Tropical soil

Ferruginous and aiuminous clay soils are frequent products of weathering in tropical latitudes. They are characterized by the presence of iron and aluminium oxides and hydroxides. These compounds, especially those of iron, are responsible for the red, brown and yellow colours of the soils. The soils may be fine grained, or they may contain nodules or concretions. Concretions occur in the matrix where there are higher concentrations of oxides in the soil. More extensive accumulations of oxides give rise to laterite. 

Laterite hardens on exposure to air. Hardening may be due to a change in the hydration of iron and aluminium oxides. 

Laterite commonly contains all size fractions from clay to gravel and sometimes even larger material (Fig. 5.6). Usually, at or near the surface, the liquid limit of laterite does not exceed 60% and the plasticity index is less than 30%. Consequently, laterite is of low to medium 

Grading curves of laterite (after Madu, 1977). With kind permission of Elsevier. 

Lateritic soils, particularly where they are mature, furnish a good bearing stratum (Blight. 1990). The hardened crust has a low compressibility and, therefore, settlement is likely to be negligible. In such instances, however, the strength of the soil may decrease with increasing depth. 

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Stratospheric distribution of NjO Atmospheric accumulation of NjO (0.25% yr ) Natural emissions (largely from tropical soils) Anthropogenic emissions cultivated soils (-h industry and combustion) 40 8.0 (. 1 sources... 

Parlq)ian P, Anuralqtongsatorn P, Patrick WHJ. 1998. Adsorption, desorption and degradation of a-endosulfan in tropical soils of Thailand. J Environ Sci Health B 33(3) 211-233. 

Figure 1.1. (a) Climate categories based on mean annual precipitation (b) Desert and steppe boundaries as a function of both mean annual precipitation and temperature according to the Koeppen system arrows show how boundaries shift according to whether precipitation falls mainly in in the summer or winter (after Monger et al., 2004. Reprinted from Encyclopedia of Soils in the Environment, D. Hillel, Tropical soils Arid and Semi-arid, p 183, Copyright (2004), with permission from Elsevier)... 

Monger H.C., Martinez-Rios J., Khresat S.A. Tropical soils Arid and Semi-arid. In Encyclopedia of Soils in the Environment, D. Hillel, ed. Amsterdam Elsevier, 2004. 

Fig. 8. Arsenic extraction from a reddish brown tropical soil deliberately contaminated with arsenate as a function of reaction time by 0.005M chloride, sulphate, carbonate and phosphate. Redrawn from Goh and Lym (2005).

Waldrop MP, Balser TC, Firestone MK (2000) Linking microbial community composition to function in a tropical soil. Soil Biol Biochem 32 1837-1846... 

J Polym Environ 15 125-150. doi 10.1007/sl0924-007-0053-8 Lai R (1974) Soil temperature, soil moisture, and maize yield from mulched and unmulched tropical soils. Plant Soil 40 129-143... 

Geochemical conditions of tropical soils favor the biogeochemical migration of iron and manganese. The turnover of other metals is from 1.1 g/ha/yr for Cd to 1,050.0 g/ha/yr for Sr with the relevant rates of exposure to living organisms. 

Mohr, E. C. J., F. A. Van Baren, and J. Van Schuylenborgh (1972), Tropical Soils, 3rd Edition, Mouton-Ichtiar Baru-Van Hoeve, The Hague, Netherlands. 

From the amino acid data in Table 8.2, protein N was calculated to make up 36, 40.46 and 45 % of the total N in the arctic, cool temperate, subtropical and tropical soils, respectively, averaging 42 %. Thus, about 58 % of the total N in soils was nonprotein. Amino sugars in the soils constituted between 4.5 and 7.4% of the total N, with soils under warmer climates containing more amino sugars than those under cooler dimates. 

Ricefields in Asia Calculated from contents of tropical soils and assumed high sedimentation rate (1kg m year ) 0.4-0.7... 

Scharpenseel UW. 1997. Preface to workshop Management of carbon in tropical soils under global change science, practice and policy . Geoderma 79 1-8. 

The example of a total extract composition of a tropical soil from the Amazon, Brazil, shows mycose as the major compound, numerous other monosaccharides, lipid components such as fatty acids and fatty alcohols, and natural product biomarkers (Fig. 9a). The mycose and elevated levels of the other saccharides reflect the efficient fungal/microbial degradation of plant detritus in the tropics. This can be compared to the saccharides in the soil from an almond orchard in California, where glucose and mycose are the main sugars with lipids, sterols and triterpenoids (Fig. 9b, ). 

Wong, T. P., Byappanahalli, M., Yoneyama, B., and Ray, C. (2008). An evaluation of the mobility of pathogen indicators, Escherichia coli and bacteriophage MS-2, in a highly weathered tropical soil under unsaturated conditions. ]. Water ELealth 6,131-140. 

Where stream waters contain Fe, boulders on the bottom are often coated with Fe oxides with no relationship to the petrography of the boulders. The amount of Fe oxide deposited is around a few mg cm (Schwertmann and Friedl, 1998) and the annual accretion rate is in the range of 100 xg cm (Carpenter Hayes, 1980). Suspended particles in brownish, drainage waters from tropical soils in the Cameroons, in which goethite with some hematite were identified, are transported from the soil profile to a spring and then to the water course (Olovie-Lauquet et al. 2000). 

Da Motta Kampf, 1992), but no correlation has been found in others (Anand Gilkes, 1987 Zeese et ah, 1994). The ratio may depend on whether or not the two oxides were formed simultaneously in the same environment. Maghemites from tropical soils contained A1 up to an Al/(Fe -i- Al) ratio of ca. 0.15 as indicated by chemical analysis and reduction in unit cell size (Schwertmann Fechter, 1984 Fontes Weed, 1991). 

Natural Fe oxides have also been used for water purification. In a laboratory study, a natural ferrihydrite (surface area of 243 m g ) originating from a ferriferrous acid spring turned out to be capable of removing > 95 % of the inorganic phosphate from water with 0.1 mg P L (WeiE et al., 1992). The so-called Red Mud, a waste product of the alumina industry, containing 330 g Fe/kg was also effective, whereas a tropical soil with 80 g kg Fe was comparatively less so (WeiE et al., 1992a). Nine... 

Shang, C. Tiessen, H., (1998). Organic matter stabilization in two semiarid tropical soils size, density and magnetic separation. Soil Sci. Am. J.62 1247-1257. 

Sissingh, H.A. (1983) Estimation of plant-avail-able phosphate in tropical soils A new analytical technique. Note 235, Institute for Soil Fertility, Haren, Netherlands Skinner, H.G.W. Fitzpatrick, R.W (eds.)... 

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