixed with soil to obtain substrates enriched at 0% (T0), 5% (T5), 10% (T10), 15% (T15) and 20% (T20). Results: Several fungal genera, including Aspergillus, Trichoderma, Mucor, Rhizopus, Neurospora, Sclerotinia, as well as Pseudomonas bacteria, were identified in the collected earthworm casts and soil. The highest and lowest pH values in experimental substrates was 7.16 and 6.7, respectively. Titratable acidity varied between 0.004% and 0.1%. Experimental substrates T5 and T10 enriched with 5% and 10% casts exhibited the highest bacterial biomasses, with 3.4 × 105 CFU/g and 2.5 × 105 CFU/g, respectively. Conclusion: Earthworm casts and the surrounding soil demonstrated fungal and bacterial diversity of agricultural interest. Experimental substrates T5 and T10 presented the highest bacterial biomasses. These substrates provide improved conditions for soil fertilization.