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.” In the world of soil conservation; however, “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 more.
Farming Below “T” Builds Soil
“T” is measured in “tons per acre.” One ton of soil over one acre is about the thickness of a sheet of paper. 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.
99 Soils in Augusta County
In Augusta County where 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.
1985 Farm Bill
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.
Farm Below “T”
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.