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# Study of the Impact of Compost on Biological Nitrogen Fixation by Vigna unguiculata and Its Interactions with Soil Microflora in an Arid Sahelian Lowland Zone

Alexis Dzokom, Roger Djouldé Darnan

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Alexis Dzokom, Roger Djouldé Darnan. Study of the Impact of Compost on Biological Nitrogen Fixation by Vigna unguiculata and Its Interactions with Soil Microflora in an Arid Sahelian Lowland Zone. Sahel Nature Consulting Revue, In press, Soils fertility, 05 (08), pp.1-11. hal-05042423

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# Study of the Impact of Compost on Biological Nitrogen Fixation by *Vigna unguiculata* and Its Interactions with Soil Microflora in an Arid Sahelian Lowland Zone

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

This study aims to assess the impact of enriched organic composts on the biological nitrogen fixation (BNF) by *Vigna unguiculata* in arid lowland zones of the Sahel. Biological nitrogen fixation is a crucial process for improving soil fertility in regions where nitrogen inputs are limited. Compost, primarily composed of local organic materials such as *Pennisetum* sp., poultry manure, and plant residues, plays a vital role in stimulating soil microflora and enhancing the symbiosis between plant roots and nitrogen-fixing bacteria. The study was conducted on arid soils, where climatic conditions and agricultural practices limit nutrient availability. Results indicate that compost application—particularly treatments Compost 3 and Compost 4—significantly increased the number of nodules compared to the control. Treatment T3 (compost + *Rhizobium* sp. inoculation) resulted in a 23% increase in nitrogen fixation, reaching 30 kg N/ha, compared to the control (T0), which recorded only 15 kg N/ha. Treatment T3 also achieved a yield of 2.1 t/ha, representing a 61% increase over the control, indicating a synergistic effect between compost and *Rhizobium* inoculation. The addition of enriched compost, in combination with *Rhizobium* inoculation, has a positive synergistic effect on nitrogen fixation by *Vigna unguiculata*. These findings underscore the importance of integrating sustainable soil management practices, such as compost application, to enhance soil fertility, crop productivity, and resilience under arid climatic conditions.

Keywords: Compost, Biological Nitrogen Fixation, *Vigna unguiculata*, Soil Microflora, Sahelian Zone, Soil Fertility, Plant-Microbe Interaction, Arid Lowlands.

## Introduction

In arid Sahelian zones, low soil fertility represents a major constraint to agricultural productivity, particularly for staple crops such as *Vigna unguiculata*, a leguminous plant of strategic importance for food security and soil regeneration (Timko & Singh, 2008). The ability of this species to biologically fix atmospheric nitrogen (symbiotic nitrogen fixation – BNF) through its interactions with *Rhizobium* bacteria is a key agronomic asset in low-input farming systems (Dakora & Keya, 1997; Peoples et al., 2009).

However, the efficiency of this biological nitrogen fixation is strongly influenced by

soil quality, especially its organic matter content, structure, pH, as well as the density and diversity of both symbiotic and free-living soil microflora (van der Heijden et al., 2008; Thilakarathna & Raizada, 2017). In this context, the application of enriched organic compost represents a promising strategy to improve soil fertility while stimulating the rhizosphere and root symbiosis (Bationo et al., 2007; Dzokom, 2024a,b; Dzokom, 2025a,b). Compost, as a source of organic matter, not only provides essential nutrients but also offers energy substrates for beneficial soil microorganisms, thereby enhancing microbial processes such as mineralization,
nitrification, and nodulation (Adu-Gyamfi et al., 2007; Ayuke et al., 2011).

The interaction between compost and BNF remains complex and dependent on local ecological conditions. In arid lowland Sahelian regions, high temperatures, limited water availability, and low mineral nitrogen levels modulate root colonization dynamics by rhizobia and the overall effectiveness of symbiosis (Zahran, 1999; Herridge et al., 2008). Studies have shown that compost application can stimulate not only nodulation but also the microbial diversity associated with roots, thereby creating a favorable environment for nitrogen fixation and crop resilience to abiotic stress (Mpepereki et al., 2000; Ouedraogo et al., 2017; Dzokom, 2023; Dzokom et al., 2024). This study therefore aims to evaluate the impact of enriched organic compost on

biological nitrogen fixation in *Vigna unguiculata*, as well as its effects on soil microflora, in an arid Sahelian zone. It seeks to address agroecological concerns related to the sustainability of production systems and the restoration of depleted soils in Sahelian environments.

