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Geology and Soils

"Land, then, is not merely soil; it is a fountain of energy flowing through a circuit of soils, plants, and animals." - Aldo Leopold, A Sand County Almanac, 1949. Geology and Soils. Chapter 10 December 2008. Earth Structure and Geological Processes. Earth’s Structure Crust – lithosphere

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Geology and Soils

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  1. "Land, then, is not merely soil; it is a fountain of energy flowing through a circuit of soils, plants, and animals." - Aldo Leopold, A Sand County Almanac, 1949 Geology and Soils Chapter 10 December 2008

  2. Earth Structure and Geological Processes • Earth’s Structure • Crust – lithosphere • Oceanic: • generally less than 10 kilometers thick, but more dense than the contenential cruse • Most of the present day oceanic crust is less than 200 million years • Contential • mostly 35 to 40 km versus the average oceanic thickness of around 7-10 km • 40% of the Earth's surface is now underlain by continental crust. • Part of lithosphere • Mantle • Asthenosphere • Core

  3. Spreading center Oceanic tectonic plate Oceanic tectonic plate Ocean trench Collision between two continents Plate movement Plate movement Tectonic plate Oceanic crust Oceanic crust Subduction zone Continental crust Continental crust Material cools as it reaches the outer mantle Cold dense material falls back through mantle Hot material rising through the mantle Mantle convection cell Mantle Two plates move towards each other. One is subducted back into the mantle on falling convection current. Hot outer core Figure 10-4Page 206 Inner core

  4. Features of the Crust Fig. 10-3 p. 205

  5. Plate Boundaries • Divergent • Convergent • Transform

  6. Minerals, rocks, rock cycle • Element or inorganic “pure” compound • Gold, silver, sulfur • Salt, mica, quartz • Rock: most two or more minerals • Rock Types • Igneous: lava rock or granitic (under earth’s surface) • Sedimentary: sandstone, shale, limestone, dolomite • Metamorphic: Preexisting rock, due to pressure and temperature, is changed.

  7. Earthquakes • Abrupt shifting of earths crust • Epicenter • Magnitude : Richter Scale • Insignificant: less than 4 • Minor: 4-4.9 • Damaging and destructive: 5-6.9 • Major and great: above 7

  8. What is Soil • NOT DIRT - dirt is a four letter word! • Mineral particles - non-living - 45% • Organic matter - 5% • bacteria and other microorganisms • partially decomposed plants - humus • macroinvertebrates • Pore space - 50% • air spaces • water filled spaces

  9. Why Soil Science? • Soil science at Penn State

  10. Functions of Soil • Store Water • Provide nutrients for plants • Decompose materials • Recycle nutrients • Return carbon dioxide

  11. Physical Properties and Use • Plants - agriculture and forestry • Building-bearing strength and drainage • Waste disposal - good drainage

  12. Soil Formation – Factors"Each soil has had its own history. Like a river, a mountain, a forest, or any natural thing, its present condition is due to the influences of many things and events of the past." - Charles Kellogg, The Soils That Support Us,1956 • Parent material • Climate • Living Organisms • Topography – slope • Time

  13. Soil Formation • Weathering • Temperature fluctuation • erosion • plant roots • Chemical reactions: eg limestone • Organic Material – amount available • Climate - determines degree of weathering, type of plants, rate of decomposition(thus, directly related to organic material)

  14. Parent Material • Bedrock • In PA, most is not the bedrock • Transported materials: • glaciers • water (alluvial) • erosion and gravity (colluvial) • Affects particle size and chemistry

  15. Soil Color • Color determined by minerals and oxygen availability • Red, yellow, brown hues - good aeration • Gray or olive - poorly aerated, poor drainage • Mottling - seasonable wet; poor drainage

  16. Soil Structure • Aggregates • Result of soil texture classes • Result of organic matter • Provides pores • Decreased/lost by compaction • Granular, platy, blocky, columnar

  17. Soil Texture • Sand, silt, and clay • Affects infiltration • Affects water holding capacity (drainage) • Indirectly affects fertility - adhesion ions to clay • “Strength” for building • Affects soil structure

  18. Clay • Less than .002 mm • Holds water • Forms aggregates - provides soil structure - “sticky” • Excess clay - poor drainage and compaction • Derived from shales • Good adsorption of ions

  19. Silt • .002 to .05 mm • Optimal amount of soil water retention and soil air circulation

  20. Sand • .05 to 2 mm • 1000 times larger than clay • Rapid infiltration/low water holding capacity • Good strength for building

  21. Organic Content • 1 to 20% • Determines structure- aggregates of soil particles • Water holding capacity • Rate of infiltration - • affect porosity • aggregates • Color - darker, more organic • Fertility (chemistry) and pH - high ion exchange

