<P> Soil colour is often the first impression one has when viewing soil . Striking colours and contrasting patterns are especially noticeable . The Red River of the South carries sediment eroded from extensive reddish soils like Port Silt Loam in Oklahoma . The Yellow River in China carries yellow sediment from eroding loess soils . Mollisols in the Great Plains of North America are darkened and enriched by organic matter . Podsols in boreal forests have highly contrasting layers due to acidity and leaching . </P> <P> In general, color is determined by the organic matter content, drainage conditions, and degree of oxidation . Soil color, while easily discerned, has little use in predicting soil characteristics . It is of use in distinguishing boundaries within a soil profile, determining the origin of a soil's parent material, as an indication of wetness and waterlogged conditions, and as a qualitative means of measuring organic, iron oxide and clay contents of soils . Color is recorded in the Munsell color system as for instance 10YR3 / 4 Dusky Red, with 10YR as hue, 3 as value and 4 as chroma . Munsell color dimensions (hue, value and chroma) can be averaged among samples and treated as quantitative parameters, displaying significant correlations with various soil and vegetation properties . </P> <P> Soil color is primarily influenced by soil mineralogy . Many soil colours are due to various iron minerals . The development and distribution of colour in a soil profile result from chemical and biological weathering, especially redox reactions . As the primary minerals in soil parent material weather, the elements combine into new and colourful compounds . Iron forms secondary minerals of a yellow or red colour, organic matter decomposes into black and brown humic compounds, and manganese, sulfur and nitrogen can form black mineral deposits . These pigments can produce various colour patterns within a soil . Aerobic conditions produce uniform or gradual colour changes, while reducing environments (anaerobic) result in rapid colour flow with complex, mottled patterns and points of colour concentration . </P> <P> Soil resistivity is a measure of a soil's ability to retard the conduction of an electric current . The electrical resistivity of soil can affect the rate of galvanic corrosion of metallic structures in contact with the soil . Higher moisture content or increased electrolyte concentration can lower resistivity and increase conductivity, thereby increasing the rate of corrosion . Soil resistivity values typically range from about 2 to 1000 Ω m, but more extreme values are not unusual . </P>

Different types of soil found in india wikipedia