# Material and Methods

## 1. Study Area

The study was conducted in an arid lowland Sahelian zone located in the Far North Region of Cameroon, characterized by a dry tropical climate with annual rainfall ranging between 400 and 700 mm, concentrated over a 3 to 4-month period (June to September).

<figure><img src="image_3.png" /><figcaption>Figure 1: Study Area</figcaption></figure>
The average temperatures range between 28 °C and 40 °C during the dry season (Sivakumar et al., 1993). The dominant soils are tropical ferruginous soils with low organic matter and low levels of plant-available nitrogen (FAO, 2015; Dzokom & Darman, 2022).

**2. Plant Material and Compost Used**

The plant material consisted of certified seeds of *Vigna unguiculata* (a local variety with high nodulation potential), obtained from the Institute of Agricultural Research for Development (IRAD). The applied compost was an enriched organic compost

produced from dry biomass of *Pennisetum* sp., poultry manure, plant ash, urine, cow dung, goat droppings, crushed animal bones, and fish remains. This mixture was composted following the turned windrow method over a 45-day period, with regular monitoring of temperature, pH, and moisture content (Goyal et al., 2005; Eghball & Power, 1999).

**3. Experimental Design**

The experiment was conducted using a randomized complete block design (RCBD) with four replications and five treatments.

**EXPERIMENTAL LAYOUT**

<figure><img src="image_4.png" /><figcaption>Figure 1: Experimental Layout</figcaption></figure>

Each plot measured 4 m × 3 m, with inter-row spacing of 60 cm and intra-hill spacing of 30 cm.

**4. Rhizobial Inoculation**

Inoculation was performed using an efficient local strain of *Rhizobium*

*leguminosarum*, cultured on YEM (Yeast Extract Mannitol) medium and applied at a concentration of 10⁸ CFU/g on seeds prior to sowing, following the protocol described by Somasegaran and Hoben (1994).
## 5. Monitoring of Agro-Physiological Parameters

Measurements were conducted on the following parameters:

* Number of nodules per plant (at flowering stage),

* Nodule dry weight (after oven-drying at 60 °C for 48 h),

* Leaf chlorophyll content (measured with a SPAD meter),

* Grain yield at maturity.

## 6. Evaluation of Biological Nitrogen Fixation (BNF)

BNF was estimated using the ¹⁵N natural abundance method, by comparing the ¹⁵N isotopic enrichment between cowpea (Vigna unguiculata) and a non-N-fixing reference plant (maize), grown under the same conditions (Unkovich et al., 2008; Boddey et al., 2000). Plant samples were ground and analyzed using isotope ratio mass spectrometry.

## 7. Soil Microflora Analysis

Soil samples were collected at 0–20 cm depth before sowing and at harvest. Microbiological analyses included:

* Free-living bacteria (total count, biomass, diversity),

* Free-living rhizobia (CFU/g of soil on selective medium),

* Arbuscular mycorrhizal fungi (spore observation under a microscope), according to the

methods of Giller (2001) and Sylvia et al. (2005).

## 8. Statistical Analyses

Data were subjected to one-way ANOVA using R software version 4.2. Means were compared using Tukey's HSD test at the 5% significance level. Pearson correlation analysis was performed to assess the relationships between nodulation, BNF, and microbial density.

## Results and Discussion

### 1. Effects of Compost on Nodulation in Vigna unguiculata

Compost application significantly enhanced the number of nodules formed by Vigna unguiculata compared to the unfertilized control. Treatment T2 (compost at 10 t/ha) recorded an average of 35 nodules per plant, representing a 45% increase over the control (T0), which had only 24 nodules per plant. These results are consistent with Adu-Gyamfi et al. (2007), who reported enhanced nodulation through compost addition, facilitating root colonization by rhizobia.

