Mineralogical and physico-chemical properties of Ferralic Arenosols derived from unconsolidated Plio-Pleistocenic deposits in the coastal plains of Congo
Research Highlights
► Minerals reveal current and former pedogenesis, resulting from changing environments. ► Kaolinite had different origins: current precipitation and older before soil deposit. ► Goethite precipitated only in the original soils before the deposition process. ► Three percent of vermiculite in clay fraction represented 49% of the soil mineral CEC. ► At soil pH, CEC values for kaolinite ranging from 6.2 to 6.9 cmolc kg− 1.
Introduction
Physical breakdown and chemical weathering of minerals are always intense under tropical climates, whatever the nature of the parent material (Churchman, 2000). Depending on their age, soils exhibit various stages of mineralogical weathering due to water-rock interactions. Element losses start with alkali and alkali-earth elements, followed by silicon, which results, at the end of the sequence, in the production of an assemblage of oxides and oxyhydroxides (He et al., 2008). Moreover, in geologically stable areas in the tropics, climate changes and geomorphic cycles may lead to polygenetic soils. Polygenesis involves new soil formation phases taking place on pre-weathered materials from previous phases (Muggler et al., 2007). In this context, large portions of the soil in the coastal plain near Pointe Noire in western Congo are derived from remobilized soils and saprolites partly deposited as slope deposits from the adjacent Mayombe Mountains (Cosson, 1955, Jamet and Rieffel, 1976). This detritic formation of continental origin dating from the Plio-Pleistocene (Jamet and Rieffel, 1976) supports deep Ferralic Arenosols (FAO, 1998). Their apparent chemical poorness makes them unsuitable for productive agricultural uses. The natural vegetation established on these soils consists of herbaceous savanna which has occupied this area since the Upper Holocene (Schwartz et al., 1995, Trouvé, 1992). Since 1978 42,000 ha of eucalypt hybrids have been planted in the area. Nutrient losses from this intensive forestry practice are compounded by the notoriously low CEC produced by chemical weathering that ultimately results in a relatively steady-state mineralogical–chemical state characterized by kaolinite and oxyhydroxides (Birkeland, 1999). Many studies have been undertaken in these eucalypt plantations on carbon cycles (D'Annunzio et al., 2008, Epron et al., 2009, Marsden et al., 2008, Nouvellon et al., 2008), water and nutrients (Laclau et al., 2003a, Laclau et al., 2003b, Laclau et al., 2005, Laclau et al., 2010), root architecture and dynamics (Bouillet et al., 2002, Laclau et al., 2001, Marsden et al., 2008, Thongo M'Bou et al., 2008), and tree growth (Nouvellon et al., 2010, Safou-Matondo et al., 2005, Saint-André et al., 2005). However, little is known about the mineralogical and physico-chemical properties of the soil, which is a major constraint for comprehensive ecological studies and sustainable land uses. Moreover, different local studies, mainly gray literature (unpublished data and soil cartography) have shown that this type of soil is the one most frequently found in several countries of the Atlantic coast of central Africa from Gabon to Cabinda (Collinet, 1969, Delhumeau, 1969, Jamet and Rieffel, 1976). The objectives of this paper were to: i) assess the capacity of mineralogical studies to gain an insight into current and former pedogenetic processes in a tropical soil, and ii) accurately characterize soil chemical properties in a toposequence of highly weathered sandy soils largely represented in the coastal plains of central Africa that have remained largely unstudied.
Section snippets
Study site
The Eucalyptus plantation extends from near the city of Pointe Noire on the Atlantic coast (Bas-Congo) of the Congo for about 90 km inland, at 4°S, 12°E (Fig. 1). The ecological situation has been described previously in Laclau et al. (2003a). In brief, the climate of the coastal plain is characterized by high atmospheric humidity (85% on average) with low seasonal variations (2%), and a mean annual rainfall of about 1200 mm with a marked dry season from May to October. The mean annual
Soil characteristics
The particle size distributions of the three soil profiles showed the predominance of the sandy fraction in all the soil horizons, with small amounts of clay and extremely small amounts of silt (Table 1). The three profiles of soil present a weak structure and peds are barely observable in place. The structure of A1 horizons is slightly granular with low stable macro-aggregate (mean size 5 mm). More in depth, the structure is single grain type with a low coherence of individual particle. The
Conclusion
In mineral horizons, nutrient levels are low due to the extremely small base cation reserve of the pre-weathered parent materials. Due to intense pre-weathering, rejuvenation of the landscape, promoted by intense depositing, is not translated into soil enrichment as observed in areas where less weathered parent materials exist. The mineralogical assemblages and chemical properties of the highly weathered sandy soils we studied made it possible to gain an insight into the origin of the soil
Acknowledgments
We thank Karine Alary (CIRAD), for carrying out the chemical analyses and Armand Séraphin Dzomambou for drawing up the map. We are also grateful to the founders of CRDPI, Republic of Congo, CIRAD and EFC s.a., for their financial support. This work received support from GIP Ecofor, which contributes to the management of the field site as a part of the ORE Network (Observatoire de Recherches pour l'Environnement, F-ORE-T).
References (85)
- et al.
Soil-elevation relationships on a volcanic plateau in the southern Cascade Range, Northern California, USA
Catena
(1993) - et al.
