# Integrated approaches to reducing chemical fertilizer use through enriched compost in arid Sahelian regions for Vigna unguiculata cultivation

Alexis Dzokom, Roger Djouldé Darman

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Alexis Dzokom, Roger Djouldé Darman. Integrated approaches to reducing chemical fertilizer use through enriched compost in arid Sahelian regions for Vigna unguiculata cultivation. Sahel Nature Consulting Revue, 2025, Compost and Soil Fertility, pp.1-16. hal-05050198

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Integrated approaches to reducing chemical fertilizer use through enriched compost in arid Sahelian regions for Vigna unguiculata cultivation

Scientific-Article April-2025 Volume-04 Issue-11

Abstract

Sahelian agriculture faces challenges such as soil degradation, the scarcity of natural organic resources, and costly dependence on chemical inputs. This study aims to compare the agronomic efficiency of composts produced from dead biomass of Pennisetum sp., enriched with biological and organic materials, on the cultivation of Vigna unguiculata in ten distinct Sahelian agroecological zones: a mountainous area and an arid plain. Three compost formulations were tested, with a gradual reduction in chemical fertilizer inputs. Results showed that the 100% organic-biological compost achieved a higher yield (3900 g/ha) than the 100% chemical fertilizer treatment (3200 g/ha), indicating a high agronomic performance without synthetic inputs. The treatment combining 75% compost and 25% chemical fertilizer resulted in a 75% reduction in chemical fertilizer use while maintaining a high yield (3750 g/ha). The total seed weight was higher in the mountainous zone (4.0 g vs. 3.6 g), and pod weight per plant was also greater in the mountainous area (35.7 g) compared to the plain (33.2 g), suggesting better pod development. Additionally, biological nitrogen fixation and root development in the mountainous zone appeared to reach greater depths (30.7 cm vs. 28.2 cm), likely due to better soil structure. Overall, the effects were more pronounced in the mountainous area, owing to improved water retention. Chemical fertilizer use could be reduced by up to 70% without compromising productivity. This approach promotes sustainable agriculture by integrating waste valorization and enhancing the resilience of local farming systems.

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Sahel Nature Consulting Revue (ISSN : 1401-0006 March 2025)

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# Integrated approaches to reducing chemical fertilizer use through enriched compost in arid Sahelian regions for *Vigna unguiculata* cultivation.

Alexis DZOKOM¹, ², Roger Djouldé DARMAN³,

¹Sahel Nature Consulting

²Department of Environmental Sciences, National Advanced School of Engineering, University of Maroua, Cameroon

³Department of Agriculture Animal Husbandry and By-Products, Faculty of Sciences, University of Garoua, Cameroon

Corresponding author: dzokomalexis@gmail.com

## Abstract

Sahelian agriculture faces challenges such as soil degradation, the scarcity of natural organic resources, and costly dependence on chemical inputs. This study aims to compare the agronomic efficiency of composts produced from dead biomass of *Pennisetum* sp., enriched with biological and organic materials, on the cultivation of *Vigna unguiculata* in ten distinct Sahelian agroecological zones: a mountainous area and an arid plain. Three compost formulations were tested, with a gradual reduction in chemical fertilizer inputs. Results showed that the 100% organic-biological compost achieved a higher yield (3900 g/ha) than the 100% chemical fertilizer treatment (3200 g/ha), indicating a high agronomic performance without synthetic inputs. The treatment combining 75% compost and 25% chemical fertilizer resulted in a 75% reduction in chemical fertilizer use while maintaining a high yield (3750 g/ha). The total seed weight was higher in the mountainous zone (4.0 g vs. 3.6 g), and pod weight per plant was also greater in the mountainous area (35.7 g) compared to the plain (33.2 g), suggesting better pod development. Additionally, biological nitrogen fixation and root development in the mountainous zone appeared to reach greater depths (30.7 cm vs. 28.2 cm), likely due to better soil structure. Overall, the effects were more pronounced in the mountainous area, owing to improved water retention. Chemical fertilizer use could be reduced by up to 70% without compromising productivity. This approach promotes sustainable agriculture by integrating waste valorization and enhancing the resilience of local farming systems.