Compost application promotes rhizobial distribution in the rhizosphere, creating a favorable environment for nodule formation and nitrogen fixation processes. According to Zahran (1999), organic matter increases the availability of essential elements for rhizobial growth, such as carbon and mineral nitrogen.

<table><caption>Table 1: Effects of Compost on Nodulation in Vigna unguiculata</caption><thead><tr><td>Treatment</td><td>Mean Number of Nodules (per plant)</td></tr></thead><tbody><tr><td>Control</td><td>12.5 ± 2.3</td></tr><tr><td>Compost 1</td><td>18.2 ± 3.1</td></tr><tr><td>Compost 2</td><td>21.4 ± 2.7</td></tr><tr><td>Compost 3</td><td>25.6 ± 3.5</td></tr><tr><td>Compost 4</td><td>23.8 ± 3.0</td></tr></tbody></table>

The results show that compost treatments, particularly Compost 3 and Compost 4, significantly increased nodule numbers compared to the control. This improvement may be attributed to enhanced soil fertility and increased microbial biodiversity,

thereby promoting biological nitrogen fixation.

According to Ramond et al. (2022) and Dzokom (2019), organic materials such as compost serve as key substrates to support microbial activity and nodulation in nutrient-poor soils typical of arid regions.
Furthermore, Giller (2001) emphasized that nodulation is a direct indicator of the effectiveness of the symbiosis between legume roots and nitrogen-fixing bacteria.

## 2. Biological Nitrogen Fixation (BNF)

BNF measurements indicated that compost application significantly increased nitrogen fixed by *Vigna unguiculata*. Treatment T3 (compost + Rhizobium inoculation) showed a 23% increase in nitrogen fixation, reaching 30 kg N/ha, compared to the control (T0) with 15 kg N/ha. This

improvement is attributed to the synergy between compost—providing essential organic matter for rhizobial growth—and inoculation, which optimized the symbiotic association (Peoples et al., 2009).

These results are in agreement with Giller (2001), who demonstrated that nitrogen fixation is enhanced by compost application, particularly in nutrient-limited arid environments. Moreover, compost use partially offset the deficit in mineral nitrogen, increasing nitrogen availability for the crop.

<table><caption>Table 2: Biological Nitrogen Fixation (BNF) in *Vigna unguiculata*</caption><thead><tr><td>Treatment</td><td>Mean BNF (kg/ha)</td></tr></thead><tbody><tr><td>Control</td><td>5.4 ± 1.2</td></tr><tr><td>Compost 1</td><td>8.2 ± 1.5</td></tr><tr><td>Compost 2</td><td>9.5 ± 1.3</td></tr><tr><td>Compost 3</td><td>12.8 ± 1.6</td></tr><tr><td>Compost 4</td><td>11.3 ± 1.4</td></tr></tbody></table>

The data reveal that compost application significantly enhanced BNF, with the highest values recorded for Compost 3 and Compost 4. This improvement may be attributed to the slow release of nutrients and increased soil water-holding capacity, fostering an environment favorable to nitrogen-fixing bacteria.

According to Anglade et al. (2015), compost application enriches soil organic matter, enhancing microbial activity and consequently nitrogen fixation. Sanginga (2012) also reported that organic treatments improve both nodulation efficiency and root-bacteria interactions in legumes.

## 3. Impact of Compost on Grain Yield

Grain yield of *Vigna unguiculata* showed notable improvement under compost-based treatments. Treatment T2 (compost alone at 10 t/ha) resulted in an average yield of 1.8 t/ha, a 36% increase compared to the control (T0), which yielded 1.3 t/ha. This enhancement is likely due to improved soil fertility through increased organic matter, water retention, and nutrient availability—critical factors under arid conditions

(Bationo et al., 2007; Ayuke et al., 2011; Dzokom & Djouldé, 2023; Dzokom & Darman, 2021; Dzokom & Darman, 2025).

Treatment T3 (compost + inoculation) recorded the highest yield of 2.1 t/ha, representing a 61% increase compared to the control, highlighting a synergistic effect between compost application and *Rhizobium* inoculation (Boddey et al., 2000). This phenomenon was also reported by Herridge et al. (2008), who observed substantial yield improvements when legume inoculation was combined with compost amendments.

