1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Enger & Smith Environmental Science A Study of Interrelationships Eleventh 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  Earth is not a stable and unchanging thing, events such as earthquakes, volcanic eruptions, floods, & windstorms change it frequently. Some of these events build new land & some tear it down.  Earth is composed of an outer crust, a thick layer of plastic mantel, and a central core.

5. 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.  Below the asthenosphere, the mantel is more solid.  The core is consist primarily of iron & nickel, w/ a solid center and a liquid outer region.

6. Geologic Processes Structure of the Earth

7. 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. Places that plates pull apart, liquid mantle moves upward, fill the gap & solidifies which forms new crust. These building processes are counteracted by processes tending to make elevated surfaces lower.

8. –If some plates are pulling, some others must be colliding which can results in: –One plate slides under the other & is melted, some liquid mantle makes it to the surface & volcanoes are formed & new mountains are formed. –If two plates collide under the ocean, volcanoes may eventually reach the surface & form a chain of volcanic islands (Aleutian Islands). –When two continental plates collide, neither slides under the other and the crust buckles to form mountains. –Gravity tears down the high places, moving water, ice & wind assist in the process.

9. Geologic Processes Tectonic plates The plates that make up the outer surface of the earth move w/ respect to another.

10. Geologic Processes Tectonic plates

11. Geological Processes  Weathering processes are important in reducing the size of particles that can then be dislodged by moving water and air.  These are factors bringing about fragmentation or chemical change of parent material, important in reducing the size of particles.  Mechanical weathering results from physical forces that reduce the size of rock particles without changing the chemical nature of the rock.

12.  Common causes are: –Changes in temperature, causing fractures in rock –Freezing and Thawing Cycles –Erosion from Wind and Moving Water –Abrasion, forces that move & rub rock particles against each other. –Actions of plants and animals.

13. Geologic Processes Physical fragmentation by freezing and thawing

14. 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 otherwise chemically change to different compounds; some become hydrolyzed when combined w/ water molecules and can be removed by rain.  The process of loosening and redistributing particles is called erosion.

15. Geologic Processes An eroded landscape

16. Soil and Land  Land: portion of world not covered by water.  Soil: 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 Soil needs to be protected because both urban & rural residents will suffer if soil is abused.

17. Soil and Land The components of soil.

18. Soil Formation  Soil formation is a combination of physical, chemical, & biological events which begins with fragmentation of parent material. Parent material consists of ancient layers of rock, or more recent deposits from lava flows or glacial activity.  First organisms to gain a foothold in weathered parent material also contribute to soil formation. Lichens often form pioneer community. –Decomposition of lichens further alters underlying rock, & release of chemicals from roots of plants causes further break down of rocks.

19. 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 & increases water holding capacity, acidity of the soil & availability of soluble organic materials. It creates a crumbly soil that allows adequate water absorption and drainage. Burrowing animals, soil bacteria, fungi, roots of plants are all parts of biological process of soil formation.  Burrowing animals such as earthworms bring nutrients up from deeper soil layers, improving soil fertility.

20. Soil Formation Other factors influencing soil formation include:  Plant Roots  Bacteria and Fungi (Decomposers): improve quality of soil  Position on Slope: formation on slop vs a flat area  Climate: extremely dry/ cold area have very slow soil formation bec of slow accumulation of organic matter, chemical weathering proceeds more slowly at lower temp & in absent of water. Under poor climate take longer time  Time  Rainfall & organic matter influence soil pH. In high rain areas basic ions leached from the soil & acidic ones are left behind.  Soil pH: influences availability of nutrients which affect kinds of plants that grow & amt of organic material added. K, Ca, mg important nutrients, high Al in acidic soil cause toxicity to plants. Best pH for plants is 6-7

21. 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. –Gravel >2.0 mm –Sand 0.05 - 2.0 mm –Silt 0.002-0.05mm –Clay < 0.002 mm Soil is not consist of a single size particle, an ideal soil for agricultural use is called Loam which combines good aeration & drainage properties of large particles w nutrient-retention & water-holding ability of clay particles.

22. Soil Properties Soil texture Texture depends on the percentage of clay, slit, & sand particles in the soil. 40% san, 40% slit, & 20% clay forms loam.

23. Soil Properties  Soil structure refers to the way various soil particles clump together. Sandy soil has granular structure while clay form smaller aggregates. 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.

24. Typical inhabitants of soil: –Protozoa (act as parasites & predators on other forms of soil organisms so regulate their pop), –nematodes (aid in breakdown of dead organic matter), –earthworms, –insects (form burrows & consume & fragment organic materials), –algae (photosynthesis), –bacteria (nitrogen fixing bacteria & decaying & recycling), –and fungi (decaying & recycling). Soil contains a complicated food chain. All of these organisms are active w/in distinct layers of the soil, known as soil profile.

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. Uppermost layer of the soil contains more nutrients & organic matter than the deeper layers.

26. Soil Profile  O horizon is made of litter, undecomposed or partially decomposed organic material on top of A Horizon. Common in forest, but agricultural soil not have it.  A horizon is the topsoil, or the uppermost layer. It contains most of the soil nutrients and living organisms.  Thickness varies from less than a centimeter on steep mountain slop to over a meter in the rich grasslands of central N America.

27.  Leaching : moving water dissolving organic matter & minerals to lower layers, causing formation of a light layer below the A horizon as the result of iron leaching  E horizon is formed from leaching darker materials. Not formed in all soils. Usually very nutrient poor, bec water moves nutrients to underlying B horizon.