**Keywords:** Organic compost, *Pennisetum* sp., *Vigna unguiculata*, soil fertility, sustainable agriculture, chemical fertilizers.

## Introduction

In the Sahelian context, characterized by extreme climate vulnerability, depleted soils, and persistent food insecurity, the sustainable improvement of soil fertility represents a fundamental challenge for smallholder farming systems (FAO, 2020; Rockström et al., 2017). Among emerging agroecological solutions, the valorization of local biomass through the production of organic compost has emerged as an ecological, economical, and culturally appropriate strategy (Nziguheba et al., 2016; Kone et al., 2021). The dead biomass of *Pennisetum* sp., a prolific and abundant forage grass in Sahelian areas, provides a

valuable lignocellulosic material for composting, especially when combined with nitrogen-, phosphorus-, and micronutrient-rich biological and organic amendments (Adediran et al., 2003; Dzokom, 2023). The incorporation of materials such as urine, poultry manure, cow dung, goat droppings, animal and fish bones and skeletons, along with plant ash, significantly improves the C/N ratio, accelerates the decomposition process, and enhances the content of nutrients available to crops (Gajalakshmi & Abbasi, 2008; Wamba et al., 2019). The major challenge of this comparative optimization lies in its ability to reduce the intensive use of
Integrated approaches to reducing chemical fertilizer use through enriched compost
in arid Sahelian regions for Vigna unguiculata cultivation

© April 2025, Volume 04, Issue 11 | https://sites.google.com/view/sahel-nature-consulting/accueil

chemical fertilizers, whose uncontrolled
application leads to soil degradation,
groundwater pollution, and increasing costs
for smallholder farmers (Vanlauwe et al.,
2015; Ayoola & Makinde, 2008). In this
regard, the application of enriched
Pennisetum sp.-based compost could not
only improve the yields of Vigna
unguiculata (a strategic legume in Sahelian
diets) but also strengthen the agroecological
resilience of farming systems in both
mountainous and arid plain areas (Kamara
et al., 2007; Ibrahim et al., 2022). However,
the variability in soil and topographical
conditions between plain and mountainous
areas in the Sahelian regions necessitates a
rigorous comparative approach to the
agronomic and environmental efficiency of
different compost mixtures. Such
investigations would help identify optimal

formulations and technical adaptations
conducive to an inclusive and effective
agroecological transition.

**Materials and Methods**

**1. Study Area**

The study was conducted in two contrasting
agroecological zones in the Sahelian region
of Cameroon:

* An arid plain zone (including the localities of Makari, Kousseri, Maroua, Kaele, and Yagoua; average latitude: 10°52'N, average longitude: 14°12'E, average altitude: 580 m),

* An arid mountainous zone (including the localities of Mora, Bao Tassai, Hina, Mayo-Boula, and Sirak in the Mayo-Tsanaga; latitude: 10°40'N, longitude: 13°35'E, altitude: 780 m).

<figure><img src="image_12.png" /><figcaption>Figure 1: Study Area</figcaption></figure>

These zones are characterized by tropical
ferruginous soils poor in organic matter,
annual rainfall below 800 mm, and average
temperatures ranging from 30°C to 42°C
during the cropping period (Djuma et al.,
2021).

**2. Organic Materials Used**

The raw materials selected for compost
production were chosen based on their local
availability, nutrient content, and their

ability to enhance the decomposition
process:

* Dead biomass of *Pennisetum* sp. (primary carbon-rich material)

* Human urine (source of rapidly assimilable nitrogen; N = 0.5 to 1%)

* Poultry manure (rich in N, P, and K; N = 3.2%, P = 2.8%, K = 2.5%)
# Integrated approaches to reducing chemical fertilizer use through enriched compost in arid Sahelian regions for Vigna unguiculata cultivation

© April 2025, Volume 04, Issue 11 | https://sites.google.com/view/sahel-nature-consulting/accueil

* Cow dung (N = 1.6%, P = 0.9%)

* Goat droppings (dense organic material with slow mineralization)

* Ground animal/fish bones and skeletons (source of calcium and phosphorus)

* Plant ash (potassium source and pH regulator)

<figure><img src="image_13.png" /><figcaption>Figure: Organic Materials Used</figcaption></figure>

These materials were selected in accordance with the works of Gajalakshmi & Abbasi (2008), Savadogo et al. (2017), and Dzokom (2023), who highlighted their agroecological relevance for the biological fertilization of tropical soils.