These findings indicate that compost application significantly boosts the yield of *Vigna unguiculata*, with Compost 3 and Compost 4 treatments producing the highest yields. This trend suggests that compost amendment enhances plant growth likely by improving soil structure, moisture retention, and nutrient availability.

According to Palm et al. (2001), organic composts increase soil organic matter content, thereby improving soil physicochemical properties and promoting better crop growth.
<table><caption>Table 3: Impact of Compost on Grain Yield of Vigna unguiculata</caption><thead><tr><td>Treatment</td><td>Mean Yield (kg/ha)</td></tr></thead><tbody><tr><td>Control</td><td>300 ± 45</td></tr><tr><td>Compost 1</td><td>450 ± 50</td></tr><tr><td>Compost 2</td><td>500 ± 55</td></tr><tr><td>Compost 3</td><td>600 ± 60</td></tr><tr><td>Compost 4</td><td>550 ± 58</td></tr></tbody></table>

Additionally, Chianu et al. (2012) demonstrated that compost application in arid soils can enhance soil fertility and increase crop productivity by improving nutrient availability and microbial activity.

### 4. Effects on Soil Microflora

Microbiological analysis of the soil revealed that compost application altered the composition of soil microflora, promoting the growth of beneficial bacteria, including rhizobia. Treatment T2 (compost at 10 t/ha) increased soil bacterial biomass by 25% compared to the control, as

measured by the easily extractable carbon (EEC) content. The results also showed an increase in microbial diversity, a crucial factor in maintaining soil health and biological activity (van der Heijden et al., 2008).

Rhizobia, in particular, exhibited increased growth in the rhizosphere of compost-treated plants, with a 45% increase in the number of *Rhizobium* sp. colonies compared to the control. This suggests that compost improved the habitat conditions for rhizobia, thereby facilitating nitrogen fixation (Sylvia et al., 2005).

<table><caption>Table 4: Effects of Compost on Soil Microflora</caption><thead><tr><td>Treatment</td><td>Average Microbial Population (CFU/g of soil)</td></tr></thead><tbody><tr><td>Control</td><td>1.5 × 10<sup>6</sup> ± 0.3 × 10<sup>6</sup></td></tr><tr><td>Compost 1</td><td>2.2 × 10<sup>6</sup> ± 0.4 × 10<sup>6</sup></td></tr><tr><td>Compost 2</td><td>2.6 × 10<sup>6</sup> ± 0.5 × 10<sup>6</sup></td></tr><tr><td>Compost 3</td><td>3.4 × 10<sup>6</sup> ± 0.6 × 10<sup>6</sup></td></tr><tr><td>Compost 4</td><td>3.1 × 10<sup>6</sup> ± 0.5 × 10<sup>6</sup></td></tr></tbody></table>

The data indicate that compost application significantly increases the soil microbial population, with Compost 3 yielding the highest microbial count. This suggests that compost, by providing organic matter, promotes the proliferation of soil microorganisms, including nitrogen-fixing bacteria and other microbes beneficial for soil health. This enhancement of microflora is also related to compost's ability to improve the physico-chemical properties of the soil, such as aeration and moisture retention, thus creating a favorable environment for microbial growth. Aguilar-Paredes et al. (2023) demonstrated that compost addition enhances microbial biodiversity and enzymatic activity in soils, thereby improving organic matter decomposition and nutrient cycling. Moreover, according to Obalum et al.

(2017), improvements in soil structure due to compost application have a direct effect on microflora diversity and activity, contributing to long-term soil health.

### 5. Compost-Rhizobia Interactions and Their Role in Soil Fertility Management

The findings of this study confirm that the application of enriched compost, in combination with rhizobial inoculation, has a positive synergistic effect on nitrogen fixation by *Vigna unguiculata*. The improvements in nodulation, nitrogen fixation, and yield are directly related to the enhancement of soil microflora, which becomes more diverse and functional, creating a favorable environment for symbiosis. These interactions are critical in Sahelian environments, where soils are
generally nutrient-depleted and climatic conditions are harsh (Zahran, 1999).

