Ngong is a famous groundnut (Arachis hypogaea L.) producing locality in Cameroon, contributing to the supply of local markets and neighboring countries. Official figures showed gradual yield decrease over recent years, attri- butable to various factors, with poor soil conditions among the most acute. However, missing information on soil quality and fertility status in these areas is jeopardizing efforts of improving agricultural productivity. This study aimed to assess the soil fertility status in the groundnut production basin of Ngong. Three main ground-nut production areas (Douka-longo, Tamound & eacute;1, and Sabongari) of the basin were selected and twenty-three topsoil samples (0 - 30 cm) collected. Soil fertility attributes (index of structural stability (ISS), index of soil sealing (IB), Forestier index (IF), aluminium toxicity (m) and Soil Quality Index (SQI)) were assessed. The studied sites were effectively poor in soil fertility, having very low values of N, P, K, S, and cation exchange capacity (CEC). These soils are under high risk of degradation because of the low soil aggregate stability (ISS < 9%) and fertility (IF < 1.5) indexes. The SQI ranged from 0 to 0.4 indicative of poor fertility with degraded soil condition. The main factors controlling soil quality include Ca, pH, organic matter (OM), available P, total Nitrogen and CEC. Longterm maintenance of soil quality requires better integrated soil fertility management practices. Optimal soil nutrients management system such as the application of organo-mineral amendments rich in N P, K, Ca and Mg to promote plant root establishment, which will also improve the soil structure should be considered to enhance the soil fertility status along with the inclusion of good cultivars for yield improvement.

Soil degradation emerges as one of the major problems in the locality of Sir in the Mandara Mountains, Far-North Cameroon. Inappropriate agricultural techniques resulting in land use change affect soil functions and seriously harm forest ecosystems. This study was conducted to analyse the current character of soils and access their degradation and their level of fertility. Twenty soil samples were taken at 15 cm depth. This includes ten in the plot under forest reserve and ten others in the plot under cultivation. Cultivation is responsible for the increase in bulk density (BD) (1.59 to 2.23 g/cm3), Mg (4.76 to 6.40 cmol·kg−1), Ca (10.44 to 11.26 cmol·kg−1), P (7.93 to 9.93 g/kg), and Mg/K (2.28 to 5.84) and decrease in CEC (38 0.15 to 31.46 cmol·kg−1), OM (2.76 to 1.08%), OC (1.66 to 0.62%), total nitrogen (0.08 to 0.05%), K (4.59 to 1.15 cmol·kg−1), Na (1.32 to 0.91 cmol·kg−1), C/N (25.69 to 13.86), and Ca/Mg (2.32 to 1.89). This variability in physicochemical properties reflects progressive soil degradation. Cultivated soils are subject to severe degradation or potential vulnerability (SDR/Vp = 4/2) due to texture, organic carbon, soil aggregate stability, sealing index, and total nitrogen. On the other hand, soils under forest reserve are subject to severe degradation or vulnerability due to the total nitrogen and sodium absorption ratio. The soils of the study area are subject to severe and extreme potential degradation or vulnerability due to BD, respectively, under forest reserve and cultivation. Two classes of fertility were identified: class II (plots under forest reserve) having a good level of fertility, characterized by good physical properties and severe limitations in nitrogen and phosphorus and class IV (cultivated plots) with a low level of fertility due to severe limitations in organic matter, phosphorus, and poor physical characteristics. The best indicator of the good quality of the luvisols of Sir is the pH, while the bulk density is an indicator of severe to very extreme degradation or high to very high vulnerability. The application of organic and mineral amendments is essential for raising the organic matter and nitrogen and phosphorus contents in these soils.

Climate disruption has serious impact on the entire agricultural production system at global scale. Research and development efforts as well as innovations may be necessary to offset the negative impact of climate change. Adaptation to climate change has remained a major socio-ecological issue in the Northern Region of Cameroon for three decades. Several agricultural innovations have been promoted in this region by international organizations and NGO, within the framework of different projects and programs, with a strong potential for adaptation to climate change. However, little is still known about agricultural innovations that have evolved over time in response to climatic factors. Therefore, research aiming at identifying adaptation strategies and practices at the local level is still limited. Also, rural communities and households do not always have access to these agricultural innovations because of lack of efficient innovation support service for agriculture. Through surveys and focus group discussions carried out in several villages in the Northern Cameroon Region, this study provides empirical data on emerging agricultural innovations in contrasting socio-economic, agricultural and ecological contexts. The study demonstrated that the process of adaptation at the village level using agricultural innovations is the result of various forms of support provided by a diversity of actors. However, heads of household (83%) are more involved in innovative initiatives to the detriment of other social strata, resulting in an imbalance in access and proximity to agricultural innovations. Also, support for agricultural innovations is segmented over time and weakens the sustainable transformation of adaptation due to the lack of coordination and the very low visibility of permanent structures dedicated to supporting agricultural innovations.

