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Organisation of Soils Along the Sides of Interfluves in the Western

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Organisation of Soils Along the Sides of Interfluves in the Western Asian Journal of Soil Science and Plant Nutrition 5(1): 1-19, 2019; Article no.AJSSPN.51629 ISSN: 2456-9682 Organisation of Soils along the Sides of Interfluves in the Western Highlands of Cameroon: Case Study of an Andosolic Toposequence on Trachyte in the Upper Part of the Southern Limb of Bambouto Mountains J. C. Fopoussi Tuebue1*, S. D. Basga2, P. Tematio3 and J. P. Nguetnkam4 1Department of Sciences, Jesus and Mary Secondary High School, P.O.Box 185CS101, Yaounde, Cameroon. 2Institute of Agricultural Research for Development (IRAD), P.O.Box 41, Garoua, Cameroon. 3Department of Earth Science, University of Dschang, P.O.Box 67, Cameroon. 4Department of Earth Sciences, University of Ngaoundéré, P.O.Box 454, Dschang, Cameroon. Authors’ contributions This work was carried out by author JCFT under the supervision of authors JPN and PT. Author SDB contributed to the exploitation of results. All authors read and approved the final manuscript. Article Information DOI: 10.9734/AJSSPN/2019/v5i130058 Editor(s): (1) Dr. Pankaj Gupta, Dolphin (PG) College of Science & Agriculture, Punjabi University, India. Reviewers: (1) Seweta Srivastava, Lovely Professional University, India. (2) Balthazar Michael Msanya, Sokoine University of Agriculture, Tanzania. Complete Peer review History: https://sdiarticle4.com/review-history/51629 Received 16 July 2019 Accepted 21 September 2019 Original Research Article Published 12 October 2019 ABSTRACT The acquisition of knowledge on soils tells how to use them sustainably. So, the organization of soils along the sides of interfluves in the western highlands of Cameroon was put into relief in order to understand their genesis, organization, and evolution. Field work and lab analysis helped to reach the focuses. These soils are thin, highly differentiated, with many local specificities. Their organization and their thickness vary from up to downhill. Vertically, they include: An isalteritic horizon; a yellow vague polyhedral horizon; a red distinct polyhedral horizon; a discontinuous breastplate with two facies; a porous vague crumby dark reddish brown horizon; and a strongly dark grey, porous, thixotropic and crumby superficial horizon. The pedon/alterite ratio is about 2/1, _____________________________________________________________________________________________________ *Corresponding author: Email: [email protected]; Tuebue et al.; AJSSPN, 5(1): 1-19, 2019; Article no.AJSSPN.51629 and the hardened level/alterite ratio is 1/4. The alteritic level represents about 1/3 of the whole soil profile. Microscopically, these soils lack plasmic separations. Plasmas are respectively isotic in the dark reddish brown and strongly dark grey horizons, clayey asepic in the yellow and red polyhedral horizons, cristic in the isalteritic horizon, cristic and locally isotic in the discontinuous breastplate. Gibbsite, halloysite, kaolinite and allophane are the main minerals; goethite, quartz, hematite and rutile are also present. Geochemically, aluminum is the main chemical component in the deepest horizons, while in those at the top of the soil profile, silicon and aluminum has quite similar concentrations. Others specificities include their low bulk density (0.6 to 0.9 gcm-3), the abundance of clayey particles at the bottom of the soil profile, sand and silt at its summit. Ferrallitic and andosolic characteristics coexist in the studied soils. This ambivalence makes them to be simply «andic ferallitic, desaturated, humic and strongly rejuvenated soils». Keywords: Gravity; breastplate; rejuvenation; ambivalence; gibbsite. 1. INTRODUCTION evolution, and the functioning of Andosols along the sides of interfluves of the Cameroonian Andosols are young soils developed on volcanic Western Highlands, which have first of all the materials, or sometimes on fine crystallized rocks particularity to be highly considered for cropping on which alteration can quickly act to release [7], and secondly to have risen up from massive sufficient poorly crystallized substances that and compact parent rocks of Miocene age [9], protect organic matter against bacterial attacks under an equatorial monsoon and highly rainy [1]. The conditions required for their formation type of climate [10]. The parent rock of the are found in temperate zone, or in rainy tropical presently studied soils is an alkaline trachyte areas (>2000 mm of rain per year) with low [11], outcropping in the middle and upper zones temperatures (<15°C) [2,3,4]. Those soils, of the southern limb of the Bambouto Mountains. previously less studied, constitute today the major focus of many researchers since the 2. MATERIALS AND METHODS beginning of the year 1950. In