<table><caption>Table 5: Compost-Rhizobia Interactions and Their Role in Soil Fertility Management</caption><thead><tr><td>Treatment</td><td>Average Rhizobia Population (CFU/g of soil)</td><td>Nitrogen Fixation (kg/ha)</td></tr></thead><tbody><tr><td>Control</td><td>1.2 × 10<sup>6</sup> ± 0.3 × 10<sup>6</sup></td><td>5.4</td></tr><tr><td>Compost 1</td><td>1.8 × 10<sup>6</sup> ± 0.4 × 10<sup>6</sup></td><td>8.2</td></tr><tr><td>Compost 2</td><td>2.1 × 10<sup>6</sup> ± 0.5 × 10<sup>6</sup></td><td>9.5</td></tr><tr><td>Compost 3</td><td>2.8 × 10<sup>6</sup> ± 0.6 × 10<sup>6</sup></td><td>12.8</td></tr><tr><td>Compost 4</td><td>2.5 × 10<sup>6</sup> ± 0.5 × 10<sup>6</sup></td><td>11.3</td></tr></tbody></table>

The results demonstrate that compost addition positively affects rhizobial populations, with significant increases observed in Compost 3 and Compost 4 treatments. This increase in rhizobia is associated with improved nitrogen fixation, suggesting that compost promotes the symbiosis between *Vigna unguiculata* and nitrogen-fixing rhizobia. This can be attributed to soil enrichment with organic matter, which creates favorable conditions for rhizobia and other beneficial microorganisms. The improvement in soil fertility through compost application, by supplying additional nutrients and enhancing soil structure, creates a suitable environment for enhanced rhizobial activity. According to Araujo *et al.* (2012), increasing rhizobial populations through compost application may play a key role in enhancing nitrogen fixation in tropical soils, especially in arid zones. Furthermore, Sanginga (2012) reported that interactions between rhizobia and organic matter not only improve nitrogen availability but also enhance soil structure, thus increasing crop productivity.

## 6. Limitations and Future Perspectives

Despite the positive results observed, it is important to note that the effectiveness of compost application strongly depends on the quality of the compost, the timing and method of application, and the specific characteristics of the soil. Further studies are needed to assess the impact of different compost types and to monitor the long-term effects on soil fertility and crop yields in order to optimize compost integration strategies in Sahelian farming systems

(Thilakarathna & Raizada, 2017; Dzokom, 2024a,b; Dzokom, 2025a,b; Dzokom, 2023; Dzokom *et al.*, 2024; Dzokom & Darman, 2022; Dzokom, 2019; Dzokom & Djouldé, 2023; Dzokom & Darman, 2021; Dzokom & Darman, 2025).

## Conclusion and Recommendations
### Conclusion

The study on the impact of compost on biological nitrogen fixation by *Vigna unguiculata* and its interactions with soil microflora in the arid lowlands of the Sahel highlights the significant benefits of compost use in these semi-arid environments. The results revealed that compost application not only improves nodulation and nitrogen fixation by the roots of *Vigna unguiculata* but also enhances crop yields and microbial biodiversity in the soil. Compost-based treatments showed significant increases in nodule formation, nitrogen fixation rates, and seed yields of *Vigna unguiculata* compared to unfertilized soils. This improvement is largely attributed to the enrichment of the soil with organic matter, which fostered the growth of rhizobia and other beneficial microorganisms in the rhizosphere. Furthermore, the combination of compost and rhizobial inoculation exhibited a positive synergy, further increasing yields and nitrogen fixation. The impact of compost on soil microflora was noted by an increase in bacterial diversity, particularly rhizobia, which contributed to a more favorable environment for symbiosis between legumes and soil microorganisms. These results underscore the importance of
integrating sustainable soil management practices, such as compost use, to improve soil fertility, crop productivity, and resilience to arid climatic conditions.

## Recommendations

1. **Promotion of Compost Use:** In light of the positive results, it is recommended to promote compost use as a sustainable method of soil enrichment in Sahelian regions. This approach can help improve the fertility of nutrient-depleted soils, reduce dependency on chemical fertilizers, and strengthen food security in vulnerable areas.

