Biogeosciences Discuss., 6, 3851–3921, 2009 Biogeosciences www.biogeosciences-discuss.net/6/3851/2009/ Discussions BGD © Author(s) 2009. This work is distributed under 6, 3851–3921, 2009 the Creative Commons Attribution 3.0 License. Biogeosciences Discussions is the access reviewed discussion forum of Biogeosciences The soils of RAINFOR Project C. A. Quesada et al. Soils of amazonia with particular reference to the rainfor sites Title Page Abstract Introduction C. A. Quesada1,2, J. Lloyd1, L. O. Anderson3, N. M. Fyllas1, M. Schwarz4,*, and C. I. Czimczik4,** Conclusions References 1 School of Geography, University of Leeds, LS2 9JT, Leeds, UK Tables Figures 2Institito Nacional de Pesquisas da Amazonia,ˆ Avenida Andre´ Araujo,´ 2936, Aleixo, CEP 69060-001, Manaus, AM, Brazil J I 3School of Geography and the Environment, University of Oxford, South Parks Road, Oxford, OX1 3QY, England, UK J I 4Max-Planck-Institut fuer Biogeochemie, Postfach 100164, 07701, Jena, Germany *now at: Fieldwork Assistance, Postfach 101022, 07710 Jena, Germany Back Close ** now at: Department of Earth System Science, University of California, 2103 Croul Hall, Full Screen / Esc Irvine, CA, 92697-3100, USA Received: 18 December 2008 – Accepted: 10 February 2009 – Published: 8 April 2009 Printer-friendly Version Correspondence to: C. A. Quesada ([email protected]) Interactive Discussion Published by Copernicus Publications on behalf of the European Geosciences Union. 3851 Abstract BGD The tropical forests of Amazonia occur on a wide variety of different soil types reflecting a rich diversity of geologic and geomorphologic conditions. We here review the existing 6, 3851–3921, 2009 literature about the main soil groups of Amazonia, describing their genesis, geographi- 5 cal patterns and principal chemical, physical and morphologic characteristics. Original The soils of data is also presented with profiles of exchangeable cations, carbon and particle size RAINFOR Project fraction illustrated for the principal soil types, also emphasizing the high diversity exist- ing within the main soil groups when possible. Maps of geographic distribution of soils C. A. Quesada et al. occurring under forest vegetation are also introduced, and to contextualize soils into an 10 evolutionary framework, a scheme of soil development is proposed having as its basis a chemical weathering index. We identify a continuum of soil evolution in Amazonia Title Page with soil properties varying predictably along this pedogenetic gradient. Abstract Introduction Conclusions References 1 Introduction Tables Figures 1.1 Soil diversity in Amazonia J I 15 Tropical soils can arise from an extremely wide variety of parent materials, climatic conditions, biotic interactions, landforms, geomorphic elements and soil age. Many J I of these factors vary more widely in the tropics than in the temperate zone (Sanchez, Back Close 1976; Richter and Babbar, 1991). Amazonia itself comprises a vast and heterogeneous region, with many of these factors, especially parent materials; landforms, geology and Full Screen / Esc 20 geomorphologic history varying widely (Sombroek, 1966, 2000; Irion, 1978). On the other hand, factors such as soil temperature and soil moisture regimes are common Printer-friendly Version to many Amazonian soils (Sanchez, 1976; van Wambeke, 1978). In the early days of soil science in Amazonia, Marbut and Manifold (1926) observed at least six different Interactive Discussion groups of soils occurring commonly in the region and suggested that many soils oc- 25 curring in the tropics had little or no morphological differences from those observed for 3852 temperate zone soils. Sanchez (1976) and Richter and Babbar (1991) argued against the old misconception that tropical soils are invariably ancient, lateritic and intensively BGD weathered, demonstrating that tropical soils are very diverse, encompassing all dif- 6, 3851–3921, 2009 ferent taxa, from the lowest to the highest pedogenetic levels. Indeed, Sanchez and 5 Buol (1975) had by this time already found that soils previously mapped as Ferralsols in the Peruvian Amazon actually were Ultisols, Alfisols and Inceptsols (Acrisols, Lu- The soils of visols/Lixisols and Cambisols in the World Reference Base soil classification system: RAINFOR Project IUSS Working Group WRB, 2006), and suggested that ancient Ferralsols may actually be confined to areas of the Guyana and Brazilian shields. Sombroek (1966) also re- C. A. Quesada et al. 10 ported a large diversity of soils in his studies of the Brazilian Amazon, describing a high diversity of “latosols”, “kaolinitic latossolic sands”, “podzols”, “lithosols”, ground water Title Page laterites, hydromorphic grey podzolics, “Regosols”, Gleysols, saline and alkali soils, Indian black earths and