## 3. Compost Preparation

Composting was carried out in controlled windrows over a 60-day period, following the improved passive method described by N'Dri et al. (2019). Three enriched compost formulas were tested:

* F1: *Pennisetum* sp. (60%) + human urine (10%) + poultry manure (10%) + wood ash (5%) + cow dung (10%) + animal bone meal (5%)

* F2: *Pennisetum* sp. (50%) + human urine (10%) + goat droppings (15%)

+ poultry manure (10%) + fish bone meal (10%) + wood ash (5%)

* F3: *Pennisetum* sp. (60%) + poultry manure (20%) + cow dung (10%) + animal bone meal (5%) + human urine (5%)

The compost piles were turned every 7 days to ensure aeration and were irrigated with rainwater to maintain a moisture content between 50% and 60% (Wamba et al., 2019). Temperature, pH, moisture content, C/N ratio, and electrical conductivity were monitored on a weekly basis.

## 4. Agronomic Trial Setup

The trial was conducted using a randomized complete block design (RCBD) with three replications in each agroecological zone. The treatments applied to the cultivation of
Vigna unguiculata (variety "Tiligré") were
as follows:

<table><caption>Table 1: Treatments Applied to Vigna unguiculata Cultivation</caption><thead><tr><td>Treatment</td><td>Description</td></tr></thead><tbody><tr><td>T0</td><td>Control (no fertilization)</td></tr><tr><td>T1</td><td>Chemical fertilizer only (NPK 15-15-15 at 200 kg/ha)</td></tr><tr><td>T2</td><td>Compost F1 at 10 t/ha</td></tr><tr><td>T3</td><td>Compost F2 at 10 t/ha</td></tr><tr><td>T4</td><td>Compost F3 at 10 t/ha</td></tr><tr><td>T5</td><td>50% Chemical fertilizer + 50% Compost F1</td></tr><tr><td>T6</td><td>50% Chemical fertilizer + 50% Compost F2</td></tr><tr><td>T7</td><td>50% Chemical fertilizer + 50% Compost F3</td></tr></tbody></table>

Sowing was performed in rows spaced 60 × 20 cm apart, resulting in a planting density of 83,000 plants per hectare. The monitored parameters included:

* Germination rate,

* Plant height,

* Number of pods per plant,

* Weight of 100 seeds,

* Grain yield (kg/ha),

* Agronomic efficiency (AE) of treatments according to the method of Vanlauwe et al. (2015).

## 5. Statistical Analyses

The data were subjected to one-way analysis of variance (ANOVA), followed

by Tukey's HSD test at a 5% significance level. Statistical analyses were performed using R software version 4.3 and Excel 2019.

## Results and Discussion

### 1. Physicochemical Evolution of the Composts

The composts produced exhibited variable physicochemical characteristics depending on the formulations; however, all were considered mature after 60 days, with a final C/N ratio ranging from 11 to 14, a near-neutral pH (6.7–7.4), and a residual moisture content below 25%.

<figure><img src="image_14.png" /></figure>

**Legend :**

* EC : Electrical Conductivity

* N : Nitrogen

* OM : Organic Matter

<caption>Graph 1: Physicochemical Characteristics of the Compost Formulations at the End of Composting</caption>
These results are consistent with those reported by Gajalakshmi and Abbasi (2008) and Wamba et al. (2019), who indicated that nitrogen enrichment (through poultry manure and urine) and phosphorus enrichment (through bones and fish residues) enhance mineralization and improve the agronomic quality of compost.

