1. © 2011 Pearson Education, Inc. CHAPTER 11 Soil: The Foundation for Land Ecosystems

2. © 2011 Pearson Education, Inc. https://www.soils.org/videos/play/smithsoni an/substance-of-soil.flv First… a video…

3. © 2011 Pearson Education, Inc. An introduction to soil and agriculture Some farmers follow the five golden rules of the tropics Keep soil covered Use minimal or no tillage Use mulch to provide nutrients to the soil Maximize biomass production Maximize biodiversity Harvests have increased dramatically Farmer experimenters experiment and educate others, leading to sustainable agriculture

4. © 2011 Pearson Education, Inc. Desertification in China

5. © 2011 Pearson Education, Inc. Past neglect 90% of all food comes from land-based agriculture Oceans and natural systems are being depleted Protecting and nurturing soil is the cornerstone of food production and sustainability But it has been overlooked repeatedly The Greek, Roman, and Mayan empires collapsed The result of decreased agricultural productivity Brought on by soil erosion Plowing the prairie and drought caused the U.S. Dust Bowl

6. © 2011 Pearson Education, Inc. Asking more of the land Increased population pressures croplands and grazing lands to increase production But, we’re degrading the soil more now… 15% of Earth’s land was degraded in 1991 Now, land degradation is even worse 20% of cultivated land, 30% of forests, 10% of grasslands were degraded between 1981 and 2003 Future productivity is undermined

7. © 2011 Pearson Education, Inc. A rich soil is much more than dirt Soil: solid material of geological and biological origin Chemical, biological, and physical processes change soil Giving it the ability to support plant growth In productive soil, detritus feeders and decomposers constitute a biotic community Facilitating the transfer of nutrients Creating a soil environment favorable to root growth Productive topsoil involves dynamic interactions among organisms, detritus, and mineral particles of the soil

8. © 2011 Pearson Education, Inc. Topsoil formation

9. © 2011 Pearson Education, Inc. Soil characteristics Most soils are hundreds of years old They change very slowly Soil is classified by profile, structure, and type Soil texture: relative proportions of each soil type Parent material: mineral material of the soil Soil has its origin in the geological history of an area Weathering: gradual physical and chemical breakdown of parent material It may be impossible to tell what the parent material was

10. © 2011 Pearson Education, Inc. Classification of soil Soil separates: small fragments smaller than stones Sand: particles from 2.0 to 0.063 mm Silt: particles range from 0.063 to 0.004 mm Clay: anything finer than 0.004 mm Gravel, cobbles, boulders: particles larger than sand You can see the individual rock particles in sand Clay particles become suspended in water Clay is “gooey” because particles slide around each other on a film of water

11. © 2011 Pearson Education, Inc. The soil texture triangle

12. © 2011 Pearson Education, Inc. Proportions Sand, silt, and clay constitute the mineral part of soil If one type of particle predominates, the soil is sandy, silty, or clayey Loam: a soil with 40% sand, 40% silt, and 20% clay To determine a soil’s texture: Add soil and water to a test tube and let the soil settle Sand particles settle first, then silt, then clay Scientists classify soil texture with a triangle It shows relative proportions of sand, silt, and clay

13. © 2011 Pearson Education, Inc. Properties Workability: the ease with which soil can be cultivated Sandy soils have poor water-holding capacity, but are workable Clay soils do not allow infiltration or aeration & have poor workability: too sticky or too hard

14. © 2011 Pearson Education, Inc. Soil profiles Horizons: horizontal layers of soil from soil formation Can be quite distinct Soil profile: a vertical slice through the soil horizons Reveals the interacting factors in soil formation O horizon: topmost layer of soil Dead organic matter (detritus) deposited by plants High in organic content Primary source of energy for the soil community Humus: decomposed dark material at the bottom of the O horizon

15. © 2011 Pearson Education, Inc. Subsurface layers A horizon (topsoil): below the O horizon A mixture of mineral soil and humus Permeated by fine roots Usually dark May be shallow or thick Vital to plant growth Grows an inch or two every hundred years E horizon: pale-colored layer below the A horizon Eluviation: process of leaching (dissolving) minerals due to downward movement of water

16. © 2011 Pearson Education, Inc. Subsurface layers B horizon (subsoil): below the E horizon Contains minerals leached from the A and E horizons High in iron, aluminum, calcium, other minerals, clay Reddish or yellow colored from oxidized metals C horizon: parent mineral material Weathered rock, glacial deposits, volcanic ash Reveals geologic process that created the landscape Not affected by biological or chemical processes

17. © 2011 Pearson Education, Inc. Soil profile

18. © 2011 Pearson Education, Inc. Soil classification Soil comes in an almost infinite variety of structures and textures Soils are classified by: Order: the most inclusive group Four major soil orders most important for agriculture, animal husbandry and forestry: Mollisols, oxisols, alfisols, aridisols