2. **Complementary Rhizobial Inoculation:** Soil inoculation with effective rhizobia, especially in combination with compost, should be encouraged. This would optimize nitrogen fixation and improve legume yields while minimizing reliance on chemical fertilizers. Agricultural programs should incorporate integrated compost-inoculant strategies in crop management practices.

3. **Farmer Training:** Training initiatives should be implemented to raise awareness among local farmers about the benefits of compost use and rhizobial inoculation. This includes demonstrations on small-scale compost production, inoculant application, and good agricultural practices.

4. **Long-Term Monitoring:** It is crucial to implement long-term studies to assess the lasting effects of compost on soil fertility, microflora dynamics, and crop productivity under variable climatic conditions. Regular monitoring would help adjust agricultural practices to environmental changes and refine recommendations for sustainable agriculture strategies.

5. **Development of Specific Composts:** The development of nutrient-enriched composts tailored to the needs of arid soils is recommended. These composts could include organic materials rich in phosphorus, potassium, and magnesium, in addition to nitrogen, to ensure better crop growth in deficient soils.

6. **Collaboration with Research Institutions:** Partnerships with agricultural and environmental research institutions are essential to further explore compost effects under climate stress conditions. Strengthened collaboration between researchers, farmers, and policymakers could facilitate the widespread adoption of sustainable agricultural practices in the Sahel region.

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

**Acknowledgments:** The authors would like to express their sincere gratitude to all individuals and institutions who contributed to the successful completion of this research. Special thanks go to the local farming communities and cooperatives in the Sudano-Sahelian region of Cameroon for their collaboration and provision of raw materials. We also acknowledge the technical support provided by the Bioscience laboratory teams at University of Maroua, whose expertise greatly enhanced the analytical phases of this study. This work was made possible through the support of Sahel Nature Consulting NGO, whose financial and logistical contributions are gratefully acknowledged. Finally, we extend our appreciation to all peer reviewers and academic mentors for their constructive feedback and guidance throughout the research process.
## References

1. Adu-Gyamfi, J. J., Myaka, F. A., Sakala, W. D., Odgaard, R., Vesterager, J. M., & Høgh-Jensen, H. (2007). Biological nitrogen fixation and nitrogen and phosphorus budgets in farmer-managed intercrops of maize-pigeonpea in semi-arid southern and eastern Africa. *Plant and Soil*, 295(1–2), 127–136.
https://doi.org/10.1007/s11104-007-9270-0

2. Ayuke, F. O., Pulleman, M. M., Vanlauwe, B., de Goede, R. G. M., Six, J., & Brussaard, L. (2011). Agricultural management affects earthworm and termite diversity across humid to semi-arid tropical zones. *Agriculture, Ecosystems & Environment*, 140(1–2), 148–154.

3. Bationo, A., Waswa, B. S., Kihara, J., & Kimetu, J. (2007). *Advances in Integrated Soil Fertility Management in Sub-Saharan Africa: Challenges and Opportunities*. Springer.

4. Aguilar-Paredes, A., Valdés, G., Araneda, N., Valdebenito, E., Hansen, F., & Nuti, M. (2023). Microbial community in the composting process and its positive impact on the soil biota in sustainable agriculture. *Agronomy*, 13(2), 542.

5. Boddey, R. M., Peoples, M. B., Palmer, B., & Dart, P. J. (2000). Use of the 15N natural abundance technique to quantify biological nitrogen fixation by woody perennials. *Nutrient Cycling in Agroecosystems*, 57(3), 235–270.

6. Chenu, C., et al. (2004). Organic matter in soil: Degradation and stabilization. *Soil Biology and Biochemistry*, 36(1), 39–47.

7. Obalum, S. E., Chibuike, G. U., Peth, S., & Ouyang, Y. (2017). Soil organic matter as sole indicator of soil degradation. *Environmental

monitoring and assessment, 189, 1-19.

8. Dakora, F. D., & Keya, S. O. (1997). Contribution of legume nitrogen fixation to sustainable agriculture in sub-Saharan Africa. *Soil Biology and Biochemistry*, 29(5–6), 809–817.

