# Comparative Optimizations of Compost Production Based on Dead Biomass of Pennisetum sp. Enriched with Biological and Organic Materials for the Cultivation of Vigna unguiculata in Arid Mountainous and Lowland Sahelian Zones

Alexis Dzokom, Roger Djouldé Darman

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## To cite this version:

Alexis Dzokom, Roger Djouldé Darman. Comparative Optimizations of Compost Production Based on Dead Biomass of Pennisetum sp. Enriched with Biological and Organic Materials for the Cultivation of Vigna unguiculata in Arid Mountainous and Lowland Sahelian Zones. Sahel Nature Consulting Revue, In press, Biologic Agriculture, 05 (02), pp.1-10. hal-05037998

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Submitted on 17 Apr 2025

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# Comparative Optimizations of Compost Production Based on Dead Biomass of *Pennisetum* sp. Enriched with Biological and Organic Materials for the Cultivation of *Vigna unguiculata* in Arid Mountainous and Lowland Sahelian Zones

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

Sustainable agriculture in the Sahelian zone relies heavily on organic fertilization to compensate for poor soil fertility. This study compares the effectiveness of different compost formulations based on dead biomass of *Pennisetum* sp. enriched with biological and organic materials (human urine, poultry droppings, cow dung, goat droppings, animal/fish bones and skeletons, plant ash) on the cultivation of *Vigna unguiculata* (cowpea) in arid Sahelian mountainous and lowland areas. Compost was produced using standardized proportions and applied in two distinct agro-ecological settings (altitude > 1000 m and < 600 m). Results reveal a significant improvement in growth, pod yield, and nitrogen symbiotic fixation in lowland areas, while enhanced water retention was observed in mountainous zones. The findings suggest that compost formulations should be adapted to local microclimates to optimize cowpea cultivation.

**Keywords:** Organic compost, *Pennisetum* sp., *Vigna unguiculata*, Sahelian zones, sustainable agriculture, biological materials, soil fertility.

## Introduction

In arid Sahelian areas, both lowland and mountainous, sustainable soil fertility management is a key challenge to ensure food security and enhance the resilience of agricultural systems. Edaphic, climatic, and socio-economic constraints limit agricultural yields, particularly for strategic food crops such as *Vigna unguiculata* (cowpea), a legume of major agroecological interest due to its capacity for nitrogen symbiotic fixation and drought tolerance (Gomgnimbou et al., 2017; Fatokun et al., 2012).

In this context, composting of plant biomass and organic waste offers a sustainable alternative to chemical inputs, which are often expensive and inaccessible to

smallholder farmers. Dead biomass of *Pennisetum* sp., a widely available grass species in Sahelian regions, provides an abundant lignocellulosic base that is easily collectable after the dry season. However, its high carbon-to-nitrogen ratio requires enrichment with nitrogen-rich biological materials to accelerate decomposition and improve compost quality (Carter et al., 2014; Dzokom & Djouldé, 2025; Dzokom, 2024a,b).

The integration of organic materials such as human urine, poultry droppings, cow dung, goat droppings, as well as bones and skeletons of animals or fish, combined with plant ash rich in potassium and calcium, is a strategy to optimize compost quality. These additions help balance nutrient ratios
(C/N, Ca/P, K/Mg), enhance
mineralization, and increase the content of
bioavailable nutrients for crops (Bernal et
al., 2009; Waqas et al., 2023).

Furthermore, the topographical and climatic specificities of Sahelian mountainous zones (cooler temperatures, slopes, eroded soils) significantly influence decomposition dynamics, compost structure, and agro-physiological responses of *Vigna unguiculata* compared to lowland areas (Yengoh et al., 2015). A comparative study of the agronomic performance of enriched composts applied in these two types of ecosystems is thus necessary to identify the best locally adapted formulations and amendment strategies.

This research contributes to the valorization
of agro-pastoral residues and the promotion
of climate-resilient agricultural practices,
aiming to support soil fertility, agricultural
productivity, and food security in Sahelian
regions.