This study was focused to assess major and trace elements in bauxitic duricrusts from Ngaoundal and its surroundings in order to establish their mining interest. To this end, fieldworks, mineralogical and geochemical analyses were carried out. Four facies of duricrust were identified and characterized from the summit to the top of the slope of the Ngaoundal mountain: scoriaceous, pisolitic, nodular and massive. Mineralogical and geochemical analyses performed on 16 samples, revealed a significant concentration of Al2O3 mainly in the scoriaceous facies (over 45% in grade), moderate in Fe2O3 (averaging 23.69%) and SiO2 (averaging 21.7%). Trace elements were generally low, excluding Cr (421 ppm on average), Zr (327 ppm on average and V (213 ppm on average). In addition, the limited quantities of alkalis (Na2O, K2O) and alkaline earths metals (MgO, CaO) coupled with the very high values of Chemical Index of Alteration (CIA) and Mineralogical Index of Alteration (MIA), (more than 99%) attest to the intense weathering of the studied materials. Allitization and monosiallitization constituted the crystallochemical phenomena that have led to the development of bauxitic minerals. More than 90% of gibbsite in scoriaceous facies, 52.21% - 76.01% of kaolinite in pisolitic facies and more than 40% of hematite in nodular facies were quantified. The relationships between the constitutive components indicated their interdependency during the bauxitization phenomenon. The mineralogical and geochemical properties highlighted the mining interest of the studied duricrusts to be valorized.

Adaptation to climate change has remained a major socio-ecological issue in the Northern Region of Cameroon since 1973. Presently, this region is subject to the severe chaos of drought, floods, and ecosystem degradation, causing harm and disrupting climatic patterns. Climate change results in the drying of surface water and crops, threatening food security and the well-being of households. It has a serious impact on the entire agricultural production system at global scale. Here, it is suggested that successive adjustments to deeper systemic and transformational adaptations through efforts from NGOs, the Government, and donors, as well as innovations, are necessary to offset the negative impact of climate change on the agricultural value chain. Therefore, this research aimed to identify adaptation strategies and practices for rural communities and households, who suffer from limited access to these agricultural innovations, for a transformative adaptation. Through surveys and focus group discussions carried out in several villages in the Northern Cameroon Region, this study provides empirical data on emerging agricultural innovations in contrasting socio-economic, agricultural, and ecological contexts. Our findings demonstrate that agricultural innovations fostered at the village level have several characteristics that contribute to adaptation and mitigation of the impact of climate change. To begin with, conservation agriculture is very interesting, because crop residues left on the soil protect it from rainfall and dry winds, and gradually add humus to the top soil. In addition, agroforestry plays an important role for the household regarding ecosystem services, including food supply, soil fertility, protection from erosion, regulation of water regime, and sociocultural value. Generally, heads of households (83%) were more involved in innovative initiatives than other social strata, resulting in unequal access and proximity to agricultural innovations. Furthermore, the results highlight a significant lack of coordination and poor visibility of permanent structures supporting agricultural innovations at local level, weakening the sustainable transformation of adaptation. From a scientific perspective, this study could help build a conceptual relationship between agricultural innovation and sustainability transformation, i.e., a climate-smart agriculture. In practice, it provides levers that can be used to multiply and expedite agricultural innovation processes, water conservation, and livestock sustainability, thus contributing to the sustainability of the whole agricultural system in Cameroon and within the Sahel region of Africa.

