1. Soils Mr. Smith

2. Components of the soil profile The "A" horizon The "B" horizon The "C" horizon

3. Characteristics of the soil horizons The "C" horizon –Generally called parent material –It is the deepest of the three major horizons –Usually very low in organic matter –Usually no structure

4. Characteristics of the soil horizons The "B" horizon –Generally called the subsoil –Usually lower in organic matter and lighter in color than "A" horizon –Usually red or yellowish in color –Structure is less desirable than the "A" horizon; it may have a blocky or prismatic structure –Frequently heavier texture than "A" horizon

5. Characteristics of the soil horizons The "A" horizon –It includes the upper part of the profile in which life is most active; generally called the topsoil –It is the most productive horizon because of its normally high organic matter content and is usually dark colored –May be from a few inches to a foot or more deep –Lighter in texture than the "B" or "C" horizons –More likely to have granular structure than the other horizons

6. Importance of soils Plants grow in and on soil Plants support animal life Plants and animals support human life World population is rapidly increasing and/or has inadequate nutrition Supply of productive soil is limited Improved soil management could feed more people

7. Function of soil as related to plant growth, development and maintenance Media for seed germination Media for support of plants Storehouse of plant nutrients Storehouse of water for the plant

8. Soil composition TM 3

9. Soil composition Solids--Approximately 50% –Mineral matter –Organic matter –Living organisms Pore space--Approximately 50% –Water –Air

10. Factors affecting soil formation Parent materials –Residual Igneous--Derived from molten materials in the center of the earth's crust (granitic, basaltic) Metamorphic--Formed from the pre-existing rocks through the action of extreme heat and pressures (quartzite, schist) Sedimentary--Formed from sediments deposited by wind, water or ice (shale, sandstone, limestone)

11. Factors affecting soil formation Parent Material –Transported Wind (loess) Water (alluvial) Glaciers (glacial drift) Gravity (colluvial)

12. Factors affecting soil formation Decomposition by weathering –Physical weathering Wind Plants and animals Heating and cooling Freezing and thawing Wetting and drying –Chemical weathering--Chemical reactions of water, oxygen and carbon dioxide –Biological weathering--Micro-organisms secrete a gummy substance which aids in decomposing rocks

13. Factors affecting soil formation Climate –Temperature –Rainfall Vegetation and organisms –Plant--Lichens, mosses, weeds, grasses, shrubs, trees –Animal--Bacteria, fungi, large animals (cattle, horses, etc.) birds, man

14. Factors affecting soil formation Slope and drainage –Hillsides Thin topsoil due to soil loss by erosion Reduced plant growth Low organic matter Less leaching (due to runoff) –Flat lands Deeper topsoil More vegetation High organic matter Greater leaching

15. Explore the physical properties of soil A.Soil texture B.Soil structure C.Soil depth D.Soil color

16. Soil particles Sand –Diameter--2.00 to 0.05 mm –Coarse and gritty –When moist, individual grains can be seen –Its presence decreases water-holding capacity –Its presence decreases nutrient holding capacity

17. Soil particles Silt –Diameter--.05 to.002 mm –Its presence increases water-holding capacity –Its presence increases nutrient holding capacity –Moderate to high exchange capacity –Feels smooth and velvety

18. Soil particles Clay –Diameter--less than.002 mm –Its presence increases water-holding capacity –Its presence increases nutrient holding capacity –High to very high exchange capacity

19. Determine soil texture Mechanical analysis –A mechanical analysis of a soil reports the percentage of each of the soil particles (sand, silt and clay) –Percentages can be applied to the texture triangle to determine the texture of a soil

20. Determine soil texture Feel method –Texture is determined by moistening the soil and rubbing between thumb and fingers –The wet sample is worked into a ball and placed between thumb and index finger, the thumb is pushed gradually forward in an attempt to form the soil into a ribbon (clayey soil) –If the wet sample will not form a ribbon, evaluate for grittiness (sandy soil) –Evaluate wet sample to determine if it feels velvety and slick, but will not ribbon (silty soil)

21. Soil Texture Descriptions of soils of different texture using the feel method –Sandy soil Coarse and gritty When moist, individual grains can be seen Called a "light" soil –Silty soil Feels smooth, flowing when dry Feels velvety or slick when wet –Clayey soil Sticky and will form a ribbon when wet Very hard when dry Called a "heavy" soil

22. Soil Structure Granular (sphere shaped) -- Ideal for plant growth

23. Soil Structure Blocky (sharp and angular faces) –Water storage good –Circulation of air and water is poor

24. Soil Structure Platy (flat, horizontal, plate-like)--Poor permeability

25. Soil Structure Prismatic and columnar (column-like)-- Poor air-water relationship

26. Soil Structure Massive

27. Color and importance Color is an important characteristic used in the identification of soil conditions that affect the value of land for agricultural uses Influenced mainly by organic matter content; benefits of organic matter include –Makes soil porous –Supplies nitrogen and other nutrients to the plant –Holds water in the soil –Reduces leaching –Improves soil structure

28. Soil colors Dark brown to black--Regarded as the most productive; usually contains a higher organic matter content Red or reddish brown--Usually less fertile than black or dark brown soils; may contain a high iron content Yellow or gray--Usually caused by imperfect drainage

29. Acidity or alkalinity The acidity or alkalinity of the soil solution is determined by the relative number of hydrogen (H + ) ions and hydroxyl (OH - ) ions When a soil solution contains more H + ions than OH - ions, it is acidic. When the OH - ions are more abundant, the solution is alkaline. A neutral solution has an equal amount of H + and OH - ions

30. pH pH ranges on a scale from 1 to 14 –1 to 7--Acidic soil –7--Neutral soil –7 to 14--Alkaline soil

33. Liming soils Soil acidity can be corrected by adding lime to the soil. The function of lime is to neutralize the hydrogen (H+) ions that cause soil acidity

34. Liming soils Amount of lime to apply depends on –The degree of acidity of the soil –The crops to be grown –The grade or purity of the lime materials –The frequency of application –Soil texture –Soil exchange capacity

35. Types of alkali soils Saline--Soils in which there has been an accumulation of soluble salts, for example: NaCl (table salt); these are referred to as "white alkali" soils Sodic--Soils in which there has been an accumulation of sodium (Na); sodium affected soils have low permeability to water Saline-sodic--Both salty and sodic affected

36. Reclamation of alkali soils Saline –Flood with water and leach out salts –Install drainage tiles to remove accumulated salts –Grow salt tolerant crops Sodic –Apply gypsum (CaSO4) –Grow sodic tolerant crops Saline-sodic –First correct sodic –Then correct salt problem