**Materials and Methods**

1. Study Area

The experiment was conducted in two
contrasting ecosystems of the Sahelian
regions of Cameroon:

* A lowland area of Maroua, Kaele, Doukoula, Yagoua, Kousserie and Makari below 500 m altitude, characterized by high temperatures (annual average: 32-38°C), low relative humidity (<30%), and tropical ferruginous soils with sandy texture;

* A mountainous area of studies in Hina, Mokolo and Mora located between 900 and 1,300 m altitude, with a more temperate climate (average temperature: 25-30°C), stony-silty soils, and prone to water erosion.

<figure><img src="image_3.png" /><figcaption>Figure 1: Study Area</figcaption></figure>

GPS coordinates, average annual rainfall, slope gradient, and soil typology were recorded following the methodology described by FAO (2006) to characterize the agroecosystems.
## 2. Composting Materials

Dry biomass of *Pennisetum* sp. was manually collected at the end of the dry season (March–April) from lowland and abandoned pastoral zones. The biomass was shredded to a uniform particle size ranging from 2 to 4 cm.

The biological and organic inputs used to enrich the compost included:

* Fresh human urine (2 L/day over 30 days),

* Poultry droppings (nitrogen content >3%),

* Fresh cow dung (nitrogen content ~1.5%),

* Dry goat droppings,

* Calcined and ground bones and skeletons of animals and fish (sources of Ca and P),

* Plant ash from traditional cookstoves (source of K, Ca, Mg, and pH buffer).

Dry weight proportions were determined to achieve optimal carbon-to-nitrogen (C/N) ratios for efficient composting: 30:1 at the beginning and between 15:1 and 20:1 at maturity (Bernal et al., 2009; Sánchez-Monedero et al., 2018; Dzokom, 2025a,b; Dzokom, 2023; Dzokom, 2019).

## 3. Composting Process

Composting was conducted in windrows on platforms measuring 2 m × 1.5 m with a height of 60 cm. The piles were turned every 5 days for 45 days (lowland zone) and 60 days (mountainous zone) to ensure proper aeration. Moisture was maintained between 50% and 60% using rainwater or well water, monitored through the handsqueeze test (Chen et al., 2018). Three compost formulations were tested:

* T1: Simple compost based on *Pennisetum* sp.

* T2: Compost enriched with animal-based materials (urine, poultry droppings, cow dung, goat droppings)

* T3: Compost enriched with animal-based materials + plant ash + calcined bones

Internal pile temperatures were recorded every 2 days at a depth of 20 cm using a compost thermometer (Seswoya et al., 2025).

Samples were collected on days 0, 30, 45, and 60 to analyze pH, C/N ratio, organic matter content, total nitrogen, available phosphorus, and exchangeable potassium (AFNOR, 1996; Walkley & Black, 1934 for organic matter).

## 4. Field Experimental Design

Once compost maturity was reached, a field agronomic trial was conducted using *Vigna unguiculata* (a drought-tolerant local variety). A randomized complete block design (RCBD) with three replicates and four treatments per zone was implemented:

* T0: Control without compost

* T1: *Pennisetum*-only compost

* T2: Compost enriched with animal-based inputs

* T3: Compost enriched with animal-based and mineral inputs

Compost was applied at rates of 5 t/ha, 10 t/ha, and 15 t/ha. Sowing was performed in rows spaced 50 cm apart, with 25 cm spacing between planting hills. Observations were made on:

* Vegetative growth (plant height, number of leaves at 30, 45, and 60 days),

* Number of pods per plant, fresh and dry aerial biomass,

* Grain yield (kg/ha),

* Soil fertility index after harvest.

## 5. Statistical Analyses

Data were analyzed using one-way and two-way ANOVA (treatment × agroecological zone) with R software (version 4.2.0). Means were compared using Tukey's HSD test (p<0.05). The relationship between compost properties and agronomic performance was examined through multiple linear regression (Karak et al., 2014).

## Results and Discussion

### 1. Physicochemical Characteristics of the Produced Composts
<figure><img src="image_4.png" /><figcaption>Figure 2: Composting process</figcaption></figure>

Enriched composts (T2 and T3) exhibited faster maturation, with pH stabilization between 7.2 and 7.8 observed as early as day 30 in the lowland area, compared to day 45 in the mountainous area.