Le riz est une céréale cultivée et consommée partout en Afrique. Au Cameroun, il est cultivé en système irrigué, pluvial et bas fond. Sa production par an estimée à 360 000 t, est très inférieure à la demande estimée à environ 800 000 t de paddy. L’Est – Cameroun présente des riches potentialités favorables à la riziculture pluviale, qui reste cependant faiblement pratiquée. Pour cette étude, l’objectif est d’identifier les causes qui freinent la pratique de la riziculture dans cette région potentiellement favorable. Des bassins de productions du riz ont été identifiés par la Délégation Régionale de l’Agriculture et de Développement Rural de l’Est (DRADERE) et la Station Polyvalente de Recherche Agricole de Bertoua (SPRAB) dans les départements de la Kadey, de Lom et Djerem et du Haut Nyong. Ainsi 200 producteurs ont été enquêtés dans 25 villages afin d’identifier les facteurs qui limitent la pratique de la riziculture dans cette région. Il ressort que le rendement moyen régional est de 1,7 t/ha, alors qu’ils sont de 2,2 t/ha dans la Kadey, 1,6 t/ha dans le Lom et Djerem et de 1,2 t/ha dans le Haut Nyong. Les contraintes telles que la baisse de fertilité des sols, les oiseaux ravageurs, la qualité de semence, le traitement post - récolte (TPR), la non maitrise de l’itinéraire technique (ITK), les maladies, les insectes ravageurs, le stress hydrique et la destruction par les hérissons ont été révélées dans tous les trois départements. Cependant, la baisse de fertilité des sols, les oiseaux ravageurs et le traitement post - récolte sont identifiées comme contraintes principales alors que la destruction des hérissons et le déficit hydrique sont des contraintes mineures. Pour réussir la riziculture à l’Est-Cameroun, il faudrait tenir compte de toutes ces contraintes de production qui peuvent compromettre le rendement. Abstract Rice is a cereal grown and consumed everywhere in Africa. In Cameroon, it is grown in irrigated, rainy and lowland system. Its production per year estimated at 360 000 t is much inferior to the estimated demand for about 800,000t of paddy. East - Cameroon has rich potential favorable to upland rice cultivation, which is however weakly practiced. For this study, the objective is to identify the causes that hinder the practice of rice growing in this potentially favorable region. Rice production pools have been identified by the Regional Delegation of Agriculture and Rural Development of Bertoua (RDARDB) and Bertoua Polyvalent Agricultural Research Station (BPARS) in the Kadey division, Lom and Djerem division and Haut Nyong division. Thus 200 producers have been administered questionnaire in 25 villages to identify the factors that limit the practice of rice growing in this region. This study shows that the regional means is 1,7 t/ha, meanwhile in the Kadey Division we have 2,2 t/ha, in the LOM and Djerem Division we have 1,6 t/ha and 1,2 t/ha in Haut Nyong Division. Several constraints have been revealed in the tree divisions, such as: low soil fertility, bird’s damages, seed quality, post-harvest treatment, no mastery of farming technique, diseases, pests, water stress, and hedgehog destruction. However, low soil fertility, bird’s damages and the post - harvest treatment (PHT) are primarily identified, whereas hedgehog destruction and water stress are minor. To succeed rice cultivation in East - Cameroon, it is better to be aware of constraints which could lower the yield.

The sandy-loam soils of the Sudanian zone of Chad were subject to increased depletion. One of the solutions to this problem of declining soil fertility would be to apply a reasoned organic fertilisation. The aim of this study was to evaluate the fertilising potential of biochar and compost on this depleted soil and to determine the optimal doses and the best periods of application on maize. Seven treatments with inputs such as two weeks before sowing, during sowing and two weeks after emergence were conducted in controlled environment : the control, soil + 5tha-1 of biochar, soil + 7.5tha-1 of biochar, soil + 10tha-1 of biochar, soil + 5tha-1 of biochar + 5tha-1 of compost, soil + 7.5tha -1 of biochar + 5tha-1 of compost, soil + 10tha-1 of biochar + 5tha-1 of compost. Each treatment was repeated four times. Eight agro-morphological variables were evaluated: vigour of plant, harvested plant ratio, cob circumference, cob length, cob weight, plant height on maturity, weight of one thousand grain and aerian biomass yield. These variables showed that growth and yield are clearly improved on fertilized treatements whatever dose and bringing period (in average: 3 ≤ VIG ≤ 7, 41.7 ≤ TPR ≤ 91.7%, 7.9 ≤ CIE ≤ 11.4 cm, 66.4 ≤ POE ≤ 83.4g, 115.2 ≤ PMG ≤ 187.3g) comparatively to control (VIG = 3, TPR = 25%, CIE = 6.5 cm, POE = 51.9g, PMG = 102g). These results confirmed more the importance of biochar and compost on soils fertilisation. The treatment at two weeks before seedling for 10tha1 of biochar alone and 10tha-1 of biochar+5tha-1 of compost were judged the best indicated to be applied in the field like alternative to chemical fertiliser for the best maize productivity in the sudanian zone of Chad. English title: Détermination des doses optimales et des périodes d’apport de biochar et de compost sur la productivité du maïs dans la zone soudanienne du Tchad Les sols sablo-limoneux de la zone soudanienne du Tchad sont sujets aux phénomènes d'appauvrissement accru. L'une des solutions pour palier à ce problème de baisse de fertilité des sols serait d'apporter une fertilisation organique raisonnée. Cette étude avait pour but d’évaluer le potentiel fertilisant du biochar et du compost sur ce sol appauvri et déterminer les doses optimales et les meilleures périodes d’apport sur du maïs. Sept traitements aux apports à deux semaines avant le semis au semis et deux semaines après la levée ont été conduits en milieu contrôlé : sol témoin, sol + 5t/ha de biochar, sol + 7,5t/ha de biochar, sol + 10t/ha de biochar, sol + 5t/ha de biochar + 5t/ha de compost, sol + 7,5t/ha de biochar + 5t/ha de compost, sol+10t/ha de biochar + 5t/ha de compost. Chaque traitement a été répété quatre fois. Huit variables agromorphologiques ont été évaluées : vigueur de la plante à la levée, taux des plantes récoltées, circonférence de l’épi, longueur de l’épi, le poids de l’épi, hauteur de la plante à maturité, poids de mille grains, rendement de biomasse aérienne. Ces variables ont montré que les croissances et les rendements sont nettement améliorés dans les traitements fertilisés au biochar et compost quelques soit la dose et la période d’apport (en moyenne : 3 ≤ VIG ≤ 7, 41,7 ≤ TPR ≤ 91,7%, 7,9 ≤ CIE ≤ 11,4 cm, 66,4 ≤ POE ≤ 83,4g, 115,2 ≤ PMG ≤ 187,3g) comparativement au témoin (VIG = 3, TPR = 25%, CIE = 6,5 cm, POE = 51,9g, PMG = 102g). Ces résultats confirment davantage l’importance capitale du biochar et du compost dans la fertilisation des sols. Les traitements à deux semaines avant le semis pour les doses de 10t/ha de biochar seul et de 10 t/ha de biochar+5t/ha de compost ont été jugées les mieux indiquées à être appliquées en champ en alternatif aux engrais chimiques pour une meilleure productivité de maïs en zone soudanienne du Tchad.

