Erosion Control

Soil is one of the necessities of social well being: no soil, no food, no society.
When soils were exhausted or when soils were removed from wind or rain and the replenishment rate could not keep up with the erosion, then human societies fell into rapid decline.

A good article on good husbandry of the soil:
Mother Jones
http://www.motherjones.com/tom-philpott/2014/02/iowas-vaunted-farms-are-losing-topsoil-alarming-rate

Iowa Is Getting Sucked Into Scary Vanishing Gullies
—By Tom Philpott
| Fri Feb. 7, 2014 3:00 AM GMT
Last year, after a record drought in 2012, Iowa experienced the wettest spring in its recorded history. The rains triggered massive runoff from the state's farms into its creeks, streams, and rivers, tainting water with toxic nitrate from fertilizer. Nitrate levels in the state's waterways reached record levels—so high that they emerged as "a real issue for human health," Bob Hirsch, a hydrologist for the US Geological Survey, told the Associated Press.

 

The event illustrated two problems facing Iowa and the rest of the nation's topsoil-rich grain belt. The first is the challenge of climate change: how to manage farmland in an era when weather lurches from brutal drought to flooding, as it likely will with increasing frequency. The second, related one is the largely invisible crisis of Iowa's topsoil, which appears to be eroding at a much higher rate than US Department of Agriculture numbers account for—and, more importantly, at as much as 16 times the natural replacement rate...

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