28. 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 & grassland w low rain since rainfall is important in formation of this layer, while woodlands have a well developed one.  C Horizon - Weathered parent material, very little organic material. It helps to determine the pH, depending on parent materials (limestone/granite rock)  R Horizon – Bedrock where C horizon rest on

29. Soil Profile

30.  Over 15,000 separate soil types have been classified in North America & three major ones are grassland, forest, & desert.  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. Because low rainfall, rain does not penetrate into the soil layer very far, most of the roots of the grasses & other plants remain near the surface in A horizon, there is limiting topsoil leaching. 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.

31. Soil Profile Two features of tropical rainforests (bec it support so many plant & animals, people assume is very fertile, but traditional crops can not be raised bec of the two features) have great influence over the nature of the soil: High temperatures lead to rapid decomposition of organic matter, with little litter. High rainfall »Causes excessive leaching of nutrients from upper layers leave behind a soil reach in iron & Al.

32. Desert soil have »a poorly developed horizon, »not support a large amt of plant growth, »much of soil is exposed, »little organic matter added to the soil, little leaching. »In cold, wet climate there is accumulation of organic matter bec of reduced decomposition rate.

33. Soil Profile Major soil types

34. 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. –Badly eroded soil has lost all topsoil & some subsoil & is no longer productive.

35. 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, where soil is exposed. Great Plains of North America have had four serious bouts of wind erosion since European settlement in the 1800s.

36. –According to the International Fund for Agricultural Development (IFAD) traditional labor-intensive, small scale soil conservation efforts that combine maintenance of shrubs & trees w crop growing & cattle grazing is the best approach to control erosion. –Contour farming & terracing can also reduce erosion.

37. Soil Erosion Worldwide soil erosion Soil erosion is widespread throughout the world Silty rivers are evidence of poor soil conservation practices upstream.

38. Soil Conservation Practices  Soil structure, texture, drainage, fertility, rockiness, slope of the land, amt & nature of rainfall, & other climatic conditions determines kind of agricultural activities.  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.

39. Dirty streams are less aesthetically pleasing, too much sediment affect fish popn by reducing visibility, covering spawning sites, & clogging the gills of the fish. Soil carried by water must be deposited somewhere & in many cases has to be removed by dredging which is very expensive & is a cost to the public through taxes.

40. 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.

41. 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.

42. Soil quality Management Components  Enhance organic matter by: leaving crop residues in the field, choosing crop rotations that include high-residue plants, using optimal nutrient & water management practices to grow healthy plants w large amt of roots & residues, growing cover crops, applying manure or compost, using low-or-no-tillage systems, & mulching Avoid excessive tillage: –by using new equipments w minimal disturbance of the soil.

43.  Manage pests & nutrients efficiently by: Testing & monitoring soil & pests; Applying only the necessary chemicals, at the right time & place to get the job done, Taking advantages of nonchemical approaches to pest & nutrient management.  Prevent soil compactation is essential.  Diversity cropping systems: by using buffer strips, small fields, or contour strip cropping, long crop rotation.

44. 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.

45. Soil Conservation Practices Contour farming

46. Soil Conservation Practices Strip farming

47. 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. Many factors such as length & steepness of slope, type of soil, & amt of precipitation, determine whether terracing is feasible.

48. Soil Conservation Practices  Even with soil conservation methods, farmers must provide protected channels for the movement of water.  Waterways are depressions in sloping land where water collects and flows off the land. Channels movement of water. Wind is also a problem w certain soils.  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.

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

50. Soil Conservation Practices Windbreaks

51. Conventional vs. Conservation Tillage  Conventional tillage methods require the excessive use of farm machinery to plow the field & then disked or harrowed one to three times.  Plowing has multiple desirable effects: Weeds and weed seeds are buried or destroyed. Crop residue is turned under, where it will contribute to soil structure when is incorporated into soil. Leached nutrients brought to surface. Cooler, darker soil brought to top and warmed. which is important in areas w short growing seasons. In many areas, fields are plowed in the fall, after harvesting, and the soil is left exposed all winter.

52. 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.  Several new system of tillage have been developed: 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.

53. Conventional vs. Conservation Tillage Conservation tillage further reduces amount of soil disturbance and leaves 30% or more of soil surface covered with crop residue.  Selective herbicides kill weeds before new planting of crops & to control weeds afterward.  Several variations of conservation tillage are used: 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.

54. Conventional vs. Conservation Tillage  Positive Effects of Reduced Tillage: Wildlife gain food and cover so inc wildlife pop. Less runoff - reduced siltation of waterways making water more clear and reducing dredging. Row-crops can be planted in sloped areas which allows farmer to convert low-value pastureland into crop-land w greater economic yield. Fewer trips means lower fuel consumption. Double – cropping is possible to grow 2 crops at the same time. Fewer trips means less soil compaction by reducing # of trips over the field by farm machinery.

55. Conventional vs. Conservation Tillage  Drawbacks of Conservation Tillage Plant residue may delay soil warming & delay planting some crops. Crop residue reduces evaporation and upward movement of water & nutrients through the soil. Accumulation of plant residue can harbor plant pests and diseases, requiring more insecticides and fungicides specially if some crop are planted repeatedly in same location.

56. Protecting Soil on Nonfarm Land  Each piece of land has a unique characteristic that influences the way it can be used.  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.

57. 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.

58. 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.

59. 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.