David montgomery dirt

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David montgomery dirt

  1. 1. 11
  2. 2. Soil is a Strategic Resource Global soil degradation is an under appreciated crisis
  3. 3. Natural Disasters No real mystery that some of the key controls on the longevity of human societies are … Politics, War, and Social Evolution Climate Change But what about soil? The fundamental condition for sustaining a civilization is sustaining the soil and its fertility.
  4. 4. Mesopotamia Minoans Greece Rome Indus Angkor Watt Olmec Maya Inca Soil erosion resulting from deforestation has been proposed to explain the demise of ancient civilizations around the world.
  5. 5. But in many regions trees can grow back before soil disappears… Was the agriculture that followed the real culprit?
  6. 6. Could agricultural soil erosion and degradation limit the life span of civilizations?
  7. 7. Over the last 40 years soil erosion has caused farmers to abandon about 430 million ha of arable land, an area equivalent to about one-third of all present cropland. The estimated rate of world soil erosion in excess of new soil production is 23 billion t yr, or about 0.7% loss of the world's soil inventory each year. Pimental et al., 1992, BioScience
  8. 8. Recent archaeological studies showed that soil erosion played a role in the demise of ancient civilizations of Neolithic Europe, Classical Greece, Rome, the Southern United States, and Central America.
  9. 9. Weathering
  10. 10. Under native vegetation, a typical soil thickness develops, reflecting the local climate, vegetation, topography, and geology Over time, any net difference between soil production and soil loss changes the soil thickness.
  11. 11. In the permanence …of a coat of vegetable mould on the surface of the earth, we have a demonstrative proof of the continual destruction of the rocks; and cannot but admire the skill, with which the powers of the many chemical and mechanical agents employed in this complicated work, are so adjusted, as to make the supply and the waste of the soil exactly equal to one another. - [Playfair, 1802, p. 106-7]
  12. 12. Invention of the plow fundamentally altered the balance between soil production and soil erosion, dramatically increasing soil erosion…
  13. 13. Cycles of erosion and soil formation in ancient Greece began with Bronze Age erosion after introduction of plow-based agriculture.
  14. 14. Van Andel and Runnels (1987)
  15. 15. Van Andel and Runnels (1987)
  16. 16. Van Andel and Runnels (1987)
  17. 17. Population density of the Southern Argolid Van Andel and Runnels (1987 Bronze Age Classical Age Modern Age
  18. 18. Plato The rich, soft soil has all run away leaving the land nothing but skin and bone. But in those days the damage had not taken place, the hills had high crests, the rocky plain of Phelleus was covered with rich soil, and the mountains were covered by thick woods, of which there are some traces today. 427-347 B.C.
  19. 19. A few years more of increased sterility will drive the Inhabitants of the Atlantic States westward for support; whereas if they were taught how to improve the old, instead of going in pursuit of new and productive soils, they would make these acres which now scarcely yield them any thing, turn out beneficial to themselves. - [G. Washington, 1892, v. XIII, p. 328- 329] In a 1796 letter to Alexander Hamilton…
  20. 20. Historical soil erosion in the Piedmont region after Trimble
  21. 21. Most of the erosion-control practices in use at the present time … were either developed by the Virginia farmers or became known to them during the first half of the nineteenth century. - [Hall, 1937, p.] Extensive soil erosion did not occur because of ignorance of soil conservation practices
  22. 22. Men may, because of ignorance or habit, ruin their soils, but more often economic or social conditions, entirely outside their control lead or force them to a treatment of their lands that can end only in ruin. - Craven (1925)
  23. 23. I suspect that when people along the seaboard of the eastern United States began to taste fresh soil from the plains 2,000 miles away, many of them realized for the first time that somewhere something had gone wrong with the land. - Soil Conservation Chief Hugh Bennet, 1941
  24. 24. USDA (1979) 1970Palouse, Washington
  25. 25. Kaiser (1961) 1911 1961 Palouse, Washington
  26. 26. In researching the book, I began compiling additional data on both contemporary and long-term (geological) erosion rates—and agricultural erosion rates in particular…
  27. 27. 1402 measurements of agricultural and geological erosion rates Did not include sediment yield and USLE-based studies
  28. 28. USDA soil loss tolerance values range from 0.4 to 1 mm/yr Conventional farms erode like steep alpine topography Conventional agriculture unsustainable in soil-mantled
  29. 29. Probability distributions for geological erosion rates, erosion under native vegetation, and by no-till agriculture are all comparable.
