Effets des changements climatiques et des modes de gestion sur la fertilité des sols dans la commune de Banikoara au nord-ouest du Benin

Le présent diagnostic réalisé dans la commune de Banikoara vise à étudier les effets des changements climatiques et des modes de gestion sur la fertilité des sols. A cet effet, les caractéristiques morphologiques et physico-chimiques de 6 unités de sols répétées 3 fois dans 3 différents arrondissements ont été déterminées et comparer à ces mêmes caractéristiques déterminées en 1971. Les résultats d’analyses physicochimiques ont été soumis à des analyses statistiques. Il ressort de l’étude des 2 séries de caractéristiques constituées de ces résultats que les taux de matière organique des différentes unités pédologiques de la Commune de Banikoara ont varié très significativement entre 1971 et 2010 (p<0,01). Cependant, ces taux de matière organique n’ont pas varié significativement suivant les unités pédologiques (p>0,05). Il en est de même pour les taux d’azote des différentes unités pédologiques qui ont connu une variation très significative entre la période de 1970 et 2013 (p<0,01) mais n’ont pas varié significativement d’une unité à l’autre dans la même série. Les résultats d’analyse de la variance indiquent que les teneurs des bases échangeables et de la capacité d’échange cationique ont varié significativement (p <0,01) entre 1971 et 2010 et suivant les unités pédologiques (p<0,01). Les changements climatiques ont donc eu un impact négatif très significatif sur la fertilité des sols pendant les 40 années d’exploitation, alors que les modes de gestion des sols n’ont induit entre eux aucune différence significative au niveau de la matière organique et de l’azote, paramètres majeurs de la fertilité des sols. Par ailleurs, les niveaux de fertilité des unités pédologiques sont passés de moyen en 1971 à très bas en 2010 en dehors des sols hydromorphes et des sols ferrugineux hydromorphes sur roche basique dont les niveaux de fertilité sont restés moyens et moyen à bas respectivement.© 2016 International Formulae Group. All rights reserved.Mots clés: Changements climatiques, niveau de fertilité, carbone, azote, hydromorphe, ferrugineuxEnglish Title: Impact of climate change and types of soil management on soil fertility in Banikoara municipality at the North West of BeninEnglish AbstractThe soil survey conducted throughout the Banikoara municipality within the diagnostic effects of climate change on soil fertility was used to determine the morphological and physico-chemical characteristics  of six soil units repeated three times in three different districts and compare them to those same characteristics determined in 1971, 40 years earlier. It appears from the study of two sets of characteristics through statistical analyzes made from these results that the rate of carbon or organic matter in different soil units of the municipality of Banikoara has varied significantly between 1970 and 2010 (p<0.01). However, the carbon content did not vary significantly between the soil units (p>0.05). It is the same for the different soil nitrogen units that have experienced a very significant variation between the period 1971 and 2010 rates (p<0.01) but did not differ significantly between one unit to another in the same series. The ANOVA results indicate that the levels of exchangeable bases (BE) and cation exchange capacity (CEC) varied significantly (p <0.01) between 1971 and 2010 and according to the soil units (p<0.01). Climate change has thus had a significant negative impact on soil fertility during the 40 years of operation, while the modes of land management did not induce a significant difference between them in terms of organic matter and nitrogen major parameters of the soil fertility. Furthermore, levels of fertility soil units went from average in 1971 to very low in 2010 out of waterlogged soils and waterlogged ferruginous soils on basic rock whose fertility levels have remained low medium and medium respectively.© 2016 International Formulae Group. All rights reserved.Keywords: Climate change, soil fertility, carbon, nitrogen, hydromorphic, ferrugenou

Dynamique de la matière organique et de l'azote dans le système Mucuna-maïs sur un sol ferrallitique (terres de barre) au Sud-Bénin

