The experiment was conducted in Yamoussoukro (6.821˚N, 5.277˚W; altitude 214 m), the capital of Côte d’Ivoire (Figure 1). Located in the south-central part of the country, at the transition zone between savanna and forest, the city lies 216 km from Abidjan, the economic capital. Average annual precipitation in the area is 1,098 mm, following a bimodal pattern characterized by two rainy seasons (April to June and August to October) and two dry seasons (one in July and the other from November to March). The average daily temperature ranges from 31˚C to 35˚C during the day and from 19˚C to 23˚C at night (Figure 2). The average sunshine duration is 12.3 hours per day [15]. The trials took place from February 2025 to October 2026. The soil exhibited low organic carbon content (TOC = 1.02), a pH of 6.1, and a cation exchange capacity of 4.2 cmol/kg, with a sandy-clay texture (8.83% clay).

The experiment used the hybrid eggplant (Solanumaethiopicum Gilo) cultivar Ndrowa developed by CNRA, which is referenced Aub 21/06Du “Ndrowa” and was harvest between the 90th and 120th day after direct seeding.

Cocoa pod husks were collected from Toumbokro (5˚22 N, 4˚8 W) in the district of Yamoussoukro and were air-dried 7 days and grounded to pass through a 2 mm sieve.

The Moringa oleifera leaves were collected from Yamoussoukro under the trees and were air-dried 7 days, grounded then crushed and sieved (Ø < 2mm).

Figure 1. Map showing the study area and the trial site.

Figure 2. Yamoussoukro ombrothermic diagram 2025.

The reagents used were of analytical quality, quercetin, Folin-Ciocalteu reagent, were purchased from Sigma (St Louis, USA). Gallic acid, sodium carbonate and iron sulfate were obtained from Merck (Damstad, Germany), methanol, Tris-HCL, iron chloride from Pro labo (Briare, France). Sodium nitrate was obtained from Fluka laboratories. Aluminum trichloride was obtained from Panreac (Spain) and potassium iodate from Prolabo (Sion, Switzerland). Potassium chloride, Sodium acetate, Methanol, Sodium carbonate, Sodium hydroxide, Hydrochloric acid and acetone reagents were purchased from Merck (Damstad, Germany). Gallic acid, Sodium nitrite, Aluminum chloride, were purchased from Fisher Scientific (Pittsburgh, PA, USA). All other reagents were of analytical quality grade. The water used is produced by a Selecta L-4B bi-distiller at the Soil Health and Plant Nutrition Laboratory (LASSNP).

Each large block received the various formulations at increasing application rates (1, 2, and 4 kg/m²). The trials were conducted using a randomized complete block design with three replicates for each of the five formulations (F1, F2, F3, F4, F5). The treatments compared were based on a two-component mixture (A and B), where the sum of the proportions always equaled 100%; thus, the percentage of the second component was determined by the percentage of the first. Each block included the following treatments:

- T0: absolute control (soil with no fertilizer application);

- F1: application of crushed cocoa pod husks only;

- F2: application of 75% crushed cocoa pod husks and 25% crushed Moringa leaves;

- F3: application of 50% crushed cocoa pod husks and 50% crushed Moringa leaves;

- F4: application of 25% crushed cocoa pod husks and 75% crushed Moringa leaves;

- F5: application of crushed Moringa leaves only.

A total of 54 experimental plots were maintained during the trial. Organic fertilizer doses were applied manually and incorporated into the soil to a depth of approximately 10 cm. Treatments were assigned to experimental units randomly (Figure 3).

Sowing was performed manually with a spacing of 80 cm between rows and 40 cm between plants (or planting holes) within the row (Figure 1). This geometric layout defines a growing area of 0.32 m² per planting station (0.80 m × 0.40 m), corresponding to a theoretical planting density of 31.25 plants per hectare (based on one plant per station after thinning). At the level of the individual plot, each unit comprises four crop rows with ten plants each, resulting in a total of 40 plants per plot. The two central rows (20 plants) served as the harvestable area for agronomic measurements, in order to eliminate edge effects.

