“T” Stands For Tolerance
There has been a lot of talk about “T” these days because of
the Chesapeake Bay TMDL. I hate jargon
so here’s a quickie on these two terms.
The TMDL is the agreed upon pollution diet for the Bay; it stands for
Total Maximum Daily Load. It’s the
maximum amount of pollution loading on a daily basis allowed by state law.
The “T” in TMDL stands for “Total”; but in the world of soil conservation “T” stands for the “Tolerance” level of soil
erosion that scientists tell us is sustainable.
“T” is one of the factors in the “Revised Universal Soil Loss Equation”. It’s called RULSE for short. It estimates sheet and rill erosion over long
periods of time. The USDA’s Natural
Resources Conservation Service (NRCS) developed these factors decades ago through
the scientific method and they continue to revise the factors as they learn
“T” is measured in “tons per acre”. One ton of soil over one acre is about the
thickness of a sheet of paper and an acre is about the size of a football
field. Here’s what “T” means in a
nutshell: It’s the level of soil erosion
that can be “tolerated” without sacrificing its quality or quantity. Allowing soil to erode or wash away above the
“T” value is unsustainable and has led to the collapse and demise of many
civilizations. If we can farm below the
“T” value then we are building soil.
County were I live there
are 99 different soils. Each soil has
its own chemical and physical properties and the “T” value for these soils
ranges from 2 tons of soil erosion per acre per year to 5 tons of soil erosion per
acre per year. Most of the soils in this
country have been mapped and anyone with a computer can view the soil maps and
their properties by going to Web Soil Survey.
Back in 1985 the U.S. Congress debated on a Farm Bill that would
require farmers to show that they were not allowing the soil on their crop
fields to wash away in order to receive USDA benefits. It was quite a debate. The farmers didn’t want any requirements at
all and the environmentalists wanted soil erosion checked at the soil’s “T”
value. What resulted was “The Great
Compromise”. Farmers were allowed to
farm their crop fields at 2 times the “T” value and still receive USDA
benefits. So, by law then, farmers could
receive benefits funded by the taxpayers of this country while their soil could
erode at twice what science tells us is sustainable. This act may have been a good example of democracy
and compromise but it was a lamentable example of reckless stewardship of a
precious natural resource.
Now with the Chesapeake Bay TMDL, there are renewed discussions to get our soil erosion on cropland down to “T”. This would be a giant step towards
sustainability and something that will definitely improve the water quality of
our streams and the Bay by reducing the amount of soil entering streams.