Depuis des décennies, les sols du Bénin sont en proie à une dégradation importante suite à leur surexploitation. Cette dégradation affecte tout particulièrement les sols ferrallitiques sableux à argilo-sableux du sud-Bénin appelés "terres de barre". Ce qui entraine une baisse constante des rendements et menace l'autosuffisance alimentaire. Pour restaurer ces sols dégradés, de nombreux systèmes de culture sont mis en essai aussi bien en station qu'en milieu paysan. Notre étude compare quatre systèmes de culture pendant huit ans ; le système Mucuna-maïs (M1) où le Mucuna, une légumineuse de couverture, est renouvelé tous les ans ; le système de fertilisation minéral (NPK) avec 76 N, 30 P et 30 K ; le système Mucuna-maïs où le Mucuna est renouvelé tous les deux ans (M2) et le système traditionnel (T) d'agriculture minière où le sol ne reçoit que les restitutions végétales. Après huit ans d'essai, le système Mucuna-maïs (M1) s'est révélé, en terme de productivité végétale et d'amélioration de certaines propriétés physico-chimiques du sol, une alternative particulièrement intéressante pour la gestion des terres dans le sud Bénin, non seulement par rapport aux systèmes traditionnels (T), mais aussi par rapport aux systèmes plus intensifiés avec fertilisation chimique (NPK). (AZONTONDE et al., 1998). Globalement, les taux et stocks de C diminuent de la surface vers la profondeur du sol. Et si l'on se réfère aux modes de gestion des sols, le sens de variation des teneurs ou stocks en C organique est le suivant : M1 est supérieur à M2 = NPK est supérieur à T. Par ailleurs, le rendement en maïs est étroitement corrélé avec C de la couche 0-10 cm (r=0.98) qui peut donc servir, pour ces systèmes d'indicateur de fertilité... (D'après résumé d'auteur

Ecological and silvicultural indicatory value of plant-communities of Koto forest reserve (Centre-Benin)

A study was carried out in Koto forest reserve in central Benin (6°56’ to 7°02’ of north lat. and 02°03’ to 02°09’ of east long), in order to contribute to the sustainable management of the forest. Phytosociological inventory was done using the synusial approach. Soils were studied through texture surveys, pedological profiles description and laboratory analysis. Silvicultural parameters of plantations were studied using temporary sample plots of 300 m². The study helps to identify and describe twenty-two basic plantcommunities named synusia. Based on their relationships, the synusia have been combined to describe seven phytocoenoses (plant-communities). Each non pioneer phytocoenose is an expression of specific ecological conditions. The study of plantation productivity has shown remarkable homogeneity of productivity level within each non pioneer phytocoenose. Analysis of variance reveals a significant difference at 5% of probability level between the productivity levels of the phytocoenoses. Three productivity levels are identified according to phytocoenoses. The study leads to the conclusion that phytosociology is a reliable tool for forest management

Effet des pratiques de conservation du sol sur la croissance et les composantes du rendement du mais dans le bassin versant de Lokogba au Benin

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, watershe

Farmers’ Perceptions on Soil Degradation and Their Socioeconomic Determinants in Three Watersheds of Southern Benin

Soil degradation is one of the most serious ecological and environmental problems in south of Benin. Understanding farmers’ perceptions of soil degradation and its causes is important in promoting soil and water conservation practices. The objective was to examine farmers’ perceptions, understanding and interpretation of soil degradation factors and socioeconomic characteristics that influence these perceptions. A survey was conducted in Allada, Aplahoué and Djidja districts, which had respectively the watersheds of Govié, Lokogba and Linsinlin in southern Benin. The study was based on the data obtained from 427 sample households heads using pre-tested structured interview schedule. The data were analyzed using simple descriptive statistics and frequencies with the chi-square test. The finding of the study shows that almost all farmers of the study area had good perception on the causes, indicators and problems of soil degradation. Farmers explained soil degradation as soil fertility depletion and soil erosion (soil loss). The main causes of soil erosion perceived by farmers were slope, runoff, rain intensity and duration. According to the farmers, the soil fertility depletion is mainly caused by deforestation, bushfires, continuous cropping, soil type and animal trampling. Several socioeconomic characteristics influence significantly the farmers’ perceptions as gender, literacy, agricultural extension and/or membership of farmers’ organization. The farmers’ perceptions vary significantly according to cropping systems, therefore, from village to village, with their socioeconomic determinants. Keywords: Farmers’ perceptions, soil degradation, soil erosion, soil fertility decline, socioeconomic determinants, southern Benin

Effect of a legume cover crop on carbon storage and erosion in an ultisol under maize cultivation in southern Benin