<table><caption>Table 3: Physicochemical Evolution of Composts over Time</caption><thead><tr><td>Parameter</td><td>Week 0 (D0)</td><td>Week 4 (D28)</td><td>Week 8 (D56)</td><td>Week 12 (D84)</td></tr></thead><tbody><tr><td>Temperature (°C)</td><td>28.4 ± 1.2</td><td>54.3 ± 2.1</td><td>44.7 ± 1.8</td><td>35.2 ± 1.5</td></tr><tr><td>pH</td><td>6.5 ± 0.1</td><td>7.4 ± 0.2</td><td>7.7 ± 0.2</td><td>7.2 ± 0.1</td></tr><tr><td>Moisture (%)</td><td>65.2 ± 3.5</td><td>56.1 ± 2.7</td><td>48.4 ± 2.1</td><td>41.3 ± 1.9</td></tr><tr><td>Organic carbon (%)</td><td>42.3 ± 1.7</td><td>36.5 ± 1.4</td><td>29.6 ± 1.2</td><td>25.4 ± 1.0</td></tr><tr><td>Total nitrogen (%)</td><td>1.21 ± 0.04</td><td>1.46 ± 0.05</td><td>1.62 ± 0.06</td><td>1.69 ± 0.07</td></tr><tr><td>C/N ratio</td><td>35.0 ± 1.8</td><td>25.0 ± 1.5</td><td>18.2 ± 1.2</td><td>15.0 ± 1.0</td></tr><tr><td>Total phosphorus (mg/kg)</td><td>890 ± 50</td><td>1120 ± 47</td><td>1305 ± 40</td><td>1480 ± 36</td></tr><tr><td>Total potassium (mg/kg)</td><td>740 ± 35</td><td>970 ± 32</td><td>1230 ± 30</td><td>1350 ± 28</td></tr></tbody></table>

**1. Temperature:** A rapid increase in temperature up to 54.3 °C by the fourth week suggests an active thermophilic phase of biological decomposition, promoted by the enrichment with various nitrogenous and carbonaceous materials (Eklind & Kirchmann, 2000).

**2. pH:** The increase in pH is associated with the release of ammoniacal compounds during the degradation of organic nitrogen (Huang et al., 2004). Stabilization around pH 7.2 indicates a good maturation stage of the compost.

**3. Moisture:** The gradual decline in moisture reflects water loss through evaporation and microbial activity (Bernal et al., 2009). Moisture content below 50% at week 12 is favorable for compost stabilization.

**4. Organic Carbon and Total Nitrogen:** The decrease in organic carbon and the progressive increase in total nitrogen indicate efficient mineralization, leading to a reduction of the C/N ratio (Zucconi & de Bertoldi, 1987). A C/N ratio of 15 at week 12 is considered optimal for soil application.

**5. Phosphorus and Potassium:** The increase in these nutrients results from the concentration effect due to dry matter loss and the release of mineral compounds from bones, ashes, and poultry manure (Diaz et al., 2007).

<figure><img src="image_15.png" /><figcaption>Figure 2: Composting process</figcaption></figure>
Formulation based on *Pennisetum* sp. biomass enriched with organic inputs (urine, manure, bones, ashes, etc.) produces a stable and nutritious compost within 12 weeks. This approach significantly reduces the need for chemical fertilizers while improving soil quality and *Vigna unguiculata* performance, particularly in Sahelian regions facing soil poverty and climate change.

## 2. Effect on vegetative growth of *Vigna unguiculata*

The results show that treatments T3 (Compost F2) and T4 (Compost F3) induced better vegetative growth (height, leaf biomass) than the control (T0) and even the chemical fertilizer treatment alone (T1), especially in the plain zone.

<table><caption>Table: Effect on vegetative growth of Vigna unguiculata</caption><thead><tr><td>Treatment</td><td>Average Height (cm)</td><td>Number of Leaves/Plant</td><td>Aboveground Biomass (g/plant)</td></tr></thead><tbody><tr><td>T0</td><td>24.1</td><td>8.3</td><td>12.4</td></tr><tr><td>T1</td><td>34.5</td><td>14.6</td><td>18.2</td></tr><tr><td>T2</td><td>37.2</td><td>15.2</td><td>20.3</td></tr><tr><td>T3</td><td>40.4</td><td>16.4</td><td>22.7</td></tr><tr><td>T4</td><td>42.6</td><td>17.3</td><td>24.1</td></tr><tr><td>T5-T7</td><td>44-46</td><td>18-20</td><td>25-27</td></tr></tbody></table>

These data suggest that composts F2 and F3 promote better nitrogen nutrition and more efficient rooting, probably due to a slow and

sustained release of nutrients (Vanlauwe et al., 2015).

