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Universität Hohenheim (2018)

Seedball technology development for subsistence-oriented pearl millet production systems in Sahelian West Africa

Nwankwo, Charles Ikenna

Titre : Seedball technology development for subsistence-oriented pearl millet production systems in Sahelian West Africa

Entwicklung der Saatkugeltechnologie für Perlhirse-basierte Subsistenzproduktion-systeme in Sahelinische Westafrika

Auteur : Nwankwo, Charles Ikenna

Université de soutenance : Universität Hohenheim

Grade : Doktor der Agrarwissenschaften (Dr.sc.agr. in Agricultural Sciences) 2018

Résumé
The objectives of this study were to review the potential of the local material-based innovation – i.e. the seedball technology, at enhancing pearl millet seedlings establishment under Sahelian conditions, identify its potential constraints as well as applicability, chemically and mechanically optimize the seedball, and validate its performance under Sahelian field conditions. Seedball is a local seed pelleting techniques that aims at improving seedlings performance and to stabilize yield. First, the potential local materials such as sand, loam, wood ash, gum arabic, termite soil, charcoal as well as animal dung as the seedball components were identified and reviewed. These materials were selected based on their affordability to the local farmers. Potential constraints to seedball applicability as well as adoption in the Sahel were evaluated, and options for adaptation were discussed with the farmers. Afterwards, mechanical and chemical optimization of the seedball technology in several greenhouse experiments were conducted, followed by a germination test of the optimized seedball in the Sahelian field. Lastly, the mechanism of pearl millet seedlings root and shoot enhancement was investigated using micro-suction cup and computer tomography. Our evaluation showed that the materials needed for seedball production are locally available at affordable costs. The seedball technology totally conforms to the agronomic management practices in the African Sahel. In addition, the socio-economic status as well as cultural practices seemed not to reduce the chances of seedball technology adoption in this region. Our greenhouse studies showed that the seedball base dough, from which about ten 2 cm diameter-sized seedballs can be produced, is derived from the combination of 80 g sand + 50 g loam + 25 ml water. Either 1 g mineral fertilizer or 3 g wood ash can be added as nutrient additive to enhance early biomass of pearl millet seedlings. With respect to nutrient additives, ammonium fertilizers and urea hampered seedlings emergence. Wood ash amended (Sball+3gAsh) and mineral fertilizer-amended seedballs (Sball+1gNPK)enhanced shoot biomass by 60 % and 75-160 %, root biomass by 36 % and 94 %, and root length density of pearl millet by 14 % and 28 %, respectively, relative to the control. Again, the mineral fertilizer amended seedball in particular enhanced root dry matter by 227 %, compared to the control. Although the shoot nutrient content was not clearly enhanced by the seedball, nutrient extraction, calculated as the product of biomass yield and nutrient content, was higher in the nutrient-amended seedballs, compared to the conventional sowing. In Senegal, optimized seedballs showed over 95 % emergence in an on-station trial, indicating its viability in the Sahel region. With respect to seedball enhancement mechanism, the mineral fertilizer-amended seedball in particular promoted root growth within the vicinity of the seedball as early as 7 days after planting. The analysis of the sampled soil solution revealed that P as well as other cations and anions, observed through EC measurement, were released by the seedball in direct proximity of the seedball. Most likely, the nutrient release by the seedball triggered the observed fine root growth and overall higher root biomass of pearl millet seedlings. However, due to nutrient depletion in the root zone, nutrient supplementation was needed after three weeks after sowing to further promote growth of the well-established seedlings. At the Sahelian field, where seedlings enhancement is decisive for higher panicle yield in pearl millet, nutrient amended seedballs can potentially increase panicle yield under subsistence production. The seedball technology is cheap, and seems to have favorable conditions for adoption in the Sahel, coupled with its minimal seed usage and simple sowing on the sandy soil. A recommendation will be to conduct long-term, on-farm as well as on-station field trials, testing the seedball technology under different seasonal weather conditions. Pearl millet and sorghum are the major Sahelian staple crops. Fonio (Digitaria spp) is often neglected despite its high nutritional values. It is, therefore, recommended to test the seedball technology on the other fine-grained cereal crops.

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Page publiée le 29 janvier 2020