The objective of this study is to evaluate the effects of the application of biochar and rice husk powder combined with mineral fertilizer on the yield of the CMS-9015 variety of maize (Zea mays) and fertility. soils. The field experiment with three replicates covered 18 plots of 2.5 m × 2 m each arranged in a randomized random block design. The base treatment in all plots excepted null control T0 (without fertilizer or amendment) was the fertilizer dose NPK + Urea in full dose and half dose: T1: 100 kg NPK ha-1 + 50 kg N ha-1 (advisable treatment); T2 = 15 t (biochar) ha-1 + 100 kg NPK ha-1 + 50 kg N ha-1; T3 = 15 t (powder) ha- 1 + 100 kg NPK ha-1 + 50 kg N ha-1; T4 = 15 t (biochar) ha-1 + 50 kg NPK ha-1 + 25 kg N ha-1 and T5 = 15 t (powder) ha-1 + 50 kg NPK ha-1 + 25 kg N ha-1. The agronomic parameters of maize and its yield as well as the physico-chemical properties of the soils after harvest were measured in these plots. The results were analyzed by STATGRAPHICS followed by the Fisher multiple comparison test (α = 0.05). The application of biochar and powder on this soil resulted in an increase in maize yield of +54.64%, +38.46% and +45.88% respectively with treatments T2, T3 and T4 compared to the recommended treatment (T1). The same positive effect was observed on the soil after harvest compared to the recommended treatment for available phosphorus: 8.67 ± 0.19 mg/kg (with biochar) and 6.34 ± 0.21 mg/kg (with the powder) together with the CEC: 22 ± 4.94 meq/100 g with the powder. Biochar and rice husk powder help rehabilitate soil fertility and increase agricultural productivity when combined with chemical fertilizers. They can ensure sustainable agricultural production.