  30. 30. Global erosion rates have increased by more than an order of magnitude due to human activity… Average erosion rate for last 500 million years = 1 inch / 1400 yrs Average rate of soil production at present = 1 inch / 500 yrs Average rate of soil erosion at present = 1 inch / 60 yrs (Wilkinson, 2005)
  31. 31. Net soil loss of ≈ 1 mm/yr implies that erosion of a typical 0.5 - 1 m thick hillslope soil could occur in roughly 500 to 1000 years; approximately the lifespan of most major civilizations outside of major river floodplains…
  32. 32. Here in a nutshell, so to speak, we have the underlying hazard of civilization. By clearing and cultivating sloping lands—for most of our lands are more or less sloping—we expose soils to accelerated erosion by water or by wind…. In doing this we enter upon a regime of self- destructive agriculture. - [Lowdermilk, 1953, p. 26]
  33. 33. National Archives: 114 SC 5089 A nation that destroys its soils, destroys itself. – President Franklin D. Roosevelt, Feb. 26, 1937.
  34. 34. Is Soil Restoration Possible? Can we reverse the historical pattern?
  35. 35. How? Change our agricultural practices... • reduce subsidies for conventional, erosive practices; • increase support for no-till practices on land where they are suitable; • promote practices that increase soil organic matter to both sequester carbon and improve soil fertility.
  36. 36. Rebuilding Soil We can make soil surprisingly fast — faster than nature does… It takes organic matter and labor — what we have in cities (organic waste and people).
  37. 37. Fertile carbon-rich soils built by anthropogenic activity in the Amazon and reclaimed sea beds in northern Europe. Terra Preta Plaggen
  38. 38. Why bother restoring soils? To Address Global Challenges of the 21st Century Climate Change Feeding a Post-Oil World Public Health / City Livability Biodiveristy / Environmental Degradation
  39. 39. Restoring soil could be the foundation for partial solutions to all of these problems…
  40. 40. Peak Oil A Question of When
  41. 41. Feeding A Growing Population …
  42. 42. How will we feed a post-oil world without fertilizer-intensive agriculture?
  43. 43. A Greener Revolution? In some cases, crop yields from no-till and organic agriculture appear able to match those from conventional agriculture… No matter how one looks at it restoring native soil fertility will be important for sustaining agriculture in a post-oil (and post-cheap fertilizer) world.
  44. 44. Soil and Climate Change By the late 20th Century, a third of carbon added to atmosphere since the Industrial Revolution came from degraded soil organic matter. We can put that much (and more) back in the ground through: (1) increasing soil organic matter (2) biochar
  45. 45. Lal (2004) estimated that changes in agricultural practices could sequester 0.4 to 1.2 Gt C per year, enough to offset 5- 15% of global fossil fuel emissions. Amundson (2001) noted that cultivation and deforestation releases >4 Gt C per year, equivalent to more than half global fossil fuel emissions. Global Agriculture, Land Use and Carbon Emissions
  46. 46. Biochar: Global soil C≈1500 Gt Global atmospheric C≈760 Gt Average residence time for SOC globally is less than 2 decades. Biomass decay ≈60 Gt/yr Fossil fuel emissions ≈7 Gt/yr Capture of ≈10% of biomass decay as biochar would offset global fossil fuel emissions.
  47. 47. ―The significant problems we face cannot be solved at the same level of thinking we were at when we created them.‖ Time For A New View of Soil?
  48. 48. Soil as a mystery, fertility to be personified, deified and revered.
  49. 49. Soil as a means to a living, land to be worked.
  50. 50. Soil as a decipherable mystery, something to be studied and understood. We know more about the movement of celestial bodies than about the soil underfoot. - Leonardo da Vinci
  51. 51. Soil as a chemical reservoir, a medium to be fertilized as needed.
  52. 52. Soil as an industrial commodity to be used (and used up).
  53. 53. Soil as an ecosystem to be understood and harnessed.
  54. 54. Soil Ecology — the Future of Agriculture? One of the biggest challenges of this century is to harness the insights of soil ecology to feed the world based on ecological processes and nutrient cycling.
  55. 55. Soil, Cities, and Public Health As of 2009, more than half of humanity lives in cities. Restoring urban soils can improve the quality of the built environment and thereby people’s health through: • Green space/Urban nature • Physical Activity • Access to Fresh Food
  56. 56. Healthy Soil: No Silver Bullet, But A Secret Weapon? Restoring soils can help address: • Feeding the World • Climate change • Public health (physical, mental, and social)
  57. 57. Since the dawn of history humanity has degraded soils. This century we are at a turning point that will set the course of humanity for the next millenium. The challenge is simple. If we are to sustain life at the top (us) we must reinvest in life at the bottom — life in and of the soil itself.
  58. 58. First and foremost soil restoration means … … we can no longer treat soil like dirt!

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