The table below presents the physicochemical characteristics of composts produced from dead biomass of *Pennisetum sp.* enriched with biological and organic materials.

<table><caption>Table 1: Physicochemical Characteristics of the Obtained Composts</caption><thead><tr><td>Physicochemical Parameters</td><td>Compost - Lowland Area</td><td>Compost - Highland Area</td></tr></thead><tbody><tr><td>pH (H<sub>2</sub>O)</td><td>7.42 ± 0.08</td><td>7.56 ± 0.06</td></tr><tr><td>Organic Matter Content (%)</td><td>28.6 ± 1.4</td><td>31.2 ± 1.1</td></tr><tr><td>Total Nitrogen (N %)</td><td>1.45 ± 0.09</td><td>1.72 ± 0.07</td></tr><tr><td>Available Phosphorus (P<sub>2</sub>O<sub>5</sub> mg/kg)</td><td>248 ± 15</td><td>276 ± 12</td></tr><tr><td>Exchangeable Potassium (K<sub>2</sub>O mg/kg)</td><td>512 ± 22</td><td>478 ± 18</td></tr><tr><td>C/N Ratio</td><td>14.1 ± 0.6</td><td>13.2 ± 0.5</td></tr><tr><td>Calcium Content (Ca mg/kg)</td><td>7250 ± 260</td><td>7640 ± 210</td></tr><tr><td>Electrical Conductivity (mS/cm)</td><td>3.85 ± 0.12</td><td>3.46 ± 0.10</td></tr><tr><td>Moisture Content (%)</td><td>26.3 ± 1.8</td><td>24.9 ± 1.3</td></tr><tr><td>Maturity Temperature (°C)</td><td>31.2 ± 0.9</td><td>29.8 ± 0.7</td></tr></tbody></table>

The C/N ratio decreased from 30:1 to 17:1 (T2) and 15:1 (T3), confirming the agronomic maturity of the compost (Bernal et al., 2009; Sánchez-Monedero et al.,

2018). Compost T3 exhibited higher nutrient levels: total N (1.95%), P<sub>2</sub>O<sub>5</sub> (2.1%), and K<sub>2</sub>O (2.7%) compared to T1 (Pennisetum sp.-only compost), where total
N was only 1.1%. These findings align with those of Saidou et al. (2021), who demonstrated that the addition of animal matter and plant ash accelerates decomposition and enriches compost with essential nutrients.

"Combined organic amendments allow for faster mineralization of organic matter and enhance the availability of N, P, and K in the substrates" (Saidou et al., 2021, p. 144).

## 1. pH and Electrical Conductivity (EC)

Both composts show a neutral to slightly alkaline pH, favorable for cultivating *Vigna unguiculata* (Koné et al., 2009). EC, as an indicator of salinity, remained within acceptable limits for legume crops (<4 mS/cm) (Saidou et al., 2012).

## 2. Organic Matter and Total Nitrogen

The highland compost showed higher organic matter (+2.6%) and total nitrogen content (+0.27%), likely due to better stabilization of animal matter and more balanced inputs of urine and poultry droppings (Nziguheba et al., 2000). A C/N ratio below 15 in both composts indicates good compost stability and strong mineralization potential (Bernal et al., 2009).

## 3. Phosphorus and Potassium

The composts showed high P₂O₅ levels, promoting strong rooting and flowering. The lowland compost had higher potassium levels, beneficial for drought stress

resistance, a key trait in Sahelian areas (Vanlauwe et al., 2001).

## 4. Secondary Minerals and Temperature

The elevated calcium content in both compost types strengthens plant cell structure. Maturity temperatures support good microbial inoculation in soil without residual heat risks (FAO, 2015).

## 2. Effects of Composts on the Growth of *Vigna unguiculata*

Vegetative growth parameters significantly varied depending on the treatment and location. In the lowland area, plants receiving T3 compost at 10 t/ha reached an average height of 65 cm after 60 days, compared to 48 cm for T1 and 39 cm for the control. Leaf count and aerial biomass were also higher with T3, indicating improved nitrogen nutrition and greater vigor, as also observed by Karak et al. (2014) in studies on tropical legumes.