At 98 and 106 days after planting, 1 kg of mature fruit was harvested from each experimental plot (accounting for replicates); the fruit had reached near-maximum size but showed no change in epicarp color. The eggplants were transported to the laboratory, washed with tap water followed by distilled water, dried on absorbent paper, placed in clear plastic bags, and stored in opaque containers at 4˚C for subsequent analysis.

Figure 3. Distribution of formulations on the experimental plot.

2.6.1. Determination of Organic Carbon

Total organic carbon (TOC) in the samples was determined by titration [16]. A 1 g sample portion was weighed into a 250 mL conical flask, and 10 mL of 1 N potassium dichromate was added and mixed thoroughly. A 20 mL volume of concentrated sulfuric acid was slowly added; the mixture was then shaken vigorously for 1 minute and allowed to stand for 30 minutes. A volume of 200 mL of demineralized water, 10 mL of concentrated phosphoric acid, and 10 to 15 drops of ferroin indicator solution were added. Following the reaction, the excess dichromate that had not reacted with the sample was titrated with 0.5 N ferrous iodate solution until a final brown color was reached. The percentage of carbon in the sample, expressed as % C, was determined as follows:

2.6.2. Determination of Cation Exchange Capacity (CEC or T)

Cation exchange capacity (CEC or T) was determined using a method developed by [17], based on contacting an alcohol-washed soil sample with a sodium chloride (NaCl) solution of known concentration. Na+ ions displace the cations from the adsorption complex and bind to it. The solution collected during saturation contains the exchangeable cations, as well as ions quantified by the difference between the initial ion concentration and the concentration remaining after contact with the soil. Exchangeable cations were determined in the same extract used for the cation exchange capacity measurement. The extract was distilled using a Kjeldahl apparatus and then titrated with hydrochloric acid (HCl). Results were expressed in cmol/kg of soil.

2.6.3. Dry Matter

The moisture content and dry matter content were determined using AOAC Official Method [18] (by measuring 2 g of the sample into a previously weighed crucible). The porcelain crucible plus sample was transferred into the oven set at 105˚C to dry to a constant weight. Regular weighing is carried out until the mass stabilizes, which reflects the evaporation of residual water from the sample. At the end of drying, the crucible plus sample was removed from the oven and transferred to the desiccator, cooled for ten minutes and weighed. The values obtained were subjected to Equations 1:

where: W0 = weight of empty crucible, W1 = weight of crucible plus sample and W3 = weight of crucible plus oven-dried sample.

2.6.4. Nitrogen and Crude Protein

The nitrogen and crude protein of organic materials were determined according titrimetric method dosage after digestion by Kjeldahl procedures [19] with some modifications. About 1 g of plant tissues are placed in pyrex Folin-Wu tubes and digested with a salt-catalyst-sulfuric acid mixture by heating the tubes in an aluminum block. The catalyst consisting of copper sulfate (CuSO₄∙5H₂O), potassium sulfate (K₂SO₄) are added with diluted sulfuric acid and water. Samples are digested at the boiling point of the mixture for 60 min after initial clearing of the digests. The mineralized sample was transferred into a 100 mL flask and adjusted with distilled water. Ten mL of the mineralized sample solution was taken and then 10 mL of 40% NaOH was added and distilled for 10 min. The distillate was trapped in a flask containing 20 mL of sulfuric acid (H₂SO₄) in the presence of methylen bromocresol red color indicator. The content of the flask was titrated against 0.1 N NaOH until the solution became colorless. The total nitrogen content is determined by Equation (2). Crude protein was deduced by multiplying the percent total organic nitrogen (N) by a conversion factor of 6.25.

where: V= volume (mL) of NaOH, P = weight of the sample, N = normality of NaOH and 0.014: coefficient assigned to the concentration of the normal nitrogen solution (14/1000).

2.6.5. Organic Carbon and Organic Matter

Total organic carbon and organic matter of soil and fertilizer were determined [20]. About 1 g of sample is weighed into a 250 conical flask and 10 ml of 1N potassium dichromate is added and homogenized. A 20 mL volume of concentrated sulfuric acid is added slowly and then shaken vigorously for 1 minute and allowed to stand for 30 minutes. A volume of 200 mL of deionized water, 10 mL of concentrated phosphoric acid and 10 to 15 drops of the ferroin indicator solution are added. After the reaction, the excess of dichromate that did not react with the sample is titrated with 0.5 N ferrous sulfate solution to the final brown color. The percentage of carbon in the sample expressed as % C is determined by Equation (3) bellow: Organic matter was deduced by multiplying the percent total organic carbon (COT) by 1.72.

where: A = volume (mL) of ferrous sulfate used for the control, B = volume (mL) of ferrous sulfate used for the sample, P = weight (g) of the titrated sample expressed on dry basis, 0.004: number of g of C per ml of dichromate.

