1. Topsoil and Erosion Neil Swanson & Olivia Miller

2. USDA-defined range of tolerable soil loss (Montgomery, 2007, Wilkinson, 2007) Current farmland erosion: ~75 Gt/yr

3. Americans move ~30 tons/year/capita (Hooke, 2000)

4. How long will it take to erode through our soil? Using geological erosion 1 mm/year, it will take a few hundred to a few thousand years T = S/(E-P) S = initial thickness E = soil erosion rate P = soil production rate Limiting lifespan of an agricultural society according to Montgomery, (2007).

5. Soil conservation USDA-defined range of tolerable soil loss (Montgomery, 2007) Organic vs. conventional farming http://ngm.nationalgeographic.com/2008/09/soil/richardson- photography