Soil properties and

1. SOIL PROPERTIES AND CLASSIFICATION

2. SOIL PROPERTIES The various properties of soil include- Color Texture Humus Soil structures

3. COLOUR Colour is the foremost physical property that can be seen with naked eye and is useful in interpretation of valuable insight into the soil environment, thus it can be very important in assessment and classification of soil.

4. DIFFERENT SOIL COLOURS The most influential colours in a well drained soil are white, red, brown and black. White indicates the predominance of silica (quartz), or the presence of salts. Red indicates the accumulation of iron oxides. Brown and black indicate the level and type of organic matter. A colour triangle can be used to show the names and relationships between the influential colours. 

5. FACTORS DETERMINING SOIL COLOUR Four main factors influence the colour of a soil: Mineral matter derived from the constituents of the parent material Organic matter The nature and abundance of iron Moisture content

6. INTERPRETATION USING SOIL COLOUR If we understand what determines soil colour, then we can use colour to make some inferences about, history, chemistry and hydrology. For example, an obvious change in colour between horizons is a real indication of changes in soil properties which are the result of biological activity, water movement and weathering.

7. DETERMINING SOIL COLOUR Soil colour should be determined on moist surfaces of freshly broken (not sliced) soil samples. Like any other soil property, colour must always be observed throughout soil profile, paying special attention to the differences between soil horizons. Colour characteristics such as mottle size, percentage and contrast should be observed and recorded. A system that uses specially printed colour charts ( Munsell Soil Colour Charts) gives an international standard. It divides colour into wavelength, lightness, and colour saturation. Where a Munsell Chart is not available, simple names as listed in the triangle can be used.

8. 8 Munsell Color Charts Hue = dominant spectral or “rainbow” color Red , Yellow, Blue, Green Number increases and the color is more brilliant as grayness decreases

9. 9 Color Determination in the field ALWAYS USE MOIST SOIL Munsell’s color charts values:- Absolute black = 0 Absolute white = 10 Light soils hue value = 7 or more Medium soils hue value = 5 – 6 Dark soils hue value = 4 or less

10. MOTTLES Spots of different colors in the soil Generally indicate that the soil has periods of inadequate aeration each year Usually rust colored Bluish, grayish, & greenish subsoils – with or w/o mottles = indicate longer periods each year of waterlogged conditions & inadequate aeration.

11. HUMUS The term was coined in1790–1800; (< Latin : earth, ground) Dark brown or black organic substance made up of decayed plant or animal organic matter, that provides nutrients for plants and increases ability of soil to retain water

12. In soil science, humus refers to any organic matter that has reached a point of stability, where it will break down no further and might, if conditions do not change, remain as it is for centuries. Humus significantly improves the structure of soil and contributes to moisture and nutrient retention. In agriculture, humus is sometimes also used to describe mature compost, or natural compost extracted from a forest or other spontaneous source for use to amend soil. It is also used to describe a topsoil horizon that contains organic matter

13. Humus also controls the colour of soil higher the humus content darker is the soil colour .

14. TEXTURE Refers to the size of particles. Three types are…. Sand (Large) Silt (Medium) Clay (Small) TEXTURE = % of sand , silt and clay.

15. SOIL STRUCTURE The soil structures commonly seen are- Blocky Platy Massive Prismatic Granular

16. BLOCKY Particles cling together in angular aggregates . Typical of soils with high clay content . Typical of B horizons . beds are large about 5 to 50 millimeters.

17. 2. PLATY Large, thin b eds. Plate-like & arranged in overlapping horizontal layers.

18. 3. MASSIVE Soil has no visible structure . Hard to break apart & appears in very large clods.

19. 4. PRISMATIC Prismatic structure are bounded by flat to rounded vertical faces. Units are longer vertically and top of the prisms are normally flat. It is commonly found in B horizons.

20. 5. GRANULAR Is the best for most plants. Particles cling together to form rounded aggregates. It is commonly found in A horizons. Beds are small usually between 1 to 10 millimeters.

21. SOIL CLASSIFICATION Soil can be classified according to the grain size as- Fine grained- Clay Medium grained- Silt Coarse grained- Sand

22. CLAY < 0.002 mm Flat plates or tiny flakes Small clay particles are colloids If suspended in water will not settle

23. Wet clay is very sticky and is plastic or it can be molded readily into a shape or rod. Easily formed into long ribbons

24. Pores spaces are very small and convoluted Movement of water and air very slow Water holding capacity Tremendous capacity to adsorb water- not all available for plants . Chemical adsorption is large

25. SILT < 0.05 mm to > 0.002 mm Not visible without microscope Quartz often dominant mineral in silt since other minerals have weathered away.

26. Does not feel gritty Floury feel –smooth like silly putty

27. Smaller particles – retains more water for plants and have slower drainage than sand . Easily washed away by flowing water – highly erosive . Holds more plant nutrients than sand.

28. SAND Feels gritty Considered non-cohesive – does not stick together in a mass unless it is very wet.

29. Sand has less nutrients for plants than smaller particles Voids between sand particles promote free drainage and entry of air Holds little water and prone to drought

30. On the basis of texture soil can be classified as :- Sandy soil Loamy soil Clayey soil

31. Sandy Soils Coarse texture Sands Loamy sands

32. Loamy Soils- Coarse Medium texture Very fine sandy loam Loam Silt loam Silt

33. Loamy Soils - Fine Moderately fine texture Sandy clay loam Clay loam Silty clay loam

34. Clayey Soils Fine texture Silty clay Clay Sandy clay

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