2.6.6. Phosphorus

Phosphorus content of fertilizers was determined by incinerating the samples in a muffle furnace at 550˚ and then determined by UV-visible colorimetry. Phosphorus present in its ortho-phosphate form, reacts with the vanadate-molybdate reagent to produce a yellow-orange complex, which absorbance is measured at a wavelength of 400 nm. The phosphorus content is then determined according to the standard calibration curve [21].

2.6.7. Mineral Composition

The determination of the mineral elements (K, Ca, Mg, Fe and Zn) of organic materials were carried out by atomic absorption to flame air-acetylene of type VARIAN AA20 after calcination at 550˚C and recovery of the ashes with hydrochloric acid [22]. A quantity of 0.4 g of ground sample was weighed into a porcelain crucible and then placed in a furnace (PROLABO) at 650˚C for 5 h. After cooling, 5mL of nitric acid 1 mol·L⁻¹ is added to the obtained ash and then evaporated on a sand bath. To the residue is added 5 mL of 0.1 mol·L⁻¹ is added to the residue and put back into the oven at 400˚C for 30 min. The final residue is recovered with 10 ml of hydrochloric acid 1 mol·L⁻¹ hydrochloric acid and poured into a 50 mL flask. The crucible is rinsed twice with 10 mL of hydrochloric acid. The flask is completed to 50 mL with hydrochloric acid. Under the same conditions, a blank test is performed. The calibration is obtained by measuring the absorbance of synthetic solutions with progressive concentrations of analyte. The mineral content of the unknown sample solution is then directly deduced by relating its absorbance value to a calibration line previously established from solutions of elements certified at 1000 ppm.

2.6.8. Total Phenol

Dried pulp (1 g) was macerated in 4 mL of a methanol/water mixture (80:20, v/v) and incubated in an ultrasonic bath at medium intensity for 30 min. The solution was centrifuged at 1200 g for 30 min, and the supernatant was transferred into vials. This procedure was repeated three times. The supernatants were pooled, made up to 50 mL with water, and filtered through a 0.45 µm nylon filter [18].

Total polyphenol content (soluble and hydrolyzable) was determined colorimetrically using the Folin-Ciocalteu method [23], with slight modifications. A 30 µL volume of blank, standard, or filtered extract was placed in a test tube, to which 1.5 mL of distilled water and 2.5 mL of Folin-Ciocalteu reagent (diluted 1:10) were added. The mixture was allowed to stand for 6 min, protected from light, at room temperature. Then, 2 mL of sodium carbonate solution (75 g/L) was added. The mixture was shaken and incubated for 15 minutes in a water bath at 50˚C, before being cooled to room temperature. Finally, absorbance was measured at 760 nm using distilled water as a blank. Analyses were performed in triplicate, and a calibration curve was established using gallic acid. Total phenolic content was expressed as mg of gallic acid equivalent (GAE) per 100 g of dry weight.

2.6.9. Total Flavonoid

Dried pulp (1 g) was macerated with 4 mL methanol: water (80:20, v/v) and incubated in ultrasonic bath at medium intensity for 30 min. The solution was centrifuged at 1200 g for 30 min and the supernatant was transferred into vials. The procedure was performed 3 times and the supernatants were combined and made up to 50 mL with water and filtered through a 0.45-micrometer nylon filter [18]. Total soluble flavonoid content was determined using the aluminum chloride colorimetric method [24]. A 2.5 mL volume of blank, standard, or filtered extract was mixed with 1250 µL of distilled water and 750 µL of a 5% sodium nitrite solution; the mixture was allowed to stand for 6 minutes in the dark at room temperature. Subsequently, 750 µL of a 10% aluminum chloride solution was added, and the mixture stood for an additional 5 minutes before the addition of 5 mL of 1 M sodium hydroxide solution and the adjustment of the final volume to 25 mL. Absorbance was measured at 510 nm using a UV-visible spectrophotometer. Total flavonoid contents were calculated from a quercetin calibration curve, and results were expressed as mg QE·100 g⁻¹ fresh weight (FW).