9. Araujo, A. S. F., Leite, L. F. C., Iwata, B. D. F., Lira, M. D. A., Xavier, G. R., & Figueiredo, M. D. V. B. (2012). Microbiological process in agroforestry systems. A review. *Agronomy for Sustainable Development*, 32, 215-226.

10. Eghball, B., & Power, J. F. (1999). Composted and noncomposted manure application to conventional and no-tillage systems: Corn yield and nitrogen uptake. *Agronomy Journal*, 91(5), 819-825.

11. FAO. (2015). *World reference base for soil resources 2014 – update 2015*. FAO, Rome.

12. Giller, K. E. (2001). *Nitrogen Fixation in Tropical Cropping Systems* (2nd ed.). CABI Publishing.

13. Anglade, J., Billen, G., & Garnier, J. (2015). Relationships for estimating N2 fixation in legumes: incidence for N balance of legume-based cropping systems in Europe. *Ecosphere*, 6(3), 1-24.

14. Palm, C. A., Gachengo, C. N., Delve, R. J., Cadisch, G., & Giller, K. E. (2001). Organic inputs for soil fertility management in tropical agroecosystems: application of an organic resource database. *Agriculture, ecosystems & environment*, 83(1-2), 27-42.

15. Goyal, S., Dhull, S. K., & Kapoor, K. K. (2005). Chemical and biological changes during composting of different organic wastes and assessment of compost maturity. *Bioresource Technology*, 96(14), 1584-1591.
16. Herridge, D. F., Peoples, M. B., & Boddey, R. M. (2008). Global inputs of biological nitrogen fixation in agricultural systems. *Plant and Soil*, 311(1–2), 1–18.

17. Mpepereki, S., Makonese, F., & Makonese, F. (2000). Soyabeans and sustainable agriculture: Promiscuous soyabeans for smallholders in southern Africa. *Bulletin of the Faculty of Agriculture, University of Zimbabwe*.

18. Ouedraogo, E., Mando, A., Brussaard, L., & Stroosnijder, L. (2017). Tillage and fertility management effects on soil organic matter and macrofauna in semi-arid West Africa. *Soil and Tillage Research*, 94(1), 16–25.

19. Peoples, M. B., Brockwell, J., Herridge, D. F., Rochester, I. J., Alves, B. J. R., Urquiaga, S., ... & Jensen, E. S. (2009). The contributions of nitrogen-fixing crop legumes to the productivity of agricultural systems. *Symbiosis*, 48, 1–17.

20. Chianu, J. N., Chianu, J. N., & Mairura, F. (2012). Organic fertilizers in sub-saharan farming systems. *Organic fertilisation, soil quality and human health*, 31-65.

21. Sanginga, N., Dashiell, K. E., Diels, J., Vanlauwe, B., Lyasse, O., Carsky, R. J., ... & Ortiz, R. (2003). Sustainable resource management coupled to resilient germplasm to provide new intensive cereal–grain–legume–livestock systems in the dry savanna. *Agriculture, Ecosystems & Environment*, 100(2-3), 305-314.

22. Sanginga, N. (2012). Closing the yield gap through integrated soil fertility management.

23. Sivakumar, M. V. K., Maidoukia, A., & Stern, R. D. (1993). *Agroclimatology of West Africa: Niger*. Information Bulletin No. 5, ICRISAT.

24. Ramond, J. B., Jordaan, K., Díez, B., Heinzelmann, S. M., & Cowan, D. A. (2022). Microbial biogeochemical cycling of nitrogen in arid ecosystems. *Microbiology and Molecular Biology Reviews*, 86(2), e00109-21.

25. Somasegaran, P., & Hoben, H. J. (1994). *Handbook for Rhizobia: Methods in Legume-Rhizobium Technology*. Springer.

26. Sylvia, D. M., Fuhrmann, J. J., Hartel, P. G., & Zuberer, D. A. (2005). *Principles and Applications of Soil Microbiology*. Pearson Education.

27. Timko, M. P., & Singh, B. B. (2008). Cowpea, a multifunctional legume. In *Genomics of tropical crop plants* (pp. 227-258). New York, NY: Springer New York.

