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In due time they will be merged.
Some time ago (apparently in 1992), in the newsgroup sci.environment, I suggested that farmers would be more motivated to take good care of their topsoil if it were a commodity. Thus a farmer with deep topsoil could sell some to a farmer with inadequate topsoil. Land with very deep topsoil, e.g. in river valleys, would become more valuable than it is today. Land with barely adequate topsoil would become somewhat less valuable than it is today. Land with no or inadequate topsoil would become more valuable, because it could be restored. Of course, quality of topsoil is not the only component of the price of agricultural land. Where rainfall is suboptimal, water rights may be even more important.
The feasibility of this idea depends on the cost of moving topsoil without damaging it too much. My intuition that it probably would be feasible was based on the fact that land is often leveled to make irrigation work better, and this requires moving most of the topsoil around, often on a multi-acre field. We have the figure that land with good topsoil in Idaho near Boise is worth $4000 per acre and land with bad topsoil is worth $1000 per acre.
When I posted the idea, some said it was ridiculous, and one said that if it were economical it would already be in use, although he later took it back. Others said it was necessary to determine the costs. This I undertook to do, but just (when?) got around to making the necessary telephone calls.
Relevant facts:
Amount of topsoil: 1,000,000 pounds per acre - Encyclopedia Britannica article on soil.
Cost of moving dirt: $1.00 to $1.50 per cubic yard - Caterpillar Performance Handbook. This includes the digging, loading and unloading but refers to short distances.
Weight of dirt: 2500 lbs per cubic yard.
Our million pounds is 400 cubic yards, 500 when swelling is taken into account. Therefore, it costs $750 per acre to move it short distances. However, the handbook in question is for construction contractors, and maybe topsoil has to be treated more gently than is customary for contractors.
A standard dump truck carries 10 cubic yards, the driver costs $30 to $40 per hour including benefits, and the truck costs $30 to $40 per hour rented wet, i.e. including fuel, etc. A double trailer could carry 20 cubic yards, might cost twice as much to rent but would cost no more per driver. It could go 40 miles per hour loaded and somewhat faster on the way back.
Using the bigger truck, there being a weight limit of 10 tons per axle including the vehicle itself on U.S. highways, we get a cost of $2400 per acre-hour, assuming the higher cost figures above. This tells us that the limit of profitability is about 20 miles.
I suppose there is a fair amount of eroded upland within 20 miles of river valleys with deep topsoil.
Of course, rail transportation is a lot cheaper, and barge transportation is a lot cheaper than that. Still the differential in price of land with good and bad topsoil will have to get somewhat larger, before it will be profitable to dig up the Mississipi delta, which largely consists of topsoil washed down the river and barge it back up the river.
To return to the beginning. Once topsoil becomes a commodity, farmers with deep topsoil will work harder than they do today to avoid erosion, since they can imagine selling some of their topsoil.
However, topsoil is unlikely to become a commodity very soon in the U.S. Yields from presently farmed land are still increasing faster than is the market for agricultural products. For example, there is still no sign of anyone growing major new crops in New England, which grew them until railroads opened up the Middle West where they can be grown cheaper. New England farms were abandoned and reverted to woodland.
This doesn't cover all the points made in the sci.environment discussion.
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