Influence of Substrate Type and Water Level on the Germination and Growth of Three Agroforestry Species.

---

Résumé

Leguminous species play a vital role in agroecosystems, particularly in semi-arid regions, due to their capacity for biological nitrogen fixation, soil restoration, and contribution to sustainable farming systems. However, despite the ecological and socio-economic importance of key species such as Faidherbia albida, Gliricidia sepium, and Pterocarpus erinaceus, limited knowledge on low-cost and reproducible germination conditions constrains their regeneration and conservation efforts.
Aims: This study examines the interaction between substrate and water availability in order to identify the optimal conditions for seedling production of Faidherbia albida (Del.) A. Chev, Gliricidia sepium (Jacq.) Walp, and Pterocarpus erinaceus Poir.
Study Design: The study material consisted of seeds from the three species. The treatments comprised three substrates combined with four irrigation regimes. The substrate formulations were as follows: 1/2 manure + 1/2 clay (M1), 1/2 manure + 1/2 sand (M2), and 1/2 manure + 1/2 sawdust (M3). Water availability was the second factor with the field capacity (FC) to have four irrigation levels: 100% FC, 75% FC, 50% FC, and 25% FC. In total, 12 treatments were studied for each species.
Place and Duration of Study: The study was conducted in Gampéla, located in the municipality of Saaba, Burkina Faso, West Africa. It was conducted in 2024 over a period of four months.
Methodology: The study consisted of the establishment of a completely randomized factorial design with three replications. The pots were filled with the different substrates, and sowing was carried out at a rate of two seeds per pot. Starting two days after sowing, the number of germinated seeds was recorded every two days, while growth parameters were measured every seven days, beginning thirty days after sowing.
Results: The results show that substrate M3 offers the best germination rates: 76.7% (G. sepium), 79.2% (P. erinaceus), and 69.6% (F. albida), unlike M1 and M2 which are less effective, with germination rates below 50% regardless of the species. Watering at 50% and 75% of field capacity optimized germination, excess water (100%) reduced the germination performance of the species. The interaction between substrate and water volume does not reveal any significant difference in the growth parameters of Faidherbia albida (P > 0.05). For seedling growth, F. albida shows a clear preference for substrate M1 (manure + clay) combined with a low water volume (25% CC), without any notable interaction. In G. sepium, the substrate influences height and foliage, with an optimum at 25% CC for both height and diameter, but significant substrate-water interactions emerge. Finally, P. erinaceus is highly dependent on substrate M3 for diameter and foliage, shows low sensitivity to water regime, and exhibits significant interactions.
Conclusion: This study provides essential data for improving agroforestry species regeneration techniques. It reveals the potential of sawdust as a substrate component and the importance of precise watering control to maximize seedling germination and growth. The combined management of substrate and water regime, adapted to the Eco physiological needs of the species, is crucial for maximizing production.

Mots-clés

Substrate; field capacity; germination; growth; tree legumes.