tropical region in general, Andosols appear in volcanic massifs in 2.1 Materials: Physical Characteristics of different topographic positions [2,3,4], where they the Bambouto Massif are sometimes the only soil type existing [4,5]. Many years ago, researchers made basic The volcanic Bambouto massif is located in the characteristics of Andosols their main focus, Cameroonian Western Highlands, between 5°25’ without any interest in their local particularities. It and 5°45’ of North latitude, and between 10°00’ is the case in the Bambouto Mountains. Here, [5] and 10°15’ of East longitude. It is a huge showed that Andosols are present in areas over volcanic shield, reaching 2740 m high at the 2000 m of altitude; in their study, they focused on summit of Mélétan Mount. Geomorphologicaly, the general characteristics of the most superficial the present massif has three main zones with horizons, known as diagnostic horizons particular environmental conditions; these according to the USDA system of classification include: the upper zone, with altitudes higher [6]. The consequence of this is the mystery that than 2000 m, the mid zone, with altitudes ranging remains in the detail about these soils in their between 1600 and 2000 m high, and the lowest different ecosystems. Thus, the major aspects zone, with altitudes ranging between 1400 and studied up to today include: morphological and 1600 m [12,13]. The upper zone shows an analytic characteristics, influence of the aggressive relief. Its climate is foggy and cold, environmental factors, notably the parent rock, with temperatures values ranging between 10 stocktaking, spatial localization, and the and 13°C. The rains are orographic type, with highlighting of the fertility parameters in relation annual average pluviometry of 2600 mm [10,14]. to the farming techniques applied [7,8]. On the The flora is natural and anthropic. The natural other hand, the organization of these soils along part is essentially made of graze, locally the sides of interfluves remains incompletely disturbed by gallery forests along water course known. Considering the importance of these soils [5]; the anthropic part is made of different crops for humans in the ecosystems where they [15,11]. The hydrographic network is radial and appear, they must therefore be better known. dense. Soils are mostly TypicDystrandepts [5]. Thus the present study aims to bring under light Many signs of anthropic activities are present [8]. more knowledge concerning the organization, the The mid zone has a subequatorial type of 2 Tuebue et al.; AJSSPN, 5(1): 1-19, 2019; Article no.AJSSPN.51629 climate, largely influenced by the altitude [16]; it mineralization by oxidation with potassium is cold and wet, with nine month of rains, from bichromate and concentrated sulfuric acid; the march to November, and a short dry season, amount of organic matter (O.M.) was then from December to February; the average annual deduced using the [19] formula, stipulating that temperature is about 18°C; the annual average %O.M. = (%O.C.)X2 in an area without human pluviometry is 1690 mm. Compared to the upper perturbation. Nitrogen amount was determined zone, the relief here is less aggressive. The using sulfuric acid after mineralization by vegetation is mainly anthropic [15], with some oxidation in a digestor. pHwater was measured local islet of the natural vegetation in the using a pH-meter on a soil-water solution in swamps. The hydrographic network is the1:2.5 ratio; concerning the pHKCl, it was subdendritic. Soils are mostly andic ferallitic [5]. measured on a mixture of soil-KCl at a 1/1 ratio. The lowest zone finally is characterized by a hot Exchangeable basic cations (Ca2+, Mg2+, Na+, and wet climate, with an annual average K+) were extracted from the soil using a neutral temperature of 23,5°C and an average annual ammonium acetate solution. The measurements pluviometry of 1750 mm. The relief is undulating. of each basic cations amount were done with The vegetation is dominantly anthropic [15]. The atomic spectrometry absorption and flame hydrographic network is subdendritic. Soils are emission. Cation exchangeable capacity (CEC) mainly ferallitic with hardpan within [5]. was determined as followed: saturation of Geologically, trachytes are the major rocks in the absorbant complex with NH4+ solution and whole massif [9,17]. There are also few outcrops removal of basic exchangeable cations, + of basalts, phonolites, rhyolites, and elimination of the excess of NH4 solution filling pyroclastites. The substratum is made of granitic the soil pores, quantitative desorption with KCl + and gneissic types of rocks, outcropping in the and NH4 measurements using Kjeldahl lowest zone of the massif [9,17]. distillation. Total exchangeable cation capacity was calculated with the following formula: CECt= 2.2 Methods ECEC + OCEC (effective
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