Soils colour

Field pH, Munsell soil colour (dry moist), EC 1 5 (soil water), pH 1 5, XRD, laser particle size analysis, XRF (multiple elements), ICP-MS (after HNO3/HCKV HF/HCI digestion for multiple elements), ICP-MS (after HF/HCI/HNO3 digestion for Se), ISE (for F), GF-AAS (for Au), and ICP-MS after MMI extraction were performed. Full details of the sampling and analytical methods are given in Caritat Lech (2007). 

Iron oxides are responsible for the vivid colours of many rocks and sods. The typical yello v-red to purple red colours of the so-called red beds are due to hematite (Torrent Schwertmann, 1987). The strong influence of hematite on soil colour is referred to in various languages and appears in the terms red earths, terra rossa and krasno-zems (see Chap. 15 16). 

Iron oxides in soils have in common that they are of extremely small crystal size and/or low crystal order. This, in combination with their low concentration (only tens g kg in most soils) explains why soil iron oxides have escaped identification for a long time in spite of their obvious existence as seen from the soil colour. In the past, therefore, Fe oxides in surface environments have been considered to be amorphous to X-rays and often called limonite , which mineralogically, is an obsolete term. Furthermore, in order to identify the clay minerals in soils properly, Fe oxides are usually removed before X-ray diffraction methods are applied (Alexander et al., 1939 Mehra Jackson, 1960). 

This reflects the fact that the colour is one of the easiest ways of distinguishing soils. Even in 1937 Alexander et al. noticed that very red soils owe their colour to the presence of hematite . An objective notation of soil colour is needed to describe... 

Barron, V. Torrent, J. (1984) Influence of aluminum substitution on the color of synthetic hematites. Clays Clay Min. 32 157-158 Barron, V. Torrent, J. (1986) Use of the Ku-belka-Munk theory to study the influence of iron oxides on soil colour. Soil Sci. 37 499-510... 

Biedermann, G. Schindler, P. (1957) On the solubility products of precipitated iron(lll) hydroxide. Acta Chem. Scand. 11 731-740 Bigham, J.M. Ciolkosz, E.J. (1993) Soil colour. Soil Sci. Soc. Am. Spec. Publ. 31, Madison, Wl, 159 p. 

Blavet, D. Mathe, E. Leprun, J.C. (2000) Relations between soil colour and waterlogging duration in a representative hillside of the West African granito-gneissic bedrock. Catena 39 187-210... 

Torrent, J. Schwertmann, U. Fechter, H. A1-ferez, F. (1983) Quantitative relationships between soil colour and hematite content. Soil Sci. 136 354-358... 

Fig. 5-I I. Propane concentrations and soil colour of augcred samples along a traverse of sample sites over an underground propane storage reservoir.

Soil Sampling. The types of land to be sampled should be distinct in some clear way - such as by soil colour, cultivation, slope, drainage or soil type. If it is available, a soil map of the area being sampled would give better definition of the samples taken. 

Use a tape measure to allow the recording of depths and hence the thicknesses of the soil horizons in the profile. Colour is used to identify the different horizons within the profile. Standardized descriptions of colour can be obtained by the use of the Munsell Soil Colour Chart System (see Chapter 1). 

A. When sampling is planned complete information about the type of soil, colour, consistency, texture, sampling horizon, drainage conditions, type of vegetation, weather conditions and human activity should be available. 

Enzymic activities of crude soil suspensions have been demonstrated to follow Michaelis-Menten kinetics. Calculated Km values have varied for different soils and for active fractions of soil extracts. The extent to which kinetic constants of soil enzymes are influenced by the state in which the enzymes occur in soils, is unknown. For some activities, two Km values have been distinguished for the one crude soil extract. Fractionation has revealed that enzymes may exist in tightly- and loosely- bound complexes with soil coloured humic compounds. Enzymes freed of coloured materials may nevertheless still be bound in complexes by their association with carbohydrates. These may not only influence enzyme kinetic properties but evidence suggests that they may also confer some degree of stability on the enzymes in soil. Whereas early speculation on the mechanism(s) by which enzymes are protected in soil tended, in the case of abiontic enzymes, to focus on the role of clay or humic colloids, fractionation studies have drawn attention to the potentially important role of soil carbohydrates. The manner in which carbohydrates are bonded to the enzymes in soil has not as yet been established and may be a fruitful line of enquiry. 

B. Jaillard, L. Ruiz, and J. C. Arvicu, pH mapping in transparent gel using colour indicator video-densitometry. Plant Soil /83 85 (1996). 

A Spectrophotometric method has been described for determining down to 2pg of this fungicide in soil based on the formation of a coloured reaction product with aniline [256],... 

In the method for extractable phosphorus [62, 64-66] the phosphorus is extracted from the soil at 20 1°C with sodium bicarbonate solution at pH8.5. After filtration and release of carbon dioxide the extracts are introduced into a flow-injection system for the determination of phosphate. Phosphate is determined by reaction with vanadomolybdate and the yellow colour evaluated at 410nm. Between 20 and lOOOmg kg-1 phosphorus in soil has been determined using this method. 

There is evidence that mixed Fe(II)-Fe(III) hydroxides are formed. These can be produced easily in vitro by partial oxidation of pure Fe(II) hydroxy salts and they have some of the observed properties of the solid phase Fe(II) found in reduced soils, including the grayish-green colours characteristic of reducing conditions in soils. This material is green rust and has the general formula Fe(II)6Fe(III)2(OH)i8 with Al + partly substituted for Fe + and Cl, S04 and C03 substituted for OH . 

In addition, because all of these soils contain Fe(OH)3(am) [the mineraloid ferrihydroxide], both before and after digestion (based on colour), the pH of each soil and the resulting solution after digestion were measured, along with the soluble iron concentration (Fe ). Using these data and the equilibrium ... 

The orange coloured lepidocrocite, y-FeOOH, is named after its platy crystal shape (lepidos scale) and its orange colour (krokus = saffron). It occurs in rocks, soils, biota and rust and is often an oxidation product of Fe ". It has the boehmite (y-AlOOH) structure which is based on cubic close packing (ccp) of anions. 

In soil and other geosciences, colour is commonly measured using the Munsell colour classification system. This system defines colour in terms of hue H (position of colour in the spectrum), chroma C (the purity of the hue going from the grey to the pure colour) and value V (the lightness of the colour on a scale ranging from black to white). The reflectance measurements can be converted into the characteristic parameters or coordinates of the different measurement systems. 

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