> But the sediment delivered to
> rivers, lakes, wetlands and streams is still too high. For example, in one
> 175 sq. mi. (453 sq. km) watershed the estimated delivery from cropland
> alone (no urban or other rural sources considerd) is over 22,000 tons
> (about 20,00 metric tons) each year. This is how most of the phosphorus
> and bad chemicals get in to the water.
Let's put Karl's figures into perspective. What proportion of that 175
sq. mi. watershed IS cropland, because the watershed as a whole is doing
quite well, soil erosion-wise. That 22,000 tons spread over 175 sq. mi.
is an erosion rate of about 0.2 tons/acre, which is quite low.
"Natural" or "non-accelerated" rates of erosion are usually cited as
between 0.1-0.2 tons/acre. The tolerable soil loss "T-values" that
Karl mentioned (i.e., the maximum erosion that can take place on a given
soil without degrading its long-term productivity) commonly range from 2
to 5 tons/acre for US soils.
-- Jeffrey G. White, Ph.D. Assistant Agronomist Mississippi State University Pontotoc Research and Extension Center 8320 Hwy 15 South, Pontotoc, MS 38863 Tel: 601-489-4621; FAX: 601-489-6011 Email: firstname.lastname@example.org
To Unsubscribe: Email email@example.com with "unsubscribe sanet-mg". To Subscribe to Digest: Email firstname.lastname@example.org with the command "subscribe sanet-mg-digest".