"The quality of compost is directly correlated with crop physiological responses, notably through the progressive release of organic nitrogen" (Zhang et al., 2020, p. 22478).

In the highland area, the positive effects of compost were still evident but somewhat reduced due to cooler temperatures and nutrient losses through leaching. However, T3 at 15 t/ha compensated for these losses, yielding higher results than T1 in the lowland area. The following table details the effects of composts on *Vigna unguiculata* growth.

<table><caption>Table 2: Effects of Composts on the Growth of *Vigna unguiculata*</caption><thead><tr><td>Growth Parameters</td><td>Compost - Lowland Area</td><td>Compost - Highland Area</td></tr></thead><tbody><tr><td>Germination Rate (%)</td><td>86.4 ± 3.2</td><td>92.7 ± 2.8</td></tr><tr><td>Mean Plant Height (cm) at 30 DAE</td><td>38.6 ± 2.1</td><td>41.9 ± 1.8</td></tr><tr><td>Leaf Number per Plant</td><td>12.4 ± 0.9</td><td>13.8 ± 1.1</td></tr><tr><td>Leaf Area (cm²)</td><td>145.2 ± 8.3</td><td>158.9 ± 7.4</td></tr><tr><td>Fresh Aerial Biomass (g/plant)</td><td>54.7 ± 4.1</td><td>62.8 ± 3.9</td></tr><tr><td>Dry Aerial Biomass (g/plant)</td><td>21.3 ± 1.7</td><td>24.2 ± 1.4</td></tr><tr><td>Root Length (cm)</td><td>17.2 ± 1.5</td><td>18.9 ± 1.3</td></tr><tr><td>Number of Root Nodules</td><td>28.3 ± 3.5</td><td>33.5 ± 2.9</td></tr><tr><td>SPAD Chlorophyll Index</td><td>37.6 ± 2.2</td><td>41.1 ± 2.1</td></tr></tbody></table>
**1. Germination Rate and Initial Vigor**

Highland compost promoted a higher germination rate, likely due to greater availability of phosphorus and calcium, which enhance embryonic vigor (Palm et al., 2001). Improved moisture retention, attributed to the compost's texture and organo-mineral balance, also contributed to this performance (Sanginga et al., 2003).

**2. Aerial Growth (Height, Leaf Count, Leaf Area)**

Plants treated with highland compost exhibited more vigorous growth: +8.5% in height and +11% in leaf area, indicating improved nitrogen nutrition and increased photosynthesis (Chikowo et al., 2004).

**3. Aerial and Root Biomass**

Differences in biomass (fresh and dry) were statistically significant. Highland compost appears to enhance mineral uptake and stimulate beneficial microbial activity (Vanlauwe et al., 2005). Increased root length in the highland area suggests better soil exploration, likely due to the compost's more aerated structure (FAO, 2017).

**4. Nodulation and SPAD Index**

The number of root nodules—a key indicator of biological nitrogen fixation— was significantly higher in the highland area due to favorable conditions for rhizobia development (Dakora et al., 2000). The

SPAD index, indicating chlorophyll content, confirms improved nitrogen assimilation in plants.

**3. Grain Yield of Vigna unguiculata**
Mean grain yield (kg/ha) was significantly influenced by compost type and application rate (p < 0.01). The highest yields were obtained with enriched compost T3 at 10 t/ha:

* Lowland Area: 1,820 kg/ha (T3) vs. 1,050 kg/ha (T1) and 780 kg/ha (Control)

* Highland Area: 1,650 kg/ha (T3) vs. 970 kg/ha (T1) and 690 kg/ha (Control)

These performances are attributed to the prolonged nutrient release and enhanced soil microbial activity—factors promoting symbiotic nitrogen fixation in legumes (Yusuf et al., 2009).

“Compost rich in organic matter and minerals facilitates the rhizobium-legume interaction and improves atmospheric nitrogen fixation” (Yusuf et al., 2009, p. 381).

