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Les pratiques d’une agriculture de conservation visant une couverture permanente du sol suivie de la réduction du travail du sol pourrait être une innovation dans les stratégies paysannes pour une agriculture durable. La présente étude a pour objectif d’évaluer l’effet du mode de travail du sol et du mulching sur les performances agronomiques du maïs semé sur le bassin versant de Lokogba, à Aplahoué. Un essai en Bloc Complètement Randomisé à quatre répétitions et 8 traitements (Semis direct, Minimum labour, Labour à plat, Billonnage, Semis direct + Mulch en surface, Minimum labour + Mulch en surface, Labour à plat + Mulch en surface, Billonnage + Mulch surface) a été installé. Les résultats indiquent que le travail du sol a affecté significativement les performances agronomiques du maïs au seuil de 5 %. Le semis direct a enregistré les valeurs les plus faibles des paramètres (2,66 cm/j de vitesse de croissance, 65,81 cm2 d’indice foliaire, 797,8 kg MS/ha de grains et 911,8 kg MS/ha de pailles de maïs) contre le billonnage qui a enregistré les meilleures performances (3,62 cm/j de vitesse de croissance, 120 cm2 d’indice foliaire, 2175,4 kg MS/ha de grains et 2475,4 kg MS/ha de pailles de maïs). L’indice de récolte et le diamètre au collet des plants les plus élevés 0,4 % et 1,37 cm, respectivement, ont été obtenus avec le labour à plat. Le mulching a amélioré le diamètre au collet des plants de 1,28 à 1,37 cm, l’indice foliaire de 73,05 à 114,02 cm2 (p < 0,0001) et la vitesse de croissance des plants de 2,91 à 3,75 cm/j (p < 0,0001). Le rendement en grains est passé de 1020,5 kg MS/ha sans couverture de mulch à 2138,1 kg MS/ha avec couverture de mulch et l’indice de récolte de 31,1 à 41,1 p.c. La combinaison des deux facteurs n’a toujours pas donné un effet significatif sur les performances agronomiques du maïs. Quels que soient le mode de travail du sol et la couverture ou non de mulch, le rendement en grains dépend significativement de l’indice de récolte, des spathes et des pailles du maïs (100r2 = 95,34).Mots clés: Semis direct, labour, mulching, maïs, bassin versantEnglish Title: Effect of soil conservation practices on maize productivity in Lokogba watershed in BeninEnglish AbstractConservation agriculture with permanent soil covering could be an innovation in farming practices dealing to sustainable agriculture. This study aims to evaluate the effect of tillage and mulching on the agronomic performance of maize, planted in the watershed of Lokogba in Aplahoué. A randomized completed bloc design with four replications was chosen. Eight treatments were concerned in the trial as followed: Direct sowing, Minimum tillage, Tillage, Conventional tillage, Direct sowing + Mulch on surface, Minimum tillage + Mulch on surface, Tillage + Mulch on surface, Conventional tillage + Mulch on surface. Results indicated that tillage significantly affected the agronomic performance of maize. Direct seeding recorded the lowest parameters (2.66 cm.day-1 of growth rate and 65.81 cm2 of leaf area index, 797.8 kg DM.ha-1 of grain and 911.8 kg DM.ha-1 of maize straw) against conventional tillage with the best performance (3.62 cm.day-1 of growth rate and 120 cm2 of leaf area index, 2175.4 kg DM.ha-1 of grain and 2475.4 kg DM.ha-1 of maize straw). The highest harvest index and collar diameter of plants (0.4% and 1.37 cm, respectively) were obtained with the tillage. Mulching improved the collar diameter of plants from 1.28 to 1.37 cm (but no significantly), the leaf area index from 73.05 to 114.02 cm2 (p < 0.0001) and the growth rate from 2.91 to 3.75 cm.day-1 (p < 0.0001). The grain yield increased from 1020.5 kg DM.ha-1 without mulch to 2138.1 kg DM.ha-1 with mulch and harvest index from 31.1 to 41.1 %. The combination of both factors have not a significant effect on the agronomic performance of maize. Whatever the type of tillage and with or without mulch, the grain yield significantly depends on the harvest index, husk and maize straw (100r2 = 95.34).Keywords: Direct seeding, tillage, mulching, maize, watershed

The Volta River and its basin form about one-third of Ghana's total land area and contributes significantly to the hydrological network of the country’s river system while River Pra basin is noted for large and small scale mining activities within it. Both river systems are important for sediment delivery for beach nourishment along Ghana’s coast. This work presents the first ever estimates of the sedimentation rates at the estuaries of these rivers using 40 cm long sediment cores. Sediment accumulation rates were estimated using the 210Pb sediment dating technique which is based on alpha and gamma emitting radionuclides. The total 210Pb concentration in the sediment was measured with an alpha spectrometer while the activities of supported 210Pb and 137Cs were measured with a gamma spectrometer with high germanium n-type detector. The unsupported 210Pb was determined by subtraction of the supported from the total at each core sediment level. Irregularities in the 210Pb activity versus depth profile, indicated variation in the net sedimentation accumulation rate during the past 96 and 182 years at the Volta and Pra estuaries, respectively. From the CRS model calculations, sedimentation rates varied markedly before (1.1 gcm-2y-1) and after (0.5 gcm-2y-1) construction of the Akosombo dam resulting in about 50% drop in sedimentation rate at the Volta estuary. Sediment accumulation rates were relatively low at the Pra estuary compared to the Volta estuary. Depositional fluxes of 210Pb were 190.1 ± 15.9 Bqcm-1y-1 and 217.8 ± 11.8 Bqcm-1y-1 in Pra and Volta estuaries respectively. 137Cs profile did not show defined peaks. However, the ages and sedimentation rates were better explained using historical events and anthropogenic activities that occurred within the catchment areas, providing a better understanding of deficit in sediment budget caused by hydric erosion processes prevailing in the Ada and Keta beaches in Ghana, due to reduction of sediment input from the Volta estuary.