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The United States loses almost 3 tons of topsoil per acre per year. [16] 1 inch (2.5 cm) of topsoil can take between 500 [17] and 1,000 years [18] to form naturally, making the rate of topsoil erosion a serious ecological concern. Based on 2014 trends, the world has about 60 years of topsoil left. [18] [19]
In its early stages of development, soil loss tolerance rates were inconsistent because they were obtained based on rough estimates. From 1961 to 1962, several groups of soil in the United States were designated with T rates ranging from 2 to 6 tons per acre per year. The rate was subsequently adjusted to 1 to 5 tons per acre per year. [5]
In 1824, these units were replaced with a single system based on the imperial gallon. [a] Originally defined as the volume of 10 pounds (4.54 kg) of distilled water (under certain conditions), [b] then redefined by the Weights and Measures Act 1985 to be exactly 4.546 09 L (277.4 cu in), the imperial gallon is close in size to the old ale gallon.
The United States Department of Agriculture defines the T Value as the maximum average soil loss (in tons per year) that will still allow economical maintenance of the current level of production into the future. [1]
For example, GW-GM corresponds to "well-graded gravel with silt." If the soil has more than 15% by weight retained on a #4 sieve (R #4 > 15%), there is a significant amount of gravel, and the suffix "with gravel" may be added to the group name, but the group symbol does not change. For example, SP-SM could refer to "poorly graded SAND with silt ...
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How many tons in an inch of topsoil, or how many 'inches' is 25 billion tons? Should be fixed or removed. The gesture of the data therein is good, just needs to be refined. --Ikyork 18:15, 17 October 2007 (UTC) According to a top soil calculator on a garden store website I recently removed, topsoil weighs 1.3 tonnes per cubic meter.
One common such material is water, used in multiple units. For the cubic ton, the situation is more complex—there are different cubic tons for different materials. The 1964 Reader's Digest Great Encyclopaedic Dictionary gave the following ton-derived volumes: Timber, 40 cubic feet or 480.0 bd ft or 1.133 m 3; Stone, 16 cubic feet (0.453 m 3)