Color attributes and mineralogical characteristics, evaluated by radiometry, of highly weathered tropical soils

Highly weathered soils are important around the world. Determination of their observed colors and acquisition of spectral curves were used to study their mineralogy. Color was determined through visual comparison with Munsell Soil Color Charts, and soils spectral characterization was made with an in...

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Bibliographic Details
Published in:	Soil Science Society of America journal Vol. 69; no. 4; pp. 1162 - 1172
Main Authors:	Fontes, M.P.F, Carvalho, I.A. Jr
Format:	Journal Article
Language:	English
Published:	Madison Soil Science Society 01-07-2005 Soil Science Society of America American Society of Agronomy
Subjects:	Absorption Agronomy. Soil science and plant productions Biological and medical sciences Color Earth sciences Earth, ocean, space Exact sciences and technology Fundamental and applied biological sciences. Psychology Kaolinite Methods and techniques Mineralogy Minerals Organic matter Radiometry Reflectance soil color soil mineralogy Soil organic matter Soil science Soil surveys, classification and mapping Soil surveys, classification and mapping, soil genesis soil weathering Soils spectral analysis spectroradiometry Surficial geology Tropical environments tropical soils Brazil South America Iron oxide Spectroradiometry color Property composition relationship Attribute tropical zone mineralogy soil sciences Physical environment Munsell chart Inorganic compound Spectral data colorimetry mineral composition evaluation Tropical soil inorganic materials radiometry Non silicate mineral Soil science soils Silicate mineral Intelligent system infrared spectroscopy Intertropical zone Iron compound Property of soil Weathered zone Earth science Oxisols optical methods laterites Intelligent spectroradiometer infrared spectra organic materials Environmental effect
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Summary:	Highly weathered soils are important around the world. Determination of their observed colors and acquisition of spectral curves were used to study their mineralogy. Color was determined through visual comparison with Munsell Soil Color Charts, and soils spectral characterization was made with an infrared intelligent spectroradiometer (IRIS) covering a spectral window from 300 to 3000 nm. The variables of color behaved differently among soils. The Munsell hue was related to hematite content and the hematite/goethite ratio (Hm/Gt), and the Munsell value to organic content of goethitic soils. The Munsell chroma was related to the presence of Fe oxides, giving an idea of relative amounts of either hematite or goethite. Regression equations relating color indices showed that the redness factor (RF) gave the highest determination coefficients to estimate hematite content and Hm/Gt, and reconfirmed that redness saturation occurs with increasing hematite amounts. The typical minerals of these soils showed characteristic absorption bands in their spectral curves. Absorption bands of 450 and 900 nm for Fe oxides, 2200 nm for kaolinite and 2280 for gibbsite, were distinctive features of the main minerals present. Organic matter decreased the intensity of reflectance for most soils and, under its influence, the characteristic bands of goethite practically disappeared while the ones for hematite, kaolinite, and gibbsite were attenuated. High amounts of hematite decreased the reflectance factor strongly as compared with the soil organic matter (SOM). Qualitative mineralogy of highly weathered soils was assessed by radiometry using measurements in the visible and near infrared regions of the electromagnetic spectrum.
ISSN:	0361-5995 1435-0661
DOI:	10.2136/sssaj2003.0312