Field experiment was conducted from 1988 to 1999 at an experimental farm at Agonkanmey, near Cotonou in southern Benin, to study the effect of relay-cropping maize through Mucuna pruriens (var. utilis). The relay-cropping system was compared with traditional maize cropping system without any input, and with a maize cropping system with mineral fertilizers (NPK). Special attention was given on the changes in soil C during the period of the experiment in relation to residue biomass C returned to the soil, runoff and soil erosion losses, and loss of C with erosion. The soils are classified as sandy loam Typic Kandiustult. The general properties of these soils are given. For this soil type, relay cropping of maize and mucuna was very effective in enhancing C sequestration: change in Ct (total C content) stock for 0 to 40 cm depth was 1.3 t C/ha per year over the 12-year period of the experiment, ranging among the highest rates recorded for the eco-region. This increase resulted first from the high amount of residue biomass provided by mucuna, which amounted to 10 t DM/ha per year (83% aboveground). Mucuna residues, supplying the soil with N, also favoured the production of maize biomass, and total mucuna plus maize residue biomass returned to the soil was approximately 20 t/ha per year. In contrast, non-fertilized and fertilized continuous maize cultivation resulted in -0.2 and 0.2 t C/ha per year change in Ct stock for 0 to 40 cm depth, respectively. Total residue biomass was 8 and 13 t/ha per year, including 77 and 29% by weeds, respectively. Thick mulch produced by mucuna decreased losses by runoff and erosion, which were 0.28, 0.12 and 0.08 mm/mm and 34.0, 9.0 and 3.0 t/ha per year in unfertilized, fertilized with NPK and mucuna treatments, respectively. Eroded C was estimated at 0.3, 0.1 and 1.0 t C/ha per year in unfertilized, fertilized with NPK and mucuna treatments, respectively. Through its benefits on soil organic matter management, weed suppression and erosion control, cropping systems including a legume crop may have an adverse impact from a global change standpoint

Mapping the risk of soil erosion using RUSLE, GIS and remote sensing: a case study of Zou watershed in central Benin

Being aware that soil erosion is one of the major environmental problems of the 21st century, this research integrates the Revised Universal Soil Loss Equation (RUSLE) with a Geographic Information System (GIS) to assess erosion risk on Zou watershed in the centre Benin. RUSLE factor values (rain erosivity, soil erodibility, slope length and steepness, cover and support practices) for the study area were determined and spatialized. The rain erosivity (R-factor) was estimated based on the daily rainfall data from five rain gauges installed in the watershed. The slope length and steepness (LS-factor) were extracted from the Digital Elevation Model of the watershed. The soil erodibility (K-factor) calculation was based on the percentage of fine sand, silt, clay and organic matter in the soil as well as the water infiltration rate. 120 representative sampling points were taken into account in the different soil-mapping units of the watershed. The land cover factor (C factor) estimation was based on the Normalized Difference Vegetation Index (NDVI). The NDVI was calculated from a 30 m resolution Landsat-8 image. The adopted support practices on the watershed were investigated. The values of the P factor were attributed to each practice based on literature review. Data sets for the RUSLE factors, along with associated maps showing geographic distributions, were established on ArcGIS. ArcGIS was used to interactively calculate soil loss and map the erosion risk. The mean R-factor value was 915 MJ.mm.ha-1.year-1. The spatial distribution of the C-factor showed that 81.0% of the surface has low protection, 8.6% has medium protection and 11.0% had from good to very good protection against water erosion. The LS-factor value ranged from 0 to 39 in the watershed. The mean soil erodibility is 0.15 t.h.MJ-1.mm-1 over the watershed. The average erosion, for the watershed is 16.2 t.ha-1.year-1 which corresponds to a very high vulnerability level. The watershed area affected by low, moderate, high and very high erosion risk are respectively 3.1%, 22.4%, 22.9% and 51.6%. However, most of the eroded soil is from the area with low vegetation cover, high soil erodibility and with moderate and Gentle undulating. The findings of this study could constitute a baseline for any future development of the watershed. Keywords: Soil Erosion, USLE, GIS, Zoo Watershed, Beni

Effect of a legume cover crop (Mucuna pruriens var. utilis) on soil carbon in an ultisol under maize cultivation in southern Benin

Long term fallow is no longer possible in densely populated tropical areas, but legume cover crops can help maintain soil fertility. Our work aimed to study changes in soil carbon in a sandy loam Ultisol in Benin, which involved a 12-year experiment on three maize cropping systems under manual tillage: traditional no-input cultivation (T), mineral fertilized cultivation (NPK), and association with Mucuna pruriens (M). The origin of soil carbon was also determined through the natural abundance of soil and biomass C-13. In T, NPK and M changes in soil carbon at 0-40 cm were -0.2, +0.2 and +1.3 t C ha(-1) yr(-1), with residue carbon amounting to 3.5, 6.4 and 10.0 t C ha(-1) yr(-1), respectively. After 12 years of experimentation, carbon originating from maize in litter-plus-soil (0-40 cm) represented less than 4% of both total carbon and overall maize residue carbon. In contrast, carbon originating from mucuna in litter-plus-soil represented more than 50% of both total carbon and overall mucuna residue carbon in M, possibly due to accelerated mineralization of native soil carbon (priming effect) and slow mulch decomposition. Carbon originating from weeds in litter-plus-soil represented c. 10% of both total carbon and overall weed residue carbon in T and NPK. Thus mucuna mulch was very effective in promoting carbon sequestration in the soil studied