A one-way analysis was used to determine whether chemical characteristic levels differed according to the fertilizers used. The same test was applied to fruit nutritional quality parameters following the application of organic matter to the soil. Differences between means were evaluated using the Newman-Keuls multiple comparison test and were considered significant at p < 0.05. All statistical analyses were performed using Statistica 7.0 software.

The chemical composition of cocoa pods, Moringa leaves and their mixing organic fertilizers are shown in Table 1. Theobroma cacao pods (F1) were a good source of potassium (4.33%) and had the highest C: N ratio (37.70). Moringa oleifera leaves fertilize (F5) had a high content of carbon, rich in nitrogen, calcium and potassium with intermediate levels of phosphorus and also contained magnesium. Increasing the rate of Moringa leaves fertilizer improved the nutrient content and resulted in a decrease on the C/N ratio of the formulations. Among all the formulated fertilizers, F4, followed by F3, was found with the adequate quantity of mineral (N, P, K, Ca and Mg) with littlest C/N ratio (Table 1).

Table 1. Chemical characteristics of organic fertilizer powders as percentage of dry matter.

Means with the same letter along the columns were not significantly different at the p < 0.05.

Mean values for eggplant dry matter content are summarized in Table 2. There is a significant difference in dry matter content among eggplants from the various treatments.

3.2.1. Effects of Fertilizers on Dry Matter Content

The analysis results are presented in Table 2 and Table 3. Overall, fertilizer applications had a positive effect on both fruit size and dry matter content compared to the control (T0). At the 1 kg/m² rate, no significant difference (p > 0.05) in fruit dry matter content was observed between treatments F1 (8.40%) and F2 (8.35%), which showed the lowest values. In contrast, higher dry matter contents were recorded for treatments F3 (9%), F4 (9.20%), and F5 (8.70%) (Figure 4). Furthermore, a gradual decline in dry matter content was observed across successive production cycles for all treatments. At the 2 kg/m² rate, treatments F3 (9.45%) and F4 (9.5%) yielded the highest dry matter contents, surpassing F1 (8.73%), F2 (8.75%), and T0 (8.2%) (Figure 4). Significant differences were observed between cycles (p < 0.001), revealing that fruit dry matter content was strongly affected by a depletion effect during the last two cycles (C2 and C3) due to the lack of further fertilizer application. Finally, at the 4 kg/m² rate, treatments F3 (9.75%), F4 (9.9%), and F5 (9.45%) improved dry matter content more effectively than F1 (8.78%) and F2 (8.80%), although no significant difference was detected between F2, F3, and F4 (Figure 4).

Table 2. Protein, total polyphenol, and flavonoid contents (expressed on a dry weight basis) were analyzed in the various fruits of the plants harvested at the end of the experiment.

Table 3. Average content of five major minerals in the fruit of *Solanumaethiopicum* (N’Drowa variety) (mg per 100 g dry weight) according to organic fertilizer rates.

Rate D1: 1 kg·m⁻² of fertilizer applied to the soil; D2: 2 kg·m⁻² of fertilizer applied to the soil; and D3: 4 kg·m⁻² of fertilizer applied to the soil. C1: First cropping cycle; C2: Second cropping cycle; C3: Third cropping cycle; F1: Formulation consisting exclusively of cocoa husks; F2: Formulation consisting of 75% cocoa pod husks and 25% moringa leaves; F3: Formulation consisting of 50% cocoa pod husks and 50% moringa leaves; F4: Formulation consisting of 25% cocoa pod husks and 75% moringa leaves; F5: Formulation consisting exclusively of moringa leaves; T0: Control without fertilizer.

Figure 4. Eggplant dry matter content according to fertilizer rate and cropping cycle.