Mineralogical, chemical and charge properties of Geric Ferralsols from New Caledonia
Geoderma
(2001) - et al.
Changes with age in the spatial distribution of roots of a Eucalyptus clone in the Congo. Impact on water and nutrient uptake ability
For. Ecol. Manage.
(2002) - et al.
Pairwise comparison of soil organic particle-size distributions in native savannas and Eucalyptus plantations in Congo
For. Ecol. Manage.
(2008) - et al.
TEM study of progressive alteration of igneous biotite to kaolinite throughout a weathered soil profil
Geochim. Cosmochim. Acta
(1998) - et al.
Quantification of weathering processes in an acid brown soil developed from tuff (Beaujolais, France)/Part I. Formation of weathered rind
Geoderma
(1999) - et al.
Distribution and dynamics of gibbsite and kaolinite in an oxisol of Serra do Mar, southeastern Brazil
Geoderma
(2002) - et al.
Clay minerals in a soil chronosequence derived from basalt on Hainan Island, China and its implication for pedogenesis
Geoderma
(2008) - et al.
Organic matter dynamics and aggregation in soils under rain forest and pastures of increasing age in the eastern Amazon basin
Geoderma
(1997) - et al.
Nutrient cycling in a clonal stand of Eucalyptus and an adjacent savanna ecosystem in Congo. 1. Chemical composition of rainfall, throughfall and stemflow solutions
For. Ecol. Manage.
(2003)
Nutrient cycling in a clonal stand of Eucalyptus and an adjacent savanna ecosystem in Congo. 2. Chemical composition of soil solutions
For. Ecol. Manage.
Nutrient cycling in a clonal stand of Eucalyptus and an adjacent savanna ecosystem in Congo. 3 Input-output budgets and consequences for the sustainability of the plantations
For. Ecol. Manage.
Biogeochemical cycles of nutrients in tropical Eucalyptus plantations Main features shown by intensive monitoring in Congo and Brazil
Forest Ecol. Manage.
Weathering trends and parent material characteristics of polygenetic oxisols from Minas Gerais, Brazil: I. Mireralogy
Geoderma
Chemical weathering in a tropical watershed, Luquillo Mountains, Puerto Rico: II. The rate and mechanism of biotite weathering
Geochim. Cosmochim. Acta
Soil CO2 effluxes, soil carbon balance, and early tree growth following savannah afforestation in Congo: comparison of two site preparation treatments
For. Ecol. Manage.
Within-stand and seasonal variation of specific leaf area in a clonal Eucalyptus plantation in the Republic of Congo
Forest Ecol. Manage.
The temporal evolution of pedogenic Fe-smectite to Fe-kaolin via interstratified kaolin-smectite in a moist tropical chronosequence
Geoderma
Hybrid and clonal variability of nutrient content and nutrient use efficiency in Eucalyptus stands in Congo
For. Ecol. Manage.
Age-related equations for above-and below-ground biomass of a Eucalyptus hybrid in Congo
For. Ecol. Manage.
Properties of iron oxides in some New Caledonien soils
Geoderma
Is there Holocene reddening (hematite formation) in soils of axeric temperate areas?
Geoderma
Mineralogy and ion exchange properties of the particle size fractions of some Brazilian soils in tropical humid areas
Geoderma
Properties of kaolins in red Oxisols and red Ultisols in Thailand
Appl. Clay Sci.
Chemical weathering in a tropical watershed, Luquillo Mountains, Puerto Rico: I. Long term vs. short term weathering fluxes
Geochim. Cosmochim. Acta
Mineralogy and stratigraphy of three deep lateritic profiles of the Jos plateau (Central Nigeria)
Catena
Effect of land clearing method on chemical properties of an Ultisol in the Amazon
Soil Sci. Soc. Am. J.
Quantitative determination of vermiculite in soils
Soil Sci. Soc. Am. Proc.
Dynamic role of “illite-like” clay minerals in temperate soils: facts and hypotheses
Biogeochemistry
Chemical composition of soil vermiculite clays as related to their genesis
Contrib. Mineral. Petrol.
Soils and Geomorphology
Ion exchange in soil-plant root environment: II. The effect of type of clay mineral upon nutrient uptake by plants
Soil Sci. Soc. Am. Proc.
The alteration and formation of soil minerals by weathering
Contribution à l'étude des ‘stones lines’ dans la région du Moyen Ogoué (Gabon)
The Iron Oxides
Carte géologique de reconnaissance
Estimation of components of soil cation exchange capacity from measurements of specific surface and organic matter
Soil Sci. Soc. Am. J.
Kaolin and serpentine group minerals
Titanium as free oxide and substituted forms in kaolinites and other soil minerals
Clays Clay Miner.
Silica in soils: quartz and disordered silica polymorphs
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2021, Biosystems EngineeringCitation Excerpt :Subsequently, clay content followed while the silt fraction had the least portion. The particle size distribution is consistent with previous studies also assessing semi-arid soils (e.g. Eze et al., 2021; Mareschal et al., 2011). Generally, the EC levels were less than 1 dS m−1 except for a single horizon in pedon 6 [i.e. (Ap) 0–10] with an EC value of 2.23 dS m−1.