Chapter 6

1. Chapter 6 Land and Soil

2. Life Requirements • Life requires the presence of certain resources • water, sunlight, and soil • Soil is a valuable resource requiring careful management

3. Land, Soil, and Life • Soil makes up surface of Earth’s crust • unique blend of organic and inorganic material • allows for exchange of gases, water, minerals • necessary for life

4. Soil Formation • Forms extremely slowly • natural forces act on mineral and rock portions of Earth’s surface • atmosphere, sunlight, water, and living things • Soils vary in composition and character • temperature, organic matter, and amount of air and water

5. Soil Types • Types of soils differ with specific sites • shaped by forces of climate, living organisms, parent soil material, topography, and time

6. Origins of Soil • Parent material • materials underlying the soil and from which the soil was formed

7. Origins of Soil • General categories of soil parent materials • minerals and rocks • glacial deposits • loess deposits • alluvial and marine deposits • organic deposits

8. Minerals and Rocks • Minerals • solid, inorganic, chemically uniform, and naturally occurring substances

9. Minerals and Rocks • Rocks • aggregates of minerals • three major types • igneous: cooled molten material • sedimentary: solidification of sediment • metamorphic: other rock reformed by heat and pressure

10. Which is which?

11. Glacial Deposits • Massive rivers of slowly moving ice • Scrape across surface of Earth • scoop up surface material • When glaciers recede or melt, they leave material behind • great deposits of rocks, parent materials, and already formed soil materials

12. Loess Deposits • Collections of wind-blown silt • Create soil formations that look like drifting snow • Often create rich soil deposits • eastern Mississippi Valley • palouse soils of the Pacific Northwest

13. Alluvial and Marine Deposits • Soil deposits of waterborne sediments • Alluvial deposits • left by moving fresh water • moving water picks up sediment • as water slows, sediment deposited • creates alluvial fans

14. Alluvial and Marine Deposits • Marine deposits • Soil formed on ancient ocean floors • Soil in water drifts to bottom and collects

15. Organic Deposits • Lush plant life exists in swamps and marshes • Plants die and decay • Partially decayed material collects • forms muck or peat soils

16. Which is it?

17. Which is it?

18. Which is it?

19. Weathering • Minerals and rocks exposed to the weather break into smaller and smaller pieces

20. Weathering • Major weathering forces • temperature changes • water action • plant roots • ice expansion • mechanical grinding

21. Soil’s Organic Content • Decaying plant and animal parts • important part of formation and productivity of soil

22. Soil’s Organic Content • Organic matter may be in two basic forms • Original tissue • portion of organic matter that remains recognizable • twigs and leaves covering a forest floor • Humus • decomposed and constituents unrecognizable • gives topsoil its brown color

23. Soil’s Organic Content • Serves many important functions • stabilizes soil structure as cementing agent • returns plant nutrients to the soil • helps store soil moisture • makes soil more tillable for farming

24. Soil’s Organic Content • provides food (energy) for soil microorganisms • makes soil porous • provides storehouse for nutrients • minimizes leaching

25. Soil Profile • Cross-sectional view of the different layers or horizons in soil • Undisturbed soil will have four or more horizons in its profile • O horizon: on surface and composed of organic matter and small amount of mineral matter

26. Soil Profile • A horizon: topsoil; located near surface and combination of mineral matter and organic matter • B horizon: subsoil; similar to A horizon but particle size and proportions differ; less organic material • C horizon: parent material, large soil particles • How many layers do you see in this picture?

27. Properties of Soil • A variety of physical properties of soil exist • slope: angle of soil surface • texture: proportions of sand, silt, and clay • drainage: how well water flows through soil • flood hazard: likelihood area will flood • erosion: degree soil is damaged by erosion • topsoil and subsoil thickness: layer depths

28. Soil and Plants • Soil provides individual plants with four basic needs • anchorage • water • oxygen • nutrients

29. Soil Uses • Human societies depend on soil for • cropland • grazing land • urbanization • building • waste disposal • forests • recreation

30. Human Uses of Soil • Cropland • land where crops are planted, cared for, and harvested • Two basic types of crops: annual and perennial

31. Human Uses of Soil • Annual crops • planted and harvested within one growing season • requires yearly preparation of soil • prone to erosion • corn, soybeans, cotton, vegetables • Perennial crops • remain in ground several years • alfalfa, fruits, nuts, and nursery stock

32. Human Uses of Soil • Grazing land • used to feed grazing animals such as cattle and sheep • eastern United States uses pastures planted with perennial forage • western United States uses rangeland of native grasses

33. Human Uses of Soil • Urbanization • land used to build cities, towns, factories, and roads • continues to grow at expense of other land uses

34. Human Uses of Soil • Buildings • land used to prepare foundations for construction • Several properties of soil are considered, including • shrink-swell potential • load-bearing capacity

35. Human Uses of Soil • Shrink-swell potential • how much soil swells when wet and shrinks when dry • Load-bearing capacity • ability of soil to support great weight

36. Human Uses of Soil • Waste disposal • using soil to filter, contain, or confine waste • waste disposal takes a variety of forms • sanitary landfills • hazardous waste landfills • personal home septic systems

37. Human Uses of Soil • Forests • soil often left undisturbed • harvesting of trees can damage soil • tear up vegetation • compact soil • may result in increased erosion or limited growth potential

38. Human Uses of Soil • Recreation • also takes a variety of forms • golf courses, playing fields, parks, campgrounds • may require special construction or management

39. A Living Environment • Soil is living medium containing great variety of organisms • amphibians, mammals, insects, reptiles, worms, microbes, etc. • Most diverse ecosystem on Earth • Many organisms in soil are decomposers

40. A Living Environment • Decomposers • break down material that was once living • decomposers play irreplaceable role

41. Erosion • Natural process forming channels and canyons • However, human activity is accelerating the process

42. Erosion • Major environmental issue • Each year, almost 2 billion tons of soil lost • mostly result of water erosion • Approximately 21 percent of U.S. cropland suffers excessive soil losses • We must conserve soil resources by reducing or eliminating erosion losses

43. Erosion by Water • Water erosion occurs in three steps • detachment • transport • deposition

44. Erosion by Water • Factors affecting rate of erosion • soil texture and structure • organic matter content • slope • soil cover • plant cover

45. Erosion by Wind • Accounts for 40 percent of soil loss in United States • Dry areas with high winds are most prone to wind erosion • Bare soil is at greatest risk

46. Erosion by Wind • Effects of wind erosion • Removes topsoil • reduces nutrient- and water-holding capacities • “sandblasts” young plants • fills in road or drainage ditches • affects respiratory health of humans and other animals • wears down paint and other surfaces

47. Preventing and Controlling Erosion • Two key practices in controlling erosion • protecting soil surfaces • slowing movement of water and wind

48. Preventing and Controlling Erosion • Soil conservation must be practiced to preserve our soil resources • Implementation of best management practices must become a priority • A wide variety of management practices exist to help control erosion