19. © 2011 Pearson Education, Inc. Global map of soil orders

20. © 2011 Pearson Education, Inc. Important soil orders Mollisols: fertile, dark soils of temperate grasslands The world’s best agricultural soils Midwest U.S., Ukraine, Mongolia, Argentinian pampas Deep A horizon; rich in humus and minerals With less precipitation, minerals don’t leach downward Oxisols: soils of tropical and subtropical rain forests The B horizon has a layer of iron and aluminum oxides Little O horizon: rapid decomposition of vegetation Limited agriculture: minerals are in living plant matter Leached minerals form a hardpan, resisting cultivation

21. © 2011 Pearson Education, Inc. Two more important soil orders Alfisols: widespread, moderately weathered forest soils Well-developed O, A, E, and B horizons Typical of moist, temperate forests Suitable for agriculture if they are fertilized Aridisols: soils of drylands (arid, semiarid, and seasonally dry areas) and deserts Unstructured due to lack of vegetation and precipitation Thin, light colored Some areas may support rangeland animal husbandry Irrigation leads to salinization

22. © 2011 Pearson Education, Inc. The soil community To support plants, soils must Have nutrients and good nutrient-holding capacity Allow infiltration and have good water-holding capacity Resist evaporative water loss Have a porous structure that allows aeration Have a near-neutral pH Have low salt content According to the principle of limiting factors, the poorest attribute is the limiting factor

23. © 2011 Pearson Education, Inc. Soil and plant growth For best growth, plants need a root environment that supplies Mineral nutrients, water, oxygen The proper pH and salinity 1. Soil fertility: the soil’s ability to support plant growth The presence of proper amounts of nutrients and all other needs Farmers refer to a soil’s ability to support plant growth as tilth

24. © 2011 Pearson Education, Inc. Mineral nutrients Initially become available through rock weathering Phosphate, potassium, calcium, etc. Much too slow to support normal plant growth Breakdown and release (recycling) of detritus provides most nutrients Leaching: nutrients are washed from the soil by water Decreases soil fertility Contributes to water pollution 2. Nutrient-holding capacity: the soil’s capacity to bind and hold nutrient ions until they are absorbed by roots

25. © 2011 Pearson Education, Inc. Fertilizer Agriculture removes nutrients from the soil Fertilizer: nutrients added to replace those that are lost Organic fertilizer: plant or animal wastes or both Manure, compost (rotted organic material) Leguminous fallow crops (alfalfa, clover) Food crops (lentils, peas) Inorganic fertilizer: chemical formulations of nutrients Lacks organic matter Much more prone to leaching

26. © 2011 Pearson Education, Inc. Water and water-holding capacity Water is resupplied to the soil by rainfall or irrigation Infiltration: water soaks into the soil Water runoff is useless to plants and may cause erosion 3. Water-holding capacity: soil’s ability to hold water after it infiltrates Poor holding capacity: water percolates below root level Evaporative water loss depletes soil of water The O horizon reduces water loss by covering the soil

27. © 2011 Pearson Education, Inc. Water is crucial for plants Transpiration: water is absorbed by roots and exits as water vapor through pores (stomata; singular = stoma) in the leaves Oxygen enters, and carbon dioxide exits, through stomata Loss of water through stomata can be dramatic Wilting: a plant’s response to lack of water Conserves water Shuts off photosynthesis by closing stomata Severe or prolonged wilting can kill plants

28. © 2011 Pearson Education, Inc. Transpiration

29. © 2011 Pearson Education, Inc. Aeration Novice gardeners kill plants by overwatering (drowning) Roots must breathe to obtain oxygen for energy Land plants depend on loose, porous soil 4. Soil aeration: allows diffusion of oxygen into, and carbon dioxide out of, the soil Overwatering fills air spaces Compaction: packing of the soil Due to excessive foot or vehicular traffic Reduces infiltration and runoff Strongly influenced by soil texture

30. © 2011 Pearson Education, Inc. Plant-soil-water relationship

31. © 2011 Pearson Education, Inc. Relative acidity (pH) 5. pH refers to the acidity or alkalinity of any solution The pH scale runs from 1 to 14 7 is neutral (neither acidic or alkaline) Different plants are adapted to different pH ranges Most do best with a pH near neutral Many plants do better with acidic or alkaline soils Blueberries do best in acidic soils

32. © 2011 Pearson Education, Inc. 6. Salt and water uptake Buildup of salt in the soil makes it impossible for roots to take in water High enough salt levels can draw water out of a plant By osmosis Dehydrates and kills plants Only specially adapted plants grow in saline soils None of them are crops Irrigation can lead to salt buildup in soil (salinization)

