1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Enger & Smith Environmental Science A Study of Interrelationships Twelfth Edition Chapter 13 Soil and Its Uses

3. Outline  Geologic Processes  Soil and Land  Soil Formation  Soil Properties  Soil Profile  Soil Erosion  Soil Conservation Practices  Conventional Versus Conservation Tillage  Protecting Soil on Nonfarm Land

4. Geologic Processes Structure of the Earth

5. Layered Earth

6. Geologic Processes  The crust of the Earth is an extremely thin, less- dense solid covering over the mantle.  The mantle makes up the majority of the Earth, and surrounds a small core of iron.  The outermost portion of the mantle is solid.  The crust and solid outer mantle are collectively known as the lithosphere.  The asthenosphere is a thin layer below the outer mantle capable of plastic flow.

7. Plate Tectonics Fig. 2-32

8. Geologic Processes Tectonic plates

9. Geologic Processes Tectonic plates

10. Plate tectonics

11. Fig. 2.5

12. Geologic Processes  Plate tectonics is the concept that the outer surface of the Earth is made of large plates of crust and outer mantle that are slowly moving over the surface of the liquid outer mantle. Heat from the Earth causes the slow movement. Plates are pulling apart in some areas, and colliding in others. These building processes are counteracted by processes tending to make elevated surfaces lower.

13. Geological Processes  Weathering processes are important in reducing the size of particles that can then be dislodged by moving water and air.  Mechanical weathering results from physical forces that reduce the size of rock particles without changing the chemical nature of the rock. –Freezing and thawing cycles –Actions of plants and animals

14. Geologic Processes Physical fragmentation by freezing and thawing

15. Geologic Processes  Chemical weathering involves the chemical alteration of rock in such a manner that it is more likely to fragment or be dissolved. Rock fragments exposed to the atmosphere may oxidize or hydrolyze.  The process of loosening and redistributing particles is called erosion.

16. Geologic Processes An eroded landscape

17. Soil and Land  Land is the portion of world not covered by water.  Soil is a mixture of minerals, organic material, living organisms, air, and water that together support growth of plant life. Good agricultural soil: –45% Mineral –25% Air –25% Water –5% Organic Matter

18. Soil and Land The components of soil

19. Soil Formation  Soil formation begins with fragmentation of parent material. Parent material consists of ancient layers of rock, or more recent deposits from lava flows or glacial activity.  The first organisms to gain a foothold in modified parent material also contribute to soil formation. Lichens form pioneer communities. Decomposition of dead lichens further alters underlying rock.

20. Soil Formation  Humus is the organic material resulting from the decay of plant and animal remains. It mixes with top layers of mineral particles, and supplies needed nutrients to plants. It creates a crumbly soil that allows adequate water absorption and drainage.  Burrowing animals such as earthworms bring nutrients up from deeper soil layers, improving soil fertility.

21. Soil Formation  Other factors influencing soil formation include: Plant roots Bacteria and fungi (decomposers) Position on slope Climate Time Rainfall Soil pH

22. Soil Properties  Soil texture is determined by the size of mineral particles within the soil. Too many large particles (sand, gravel) lead to extreme leaching. Too many small particles (clay) lead to poor drainage.

23. Soil Properties Soil texture

24. Soil Properties  Soil structure refers to the way various soil particles clump together. An ideal soil for agricultural use is loam, which combines the good aeration and drainage properties of large particles with the nutrient retention and water- holding ability of clay particles. In good soils, one-half to two-thirds of spaces contain air after excess water has drained. A good soil is friable, which means that it crumbles easily. Protozoa, nematodes, earthworms, insects, algae, bacteria, and fungi are typical inhabitants of soil.

25. Soil Profile  The soil profile is a series of horizontal layers of different chemical composition, physical properties, particle size, and amount of organic matter.  Each recognizable layer of the profile is known as a horizon.

26. Soil Profile  O horizon is made of litter, undecomposed or partially decomposed organic material.  A horizon is the topsoil, or the uppermost layer. It contains most of the soil nutrients and living organisms.  E horizon is formed from leaching darker materials. Usually very nutrient poor.

27. Soil Profile  B horizon is the subsoil. It contains less organic matter and fewer organisms, but accumulates nutrients leached from topsoil. It is poorly developed in dry areas.  C horizon is weathered parent material.  R horizon is bedrock.

28. Soil Profile

29.  Over 15,000 separate soil types have been classified in North America.  Most cultivated land can be classified as either grassland or forest soil. Grassland soils usually have a deep topsoil layer. A lack of leaching results in a thin layer of subsoil. In forest soils, which are typically high rainfall areas, the topsoil layer is relatively thin, but topsoil leachate forms a subsoil that supports substantial root growth.

30. Soil Profile  Two features of tropical rainforests have great influence over the nature of the soil: High temperatures lead to rapid decomposition of organic matter, with little litter. High rainfall leads to excessive leaching of nutrients.