terras roxas estruturadas (equivalent to present day Nitisols) Abstract Introduction plus other minor and uncommon soil groups not properly identified. Conclusions References 15 Richter and Babbar (1991) gave an analysis of available soil surveys up to that time, comparing results from the FAO World Soil Map (1988) and the Brazilian Soil Survey for Tables Figures Amazonia (EMBRAPA, 1981), also giving estimated coverage areas for each different soil order. They estimated that Ferralsols covered 0.391 of Brazilian Amazonia, with J I Acrisols covering 0.323, Gleysols and Plinthosols 0.063 and 0.069, respectively, and 20 with Arenosols covering 0.044, Leptosols 0.045, Podzols 0.028, and Cambisols 0.013 J I of the area with Fluvisols and Nitisols covering less than 0.010. They also indicated Back Close that there was a considerable bias towards the dominance of Ferralsols in the FAO map which was related to the methodology used by the FAO system; Ferralsols being Full Screen / Esc mapped on the basis of estimates of climate and vegetation data instead of empirical 25 soil analysis. Printer-friendly Version Much of the soil diversity in Amazonia has originated from the considerable differ- ences in geology and geomorphology that occur across the area. Interestingly, much Interactive Discussion early work on this subject was actually undertaken by limnologists interested in rea- sons for observed variations in the elemental composition of river waters within the 3853 Basin. Based on such observations, Fittkau (1971) divided the Amazon Basin into four regions, as shown in Fig. 1. He considered the characteristically low levels of chemical BGD elements (especially calcium) found in the waters of the core area of Central Amazonia 6, 3851–3921, 2009 (Sub-region IV in Fig. 1) to reflect the already low soil fertility of this region (Aubert 5 and Tavernier, 1972) this being associated with the lack of geological activity in recent times. In addition, it was argued that the sediments deposited in this area would also The soils of have had a very low nutrient content, such as for the sands derived from the ancient RAINFOR Project Guyana shield, which is about 1700 million years old (Fittkau et al., 1975). High to- pographic stability combined with continuous hot and wet weather has also already C. A. Quesada et al. 10 resulted in a deep weathering and leaching of parent material with lack of erosion over the generally flat topography eliminating bedrock as a source of nutrients for this part Title Page of Amazonia. Nevertheless, Fittkau (1971) found the natural waters of his peripheral sub-regions Abstract Introduction (Northern, Western and Peripheral Amazonia in Fig. 1) to be significantly richer in Conclusions References 15 chemical elements than the central Amazon Basin with the waters of Western Periph- eral Amazonia being considerably enriched. Not surprisingly, these are also the areas Tables Figures in the Amazon Basin where relatively fertile soils occur, this particularly being the case close to the Andes where topography plays an important role in the maintenance of J I soil fertility through erosion of the soil surface and exposition of the underlying parent 20 material (Jordan and Herrera, 1981). J I The soils of Fittkau’s Central Amazonian sub-region IV are mainly derived from rocks Back Close and sediments from the middle Tertiary with a high probability of belonging to the end of the Cretaceous and thus likely to have experienced more or less continuous weath- Full Screen / Esc ering for more than 20 million years (Irion, 1978). Included in this sub-region, are the 25 Cretaceous-Tertiary sediments, derived from the erosion of the Guyana and Brazilian Printer-friendly Version shields, known as the Barreiras formation (Herrera et al., 1978). These ancient, pre- Cambrian Guyana and Brazilian shields, with their series of igneous and metamorphic Interactive Discussion rocks, are placed to the north and south of the lower Amazon River, encompassing Fittkau’s regions I and II, respectively. 3854 Between these shields and the Amazon River (Fittkau’s region IV) occur strips of Palaeozoic sediments in which Devonian shales are represented to an appreciable ex- BGD tent (Irion, 1978). By contrast, western Amazonian soils (Fittkau’s region III) mostly 6, 3851–3921, 2009 consist of pre-Andine sediments from the Cretaceous-Tertiary period uplifted in the 5 Pliocene. Thus this formation probably commenced between 1 and 2 million years ago. For instance, at the neighbourhood of Acre state, Brazil, a number of fresh water The soils of and marine sediments occur as a result of the Andean orogeny and fluctuations of the RAINFOR Project sea level during warmer climates (Irion, 1978; Kronberg et al., 1989, 1998). Also, the western Amazon