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Introduction to Soils

Introduction to Soils. By Rick Bandy, Resource Soil Scientist Natural Resources Conservation Service. Soil Forming Factors. Parent Material Climate Living Organisms Topography Time. Physical Properties of Soils. Soil Solids 1. Mineral Soil 2. Organic Matter Soil Pore Space 1. Air

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Introduction to Soils

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  1. Introduction to Soils By Rick Bandy, Resource Soil Scientist Natural Resources Conservation Service

  2. Soil Forming Factors • Parent Material • Climate • Living Organisms • Topography • Time

  3. Physical Properties of Soils • Soil Solids • 1. Mineral Soil • 2. Organic Matter • Soil Pore Space • 1. Air • 2. Water

  4. Organic Matter

  5. Organic Matter <5% <10% 33-50% 33-50%

  6. Soil Minerals • Sand • Silt • Clay

  7. Soil Minerals • Sand • - 2.0 to 0.05 mm diameter • - Individual particles visible to the eye • - Rounded or irregular shape • - Gives texture gritty feel • - Influences drainage and air movement

  8. Soil Minerals • Silt • - 0.05 to .002 mm diameter • - Magnify 10 to 100 times to see particles • - Irregular shape • - Gives texture soft, slippery, floury feel • - Largely influences water holding capacity

  9. Soil Minerals • Clay • - Less than .002 mm diameter • - Magnify 2,000 times to see particles • - Gives texture sticky, greasy feel • - Largely influences fertility, permeability, shrinking and swelling

  10. Soil Textural Triangle A. Miller

  11. Soil Mineral Properties

  12. Soil Mineral Properties

  13. Soil Mineral Properties

  14. Bulk Density of Mineral Soils • In the field one cubic centimeter of a • certain soil appears as below • If all the solids were compressed to • the bottom, the cube would look • like this: 1/2 PORE SPACES • 1.33 grams • SOILDS AND PORE SPACES • 1.33 grams • 1/2 SOLIDS • To calculate solid particle density: • Volume = 0.5 cc Weight = 1.33 grams • Solid particle density = Weight of solids/Volume of solids • Therefore • Solid particle density = 1.33/0.5 = 2.66g/cc • To calculate bulk density of the soil: • Volume = 1 cubic centimeter Weight = 1.33 grams • Bulk Density = Weight of soil/Volume of soil • Therefore • Bulk Density = 1.33/1 = 1.33 g/cc

  15. Soil Structure

  16. Granular Soil Structure

  17. Platy Soil Structure

  18. Prismatic Soil Structure

  19. Blocky Soil Structure

  20. Columnar Soil Structure

  21. Forms of water that are held in soils • Capillary Water • Soil Particle • Adsorbed Water

  22. SOIL WATER DIAGRAM • AIR SPACES

  23. Water Holding Capacity of Soils • SATURATION • FIELD CAPACITY • WILTING POINT • Solid Space • Pore Space • SATURATED SOIL • 40 g • 100 g • FIELD CAPACITY • 20 g • 100 g • Air • Air • WILTING POINT • 100 g • 10 g

  24. Soil Moisture Characteristics of Individual Soil Particles • 0 Atm. • 1/3 Atm. • Soil Particle • 15 Atm 31 Atm • Available • Water • Capacity • (AWC) Gravitational Water • Bound Water Permanent Wilting Point Field Capacity Saturated Soil

  25. SOIL MOISTURE CHARACTERISTICS AND TEXTURE FIELD CAPACITY AVAILABLE WATER UNAVAILABLE WATER WILTING POINT

  26. AVAILABLE WATER CAPACITIES FOR SOIL TEXTURAL CLASSES

  27. AWC ADJUSTED FOR ROCKS AND SALT CONTENT IN SOILS 30 .22 .02 25 .20 .04 .18 .06 20 .16 70 .08 60 50 15 .14 40 .10 30 12 20 .12 .12 10 8 4 0 Percent Rock Fragments 0 .10 .14 .08 .16 Salt Content (EC) .06 .18 .04 .20 .02 .22 0

  28. WATER TABLE CapillaryFringe Water Table

  29. STRATIFIED SOILS Clay Sand

  30. RESTRICTIVE LAYER Sandy Loam Clay

  31. SOIL REACTION The degree of acidity or alkalinity of a soil, usually expressed as a pH value or by terms ranging from extremely acid to very strongly alkaline

  32. Ranges found in soils pH scale Bleach 12 11 10 9 8 7 6 5 4 3 2 1 0 Milk of Magnesia Sodic soils Antacid tablets Calcareous soils Sea Water Pure water Humid region soils Natural rain Forest soils Beer, coffee Acid sulfate soils Vinegar Lemon Juice Battery acid

  33. PLANT NUTRIENT AVAILABILITY

  34. AFFECTS OF pH ON SOILS • Plant nutrient availability • Microbial populations • Types of Vegetation • Movement of nutrients and pollutants

  35. Where to get soil information • Each County has a published soil survey that provides detailed soil maps. • The local NRCS office has copies of the published soil survey for that county. • Web Soil Survey is a web based tool where soil maps can be generated on-line. http://soils.usda.gov/survey/

  36. Soil Food Web

  37. Soil Forming Factors • Parent Material • Climate • Living Organisms • Topography • Time

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