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International Journal of Plant & Soil Science 33(16): 156-169, 2021; Article no.IJPSS.70266 ISSN: 2320-7035 Agro-Morpho-Pedological Evaluation of Soils under Hevea in Marginal Zones: The Case of the Departments of Man and Toumodi Koffi Antoine1*, Essehi Jean Lopez2, Soro Dogniméton1, Diomandé Métangbo3, Kouakou Boukhamy Wilson Lewis4, Konan Djézou5 and Obouayeba Samuel5 1UFR Agroforestery, University Jean Lorougnon Guédé, Agricultural Production Improvement Laboratory BP 150 Daloa, Côte d’Ivoire. 2National Agricultural Research Centre (CNRA), Central Soil, Water and Plant Laboratory 01 BP 633 Bouaké 01, Côte d’Ivoire. 3UFR of Biological Sciences, University Péléforo Gon Coulibaly de Korhogo, B.P. 1328 Korhogo, Côte d’Ivoire. 4UFR Environment, University Jean Lorougnon Guédé, Daloa, Côte d’Ivoire. 5National Agricultural Research Centre (CNRA), Research Station of Bimbresso- Hevea Program, 01 BP 1536 Abidjan 01, Côte d’Ivoire. Authors’ contributions This work was carried out in collaboration among all authors. All authors read and approved the final manuscript. Article Information DOI: 10.9734/IJPSS/2021/v33i1630534 Editor(s): (1) Dr. Abdelhak Rhouma, University of Sousse, Tunisia. Reviewers: (1) Salih Kadhum Alwan, University of Alqasim Green, Iraq. (2) Samir Hadj-Miloud, Ecole Nationale Supérieure Agronomique (ENSA, ES1603), Algeria. Complete Peer review History: https://www.sdiarticle4.com/review-history/70266 Received 27 April 2021 Original Research Article Accepted 02 July 2021 Published 12 July 2021 ABSTRACT Among the ecological conditions of the environment allowing profitable rubber cultivation, rainfall and the physico-chemical characteristics of the soil are the most important. With this in mind, a study on the adaptability of rubber trees to new agro-morphopedological zones was conducted in the departments of Man and Toumodi. The methodology used to achieve this objective is the realization of pedological pits coupled with physico-chemical laboratory analyses. The open soil profiles reveal that the soils belong mainly to the Ferralsols class with distinctive characteristics, except for those of Kimoukro which belong to the Cambisols class. The Toumodi soils, with a _____________________________________________________________________________________________________ *Corresponding author: Email: [email protected]; Antoine et al.; IJPSS, 33(16): 156-169, 2021; Article no.IJPSS.70266 sandy-clay texture (15-35% clay), have a high content of coarse sand (over 40%) and good internal drainage in the surface horizons. They are less dense (≤ 1 g/cm3), with a high coarse element load (40%). These soils are chemically rich with a slightly acidic pH. For the Man soils, the sandy-clay texture, with more than 50% clay, from surface to depth, was the most representative fraction. The coarse element load (≥ 50%) and bulk density (≥ 1.5 g/cm3) were more important. These strongly acidic soils are rich in nitrogen and carbon. Exchangeable bases and CEC are important, mainly, in the upper horizons. In addition, the soil profiles observed in these two departments revealed two major pedogenetic processes: reworking and rejuvenation. At the agronomic level, vegetative growth and rubber production of rubber trees were better in Man than in Toumodi. The physico- chemical characteristics of the soils indicate that the departments of Man and Toumodi are favorable for rubber cultivation, although the soils in Man department are more suitable for cultivation. Keywords: Soils; adaptability; new rubber growing areas; Hevea brasiliensis; Côte d'Ivoire. 1. INTRODUCTION orchard. It should also be noted that the master plan for the development of the rubber sector The rubber tree, with the scientific name Hevea foresees a production of about two million tons of brasiliensis Muell Arg. (Euphorbiaceae), is a fruit natural rubber over the next five years, and thus tree, with a height of more than 30 meters and a consolidate its dominant position in Africa. To circumference of 1 to 5 meters at maturity [1]. It reach this goal and meet the ever-increasing originates from the Amazon basin in Brazil [2-3]. demand for natural rubber, two strategies can be This species, which can be continuously tapped, adopted and consider joining the top three is cultivated for its latex, whose rubber producers in the world. The first is to improve composition makes it easier to process, with a rubber productivity in traditional growing areas by yield that is significantly higher than that of any optimizing latex harvesting systems in other known latex plant species [4]. Global plantations, appropriate replanting techniques natural rubber production in 2018 is estimated at and by selecting better performing clones that over 13 million tonnes [5], of which 88% is are better adapted to local environmental produced in Asia and 6% in Africa. Rubber conditions. The second strategy consists of cultivation in Côte d'Ivoire has developed