The present work was designed to study a soil sequence in Mount Mandara, in order to identify the influence of altitude, soil characteristics, and land use on the accumulation of soil organic carbon (SOC). The study was conducted in four sites in the Far-North region of Cameroon, including Zamai, Kossohone, Sir, and Rhumsiki. Three pits were dug down to the weathering horizons in three positions (upslope, mid-slope, and footslope) along a representative toposequence in each site. Samples were taken from each pit at regular increment of 25 cm from the soil surface. The total SOC stock (T-SOCS) contents are 128.63 ± 5.25 Mg ha−1 in Arenosols at Zamai (608 m a.s.l.), 158.248 ± 10.52 Mg ha−1 in Leptosols at Kosohone (865 m a.s.l.), 158.99 ± 13.25 Mg ha−1 in Luvisols at Sir (970 m a.s.l.), and 144.79 ± 24.23 Mg ha−1 in Regosols at Rhumsiki (1050 m a.s.l.). The main secondary minerals are smectite, kaolinite, sepiolite, lepidocrocite, hematite, and calcite. Clay minerals and iron oxides are good receptacle for SOC and might constitute a major asset for the accumulation and the sequestration of SOC. Increase in elevation leads to decrease in the annual temperature which affect microbial activity, leading thus to a slow rate of soil organic matter (SOM) decomposition, which thereby affected SOCS. This is confirmed by the significant correlation between altitudinal gradient and T-SOCS (r = 0.70), with altitude contributing to the accumulation of SOC for 49.68%. Texture also plays a central role in carbon sequestration in the studied area, confirmed by the significant and positive correlation between silt fraction and SOM. Under Regosols, there is a decrease in T-SOCS value as a result of a reduction of the quantity of organic matter returned to the soil and more rapid SOM decomposition due to ploughing. This research provides a preliminary assessment for SOC stock at Mount Mandara. It suggests that altitudinal gradient, land use, and soil characteristics should be included in SOCS models and estimations at local and regional scales.

The present study aims at assessing the fertilizing potential of basalts on impoverished oxisoils from Ngaoundéré (Adamawa, Cameroon). This specifically involves the application of finely ground basalts on impoverished oxisoils and monitoring changes in physicochemical properties during six months. An experimental design which consisted in a randomized complete block design is constituted of three series of four treatments each one: the control (ST), the control soil mixed with 100 g of finely ground basalt (T0 + BA_10), the control soil mixed with 200 g of finely ground basalt (T0 + BA_20), the control soil mixed with 300 g of finely ground basalt (T0 + BA_30). Each treatment was replicated ten times in every serie. The control treatment is only soils of Ng, collected at the top soil and without any basalt application. They are clayey, acid and display an average CEC. The basalt is rich in silica (47.52%), Calcium (8.22%), Magnesium (4.03%), sodium (4.01%), potassium (2.42%) and displays average content in alumina (16.54%) and iron (11.1%). The experiment was carried out in pots, and the incubated soil samples were analyzed after 0, 1, 2, 4 and 6 months. The analyzes mainly focused on the physicochemical parameters (Grain size analysis, pH, Cation exchange capacity (CEC), the sum of exchangeable bases (SBE) and the saturation rate (V). Obtained results indicated that the application of basalt greatly improved the chemical properties of oxisoils from Ngaoundéré: the pH changes from acidic (5.5) to weakly acidic (6.5); the saturation rate, as well as the sum of exchangeable bases and the cation exchange capacity increased. Physicochemical properties of the soil are closely accompanied by an increase in fertility. It appears that 10 and 20% treatments are the most efficient treatments. Thus, the basalts from Manwi can be recommended as petrofertilizer to improve the chemical properties of impoverished soils and especially for plants requiring alkalis and alkaline earth.

Research carried out on soil organic carbon stock (SOCS) in the Sudano-Sahelian region of Cameroon is very rare. The few existing studies are mostly available in reports and concern in most cases carbon stocks in plant biomass. In order to contribute to the documentation on soils in this part of the country, the present work was designed to evaluate the SOCS in the main soil types and the influence of environmental factors and soil properties on these stocks under the natural dry tropical area of the Sudano-Sahelian zone of Cameroon. The study was undertaken in four sites, including three natural forest reserves (Laf, Zamai, Kosohon) and one national park (Mozogo), located at different latitudes. Three replicates were collected at each site, giving rise to three sampling points chosen per site, from 0 to 75 cm depth, for the determination of SOCS. At each sampling point, soils were sampled using depth increments of 25 cm from the surface. The studied area is covered by Haplic Vertisols, Dystric Arenosols, Dystric Leptosols and Dystric Planosols. Total SOCS (T-SOCS) content, which refers to a depth of 75 cm, decreases with increasing latitude, with 249±26.26 Mg ha−1 in Vertisols at Laf forest reserve most southerly located, 199±8.00 Mg ha−1 in Arenosols at Zamai forest reserve, 166±16.63 Mg ha−1 in Leptosols at Kosohon forest reserve and 161±8.88 Mg ha−1 in Planosols at Mozogo national park most northerly located, regardless of the altitude. No significant correlation was noted between T-SOCS and the altitude. A good correlation was noted between precipitation which decreases with increasing latitude and T-SOCS, indicating the importance of climate in the distribution of T-SOCS in the study area, which directly influences the productivity of the vegetation. More than 60 % of the SOCS was stored below the first 25 cm from the soil surface, a peculiarity of SOCS in drylands. The SOCS in the Sudano-Sahelian area of Cameroon is mainly influenced by climate and vegetation.