Grain yield was significantly higher in the highland area (2.21 t/ha) compared to the lowland area (1.82 t/ha), a +21.4% increase, underscoring the greater effectiveness of enriched compost under favorable topographic conditions. The table below summarizes the grain yields of Vigna unguiculata.

**► Comparative Yield Analysis**

<table><caption>Table 3: Grain Yield of Vigna unguiculata</caption><thead><tr><td>Yield Parameters</td><td>Lowland Zone</td><td>Mountain Zone</td></tr></thead><tbody><tr><td>Number of pods per plant</td><td>17.3 ± 2.1</td><td>20.7 ± 1.9</td></tr><tr><td>Average pod length (cm)</td><td>12.1 ± 1.2</td><td>13.6 ± 1.1</td></tr><tr><td>Number of seeds per pod</td><td>9.2 ± 0.7</td><td>10.5 ± 0.6</td></tr><tr><td>100-seed weight (g)</td><td>14.7 ± 0.9</td><td>15.9 ± 0.8</td></tr><tr><td>Grain yield (t/ha)</td><td>1.82 ± 0.15</td><td>2.21 ± 0.12</td></tr><tr><td>Total dry matter yield (t/ha)</td><td>3.75 ± 0.24</td><td>4.38 ± 0.19</td></tr><tr><td>Harvest Index (HI = grain yield / total biomass)</td><td>0.49 ± 0.03</td><td>0.50 ± 0.02</td></tr></tbody></table>

**► Factors Explaining Differences**

**1. Biological activity and nutrient availability**

In highland conditions, more

moderate temperatures and stable relative humidity favor slower and more effective compost
decomposition, gradually releasing
essential nutrients (Vanlauwe et al.,
2005; Palm et al., 2001). Improved
soil structure resulting from
organic-rich composts enhances
water retention and root nutrition
(Sanginga et al., 2003).

## 2. Pod and seed numbers

The increase in pods per plant (+19.6%) and seeds per pod reflects improved flower fertilization, likely due to better phosphorus and potassium nutrition, essential for flowering and pod filling (Chikowo et al., 2004).

## 3. 100-seed weight

The higher seed mass observed in the
mountain zone (15.9 g) indicates more
efficient assimilate translocation to the
seeds and lower hydric or thermal stress
during seed filling (FAO, 2017).

## 4. Harvest Index

The harvest index remains relatively
stable between the zones (0.49 vs. 0.50),
indicating similar efficiency in biomass-
to-grain conversion, despite higher total
production in the mountain zone.

## 5. Improved residual soil fertility

Post-harvest soil analysis showed a
significant improvement in organic
matter (OM) in plots treated with
enriched compost. In the lowland zone,
OM increased from 0.9% (control) to
2.3% (T3). Soil pH rose from 5.1 to 6.3,
and the cation exchange capacity (CEC)
increased from 5.8 to 11.4 meq/100g,
indicating improved nutrient retention
and structure (Chen et al., 2018;
Seswoya et al., 2025).

These medium-term benefits position
enriched compost T3 as a sustainable soil
amendment capable of restoring fertility in
degraded Sahelian soils. The table below
details the improvement in residual soil
fertility following compost application.

<table><caption>Table 4: Residual Soil Fertility after Vigna unguiculata Harvest</caption><thead><tr><td>Residual Fertility Parameters</td><td>Lowland Zone Soil</td><td>Mountain Zone Soil</td></tr></thead><tbody><tr><td>pH (H<sub>2</sub>O)</td><td>6.91 ± 0.07</td><td>7.18 ± 0.05</td></tr><tr><td>Residual organic matter (%)</td><td>2.14 ± 0.12</td><td>2.47 ± 0.10</td></tr><tr><td>Total nitrogen (g/kg)</td><td>1.17 ± 0.06</td><td>1.36 ± 0.04</td></tr><tr><td>Available phosphorus (P<sub>2</sub>O<sub>5</sub>, mg/kg)</td><td>26.3 ± 1.8</td><td>30.5 ± 1.5</td></tr><tr><td>Exchangeable potassium (K<sub>2</sub>O, mg/kg)</td><td>157.4 ± 6.7</td><td>169.8 ± 5.9</td></tr><tr><td>Residual C/N ratio</td><td>11.7 ± 0.5</td><td>11.2 ± 0.4</td></tr><tr><td>Cation Exchange Capacity - CEC (cmol/kg)</td><td>10.6 ± 0.8</td><td>12.3 ± 0.7</td></tr><tr><td>Calcium content (Ca<sup>2+</sup>, mg/kg)</td><td>1180 ± 72</td><td>1340 ± 64</td></tr><tr><td>Residual soil moisture (%)</td><td>13.2 ± 0.9</td><td>14.7 ± 0.8</td></tr></tbody></table>

