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AP ENVS

AP ENVS. BACK TO CHAP 9. CHAPTER 9. “SOIL AND AGRICULTURE”. THE GREAT DUST BOWL P.235. “First Wave”: Plough native prairie grasses for ag development. But, grasses hold soils in place. Early 1930’s, drought, strong winds, topsoil erosion. Great Dust Bowl! Dust storms: Kansas to NY!

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AP ENVS

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  1. AP ENVS BACK TO CHAP 9

  2. CHAPTER 9 “SOIL AND AGRICULTURE”

  3. THE GREAT DUST BOWLP.235 • “First Wave”: Plough native prairie grasses for ag development. • But, grasses hold soils in place. • Early 1930’s, drought, strong winds, topsoil erosion. • Great Dust Bowl! • Dust storms: Kansas to NY! • http://video.pbs.org/video/2250514396/

  4. SOIL: THE FOUNDATION FOR AGRICULTURE • AGRICULTURE • ‘The intentional human cultivation and cross-breeding of fruit, grain, and vegetable species, and the domestication of animals.’ • Modern homo sapiens: • 160,000 years: hunter-gatherers • Last 10,000 years, after last ice age: start to grow plants from seeds, domesticate animals. • 10,500 years ago, Fertile Crescent, Tigris/Euphrates, southeastern Turkey/western Iran, radiocarbon dating, wheat/barley. • 9,500 years ago, China, rice, millet, pigs.

  5. WORLD POPULATION POPULATION 185 60 10,000 YEARS BEFORE PRESENT

  6. http://www.worldometers.info/world-population/

  7. the truly great human inventions/ACHIEVEMENTS • AGRICULTURE • WRITTEN LANGUAGE • TOOL-MAKING • MEDICINES • ART • LAW • COMPUTER??

  8. not all soils are productive • Sustainable farming practices, otherwise “soil degradation”. Conversion of native grasslands to grow grains for human consumption.

  9. today: “agribusiness” THE INDUSTRIALIZATION OF FARMING

  10. SOIL AS A SYSTEMSOIL CHEMISTRY • SOIL LAB AFTER BREAK?! • What IS soil, and where do soils come from?

  11. SOIL AS A SYSTEMSOIL CHEMISTRY • SOIL LAB AFTER BREAK?! • What IS soil, and where do soils come from? • Breakdown of surface rock = minerals: • Physical weathering: wind, rain, thermal expansion/contraction • Chemical weathering: water (and acids), gases (NH3, O2) • Biological weathering: lichens • EROSION • Hundreds to thousands of years! • Decomposition of dead plant/animal matter = CARBON, N, P • “Humus”

  12. humus

  13. humus • Micropores retain soil moisture. • High oxygenation means many anionic sites for binding/chelating cations and plant nutrients. • Disease-fighting anti-oxidant activity

  14. SOIL COMPOSITION • Dr J: Collect soil chemistry parameters: • FOC: “fraction of organic carbon” • Bulk density: (dry soil bulk density) • Porosity • pH • UNIFIED SOIL CLASSIFICATION SYSTEM (USCS): • Texture • Grain size • FIGURE 9.6 (p.230)

  15. left off 11/26 SOIL COMPOSITION AND CONTAMINANT MOBILITY • SITE A: • Leaking HVOC (solvent) UST • Shallow water table • Soils: Coarse grain sands, gravels, low FOC • HIGH CONCERN! • SITE B: • Leaking fuel UST • Deeper water table • Soils: Fine-grain clays/silts, higher FOC • LOW CONCERN

  16. SOIL AS A COMPLEX, HETEROGENEOUS MEDIUM

  17. soil layers are “horizons”

  18. minerals are distributed via “leaching” Leaching is really “infiltration” Unsaturated (vadose) water table: beginning of saturated zone

  19. CHARACTERIZING SOILS

  20. SOIL PARAMETERS • pp. 229-230 + SUPPLEMENTAL • Soil texture: particle size • Clays: < 0.002 mm diameter (not visible) • Sands: 0.05 – 2 mm • Silts: Between clays and sands • “loam”: 33.3%, 33.3%, 33.3%

  21. PARTICLE SIZE • SMALL PARTICLES: Lower “porosity”, slower/shallower infiltration, slower GW flow • LARGE PARTICLES: Higher porosity, faster infiltration, faster GW

  22. QUANTITATIVE SOIL CLASSIFICATION

  23. UNIFIED SOIL CLASSIFICATION SYSTEM

  24. SOIL PARAMETERS SUMMARY • Foc • Bulk density • Porosity • pH • Texture • Ion exchange capacity • STOPPED HERE 12/6

  25. ION (CATION) EXCHANGE CAPACITY • A soil’s ability to hold cations • Plant nutrients: • Mg2+ • Ca2+ • K+

  26. C.E.C. pH Dependent • Most healthy soils: pH 6.0 – 7.5 • http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_053293.pdf

  27. ACID DEPOSITION • LOWER SOIL pH • Too many H+ ions • Compete with metal cations for anionic soil binding sites • Soil CEC goes down

  28. ACID DEPOSITION • If acid rain mobilizes nutrient metals, it can also mobilize toxic metals • MINING!

  29. Land Degradation And Soil Erosion (pp. 231 – 245)

  30. SOIL EROSION • “Erosion”: The removal of surface soil/rock structure by various forces or processes, either natural or man-made. • Reverse of “deposition”.

  31. CAUSES OF SOIL EROSION • NATURAL • Wind • Rain/Runoff • Steep slope • Glaciers • Forest fires • Disease (plant) • Climate change....expanding Sahara ?!

  32. CAUSES OF SOIL EROSION • MAN-MADE • Poor agricultural practices • Clear-cutting forests (lumber industry)

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