Soils

1. Soils Mrs. Gill

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