Soil degradation leads to a decrease in soil fertility and agricultural productivity, notably due to the reduction of organic matter (FAO, 2021). Vermicomposting is a sustainable option to valorize organic residues and produce a nutrient-rich amendment (Pandit et al., 2020). Among the earthworm species used, Eudrilus eugeniae shows strong potential for transforming organic matter (Balachandar et al., 2020). However, its multiplication depends on substrate characteristics, notably the C/N ratio, moisture, pH, temperature and the availability of nutrients (Vasanthi et al., 2013). In San Pedro, local organic substrates favorable to its development remain poorly documented. With this in mind, the present study was conducted to assess the suitability of different local organic residues to promote the development of Eudrilus eugeniae and their degradation during vermicomposting. The overall objective was to identify the substrate most favorable to the development and multiplication of Eudrilus eugeniae with a view to vermicompost production.

Specifically, it involved:

• to assess the effect of different local organic residues on the multiplication of Eudrilus eugeniae;
• to quantify the loss of biomass of organic residues during vermicomposting in order to adjust the initial masses of substrates needed to meet the nutritional needs of the crops.

I/ Material and Methods

1.1 Presentation of the study site

The experiment was carried out in San Pedro, a port city located in the south-west of Côte d'Ivoire. Within it is the study site, with an area of 5 hectares, and for geographical coordinates: latitude 4°44' N and longitude 6°38' W. It is occupied by market gardeners from the DAFCI association, which is favorable for market-gardening crops.

1.2 Materials

The biological material consisted of Eudrilus eugeniae, the fern, cacao pod husks and wood sawdust.

Figure 2: Eudrilus eugeniae

Figure 3: Cacao pod husks (Author 2026)

Figure 4: Wood sawdust

Figure 5: Fern

12 plastic 4 L buckets used as composters, a mosquito net to protect the device from earthworm predators, a watering can for humidification, a scale for weighing, and gloves and masks for handling the substrates, etc.

1.3 Methods

1.3.1 Setup of the experimental device

It was installed under natural shading with the president of market gardeners according to a randomized complete block design (RCBD) according to Montgomery (2017), including four treatments such as T1 (cocoa pod husks), T2 (fern), T3 (wood shavings) and T4 (1/3 mix of each substrate), with three replicates per treatment used. Each replicate contained 1 kg of shredded organic matter and 0.5 kg of potting soil.

Figure 6: Experimental setup

The C/N ratios of the different substrates were determined from values reported in the literature. They were 35 for cocoa pod husks, 25.67 for fern, 100 for wood shavings, and 40 for the mix. A C/N ratio between 25 and 30 is generally favorable to microorganism activity and organic matter decomposition, thus creating favorable conditions for earthworm development (Pandit et al., 2020).​​​​​​​

1.3.3 Substrate pre-composting

Before the introduction of Eudrilus eugeniae, the substrates were precomposted for two weeks. During this period, they were watered once a week (1 L of water per replicate) and turned over twice per week to favor the activity of decomposer microorganisms, notably bacteria and fungi. This step helped to initiate the decomposition of organic matter and reducing the substrate temperature to about 25 °C, a temperature favorable for the development of Eudrilus eugeniae (Coulibaly et al., 2019).​​​​​​​

1.3.4 Identification, collection and seeding of the worms

Adult worms have a reddish to dark red coloration and measure about 15 to 25 cm in length. The clitellum, a structure specialized in reproduction, is located between the 14th and 18th segments, starting from the anterior end. The body segments are clearly visible to the naked eye. In total, 60 adult worms were collected. Five adult worms were then introduced into each repetition of each of the experimental substrates (Byambas et al., 2017).

Figure 7: Eudrilus eugeniae

The counting of worms was done manually in a progressive manner for each repetition on a plastic tray. The attached formula was used for the total number of worms counted

The means were calculated and the graphical representations were made using Microsoft Excel. The analysis of variance (ANOVA) was performed with SPSS software to determine if the differences observed between treatments were statistically significant. When ANOVA revealed a significant difference, Tukey's multiple comparison test, at a 5% significance level, was applied to identify treatments showing significant differences among themselves (Montgomery, 2017).

II/ Results and Discussion

2.1 Results​​​​​​​

2.1.1 Variation in the number of Eudrilus eugniae per substrate

The analysis of variance (ANOVA) revealed a highly significant difference between treatments over the two months of observation (p = 0.001 < 0.05). The treatment T2 (fern), had the highest earthworm count (66.67 ± 0.58; 1.66 ± 0.06 individuals), followed by T4, mixture (45.33 ± 0.58; 0.66 ± 0.06 individuals), T1, cacao pod shell (16.33 ± 0.58; 0.33 ± 0.02 individuals) and T3, wood sawdust (3.00 ± 0.58; 0±0 individuals). The multiple comparison test at the 5% level showed that the four treatments were significantly different from each other, each belonging to a different statistical group (a, b, c and d) over the two months.

T1: cacao pod shell, T2: fern, T3: wood sawdust, and T4: mixture Figure
Figure 8: variation in earthworm number by treatment

​​​​​​​2.1.2 Variation in treatment volume during the experiment

The loss of substrate volume varied by treatment. The most significant reduction was recorded with T2 (fern), at 65.84%, followed by T4 (mixture) at 51.23%, T1 (cocoa bean shell) at 28.16%, and T3 (wood sawdust) at 15.20%. Thus, the T2 substrate showed the highest volume loss, while T3 recorded the lowest. Analysis of variance (ANOVA) revealed a significant difference between treatments at months 1 and 2 (p = 0.001 < 0.05). Tukey multiple comparison test at the 5% threshold showed that in the first month, T1 and T4 belonged to the same statistical group (c1), indicating no significant difference between these two treatments. In the second month, the four treatments belonged to different statistical groups (a, b, c and d), indicating significant differences among them.

Figure 9: variation in treatment volume

1.3 Discussion​​​​​​​

1.3.1 Variation in the number of Eudrilus eugniae per substrate