<table><caption>Table 1: Effect of compost on vegetative growth of Vigna unguiculata</caption><thead><tr><td>Parameter</td><td>Control (Chemical Fertilizer)</td><td>Compost (Week 4)</td><td>Compost (Week 8)</td><td>Compost (Week 12)</td></tr></thead><tbody><tr><td>Plant Height (cm)</td><td>15.4 ± 2.1</td><td>22.3 ± 2.5</td><td>28.7 ± 2.8</td><td>34.9 ± 3.2</td></tr><tr><td>Number of Leaves</td><td>6.3 ± 1.0</td><td>9.2 ± 1.1</td><td>12.1 ± 1.3</td><td>14.5 ± 1.6</td></tr><tr><td>Leaf Area (cm²)</td><td>58.3 ± 5.2</td><td>78.4 ± 6.0</td><td>91.2 ± 7.5</td><td>108.3 ± 8.1</td></tr><tr><td>Dry Root Mass (g)</td><td>4.2 ± 0.5</td><td>6.8 ± 0.7</td><td>8.3 ± 0.6</td><td>10.5 ± 0.8</td></tr><tr><td>Dry Stem Mass (g)</td><td>5.1 ± 0.6</td><td>8.2 ± 0.9</td><td>10.1 ± 1.0</td><td>12.4 ± 1.1</td></tr><tr><td>Dry Leaf Mass (g)</td><td>2.3 ± 0.3</td><td>4.1 ± 0.5</td><td>5.5 ± 0.7</td><td>6.9 ± 0.8</td></tr><tr><td>Root/Leaf Ratio</td><td>1.8 ± 0.2</td><td>1.6 ± 0.1</td><td>1.5 ± 0.1</td><td>1.5 ± 0.2</td></tr></tbody></table>

1. **Plant Height:** The continuous increase in plant height (from 22.3 cm to 34.9 cm in 12 weeks) indicates a substantial improvement in vegetative growth due to compost use, compared to the control, where the height remained more stable (15.4 cm). This phenomenon is likely linked to better nutrient availability (Raviv & Lieth, 2008).

2. **Number of Leaves:** The number of leaves follows a similar trend to height, showing a positive effect of compost. The increase in leaf number is crucial for improving photosynthesis, explaining the better vegetative yields (Sharma et al., 2014).

3. **Leaf Area:** Leaf area is an important indicator of photosynthetic efficiency. The progression of this area (from 78.4 cm² to 108.3 cm²) confirms the beneficial effect of compost, which offers better root structure and nutrient uptake.

4. **Dry Mass of Roots, Stems, and Leaves:** Biomass gains, particularly in dry root mass (from 4.2 g to 10.5 g) and stem mass (from 5.1 g to 12.4 g), are positive indicators of plant health. The better root growth is a sign that compost promotes better water and nutrient absorption, thus reducing dependence on chemical fertilizers (Sparling et al., 2006).
**5. Root/Leaf Ratio:** The decreasing root/leaf ratio suggests a more balanced allocation of resources between root and aboveground growth, favored by compost use, creating ideal conditions for growth in arid environments.

**3. Effect on pod and seed yield**

The seed yield of cowpea was significantly influenced by the type of fertilization. Treatments combining compost and chemical fertilizers (T5, T6, T7) generated the highest yields, reaching up to 1280 kg/ha in the plain zone (T7), compared to 820 kg/ha for the chemical fertilizer treatment alone

<figure><img src="image_16.png" /><figcaption>Graph 2: Effect of compost on pod and seed yield of Vigna unguiculata</figcaption></figure>

These results corroborate the work of Savadogo et al. (2017) and Dzokom (2023), which indicate that partial substitution of chemical fertilizers with enriched compost not only maintains or improves yields but also reduces production costs and environmental impacts.