extending the rubber cultivation areas to non- spectacularly over the past few decades due to traditional zones, described as marginal. These the subsidy of rubber plant production by the so-called marginal areas are characterized, on Hevea Development Fund (FDH), the increase in the one hand, by a significant annual water the purchase price of rubber in the field and, deficit ranging from 400 to 600 mm of water and, above all, the monthly income that it provides. on the other hand, by soils with coarse elements, Rubber occupies an important place in the armourstone slabs or sound rocks at shallow Ivorian agricultural sector, the "engine of depths in some places [7-9]. However, rubber is economic development" of the country, as it a fairly demanding crop in terms of soil, due to its contributes a high proportion of export earnings. taproot system, and in terms of climatic factors, The number of rubber planters increased from notably abundant and well-distributed rainfall 16,500 to 165,000 between 2005 and 2020 [6]. (more than 1600 mm/year on average, [4]). The In the same direction, the cultivated area soil and climatic parameters in these new increased from 74,000 ha to 600,000 ha, an cultivation areas, which are of major importance increase of 810%. This trend is confirmed by the for rubber, could be detrimental to its increase in natural rubber production from establishment, growth and future rubber 170,000 tonnes in 2005 to 949,000 tonnes in production. Therefore, knowledge of these (soil 2020 [6]. This prodigious progress makes the and climate) factors is an important prerequisite country the leading African producer of natural for sustainable rubber production from an rubber and the fourth largest in the world, agronomic, economic and environmental point of compared to 7th place previously. Despite this view. This study was therefore initiated to assess performance, rubber cultivation in Côte d'Ivoire is the agricultural potential of soils for rubber faced with increasing pressure from land and cultivation in the administrative departments of parasites (Corynespora spp, Loranthaceae, Man and Toumodi in order to identify the main Fomès lignosus spp, etc.) in traditionally constraints to the productivity of these soils. favourable areas, and also from the ageing of the More specifically, the aim was to evaluate the 157 Antoine et al.; IJPSS, 33(16): 156-169, 2021; Article no.IJPSS.70266 current physical and chemical characteristics of average annual rainfall of about 1700 mm. The the soils of the two study sites and to study the soils in Man are mainly Ferralsols, according to behavior of rubber plants on them. the working group WRB (2014) classification. Toumodi department is characterized by a 2. MATERIALS AND METHODS transitional equatorial climate with two maxima and two minima [12,10]. The average annual 2.1 Study Areas rainfall is estimated at 1,200 mm, with an The study was carried out in the respective average temperature of 26° C and an average localities of Zélé in the West and Kimoukro in the relative humidity of 77% [13]. The soils of Centre of Côte d'Ivoire. The Zélé site is located Toumodi are quite varied. Ferralsols, Gleysols between 7°20'00" and 7°30'00" North latitude and sometimes Cambisols are found [14]. For and 7°30'00" and 7°40'00" West longitude in the this study, two types of plots according to age administrative department of Man (Fig. 1). were chosen in order to make a comparative Kimoukro is located between 6°20'00" and study of the productivity of the soils of the two 6°30'00" North latitude and 5°10'00" and localities. The cultivation techniques practiced 4°55'00" West longitude in the administrative around or within the plot and the types of department of Toumodi (Fig. 1). The climate of cultivation guided this choice. All these Man is tropical and humid [10,11]. Rainfall is investigations made it possible to determine two monomodal with a long rainy season lasting eight plots in each of these two localities, one of which months from March to October. During the was young, 2 to 3 years old, and the other, 6 decade (2007-2018), this locality received an years old or more, was being tapped. Fig. 1. Study areas 158 Antoine et al.; IJPSS, 33(16): 156-169, 2021; Article no.IJPSS.70266 2.2 Plant Material average 58% carbon (C), by the relation: OM (g.Kg-1) = C × 1.72; the ratio (C/N) was deduced. The plant material consists of Hevea brasiliensis clone GT 1. The GT 1 clone, originating from The analysis of these results was based on the Indonesia, precisely from the Gondang Tapen critical levels of interpretation of Boyer [23] and region from which it takes its name, is a Landon [24]. reference clone in Côte d'Ivoire. This clone, the most widely grown in Côte d'Ivoire, is 2.3.1.2 Assessment of water stock in soils under characterized by an excellent grafting success rubber trees rate and has a moderate to medium radial vegetative growth [15-17].

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