3.2.2. Effects of Fertilizers on Protein Content of Eggplant Fruit

Figure 5 shows the protein content of the fruits. Despite increasing fertilizer rates, protein levels did not vary significantly between fruits from the F2 treatment (1.18% at a rate of 2 kg/m²) and the F3 treatment (1.19% at a rate of 4 kg/m²). The lowest protein content was recorded for the T0 treatment (Figure 5). Fruits from the F3 (1.38%) and F4 (1.47%) treatments at the 4 kg/m² rate exhibited high protein levels. The application of increasing rates had an additive effect on the retained protein content.

Rate D1: 1 kg·m⁻² of fertilizer applied to the soil; D2: 2 kg·m⁻² of fertilizer applied to the soil; and D3: 4 kg·m⁻² of fertilizer applied to the soil. C1: First cropping cycle; C2: Second cropping cycle; C3: Third cropping cycle; F1: Formulation composed exclusively of cocoa pod husks; F2: Formulation composed of 75% cocoa pod husks and 25% moringa leaves; F3: Formulation composed of 50% cocoa pod husks and 50% moringa leaves; F4: Formulation composed of 25% cocoa pod husks and 75% moringa leaves; F5: Formulation composed exclusively of moringa leaves; T0: Control without fertilizer.

Figure 5. Protein content of eggplant fruits according to fertilizer rate and cropping cycles.

3.3.1. Effects of Fertilizers on Total Phenol Content

There were no significant differences in total phenol content among the harvested eggplants across treatments F2, F3, F4, and F5 at increasing rates of 1, 2, and 4 kg/m² (Figure 6). In contrast, fertilizer F1 showed a significant difference in total phenol content at rates of 1, 2, and 4 kg/m². All values obtained were higher than that of the control T0 (22.4 mg GAE/g). Furthermore, total polyphenol content decreased between the first and third cycles, regardless of the treatment (Figure 6).

3.3.2. Effects of Fertilizers on Flavonoid Content

Analysis of Figure 7 reveals observations similar to those for total phenols. For any given treatment, flavonoid content increases with the dosage. This increase was significant across all treatments, particularly for treatments F3, F4, and F5. Relatively high flavonoid levels were observed with treatments F4 and F5, with maximum levels recorded at the 4 kg/m² dosage. Furthermore, flavonoid levels in the fruit from the first cycle were higher than those from the other cycles.

Dose D1: 1 kg·m⁻² of fertilizer applied to the soil; D2: 2 kg·m⁻² of fertilizer applied to the soil; and D3: 4 kg·m⁻² of fertilizer applied to the soil. C1: First cultivation cycle; C2: Second cultivation cycle; C3: Third cultivation cycle; F1: Formulation consisting exclusively of cocoa shells; F2: Formulation consisting of 75% cocoa pod shells and 25% moringa leaves; F3: Formulation consisting of 50% cocoa pod shells and 50% moringa leaves; F4: Formulation consisting of 25% cocoa pod shells and 75% moringa leaves; F5: Formulation consisting exclusively of moringa leaves; T0: Control without fertilizer.

Figure 6. Total polyphenol content of fruits according to fertilizer dose and cycle.

Dose D1: 1 kg·m⁻² of fertilizer applied to the soil; D2: 2 kg·m⁻² of fertilizer applied to the soil; and D3: 4 kg·m⁻² of fertilizer applied to the soil. C1: First cultivation cycle; C2: Second cultivation cycle; C3: Third cultivation cycle; F1: Formulation consisting exclusively of cocoa husks; F2: Formulation consisting of 75% cocoa pod husks and 25% Moringa leaves; F3: Formulation consisting of 50% cocoa pod husks and 50% Moringa leaves; F4: Formulation consisting of 25% cocoa pod husks and 75% Moringa leaves; F5: Formulation consisting exclusively of Moringa leaves; T0: Control without fertilizer.

Figure 7. Flavonoid content of fruits according to fertilizer dose and cultivation cycle.

The minerals analyzed are in Table 3.

3.4.1. Effects of Fertilizers on the Potassium Content of Eggplants

Figure 8 shows the potassium content of the fruit according to treatments, application rates, and cycles. Potassium levels in the fruit increased significantly with increasing application rates (1, 2, and 4 kg/m²). At the 1 kg/m² rate, the highest levels were observed with treatments F3 (450 mg/100g) and F4 (490 mg/100g), followed by F5 (390 mg/100g), F2 (350 mg/100g), and F1 (340 mg/100g). The control (T0) showed the lowest level (250 mg/100g). Potassium levels decreased during the two cycles in which no fertilizer was applied (Figure 8).