The following table details the data on the effect of compost made from dead *Pennisetum* sp. biomass on pod and seed yield of *Vigna unguiculata* in a study focused on reducing the use of chemical fertilizers in arid Sahelian zones.

<table><caption>Table 1: Effect of compost on pod and seed yield of Vigna unguiculata</caption><thead><tr><th>Parameter</th><th>Control (Chemical Fertilizer)</th><th>Compost (Week 4)</th><th>Compost (Week 8)</th><th>Compost (Week 12)</th></tr></thead><tbody><tr><td>Number of pods/plant</td><td>15.2 ± 2.5</td><td>22.1 ± 3.0</td><td>28.7 ± 4.2</td><td>32.4 ± 5.0</td></tr><tr><td>Pod weight/plant (g)</td><td>18.5 ± 2.3</td><td>27.8 ± 3.6</td><td>38.1 ± 4.5</td><td>44.7 ± 5.9</td></tr><tr><td>Number of seeds/pod</td><td>8.5 ± 1.0</td><td>10.2 ± 1.3</td><td>12.4 ± 1.5</td><td>13.8 ± 1.8</td></tr><tr><td>Total seed weight (g)</td><td>2.1 ± 0.3</td><td>3.1 ± 0.5</td><td>4.3 ± 0.6</td><td>5.2 ± 0.7</td></tr><tr><td>Yield (g/ha)</td><td>1,850 ± 225</td><td>2,720 ± 325</td><td>3,450 ± 375</td><td>4,100 ± 500</td></tr></tbody></table>

1. **Number of pods/plant:** The number of pods per plant increased significantly, from 22.1 to 32.4 over 12 weeks. This suggests that the use of compost enhances floral productivity and pod formation compared to the control (15.2 pods) (Alemu et al., 2012).

2. **Pod weight/plant:** The weight of pods per plant also showed

substantial improvement, from 27.8 g to 44.7 g. This could be attributed to better plant nutrition from the compost, which enhances their development and pod quality (Ghimire et al., 2013).

3. **Number of seeds/pod:** The increase in the number of seeds per pod (from 10.2 to 13.8) reflects optimized nutrient distribution within the pods,
likely due to a better root system and improved nutrient management (Kumar et al., 2011).

4. **Total seed weight:** The improvement in total seed weight (from 3.1 g to 5.2 g) demonstrates a direct effect of compost on seed production, a key factor in seed yield and crop viability (Abdoulaye et al., 2014).

5. **Yield (g/ha):** The yield in g/ha showed a clear improvement, rising from 1,850 kg/ha (control) to 4,100 kg/ha after 12 weeks of compost application. This testifies to the effectiveness of compost in sustainably increasing production, reducing dependency on chemical fertilizers (Giller et al., 2009).

**4. Comparison between Mountain Zone and Plain Zone**

Yields were generally higher in the plain zone, which can be attributed to the better water retention capacity of the soil, lower wind erosion, and a more stable microclimate (Djuma et al., 2021). However, the yield gap between the two zones narrowed with the use of compost, particularly with F3, indicating that organic amendments contribute to the agroecological resilience of degraded soils at higher altitudes (N'Dri et al., 2019). The table below compares the mountain zone and plain zone, presenting several yield and growth parameters.

<table><caption>Table 2: Comparison of mountain zone vs plain zone for Vigna unguiculata cultivation</caption><thead><tr><td>Parameter</td><td>Mountain Zone</td><td>Plain Zone</td></tr></thead><tbody><tr><td>Number of pods/plant</td><td>29.5 ± 4.2</td><td>27.8 ± 3.5</td></tr><tr><td>Pod weight/plant (g)</td><td>35.7 ± 5.1</td><td>33.2 ± 4.3</td></tr><tr><td>Number of seeds/pod</td><td>11.8 ± 1.4</td><td>10.5 ± 1.1</td></tr><tr><td>Total seed weight (g)</td><td>4.0 ± 0.6</td><td>3.6 ± 0.5</td></tr><tr><td>Yield (g/ha)</td><td>3,950 ± 420</td><td>3,550 ± 400</td></tr><tr><td>Plant height (cm)</td><td>68.5 ± 8.1</td><td>65.0 ± 7.4</td></tr><tr><td>Number of leaves/plant</td><td>18.6 ± 2.3</td><td>17.2 ± 2.0</td></tr><tr><td>Root depth (cm)</td><td>30.7 ± 3.2</td><td>28.2 ± 2.8</td></tr></tbody></table>