  22. Soil Texture Classes • Proportion of sand, silt, clay • 12 texture classes • Soil texture triangle (229)

  23. Soil Density • Largely due to soil texture and organic content • Degree of aggregation important • Affected by human use • Dense soils - high strength, low porosity, low permeability, poor for plant growth

  24. Lab - Soil Chemistry • Fertility - Ion exchange important • nitrogen (nitrates) • phosphorus • potassium • pH: 6.5 to 7.0 is best • ion (nutrient) uptake • many add lime (“sweetens” soil) • effect of rainfall • PA slightly acid soil

  25. Soil Profile • Soil Horizons - Stratified horizontal layers • Used to classify the soil • O: partially decomposed organic material • A: topsoil • E: zone of leaching • B: subsoil • C: Parent material

  26. Figure 10-15 (2)Page 215 Forest litter leaf mold Acid litter and humus Acidic light- colored humus Humus-mineral mixture Light-colored and acidic Light, grayish- brown, silt loam Iron and aluminum compounds mixed with clay Dark brown Firm clay Humus and iron and aluminum compounds Tropical Rain Forest Soil (humid, tropical climate) Deciduous Forest Soil (humid, mild climate) Coniferous Forest Soil (humid, cold climate)

  27. Soil Profiles • Class in Tennessee

  28. Classifying and Naming Soils • Age of soil • Special features (eg. Fragipans) • water related characteristics • texture • horizons - types and depths • County Soil Surveys - • Soil Conservation Service of USDA

  29. Land Degradation • Every Year • 7.4 M acres ruined by erosion • 4 M acres turned into deserts • 8 million converted to other uses • ESTIMATES: • 40% world’s land seriously degrades • 75% of land in Central America

  30. Erosion (217-221) • Natural process • Disaster: wrong place, wrong time, in too great amounts • Worldwide soil degradation • 1% of world cropland is lost each year • Has reduced food production on 16% cropland • 40% of land seriously degraded(75% in Cent. Am.) • Situation worsening in developing countries as more marginal lands being plowed and farmed

  31. What is happening to our land? • The “dirty thirties” (219) • abuse of land- intensive, monoculture farming • READ: The Dust bowl, page 219 • Soil Erosion Act (1935) • SCS born– now Natural Resources Conservation Service • Soil Conservation Districts formed • Every Year - worldwide • 7.4 M acres ruined by erosion • 4 M acres turned into deserts - removal of natural vegetation • 8 million converted to other uses - development

  32. Causes of soil degradation • Loss is “slow” but nearly permanent • 1 mm year = 25 mm in 25 years • 500 years to replace this • Water erosion • Wind erosion • Salt and toxic chemicals

  33. Erosion • Movement of soil by wind or water to new location • Types of erosion (217)- know these • Sheet erosion • Rill erosion • Gull erosion • Natural process - in natural ecosystems part of soil formation process, but • Disaster: wrong place, wrong time, in too great amounts

  34. Figure 10-18Page 217

  35. Desertification (221) • Positive feedback system – explain this • Area 12X Texas in past 50 years • About 20% land has been severely affected – reduction of crop yield • U.S. – 23% of all irrigated cropland is affected • Causes • Natural or human caused local climate change • Erosion or salinization of topsoil due to excess irrigation (severe on 21% of world’s irrigated land) • Solutions (pg. 222)

  36. Land Resources-Developed Countries • Less cultivated land than 100 years ago • Why is there much less cultivated land? • Astounding 400% increase in yield per acre • Improved crop varieties • Fertilizers • Pesticides • Irrigation

  37. Developing Countries • Many reaching limits of potential cropland • Tropical Soils: fertility rapidly depleted • Loss of tropical forests

  38. Problems of Erosion • Reduced land fertility and thus productivity • Sedimentation of waterways • Smothering of wetlands and coral reefs • Siltation of reservoirs

  39. Sources of Erosion • Agriculture (60 % in U.S.) • Construction • Logging • Off-road vehicles use

  40. Amounts in U.S. • Many areas exceed replacement limit: • max 1mm/yr • 50 million boxcars of soil lost per year • 500,000 trains, 100 cars long • Agricultural Losses: Account for 60% of impaired river miles in U.S.

  41. Soil Conservation - Four Basic Approaches (222 -226) • Managing Topography • Reduced Tillage Systems • Providing or allowing ground cover to remain • Maintain and increase soil structure and fertility • Organic methods help

  42. Providing Ground Cover • Cover cropping (don’t let the soil bear!) • Mulching • “Green” mulches • Agroforesty (223)

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