Soil Erosion Factoids

From Big Picture Agriculture:

Michael Duffy at Iowa State has come out with a new report on soil erosion and how it decreases land values in the state of Iowa. This is an ugly truth that no one wants to talk about. We are literally mining our topsoil.
Here are some interesting facts from his report:
● In 1982 there was an estimated 7.4 tons per acre of soil erosion on Iowa cropland.
● By 2007 erosion in Iowa had decreased to 5.1 tons per acre.
● For the entire United States, erosion rates dropped from 4.0 tons to 2.7 tons per cropland acre over the same time period.
● The hypoxia zone in the Gulf of Mexico is directly related to the amount of erosion on farms.
● Per acre: Soil weighs roughly 154 tons per inch. If we assume that you are losing 4 inches as you move in the different erosion phases then you would lose 616 tons of soil. The average of all the estimates for cost of erosion was $268 an acre.

The mining point is true.  Our clay-rich soils have more water erosion than the wind erosion which can occur out west in the heavy loess soils, but it is still a real problem.  The last few winters, we've gotten pummelled by big rains which cut gullies in the fields.  If that is related to global warming, we may be in for many years of issues.  I've never been able to get this anecdote from Jared Diamond's book, "Collapse," out of my head:

" ... about half of the topsoil of Iowa, the state whose agricultural productivity is among the highest in the U.S., has been eroded in the last 150 years. On a recent visit to Iowa, my hosts showed me a churchyard offering a dramatically visible example of those soil losses. A church, built there in the middle of farmland during the 19th century, has been maintained continuously as a church ever since, while the land around it was farmed ... the churchyard now stands like a little island raised 10 feet above the surrounding sea of farmland.

10 feet?  A lot of our ground is lucky to have a foot of topsoil.  No wonder the crops are so good out there. But I'd hate to be responsible for pissing away that much unbelievably rich soil.