31. Soil Profile Major soil types

32. Soil Erosion  Erosion is the wearing away and transportation of soil by wind, water, or ice.  Worldwide, erosion removes 25.4 billion metric tons of soil per year. Made worse by deforestation and desertification. Poor agricultural practices increase erosion and lead to the transport of associated fertilizers and pesticides.

33. Soil Erosion  Most current agricultural practices lose soil faster than it can be replenished.  Wind erosion may not be as evident as water erosion, but is still serious. It is most common in dry, treeless areas. Great Plains of North America have had four serious bouts of wind erosion since European settlement in the 1800s.

34. Soil Erosion Worldwide soil erosion

35. Soil Conservation Practices  When topsoil is lost, fertility is reduced or destroyed, thus fertilizers must be used to restore fertility. This practice raises food costs, and increases sediment load in waterways. Over 20% of U.S. land is suitable for agriculture, but only 2% does not require some form of soil conservation practice.

36. Soil Conservation Practices  Agricultural Potential Worldwide: –11% of land surface is suitable for crops. –An additional 24% is in permanent pasture. United States: –20% land surface suitable for crops. –25% in permanent pasture. African Continent: –6% land surface suitable for crops. –29% can be used for pasture.

37. Soil Conservation Practices  Soil Quality Management Components: Enhance organic matter. Avoid excessive tillage. Manage pests and nutrients efficiently. Prevent soil compaction. Keep the ground covered. Diversify cropping systems.

38. Soil Conservation Practices  Contour farming is tilling at right angles to the slope of the land. Each ridge acts as a small dam. Useful on gentle slopes. One of the simplest methods for preventing soil erosion.  Strip farming is the practice of alternating strips of closely sown crops to slow water flow, and increase water absorption.

39. Soil Conservation Practices Contour farming

40. Soil Conservation Practices Strip farming

41. Soil Conservation Practices  Terracing is the practice of constructing level areas at right angles to the slope to retain water. Good for very steep land. Terraces

42. Soil Conservation Practices  Waterways are depressions in sloping land where water collects and flows off the land. Channels movement of water.  Windbreaks are plantings of trees or other plants that protect bare soil from full force of the wind. Windbreaks reduce wind velocity, decreasing the amount of soil that can be carried.

43. Soil Conservation Practices A well-maintained, uncultivated waterway

44. Soil Conservation Practices Windbreaks

45. Conventional vs. Conservation Tillage  Plowing has multiple desirable effects: Weeds and weed seeds are buried. Crop residue is turned under, where it will contribute to soil structure. Leached nutrients brought to surface. Cooler, darker soil brought to top and warmed.

46. Conventional vs. Conservation Tillage  Each trip over the field is an added expense to the farmer, and at the same time increases the amount of time the soil is open to erosion via wind or water.  Reduced tillage is a practice that uses less cultivation to control weeds and prepare soil, but generally leaves 15-30% of soil surface covered with crop residue after planting.

47. Conventional vs. Conservation Tillage  Conservation tillage further reduces amount of soil disturbance and leaves 30% or more of soil surface covered with crop residue. Mulch tillage: Tilling entire surface just prior to planting. Strip tillage: Tilling narrow strips that will receive seeds. Ridge tillage: Leaves ridges; the crop is planted on the ridge with residue left between ridges. No till farming: Involves special planters that place seeds in slits cut in the soil.

48. Conventional vs. Conservation Tillage  Positive Effects of Reduced Tillage: Wildlife gain winter food and cover. Less runoff results in reduced siltation of waterways. Row crops can be planted in sloped areas. Fewer trips over the field means lower fuel consumption. Two crops may be grown on a field in areas that had been restricted to a single crop. Fewer trips over the soil means less soil compaction.

49. Conventional vs. Conservation Tillage  Drawbacks of Conservation Tillage Plant residue may delay soil warming. Crop residue reduces evaporation and upward movement of water through the soil, which may retard the growth of plants. Accumulation of plant residue can harbor plant pests and diseases, requiring more insecticides and fungicides.

50. Protecting Soil on Nonfarm Land  By using appropriate soil conservation practices, much of the land not usable for crops can be used for grazing, wood production, wildlife production, or scenic and recreational purposes.

51. Summary  The surface of the Earth is in constant flux.  The movement of tectonic plates results in the formation of new land as old land is worn down by erosive activity.  Soil is an organized mixture of minerals, organic material, living organisms, air, and water.  Organisms affect soil building by burrowing into and mixing the soil, releasing nutrients, and decomposing.

52. Summary  The ability of soil to grow crops is determined by the inorganic matter, organic matter, water, and air spaces in the soil.  A soil profile typically consists of the: O horizon of litter A horizon, which is rich in organic matter E horizon, from which materials have been leached B horizon, which accumulates materials leached from above C horizon, which consists of slightly altered parent material.

53. Summary  Soil erosion is the removal and transportation of soil by water or wind.  Proper use of conservation practices such as contour farming, strip farming, terracing, waterways, windbreaks, and conservation tillage can reduce soil erosion.  Land unsuitable for crops may be used for grazing, lumber, wildlife habitats, or recreation.