Knowledge of the combining effect of agricultural practices and slope on soil erodibility is important to promote their suitable use and constitutes a key parameter for their sustainable conservation.The aim of this study was to characterize vertisols from the Logone floodplain and evaluate their erodibility in relation to the agricultural practices and slope in order to suggest the well managing strategies to be diffused.Vertisols were characterized by describing their profile type and their erodibility was assessed by sampling topsoils at 3 positions along a toposequence (upslope, midslope and footslope).Erodibility indexes were computed by exploiting physicochemical data.The studied vertisols were classified as gleyic Vertisols.They are clayey (19-42% of clay), slightly basic (pH~7.3)and display high organic matter (OM) content and cation exchange capacity.Smectites and kaolinite were the main clay minerals associated with quartz.The water dispersible clay, clay dispersion ratio and dispersion ratio diminished from the upslope to the footslope, while clay aggregation showed an opposite trend.Hence, vertisols from the upslope and midslope cropped were more erodible than those from the not cropped footslope.From the statistical analysis, it appeared that Na + , Ca ++ and K + contributed to vertisols erodibility while Mg ++ , OM and amorphous Fe promoted aggregate stability.Managing these vertisols will tend to limit N and K rich inputs (urea and NPK fertilizers); control liming strategies and encourage substantial OM inputs.No-tillage or minimum tillage oriented perpendicularly to the slope are the practices to be implemented.

The effect of forest reserve conversion to agriculture land on soil properties in the sudano-sahelian zone of Cameroon was investigated. Agricultural activities have caused the progressive reduction of the surface area of Zamai forest reserve, which reduced from nearly 50% of its original surface in 1970 to only about one third in 2016. This study was conducted on four plots that have been cultivated for 3, 29, 50 and 90 years respectively, and a forest reserve soil used as control plot, all located along a chronosequence on Dystric Arenosols. The sandy fraction of cultivated soils varies between 70.00 +/- 2.65 and 75.00 +/- 2.65%, lower than that of the control soil (76.67 +/- 3.21%). Silt contents were very low, but clay contents were higher in cultivated plots, with the highest proportion (28.66 +/- 3.05%) seen in the 29 years cultivated plot. The stability index (SI) of different plots was greater than 9%, characteristic of stable structures. Compared to both 50 and 90 year cultivated soils, 3 and 29 years old agricultural soils had lower stability index and are thus more vulnerable to water and wind erosion in accordance with the lowest chemical characteristics observed. There was a gradual increase in acidity of cultivated plots from 3 years reaching higher values of 6.70 +/- 0.24 and 6.49 +/- 0.75 after 50 and 90 years of cultivation respectively. Ca2+ and K+ were the most represented bases. Moreover, there was an overall decrease in organic matter, sand and silt contents, SI and C:N, with a relative increase in clay content, pHw, K+, Ca2+, N, sum of bases and cation exchange capacity from 3 years cropping to 90 years. Control and 90 years cultivated plots were very similar, as a result of the restoration of soil properties after 90 years of farming activities, initiated from 50th year of farming activity. (C) 2020 Elsevier B.V. All rights reserved.

The objective of the present work was to characterize the morphological, geochemical and mineralogical features of soil with regard to weathering processes as a function of topography and spatial variation of climate in tropical high reliefs of Cameroon. Field investigations permit to select three study sites Mbalam, Meleta and Secande respectively in the humid tropical zone, pseudotropical mountainous zone and in the tropical dry climate. Macroscopically, the studied soils are thick in Mbalam, medium thick in Meleta and relatively less thick in Secande. Globally, saprolite, a loose loamy clayey horizon and humiferous horizon were observed from the bottom to the top of the profiles. These profiles differ by their thickness, the differentiation of the saprolite horizons and the presence of humiferous horizons. They are characterized microscopically by in situ replacement of primary minerals by kaolinite/halloysite, gibbsite and iron oxides. Theses minerals are associated to anatase in Mbalam and to montmorilonite and calcite in Secande. Geochemical processes involving in the spatial differentiation of soils are monosiallitisation and allitisation in the humid tropical zone, monosiallitisation and high allitisation in the pseudotropical mountainous zone with Al2O3 content reaching 41% in the saprolite, and monosiallitisation associated to bisiallitisation in the tropical dry climate of Cameroon. The development of these geochemical processes is conditioned by topography, elevation, rainfall and temperature, which appear as the main factors responsible of the spatial variation of soil weathering processes in the tropical high reliefs of Cameroon.