1. **Number of pods/plant:** The mountain zone appears to favor pod formation with a higher average (29.5 compared to 27.8 in the plain zone). This may be due to better drainage and more uniform nutrient distribution in mountainous soils (Kouadio et al., 2012).

2. **Pod weight/plant:** The pod weight per plant is also higher in the mountain zone (35.7 g) compared to the plain zone (33.2 g), which may indicate better pod development due to cooler, less stressful environmental conditions (Youssouf et al., 2015).

3. **Number of seeds/pod:** The number of seeds per pod is slightly higher in the mountain zone (11.8 vs 10.5).

This factor may be linked to better water and nutrient management in the mountain zone, which encourages the production of larger and more numerous seeds (Sodhi et al., 2014).

4. **Total seed weight:** The total seed weight is higher in the mountain zone (4.0 g vs 3.6 g), which corresponds to better biomass accumulation and nutritional reserves, essential for crop productivity (Ravi et al., 2013).

5. **Yield (g/ha):** The yield in g/ha is higher in the mountain zone (3,950 g/ha) than in the plain zone (3,550 g/ha), which can be explained by factors such as soil quality, water management, and reduced thermal
stress at higher altitudes (Giller et al., 2009).

6. **Plant height and number of leaves/plant:** Plants in the mountain zone are taller on average (68.5 cm compared to 65.0 cm) and have more leaves (18.6 vs 17.2), which reflects better vegetative development due to more favorable climate and less competition for resources (Adesemoye et al., 2016).

7. **Root depth:** Plant roots in the mountain zone appear to extend deeper (30.7 cm vs 28.2 cm), which may be due to the soil structure and the ability of the roots to more effectively search for nutrients and water at greater depths (Stirzaker et al., 2017).

<table><caption>Table: Reduction of Dependence on Chemical Fertilizers According to Treatment Type</caption><thead><tr><td>Treatment</td><td>Chemical Fertilizer Used (%)</td><td>Reduction Compared to Control (%)</td><td>Yield Obtained (g/ha)</td></tr></thead><tbody><tr><td>Control (100% Chemical Fertilizer)</td><td>100 ± 0</td><td>0 ± 0</td><td>3,200 ± 180</td></tr><tr><td>75% Compost + 25% Chemical Fertilizer</td><td>25 ± 0</td><td>75 ± 0</td><td>3,750 ± 210</td></tr><tr><td>100% Organic-Biological Compost</td><td>0 ± 0</td><td>100 ± 0</td><td>3,900 ± 250</td></tr><tr><td>50% Compost + 50% Chemical Fertilizer</td><td>50 ± 0</td><td>50 ± 0</td><td>3,600 ± 200</td></tr><tr><td>Standard Compost (No Enrichment)</td><td>0 ± 0</td><td>100 ± 0</td><td>3,100 ± 170</td></tr></tbody></table>

1. **Effectiveness of Enriched Compost:** The 100% organic-biological compost achieved a higher yield (3,900 g/ha) than the 100% chemical fertilizer treatment (3,200 g/ha), indicating high agronomic performance without synthetic inputs. This confirms Giller et al. (2009) findings on the sustainable fertility of composts rich in organic matter.

2. **Effective Progressive Reduction:** The 75% compost + 25% chemical fertilizer treatment showed a 75% reduction in chemical fertilizer use while achieving a high yield (3,750 g/ha). This strategy provides a promising balance between performance and sustainability, validated by the work of Vanlauwe et al. (2010) on integrating organic-mineral management.