At the 2 kg/m² rate, treatments F3 (460 mg/100g) and F4 (510 mg/100g) yielded the highest levels compared to the other treatments (Figure 8). Furthermore, regardless of the application rate, the highest potassium levels were obtained with treatments F3 and F4.

Dose D1: 1 kg·m⁻² of fertilizer applied to the soil; D2: 2 kg·m⁻² of fertilizer applied to the soil; and D3: 4 kg·m⁻² of fertilizer applied to the soil. C1: First cropping cycle; C2: Second cropping cycle; C3: Third cropping cycle; F1: Formulation consisting exclusively of cocoa husks; F2: Formulation consisting of 75% cocoa pod husks and 25% moringa leaves; F3: Formulation consisting of 50% cocoa pod husks and 50% moringa leaves; F4: Formulation consisting of 25% cocoa pod husks and 75% moringa leaves; F5: Formulation consisting exclusively of moringa leaves; T0: Control (no fertilizer).

Figure 8. Potassium content in fruit according to fertilizer dosage and cropping cycles.

3.4.2. Effects of Fertilizers on the Magnesium Content of Eggplants

Fruit magnesium content increased in proportion to the application rates, regardless of the treatment (Figure 9). Magnesium levels in the eggplants were particularly high with treatments F3 and F4, irrespective of the dosage. A significant difference in magnesium content was observed between cropping cycles. Analysis revealed that treatments at the 4 kg/m² rate were highly significant (p < 0.001) compared to the 2 kg/m² and 1 kg/m² rates, as well as the control (T0). Specifically, treatments F3 (200 mg/100g) and F4 (240 mg/100g) yielded the highest values among all treatments (Figure 9). Treatments T0 and F1 fell within the same range of content levels.

3.4.3. Effects of Fertilizers on the Calcium Content of Eggplants

Fertilizer application at a rate of 1 kg/m² resulted in improved calcium levels compared to the T0 control. Specifically, calcium levels in eggplants from treatments F1 and F2 fell within the same range (at the 5% significance level). These eggplants showed lower values compared to those from treatments F3 (360 mg/100g), F4 (390 mg/100g), and F5 (380 mg/100g) (Figure 10). Regarding the cropping cycles, a progressive decline in calcium levels was observed across all treatments.

Furthermore, at the 2 kg/m² application rate, treatments F3 (410 mg/100g) and F4 (420 mg/100g) yielded the highest calcium levels compared to treatments F1 (310 mg/100g), F2 (330 mg/100g), and T0 (280 mg/100g). Significant differences were observed across the cycles. Additionally, the results revealed that calcium levels were significantly influenced by the absence of fertilizer application during the final two cycles (C2 and C3). Overall, the treatments had a positive effect on eggplant calcium levels. At the 4 kg/m² rate, eggplants from treatments F3 (430 mg/100g), F4 (440 mg/100g), and F5 (410 mg/100g) exhibited higher levels than those from F1 (330 mg/100g) and F2 (340 mg/100g) (Figure 10). Analytical results indicated a decline in levels over the course of the cycles.

3.4.4. Effects of Fertilizers on Iron Content in Eggplants

Iron content in eggplants ranged from 1.14 to 1.65 ppm at the 1 kg/m² application rate. The effect of the treatments on eggplant iron content was significant (p = 0.001). Fertilizers F3 and F4 resulted in the highest iron levels, at 1.62 and 1.65 ppm, respectively (Figure 11). The lowest iron levels were observed with F1 (1.27 ppm), F5 (1.49 ppm), and F2 (1.51 ppm).

At the 2 kg/m² application rate, there was a significant difference in content levels among the treatments at the 5% significance level. Treatments F3 (1.78 ppm) and F4 (1.82 ppm) recorded the highest iron levels.