### a. pH and Organic Matter

The increase in soil pH in both zones reflects the compost's alkaline amendment effect, partially neutralizing soil acidity and improving nutrient bioavailability (FAO, 2015). Residual organic matter is significantly higher in the mountain zone due to slower mineralization and better humus retention, enhancing soil structure (Nziguheba et al., 2000).

### b. Nitrogen, Phosphorus, and Potassium

The compost significantly improved soil
nitrogen reserves (+16% in the mountain

zone), enhancing fertility for subsequent
crops. Available phosphorus remained high
post-harvest, particularly in the mountains,
confirming the slow release of phosphate
from bones and ash (Palm et al., 2001).
Exchangeable potassium was also higher,
strengthening residual soil drought
resistance (Vanlauwe et al., 2005).

### c. CEC and Calcium

Higher CEC in the mountain zone indicates
enhanced nutrient retention capacity, a key
for sustainable fertility (Saidou et al.,
2012). Calcium enrichment from bone
materials increased structural stability,
favoring root aeration.

d. Moisture Content and C/N Ratio

Higher residual moisture retention in the
mountain zone supports soil microbiology
and prolongs fertilizer effects. The residual
C/N ratio around 11 is optimal, ensuring
good nitrogen availability for subsequent
crops (Bernal et al., 2009).

Conclusion

This study demonstrated that integrating
dead biomass of *Pennisetum* sp. with
various biological and organic materials
(human urine, poultry droppings, cow dung,
goat droppings, animal and fish
bones/skeletons, and plant ash)
significantly enhances compost quality—
both physicochemically and agronomically.
The enriched compost (T3) was
characterized by:

* Accelerated maturation due to a balanced C/N ratio and mineral inputs;

* Higher concentrations of N, P, and K, essential for *Vigna unguiculata* growth;

* A positive impact on vegetative development and grain yield, especially in arid lowland zones;

* Improved soil structure and fertility, evidenced by increased organic matter, CEC, and pH regulation.

These results confirm that the rational use
of local organic resources not only valorizes
often-neglected biodegradable waste but
also sustainably restores fertility in
degraded soils under harsh agroclimatic
conditions.

Performance differences between mountain
and lowland zones highlight the need to
adapt compost application rates and
methods to local topographic and climatic
conditions.

Recommendations

For Agricultural Producers

* Prioritize enriched composts (especially T3) to improve *Vigna*

* *unguiculata* yields, targeting optimal doses of 10 to 15 t/ha depending on the zone.

* Adapt farming practices to local climatic specifics (irrigation, mulching, drought-resistant cowpea varieties).

* Valorize locally available biological waste, including underused animal-based resources (bones, droppings, urine).

For Policymakers

* Support farmer training in enriched compost production through participatory and context-sensitive approaches.

* Implement rural circular economy policies to promote conversion of organic waste into agricultural inputs.

* Fund research and development programs on organic fertilization tailored to arid Sahelian zones.

For Scientific Research

* Further investigate interactions between enriched compost and soil microflora, especially in relation to biological nitrogen fixation.

* Assess the long-term impacts of organic amendments on soil health and agroecological resilience.

* Explore combined effects of compost + biochar or compost + mycorrhizae in these challenging agroclimatic contexts.

**Conflict of Interest:** The authors declare
no conflict of interest.

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