From: marc@sisters.cs.uoregon.edu (Marc Harold Baber)
Subject: Soil Erosion (was Re: save the earth - ridiculous!)
Summary: Facts from State of the World 1993
Organization: University of Oregon Computer and Information Sciences Dept.
Date: Tue, 26 Jan 1993 02:06:42 GMT

In previous articles <travt.727410006@marsh> travt@cs.curtin.edu.au 
(Tony Travers), betel@camelot.bradley.edu (Robert Crawford) and others ? write:
>
>>>	Soil degridation through modern argiculture is a serious
>>>problem.  We are providing ourselves with unusually high yelds at the
>>>expence of the future viability.  

>>	"Modern agriculture" is not destroying soil viability. At
>>least not in the US, where most of the world's "modern agriculture" is
>>practiced. I grew up on a farm, and we carefully rotated our crops to
>>maintain the soil -- that, after all, is the wealth in that land.
>
>	I think there are degrees of destruction involved, rotating the
>crops in a sophisticated and coordinated fashion will led to a much more
>sustainable practice than slash and burn.  But I have seen some evidence
>that the modern agricultural method slowly depletes the soil depth.

"With soil erosion, global losses continue to be heavy, but the United 
States has made impressive progress.  The 1985 Conservation Reserve Program
provided for the conversion of some 14 million hectares of highly erodible
cropland to either grassland or woodland.  The result was a reduction of U.S.
soil losses by at least one third.  In the second phase of the program,
from 1990 to 1995, soil losses could be cut by another third.  This adds
up to a remarkable achievement, a substantial contribution to world food
security."
			-State of the World 1993,
			Lester Brown, et. al.
			Page xvi

"During the 20- years since Stockholm, farmers have lost nearly 500 billion
tons of topsoil through erosion at a time when they were called on to feed 
1.6 billion additional people."  (Ibid. P. 4)

"Land degradation is also taking a heavy economic toll, particularly in the
drylands that account for 41 percent of the earth's land area.  In the
early stages the costs show up as lower land productivity.  But if the
process continues unarrested, it eventually creates wasteland, destroying
the soil as well as the vegetation.  Using data for 1990, a U.N. 
assessment of the earth's dryland regions estimated that the degradation of 
irrigated cropland, rainfed cropland, and rangeland now costs the world
more than $42 billion a year in lost crop and livestock output, a sum that
approximates the value of the U.S. grain harvest...
	These losses are from the degradation of drylands only.  The
deterioration in humid regions of the world, which includes the U.S. 
Corn Belt and most of Europe's rich agricultural regions, also takes a 
heavy toll, though no one has calculated it." (Ibid. P. 7)

" Worldwide, farmers are losing an estimated 24 billion tons of topsoil 
from cropland each year.  With one hectare-inch of topsoil weighing 400 
tons, this annual loss can be visualized as one inch lost from 60 million 
hectares, an area equal to roughly half of China's cropland.  A compilation 
of more than a dozen U.S. studies analyzing the effect of erosion on land 
productivity found that losing an inch of topsoil reduces corn and wheat 
yields an average of 6 percent." (Ibid. P. 12)

The folks at WorldWatch are pretty thorough.  I would hope that a good 
percentage of the readers of this group read their reports regularly.

-Marc