Dosage D1: 1 kg·m⁻² of fertilizer applied to the soil; D2: 2 kg·m⁻² of fertilizer applied to the soil; D3: 4 kg·m⁻² of fertilizer applied to the soil. C1: First cultivation cycle; C2: Second cultivation cycle; C3: Third cultivation cycle; F1: Formulation consisting exclusively of cocoa husks; F2: Formulation consisting of 75% cocoa husks and 25% Moringa leaves; F3: Formulation consisting of 50% cocoa husks and 50% Moringa leaves; F4: Formulation consisting of 25% cocoa husks and 75% Moringa leaves; F5: Formulation consisting exclusively of Moringa leaves; T0: Control without fertilizer.

Figure 9. Magnesium content of fruits according to fertilizer dosage and cycle.

Dosage D1: 1 kg·m⁻² of fertilizer applied to the growing medium; D2: 2 kg·m⁻² of fertilizer applied to the growing medium; D3: 4 kg·m⁻² of fertilizer applied to the growing medium. C1: First cultivation cycle; C2: Second cultivation cycle; C3: Third cultivation cycle; F1: Formulation consisting exclusively of cocoa husks; F2: Formulation consisting of 75% cocoa pod husks and 25% Moringa leaves; F3: Formulation consisting of 50% cocoa pod husks and 50% Moringa leaves; F4: Formulation consisting of 25% cocoa pod husks and 75% Moringa leaves; F5: Formulation consisting exclusively of Moringa leaves; T0: Control without fertilizer.

Figure 10. Fruit calcium content according to fertilizer dosage and cultivation cycles.

Dosage D1: 1 kg·m⁻² of fertilizer applied to the soil; D2: 2 kg·m⁻² of fertilizer applied to the soil; and D3: 4 kg·m⁻² of fertilizer applied to the soil. C1: First cultivation cycle; C2: Second cultivation cycle; C3: Third cultivation cycle; F1: Formulation consisting exclusively of cocoa husks; F2: Formulation consisting of 75% cocoa pod husks and 25% moringa leaves; F3: Formulation consisting of 50% cocoa pod husks and 50% moringa leaves; F4: Formulation consisting of 25% cocoa pod husks and 75% moringa leaves; F5: Formulation consisting exclusively of moringa leaves; T0: Control without fertilizer.

Figure 11. Iron content of fruits according to fertilizer dosage and cultivation cycles.

Furthermore, organic fertilizers increased iron levels in eggplants at the 4 kg/m² application rate. The highest iron levels in the eggplants were recorded with treatments F3 (1.89 ppm) and F4 (1.98 ppm). Regarding the cropping cycles, iron levels in the eggplants decreased progressively (Figure 11).

3.4.5. Effects of Fertilizers on Zinc Content in Eggplants

Zinc levels in eggplants increased significantly with increasing application rates (1, 2, and 4 kg/m²) (Figure 12). At the 1 kg/m² rate, the highest levels were observed with treatments F3 (7.76 ppm) and F4 (7.97 ppm), followed by F5 (7.49 ppm), F2 (7.34 ppm), and F1 (7.33 ppm). The control (T0) showed the lowest level (5.78 ppm). Furthermore, zinc levels decreased during the two cycles in which no fertilizer was applied (Figure 12).

At the 2 kg/m² rate, treatments F3 (460 mg/100g) and F4 (510 mg/100g) also yielded the highest levels compared to the other treatments. Moreover, regardless of the application rate, the highest zinc levels were obtained with treatments F3 and F4. Within each cycle, there was no significant difference in zinc levels in the eggplants (Figure 12).

Dose D1: 1 kg·m⁻² of fertilizer applied to the soil; D2: 2 kg·m⁻² of fertilizer applied to the soil; and D3: 4 kg·m⁻² of fertilizer applied to the soil. C1: First cultivation cycle; C2: Second cultivation cycle; C3: Third cultivation cycle; F1: Formulation consisting exclusively of cocoa husks; F2: Formulation consisting of 75% cocoa pod husks and 25% Moringa leaves; F3: Formulation consisting of 50% cocoa pod husks and 50% Moringa leaves; F4: Formulation consisting of 25% cocoa pod husks and 75% Moringa leaves; F5: Formulation consisting exclusively of Moringa leaves; T0: Control without fertilizer.

Figure 12. Zinc content of fruits according to fertilizer dosage and cultivation cycles.