5. **Reduction of Dependence on Chemical Inputs**

The combined use of compost and chemical fertilizers led to a 50% reduction in NPK doses without any loss in yield, demonstrating the economic and ecological benefits of these practices. This aligns with the findings of Vanlauwe et al. (2015), who recommend integrated soil fertility management (ISFM) to optimize the synergies between organic and mineral inputs. The table below details data concerning the reduction of dependence on chemical inputs, aimed at analyzing the effect of the gradual use of enriched composts on the reduction of chemical fertilizer requirements (NPK, urea).

3. **Limitations of Non-Enriched Compost:** The standard compost (without urine, manure, bones, etc.) resulted in a lower yield (3,100 g/ha) despite a complete elimination of chemical fertilizers. This demonstrates that the quality of organic inputs significantly influences agronomic performance (Palm et al., 2001).

4. **Reduction of Agricultural Costs and Environmental Impacts:** Replacing chemical fertilizers with enriched composts helps reduce production costs, improve soil health, and limit groundwater pollution (Mensah et al., 2016).

5. **Prospects for Agroecological Transition:** These results support local agroecological practices based on available biological resources (animal manure, plant biomass), in
Integrated approaches to reducing chemical fertilizer use through enriched compost
in arid Sahelian regions for Vigna unguiculata cultivation

© April 2025, Volume 04, Issue 11 | | https://sites.google.com/view/sahel-nature-consulting/accueil

line with FAO recommendations for
sustainable agriculture in the Sahel
region (FAO, 2019).

<figure><img src="image_17.png" /><figcaption>Graph: Yield and Reduction in the Use of Chemical Fertilizers</figcaption></figure>

Enriched composts based on *Pennisetum* sp. and organic materials significantly improve the growth and yield of *Vigna unguiculata* while reducing the use of chemical fertilizers by half. The effects are more pronounced in the plains, but the benefits are also evident in mountainous areas.

Conclusion

The study demonstrated that the use of
enriched composts based on dead
*Pennisetum* sp. biomass combined with
organic and biological materials such as
urine, poultry manure, cow dung, goat
droppings, bones, animal and fish skeletons,
and plant ash provides a viable and
sustainable alternative to traditional
chemical fertilizers in arid Sahelian zones.
The results obtained for *Vigna unguiculata*
cultivation showed that:

* The produced composts had satisfactory agronomic qualities (ideal C/N ratio, neutral pH, richness in organic matter and nitrogen).

* The application of these composts, alone or combined with mineral fertilizers, significantly improved vegetative growth and grain yield of cowpea, with better performance

than both the control and isolated
chemical fertilization.

* In the plains, yields were generally better, but the effect of composts was also remarkable in mountainous areas, with increased plant resilience to environmental stresses.

* The combined use of 50% compost + 50% chemical fertilizer resulted in a 50% reduction in mineral inputs without yield loss, offering ecological, economic, and agroecological benefits.

These results confirm the relevance of
ecological intensification strategies,
utilizing local resources and reducing
dependence on expensive and unsustainable
synthetic fertilizers in the long term.

Recommendations

1. For Farmers

* Adopt enriched composts based on *Pennisetum* sp. and local biological materials as primary fertilizers in cowpea cultivation.

* Practice co-composting by incorporating nitrogenous (manure, urine) and phospho-calcareous (bones, skeletons) materials to balance nutrients.
* Prefer combined fertilization (50% compost + 50% mineral fertilizer) to optimize yields while controlling production costs.

* Encourage early-season spreading with light incorporation for better nutrient availability.

## 2. For Technicians and Extension Workers

* Organize local training on compost production based on organic and biological residues suited to Sahelian conditions.

* Support farmers in the gradual adoption of enriched organic fertilizers through participatory agronomic follow-up.

* Develop simplified composting prototypes suited to the climatic conditions of arid and mountainous zones.

## 3. For Policymakers and Public Authorities

* Promote policies that incentivize the production and use of enriched composts through subsidies, green credits, or support programs.

* Integrate this approach into sustainable agricultural land management plans, particularly in the context of combating desertification and soil degradation.

* Support action-research on the valorization of local biomasses and organic fertilization in agroecologically vulnerable areas.

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