Ngaoundal-Dir section was characterized in order to determine its duricrust potential and the role of topography in its mineral enrichment. The high altitude (Ngaoundal sector) and the low-altitude (Dir sector) were investigated using field methods and the collected samples were subjected to mineralogical and geochemical analysis. Six (6) facies of duricrust (scoriaceous, nodular, massive, pisolithic, conglomeratic and vacuolar) were distinguished. The scoriaceous and pisolithic facies were exclusively identified in Ngaoundal while the conglomeratic and vacuolar facies were found in Dir only. The scoriaceous facies was essentially made of gibbsite. The pisolithic facies is made up of kaolinite associated with gibbsite, goethite and hematite, while the other facies are mixture of gibbsite, hematite, quartz and kaolinite. Geochemically, the duricrusts display major oxide concentrations (in wt.%) for: Al2O3 (2.56 - 49.65), Fe2O3 (15.21 - 79.04) and SiO2 (0.89 - 34.46). A higher content of Al2O3 was recorded in scoriaceous facies (47.92 - 49.65%), while a higher content of Fe2O3 was observed in massive facies especially at Dir (79.04%). Trace elements were represented essentially by Cr (75 - 880 ppm); Zr (202 - 427 ppm); Ba (5.7 - 137.3 ppm) and Cu (5.1 - 134.2 ppm). Light rare earth elements were more concentrated than heavy rare earth elements in both sites (ƩLREE = 72.38 ppm and ƩHREE = 4.12 ppm in Ngaoundal; ƩLREE = 40.76 ppm and ƩHREE = 5.47 ppm in Dir). The low values of alkali metals and alkali earth metals combined with the high values of the Chemical Index of Alteration (˃ 99) supported an intense weathering origin of duricrusts. These findings suggested that the weathering resulted in the establishment of bauxitic formation in high-altitude and a concentration of iron-enriched formations in lower-altitude.

Objectif : Cette étude a pour objectif d'évaluer la diversité génotypique et phénotypique existante au sein des accessions de Sorgho pluvial de la zone soudano sahélienne du Cameroun et d'estimer les paramètres génétiques permettant d'orienter les futurs programmes d'amélioration variétale.Méthodologie et résultats : L'étude réalisée sur 44 accessions selon un dispositif en blocs de Fisher complètement randomisé à trois répétitions révèle une grande diversité morphologique organisée autour des caractères végétatifs et de rendement avec un groupement des accessions en trois dont le troisième renferme les accessions performantes en termes de hauteur de tiges et rendement grains. Une faible influence des facteurs environnementaux sur l'expression des performances des accessions a été observée avec des faibles écarts entre les coefficients de variation phénotypique et génotypique, une forte héritabilité au sens large pourtous les caractères.Conclusion et application : En somme, Tous les caractères étudiés ont exprimé une forte héritabilité au sens large avec un gain génétique attendu variant, mais fort chez les caractères végétatifs et modéré chez les caractères liés au rendement. La grande diversité génétique observée au sein des accessions de sorgho étudiées montre que des possibilités de sélection existent. En outre les accessions du groupe trois constituent des potentiels parents pouvant servir dans les programmes d'amélioration ou de création variétale au Cameroun.Mots clés : Sorgho pluvial, zone soudano sahélienne du Cameroun, diversité génotypique et phénotypique.

General properties of Vertisols are known world-wide, but these properties vary in different areas due to specific environmental conditions. The mastery of the specific characteristics of each Vertisols in a given area requires detailed site-scale investigation. This work aims to study the properties of the Lake Chad Basin Vertisols, attempt to highlight their genetic processes and classification. These Vertisols are dark, clayey and massive, very compact, with deep wide-opened cracks and gilgai micro-relief. They show neutral to slightly alkaline pH, low organic matter content (0.7-2.73%) and high C/N ratio values (7.34-39.64). Ca2+ and Mg2+ are the most represented exchangeable cations (5.92-30.72% and 1.28-5.44%, respectively) on the absorption complex. Smectite is the main clay mineral species, but small contents of kaolinite, illite, quartz and feldspars are also present. The most concentrated elements in the profile are silica (61.07-77.78 wt.% SiO2), aluminium (7.08-15.54 wt.% Al2O3) and iron (1.78-6.92 wt.% Fe2O3). The Si/Al ratio (> 2) and chemical index of alteration (CIA) are moderate to high (56.76-88.39) and indicate a moderate to intense weathering. Such properties reflect the pedogenic influence of the environmental factors like contrasting climate, low topographic position and the alluvial parent material. The accumulation of basic cations favours the neosynthesis of smectite minerals typical of a dominant bisiallitisation process. The Vertisols profiles, due to the presence of a perched water table, enable to classify these soils as Epiaquerts and Endoaquerts Vertisols (USDA soil taxonomy) and Gleyics and Fulvics Vertisols (WEB). Their physical characteristics and notably their difficult water management constitute a limitation to agricultural activities.