33. © 2011 Pearson Education, Inc. Soil as a detritus-based ecosystem

34. © 2011 Pearson Education, Inc. Soil enrichment Most detritus comes from green plants So green plants support soil organisms Soil organisms create the chemical and physical soil environment beneficial to plants Green plants further protect the soil by reducing erosion and evaporative water loss So keep an organic mulch around garden vegetables The mutually supportive relationship between plants and soil is easily broken Keeping topsoil depends on addition of detritus

35. © 2011 Pearson Education, Inc. The results of removing topsoil

36. © 2011 Pearson Education, Inc. CHAPTER 11 Soil: The Foundation for Land Ecosystems Active Lecture Questions

37. © 2011 Pearson Education, Inc. The process of soil formation creates a vertical gradient of layers that are known as a.loam. b.aeration. c.infiltration. d.horizons. Review Question-1

38. © 2011 Pearson Education, Inc. The process of soil formation creates a vertical gradient of layers that are known as a.loam. b.aeration. c.infiltration. d.horizons. Review Question-1 Answer

39. © 2011 Pearson Education, Inc. The residue of partly decomposed organic matter is called ______ and is found in high concentrations at the bottom of the O horizon. a.desertification b.decomposition c.humus d.topsoil Review Question-2

40. © 2011 Pearson Education, Inc. The residue of partly decomposed organic matter is called ______ and is found in high concentrations at the bottom of the O horizon. a.desertification b.decomposition c.humus d.topsoil Review Question-2 Answer

41. © 2011 Pearson Education, Inc. Mineralized soils can be revitalized through the addition of a.compost and other organic matter. b.materials from the C horizon. c.topsoil. d.all of the above. Review Question-3

42. © 2011 Pearson Education, Inc. Mineralized soils can be revitalized through the addition of a.compost and other organic matter. b.materials from the C horizon. c.topsoil. d.all of the above. Review Question-3 Answer

43. © 2011 Pearson Education, Inc. All of the following lead to the loss of soil except a.splash erosion. b.horizon erosion. c.sheet erosion. d.gully erosion. Review Question-4

44. © 2011 Pearson Education, Inc. All of the following lead to the loss of soil except a.splash erosion. b.horizon erosion. c.sheet erosion. d.gully erosion. Review Question-4 Answer

45. © 2011 Pearson Education, Inc. ______ occurs when there is an accumulation of salts in soil as a result of ______. a.The tragedy of the commons; overgrazing b.Deforestation; logging c.Salinization; irrigation d.Overcultivation; no-till farming Review Question-5

46. © 2011 Pearson Education, Inc. ______ occurs when there is an accumulation of salts in soil as a result of ______. a.The tragedy of the commons; overgrazing b.Deforestation; logging c.Salinization; irrigation d.Overcultivation; no-till farming Review Question-5 Answer

47. © 2011 Pearson Education, Inc. According to Fig. 11-3, soil with roughly 40% sand, 40% silt, and 20% clay is called a.loam. b.silt loam. c.sandy clay loam. d. loamy sand. Interpreting Graphs and Data-1

48. © 2011 Pearson Education, Inc. According to Fig. 11-3, soil with roughly 40% sand, 40% silt, and 20% clay is called a.loam. b.silt loam. c.sandy clay loam. d. loamy sand. Interpreting Graphs and Data-1 Answer

49. © 2011 Pearson Education, Inc. According to Fig. 11-2, when detritus, mineral particles, and the detritus food web interact, they form a.leaves, stems, flowers, and seeds. b.leached minerals. c.nitrogen fixation. d.topsoil. Interpreting Graphs and Data-2

50. © 2011 Pearson Education, Inc. According to Fig. 11-2, when detritus, mineral particles, and the detritus food web interact, they form a.leaves, stems, flowers, and seeds. b.leached minerals. c.nitrogen fixation. d.topsoil. Interpreting Graphs and Data-2 Answer

51. © 2011 Pearson Education, Inc. The human activities that lead to erosion and desertification are a.overcultivation, overgrazing, and deforestation. b.sustainability, stewardship, and sound science. c.pollution, overcultivation, and sustainability. d.overgrazing, sound science, and hypotheses. Thinking Environmentally-1

52. © 2011 Pearson Education, Inc. The human activities that lead to erosion and desertification are a.overcultivation, overgrazing, and deforestation. b.sustainability, stewardship, and sound science. c.pollution, overcultivation, and sustainability. d.overgrazing, sound science, and hypotheses. Thinking Environmentally-1 Answer

53. © 2011 Pearson Education, Inc. True or False: If soil conservation is to be successful, it must be practiced on the levels of both the individual landowner and public policy. a.True b.False Thinking Environmentally-2

54. © 2011 Pearson Education, Inc. True or False: If soil conservation is to be successful, it must be practiced on the levels of both the individual landowner and public policy. a.True b.False Thinking Environmentally-2 Answer