Page 1 : ee, I:, 1, \*, dT, 1, |", |, , SOIL COLOUR, , The colour of soil varies widely. It is probably the first soil property for the, “human perception. It is easily observable characteristics and is an important, iterion in description and classification of soils., , Even today soil is described by its colour such as black, red and yellow soils., he three variables that combine to give colour are hue, value and chroma., , Hue is the dominant spectral colour (rainbow) and is related to wavelength of, ” ight., , * Value refers to the relative lightness of colour andis a function of total amount, of light., , Chroma is the relative purity or strength of the spectral colour., , Tye, , wv wv, , U, , Scanned with CamScanner

Page 2 : ae. It is ratherdifficult to quantify. soil.colour. The present practice is:to. match +., colour of a soil with that in Munsell colour chart. In the Munsell colour chart,, three basic hues are considered viz. red (R) , yellow red ( YR ) and yellow (Y )é, preceded by numbers 0 to 10. Increase in the number indicates that the hue, becomes more yellow and less red. The notation for value consists of numbers from, 0 for absolute black to 10 for absolute white. The extremes are not usually met ss, within soils. The notation for chroma consists of numbers beginning at 0 for neutralte~. ’, , grays increasing at equal intervals to 8. ia, , , , The colour of soil has some relevance to soil constituents viz. organic matter, 5, oxides of iron. Black colour of organic and peat soils is due to organic matter. Undere,, tropical conditions, black scils are rather low in organic matter and the black colour, >, rather dark grey colour is due to the combination of base status (Na, Ca), humus an =, montmorillonitic clay mineral. Iron oxides occur in several hydrated and coloured, forms, which may impart red to yellow colour to soil., , Colour of a soil is inherited from its parent rock material termed =, lithochromic; for example, red soils developed ‘from red sand stone. Often the so?, , colour is a result of soil forming process and is termed as acquired or peduchromic.¢, ", , (a) Black and dark grey colour : The variations from black to dark grey_, , ), , &, , colour of soil are mainly due to organic matter. 4, (b) Brown colour : This is the most common soil colour and is due to % if, mixture of the organic matter and iron oxides. }, (c) Red yellow colour : Red colour is associated with unhydrated ferrig,. f, oxides , whereas yellow colour indicates some degree of hydration. _b, (d) White coiour: Silica and lime generally imparts white colour. we, (e) Bluish and Greenish colour : Some of the bluish and greenish colourg, @, are due to the presence of ferrous compounds. The reducing condition occurs in ¢ >, , 2, , ), , ill-drained soil. © ©, (f) Mottling colour : Colour variation or mottling in soils indicates_ |;, alternating oxidizing and reducing conditions due to fluctuating water table. we ©, , Scanned with CamScanner