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Soil and Food

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  1. Soil and Food

  2. Soil: What is it? Inorganic materials (clay, silt, and sand) weathered from solid rock Living organisms (worms, insects, mites, fungi, …) Decaying organic matter Water air

  3. Soil • Who cares?

  4. Soil • Who cares? • Critical to driving biogeochemical cycles • HNOPS in CHNOPS comes from the soil; YOU come from the soil! • C1480H2960N16O1480P1.8S Air Soil

  5. Soil • How long does it take for soil to form?

  6. Soil • How long does it take for soil to form? • 200-1,000 years for 1 inch of soil

  7. Soil • What influences soil properties?

  8. Soil Profile Dig into the soil and you see the soil’s profile: all the different layers (called horizons) of soil, from the surface litter to the bedrock

  9. Soil Horizons Topsoil Surface Litter Zone of Leaching Subsoil Parent Material Bedrock

  10. Surface Litter and Topsoil

  11. Soil • Surface litter: fresh and partly decomposed organic matter • Topsoil: where most living things and nutrients are • Zone of leaching: where dissolved materials from above move down • Subsoil: accumulated materials from above • Parent material: partially broken down rock; source of minerals and inorganic matter in soil • Bedrock: underlying, unweathered rock

  12. Not all soils have the same profile

  13. Let’s look at tropical soils

  14. Tropical rainforest soil • Have a shallow topsoil layer because of rapid decomposition • Lots of rainfall removes a lot of the silica from the topsoil, but leaves behind metals like aluminum and iron. • If you remove the plants, the topsoil washes away

  15. Tropical rainforest soil • Leaving behind the metal-rich subsoil, which hardens in the sunlight, eventually turning into a hard, red soil/dirt that doesn’t absorb water and can’t support plants • Can grow crops there for 3 yrs or so • Then switch to cattle for another 3-5 yrs • And then land is abandoned

  16. Tropical rainforest soil • So, what is the take-home message? • Where we grow crops is not just determined by climate; soil type must be considered.

  17. Types of soil profiles: • Soils have been cataloged all over the U.S. and most of the world, at this point in time. • See next two slides…

  18. U.S. Soil Map

  19. Soil Profile and Information for the Tucson Area

  20. Human impacts on soils • Soil erosion: movement of soil components (esp. topsoil) from one place to another

  21. Types of soil erosion Splash erosion Rill erosion Gully erosion Sheet erosion Figure 8.11

  22. Human impacts on soils • How is soil moved? • 1. Wind • 2. Moving water

  23. Human impacts on soils • What are the rates of soil erosion? • In U.S., for 1/3 of all cropland, erosion rates exceed replacement rates for soil • Amount of topsoil lost in the U.S. each year would fill a dumptruck 3,500 miles long

  24. Human impacts on soils • Where does the soil go? • Oceans • Somewhere else … where it’s not useful as soil anymore...

  25. Human impacts on soils • What factor makes the land more susceptible to erosion? • VEGETATION REMOVAL • Why? • 1. Vegetation (roots) hold the soil in place • 2. Plants slow down wind and running water (less energy)

  26. Human impacts on soils: erosion • Type Tons soil eroded % rain that runs off • Bare soil 41 tons/hectare 30%

  27. Human impacts on soils: erosion • Type Tons soil eroded % rain that runs off • Bare soil 41 tons/hectare 30% • Continuous corn 19.7 tons/hectare 29%

  28. Human impacts on soils: erosion • Type Tons soil eroded % rain that runs off • Bare soil 41 tons/hectare 30% • Continuous corn 19.7 tons/hectare 29% • Continuous wheat 10.1 tons/hectare 23%

  29. Human impacts on soils: erosion • Type Tons soil eroded % rain that runs off • Bare soil 41 tons/hectare 30% • Continuous corn 19.7 tons/hectare 29% • Continuous wheat 10.1 tons/hectare 23% • Rotate corn,wheat, clover 2.7 tons/hectare 14%

  30. Human impacts on soils: erosion • Type Tons soil eroded % rain that runs off • Bare soil 41 tons/hectare 30% • Continuous corn 19.7 tons/hectare 29% • Continuous wheat 10.1 tons/hectare 23% • Rotate corn,wheat, clover 2.7 tons/hectare 14% • Continuousbluegrass 0.3 tons/hectare 12% • Based on 14 years of data from the Missouri Experiment Station, Columbia, Missouri

  31. Human impacts on soils: erosion • So, what was the take-message of that last table?

  32. Human impacts on soils: erosion • So, what was the take-message of that last table? • Amount and type of vegetation affects the amount of erosion of soil that occurs

  33. Human impacts on soils: erosion • What activities lead to soil erosion?

  34. Effects of Soil Erosion • 1. Loss of productivity of the land • Less soil, less nutrients, less water-holding capacity …. Less growth

  35. Effects of Soil Erosion • 2. Increased air and water pollution • From dust in the air and soil in the water...

  36. Effects of Soil Erosion • 3. Increased flooding: due to less water holding capacity of the soil

  37. Effects of Soil Erosion • 4. Increased gullying: thus loss of productive land.

  38. Effects of Soil Erosion • 5. Increased costs due to buying fertilizer, irrigation, etc.

  39. Effects of Soil Erosion • 6. More irrigation leads to salinization of soils and eventually waterlogging (as a farmer attempts to flush out the salts…)

  40. Human impacts on soils: conservation • 1930s dust bowl was a wake-up call (in U.S.) • 1935 Soil Conservation Act established Soil Conservation Service: maintains soils in the U.S. using education, laws, incentives, disincentives...

  41. Soil Conservation Methods

  42. Chad: The Aboubakar family of BreidjingCampFood expenditure for one week: $1.23 Food United States: The Revis family of North CarolinaFood expenditure for one week: $341.98 From the book, "Hungry Planet"

  43. Food • Malthus, 1700s: • Population is increasing exponentially • Food resources are increasing linearly • ………… BIG problem!

  44. Food • Malthus didn’t/couldn’t anticipate the industrial and green revolutions, which have allowed food resources to increase exponentially for the last few 100 y

  45. Food • BUT • Is this maxed out?

  46. Per capita food production is leveling off world wide

  47. Food: Grain harvests • World grain production has been increasing thru time • But production per person has leveled off, area under production has leveled off, and the grain harvested area per person has decreased

  48. Food • So, do you think we will be able to supply enough food for everyone in the future? • Depends on • Rate of population growth • Ability to increase food availability

  49. Food • Let’s talk about our food for a minute. • What do we eat? • 2 main crops make up 60% of our calories • 1. • 2. • 2 other crops make up most of the rest • 3. • 4. ?