The once sustainable agroforestry system in the Sudano-Sahelian zone of Cameroon has been abandoned and trees overexploited. A study on the variability in seed and seedling traits of Faidherbia albida (DEL.) A. Chev populations from different climatic zones was carried out. Six populations were selected from Sudanian (Poli, Garoua III, and Figuil) and Sahelian (Yagoua, Moulvoudaye and Maroua I) climatic zones and harvested seeds were transported to the experimental farm of IRAD Yagoua for pretreatment and growth experiment. Four pretreatments (98% sulfuric acid, hot water, scarification and soaking in water for 24 hours) were used to initiate the germination. After one month, the rate of germination (%) was recorded and seedlings were transplanted in three substrates for seedling growth evaluation. Growth traits (Survival, plant height, root collar diameter, number of leaves, root length, plant fresh weight and plant dry weight) were measured after three months. The experimental design was a single tree plot randomized complete block design with 30 blocks. Results indicated there was significant difference (p = 0.002) among pre-treatments for the germination. The highest rate of germination was recorded with seedlings from scarified seeds (78.33%), followed by those from seeds treated with sulfuric acid (76.67%). Seeds and seedling traits were significant among populations with Yagoua recording the highest in most of the traits measured. Scarification can assist in seed germination and movement of seeds between populations and climatic zones should be considered during conservation programs. © 2019 International Formulae Group. All rights reserved. Keywords: Faidherbia albida , agroforestry parklands, seed pretreatments, seedling traits, conservation, Sudano-Sahelian, Cameroon

The study of the soils from Mbé and Wack is carried out in the framework of the knowledge of soils from the Adamawa Region of Cameroon and their erodibility was investigated using erodibility indices obtained through physico-chemical data. Eleven topsoils (0 - 20 cm) samples were collected on different land use and their susceptibility to erosion was assessed. The water dispersible clay (34.92 - 121.75 g•kg−1), the clay dispersion ratio (0.45 - 0.84) and the dispersion ratio (0.75 - 0.89) were high in the studied soils while the clay aggregation (13.16 - 42.27g•kg−1) and the clay flocculation index (0.16 - 0.55) were low to moderate indicating their high erodibility. The soils under natural vegetation, more clayey, displayed the highest amount of water dispersible clay while cropped soils recorded the smaller ones. Globally, in cropped soils, those under cereals displayed the highest clay dispersion indices than those under tubers. This suggests that tubers cropping practices in studied soils enhance their erodibility. Statistical analyses revealed that amorphous Al and Fe are elements which limit soils erodibility while K+ and promote soils particles dispersion. Sustainable management of these soils will consist on limiting runoff through agricultural practices such as direct seedling and orienting tillage perpendicularly to slope gradient.

Clay dispersion by water is important for soil and water conservation as well as for irrigation scheduling. In the present study, clay dispersion/flocculation of irrigated and flooded vertisols in North Cameroon was investigated using clay dispersion/stability indices. Nine vertisols topsoils (0-20 cm) samples were collected on different land use and their clay dispersion indices were assessed. Vertisols were acidic to slightly basic, with smectites as dominant clay mineral. The water dispersible clay (160-340 g kg(-1)), the dispersion ratio (0.55-0.79) and the clay dispersion ratio (0.48-0.83) were high in the studied vertisols while the clay flocculation index (0.17-0.54) and the clay aggregation (70-230 g kg(-1)) were low to moderate, indicating their high dispersion. Cropped vertisols displayed the higher amount of water dispersible clay while not cropped recorded the smaller amount. Concerning the cropped soils, irrigated vertisols displayed the highest clay dispersion indices suggesting that agricultural practices (irrigation) enhance clay dispersion. Globally, the clay dispersibility trend was: irrigated paddy ' rainy sorghum ' rainfed paddy' dry-season sorghum' not cropped. Statistical analyses revealed that amorphous Al, Na' and electrical conductivity enhance clay dispersion while organic matter, nitrogen and Ca promote clay flocculation/aggregation. The overall findings emphasized that practices such as heavy tillage and irrigation induce clay dispersion. Minimum tillage, electrolytes concentration monitoring in irrigation water, irrigation scheduling based on soil moisture control, organic matter inputs and implementation of adapted dams are measures susceptible to limit their degradation through clay dispersion. (C) 2018 International Research and Training Center on Erosion and Sedimentation and China Water and Power Press. Production and Hosting by Elsevier B.V.