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Kwame Nkrumah University of Science and Technology (2015)

Composting millet glume for soil fertility improvement and millet/cowpea productivity in semi-arid zone of Niger

Bachir, Bounou Issoufa

Titre : Composting millet glume for soil fertility improvement and millet/cowpea productivity in semi-arid zone of Niger

Auteur : Bachir, Bounou Issoufa

Université de soutenance : Kwame Nkrumah University of Science and Technology

Grade : Doctor of Philosophy in Soil Science, 2015

Résumé
Declining soil fertility is among the most limiting factors for improving crop production in the Sahel. In Niger, organic resources are unavailable due to other competitive uses. However, millet glume (residues left after threshing of millet) is readily available in most villages of Niger and represents a potential source of reusable organic material. Nevertheless, the low decomposition rate of millet glume constraint its direct-use as an organic amendment. This study therefore focused on valorising millet glume for improving soil fertility and millet/cowpea productivity in semi-arid zone of Niger. The study consisted of five parts : (i) exploration of the indigenous knowledge related to farmer management of millet glume, (ii) decomposition and nutrient release pattern of millet glume-based compost (MGB-compost), (iii) changes in soil chemical and microbial biomass C, N, P induced by combined use of MGB-compost and mineral fertilizer, (iv) influence of combined application of MGB-compost and mineral fertilizer on millet/cowpea yields and (v) economic benefit of MGB-compost and mineral fertilizer application under millet/cowpea based cropping systems in Niger. To explore the indigenous knowledge relating to farmers‟ management of millet glume, structured questionnaires were administrated in Dan Saga village, District of Aguié. Litterbags and leaching tube incubation experiments were used under field and laboratory conditions, respectively to monitor the decomposition and nutrient release pattern of the MGB-compost. A two-year field experiment was also conducted during the 2013 and 2014 cropping seasons to evaluate the potential of combined application of MGB-compost and mineral fertilizer on soil chemical and microbiological properties, millet/cowpea yields and economic benefit. The treatments used consisted of a factorial combination of three (3) rates of MGB-compost (C0, C150 and C300 g hill-1) and three (3) rates of mineral fertilizer (0 % RR, 50 % RR and 100 % RR kg ha-1 ; RR = recommended rate) and replicated four times. Composting millet glume in a 2:1 ratio (2 parts of millet glume : 1 part of goat manure) improved markedly millet glume N content by 43 % and P content by 138 %. Half - life of 4.65 weeks was recorded for MGB-compost relative to 12.38 weeks for millet glume. MGB-compost released 87 % and 90 % of its total N and P contents, respectively by the end of 10 weeks of decomposition. Soil microbial biomass P was on average 2.4 times higher on MGB-compost amended plots relative to sole N and P fertilizers treated plots. The increased microbial biomass P resulted in 223 % increase in available P on MGB-compost amended plots. Application of sole MGB-compost increased millet and cowpea grain yields by 187 kg ha-1 (21 %) and 163 kg ha-1 (20 %), respectively over the sole application of N and P fertilizers. However, the combined application of MGB-compost and N and P fertilizers increased millet and cowpea grain yields by 462 kg ha-1 (51 %) and 616 kg ha-1 (76 %), respectively over the sole application of N and P fertilizers. Combined use of MGB-compost with N and P fertilizers did not increase the Value Cost Ratio (VCR) for millet. However, the VCR for cowpea was 4.4 for MGB-compost treated plot. The study concluded that millet glume could serve as an alternative organic material for soil fertility management and for increased millet/cowpea production. It is therefore recommended that combined application of MGB-compost and N and P fertilizers could be used to reduce 50 percent mineral fertilizer investment currently made by smallholder farmers in Niger.

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