a four-fold rise - Center for Food Safety

Center for Food Safety – Science Comments – FG72 Soybean
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upon long-­‐term climate data, inherent soil and site characteristics, and cropping and management
practices.” Tillage regimes are the primary component of “cropping and management practices,” and
thus play a large role in determining soil erosion rates. It is well established that soil erosion
increases with the intensity of tillage, and decreases as farmers adopt regimes that leave more plant
residue on the soil (USDA ERS AREI 2002). Thus, the chart below reflects in large degree the tillage
regimes used by farmers.
From: NRCS
(2010), p. 2.
On a national
basis, water and wind erosion on cropland declined sharply by 38% from 1982 to 1997, from 3.06 to
1.89 billion tons. In the following decade, however, soil erosion almost leveled out, declining by just
8%, from 1.89 to 1.73 billion tons. Herbicide-­‐resistant crops were first introduced in 1996, and the
area planted to them (HR soybeans, corn and cotton) increased steadily from 16.0 million acres in
1997 to 117.2 million acres in 2007 (Benbrook Supplemental 2009, Table 5). If HR crops promoted
adoption of conservation tillage in any significant way, one would surely expect a much stronger
decline in soil erosion over a period when their adoption increased by 100 million acres.
However, NRCS’ survey offers still more compelling evidence at the regional level. The following map
(from p. 3) breaks down average annual soil erosion rates, in tons per acre per year, by farm
production region. For each region, rates for the six survey periods (1982, 1987, 1992, 1997, 2002
and 2007) are shown stacked from top (1982) to bottom (2007). The rates in this map are also listed
in Table 36 of the report (pp. 12-­‐16).