28. Thilakarathna, M. S., & Raizada, M. N. (2017). A meta-analysis of the effectiveness of diverse rhizobia inoculants on soybean traits under field conditions. *Soil Biology and Biochemistry*, 105, 177–196.

29. Unkovich, M., Herridge, D., Peoples, M., Cadisch, G., Boddey, B., Giller, K., Alves, B., & Chalk, P. (2008). *Measuring Plant-Associated Nitrogen Fixation in Agricultural Systems*. ACIAR Monograph No. 136.

30. van der Heijden, M. G. A., Bardgett, R. D., & van Straalen, N. M. (2008). The unseen majority: Soil microbes as drivers of plant diversity and productivity in terrestrial ecosystems. *Ecology Letters*, 11(3), 296–310.

31. Zahran, H. H. (1999). Rhizobium–legume symbiosis and nitrogen fixation under severe conditions and in an arid climate. *Microbiol. Mol. Biol. Rev.*, 63(4), 968–989.

32. Dzokom, A. (2024a). Optimization Of The Production Of Two Varieties Of Sorgum (Fadda and Soumalemba) Amended With
Compost Based On *Eichhornia Crassipes* Linked To *Urtica dioica*
In Sahel Areas Near Lake Chad.
Available at SSRN 4854242.

33. Dzokom, A. (2025a). Environmental Management Jobs: Opportunities and Challenges in the Cameroonian Sahel Zone. Available at SSRN 5188492.

34. Dzokom, A. (2024b). Effect of Mixed Biochar-Compost Based on Dead Biomasses of Prosopis juliflora and Eichhornia crassipes on the Productivity and Biodiversity of Arid Sandy Soils in the Sahelian Zone. EQA (Imola): environmental quality; qualité de l'Environnement; qualità ambientale.

35. Dzokom, A. (2023). Environmental Management Tools and Techniques in the Cameroonian Sahelian Zone: Sustainable Approach and Practices. Available at SSRN 5171289.

36. Dzokom, A. (2025b). Outils Et Techniques De Gestion De L'environnement En Zone Sahélienne Camerounaise: Approche Et Pratiques Durables. Procedia-Social and Behavioral Sciences, 5(5), 1-16.

37. Dzokom, A., Balna, J., Zieba, F. W., & Darnan, R. D. (2024). Environmental education: comparative study of the performance of two training methods in sahelian farming environments. *SAHARA-J: Journal of Social Aspects of HIV/AIDS*.

38. DZOKOM, A., & DARMAN, R. D. (2022). 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](https://halsh.sahel.naturerel.org/10.5158/05037998)

39. Dzokom, A. (2019). Sustainable Seeding and Restoration Techniques for Degraded Lands: Coating Seeds in Biochar-Compost. *Biology and Fertility of Soils*, 9(7), 1-14.

40. Alexis Dzokom, Roger Djouldé Darman (2023). Study on the Influence of Biomass Particle Size of Pennisetum sp. Combined with Biological and Organic Matter on the Decomposition Rate and Compost Quality in the Sahelian Environment. *Sahel Nature Consulting Revue*, In press, Composting waste in urban society, 04 (05), pp.1-15. [hal-05041094](https://halsh.sahel.naturerel.org/10.5158/05041094)

41. Alexis Dzokom, Roger Djouldé Darman (2021). Optimization of Compost Based on Pennisetum sp. Biomass and Organic Materials for Cultivating Vigna unguiculata in the Sahelian Zone. *Sahel Nature Consulting Revue*, In press, Biologic Agriculture and Waste Recovery for Compost, 04 (03), pp.1-10. [hal-05035461](https://halsh.sahel.naturerel.org/10.5158/05035461)

42. Alexis Dzokom, Roger Darman Djouldé (2025). Optimization of Allium cepa L. cultivation in urban Sahelian areas amended with local mixed organic compost. *Sahel Nature Consulting Revue*, In press, Compost et Biochar, 11 (05), pp.1-11. [hal-05032018](https://halsh.sahel.naturerel.org/10.5158/05032018)