SUMMARY: In the Sahelian zone of Niger, there is a need to develop guidelines for integrated nutrient management, which relies on the potential nutrient sources of manure, pearl millet residue and mineral fertilizers. A fully factorial on-station experiment was conducted during the 1994 and 1995 rainy seasons at Sadoré, Niger, combining application of: (i) broadcast millet residue (300, 900 and 2700 kg ha⁻¹), (ii) broadcast cattle manure (300, 900 and 2700 kg ha⁻¹) and (iii) mineral fertilizer (unfertilized control, 15 kg N ha⁻¹ + 4.4 kg P ha⁻¹ and 45 kg N ha⁻¹ + 13.1 kg P ha⁻¹). Manure and fertilizer increased millet yields in both years whereas residue was effective in 1995 only. The effect of manure and residue were additive, as was the effect of manure and fertilizer but only up to 50 kg N ha⁻¹. However in 1995, the response to fertilizer was approximately doubled in the presence of 900 or 2700 kg residue ha⁻¹ compared to fertilizer with 300 kg ha⁻¹ residue, indicating a strong synergistic effect. This synergistic effect was reflected in the partial factor productivity of nitrogen and phosphorous in both years. Two treatment combinations stand out as particularly relevant based on yield, partial factor productivity and nutrient balance criteria: 2700 kg manure ha⁻¹ combined with (i) 300 kg residue and no fertilizer (95% grain yield increase); (ii) 900 kg residue ha⁻¹ and 15 kg N + 4 kg P ha⁻¹ (132% grain yield increase). There is a need for similar, long-term experiments to confirm the present results.

The emission of greenhouse gases (GHGs) results in global warming and climate change. The extent to which developing countries contribute to GHG emissions is not well known. This study reports findings on the effects of different land-use systems on GHG emissions (CO₂ in this case) from two locations in the southern zone of Ghana, West Africa. Site one (located at Kpong) contained a heavy clay soil while site two (located at Legon) contained a light-textured sandy soil. Land-use systems include cattle kraals, natural forests, cultivated maize fields, and rice paddy fields at site one, and natural forest, woodlots, and cultivated soya bean fields at site two. CO₂ emissions were measured using the gas entrapment method (PVC chambers). Trapping solutions were changed every 12–48 h and measurement lasted 9 to 15 days depending on the site. We found that, for the same land-use, CO₂ emissions were higher on the clay soil (Kpong) than the sandy soil (Legon). In the clay soil environment, the highest average CO₂ emission was observed from the cattle kraal (256.7 mg·m⁻²·h⁻¹), followed by the forest (146.0 mg·m⁻²·h⁻¹) and rice paddy (140.6 mg·m⁻²·h⁻¹) field. The lowest average emission was observed for maize cropped land (112.0 mg·m⁻²·h⁻¹). In the sandy soil environment, the highest average CO₂ emission was observed from soya cropped land (52.5 mg·m⁻²·h⁻¹), followed by the forest (47.4 mg·m⁻²·h⁻¹) and woodlot (33.7 mg·m⁻²·h⁻¹). Several factors influenced CO₂ emissions from the different land-use systems. These include the inherent properties of the soils such as texture, temperature, and moisture content, which influenced CO₂ production through their effect on soil microbial activity and root respiration. Practices that reduce CO₂ emissions are likely to promote carbon sequestration, which will consequently maintain or increase crop productivity and thereby improve global or regional food security.

L’utilisation accrue des pesticides chimiques couplée au boom agricole à laquelle on assiste ces dernières années soulève des interrogations sur la vulnérabilité des ressources naturelles, en particulier les ressources hydrologiques des zones cotonnières du Bénin. Cette étude vise à analyser les pratiques de gestion des pesticides chimiques agricoles à l’échelle « paysan » afin de comparer ces pratiques aux normes recommandées. Les données analysées ont été collectées dans la commune de Gogounou auprès de cent cinquante (150) producteurs tous répartis dans six (6) villages. Il ressort de nos investigations que les matières actives des pesticides les plus utilisées dans le bassin cotonnier du Bénin sont le glyphosate, l’atrazine, le flubendiamide, le spirotétramate et les pyréthrinoïdes (Emamectine, Cyfluthrine, Cyperméthrine, Betacyfluthrine). Une faible proportion des insecticides est commercialisée par le circuit informel (09 %) contrairement aux insecticides dont la majorité (60 %) provient de ce circuit. De même, les pesticides non autorisés proviennent en majorité du circuit informel (93,9 % des herbicides et 21,5 % des insecticides). La majorité des producteurs (90,3 %) utilise en moyenne 3,4 flacons de Tihan par hectare (soit 0,34 litre par hectare) de plus que la moyenne recommandée. De plus, les doses de pesticides utilisées par hectare augmentent au fur et à mesure que les champs sont proches des points d’eau. La gestion et l’utilisation très peu rigoureuses des pesticides constatés dans cette zone pourraient constituer une menace pour le maintien de la biodiversité et de la productivité des écosystèmes naturels, de la qualité sanitaire des produits halieutiques et de la santé des producteurs et des consommateurs. Face à ce constat, le défit de la recherche serait la détermination du niveau actuel de contamination des eaux du bassin et celui de l’État serait l’initiation de programmes de sensibilisation des producteurs par rapport à une gestion plus rigoureuse des pesticides.

Optimizing the use of organic and mineral fertilizer in rain-fed maize production is crucial for sustainable food production in sub-Saharan Africa. This study investigates the effect of hill-placement of two nutrient sources (farmyard manure and synthetic fertilizer) on nutrient- and water-use efficiencies of maize crops i.e. recovery efficiency (NUEre), internal utilization efficiency (NUEie) and water use efficiency (WUE). A four-year trial was conducted in the tropical sub-humid zone of the northern Benin with a factorial combination of farmyard manure at three levels (0, 3 and 6 t ha⁻¹, hereafter NM, 3M and 6M, respectively) and three levels of fertilizer [0% (NF), 50% (50F) and 100% (100F) of the recommended rate (76 kg N + 13.1 kg P + 24.9 kg K ha⁻¹) by the national center for agricultural research. The NUEre decreased with increasing rate of manure and/or fertilizer, but the decreasing rate was lower under combined manure and fertilizer application. However, the NUEie increased with the increasing manure and fertilizer amounts. The WUE was significantly higher in 3M and 6M treatments than in NM treatment, and higher in 50F and in 100F than in NF treatments. The combination of 3000 kg ha⁻¹ farmyard manure with half recommended fertilizer rate (100 kg ha⁻¹) could be suggested as an optimal nutrient management practice for maize production in the Northern Benin. Future studies should target the other agro-ecological zones in Benin, and also consider other widely cultivated crops in the study area for reducing yield gaps and promote food security.