I was struck for the following reasons:
1. The laboratory included a discussion about the T-value concept
(tolerable soil loss)
2. Many students felt that if they reduced soil losses to the T-
value they had met a mandated obligation and fulfilled a moral
3. Discussions with several farmers have gone along the following
lines: We know we can produce good topsoil from subsoils because
when we put in terraces, areas where subsoils are exposed
are as productive as undisturbed sites in a couple of years if
heavy manuring is practiced.
This has me questioning to what extent is the mainstream farming
community committed to reducing soil erosion.
1. What advice does the research community give in regards reducing
2. What advice would you give a farmer as to the appropriate T-value
for his or her soil and why?
By now most farmers in my own community in NW Iowa would agree
that controlling erosion to meet the T-values for their soils is
adequate protection of soils. The "tolerable levels" of soil loss on
most soils in this part of the state are considered to be from 4-5
I would like to see several members of this group discuss their
feeling in this area especially in light on an article by
Leonard Johnson in the J. of Soil and Water Conservation which really
caught my attention. As I don't get to talk regularly with
professionals in the area of soils and since those I talked to have
dismissed my concerns, I would like some input. Am I missing
Probably Johnson's main point in his article is follows:
Soil loss tolerance values are based on faulty premises concerning
rates of topsoil development and mineral weathering processes.
For instance Johnson cites widely diverging estimates of the rate
of soil formation and then cites work of T. Logan "most estimates of
soil renewal are less than 0.2 ton/acre/year" thus " we are in
essence mining the soil in order to produce food and fiber in the
same way that we mine our coal resources. I pointed out to class
that over a 100 year period if we have soil formation at a rate of
0.2 tons/acre/year and average losses of 5.0 tons/acre/year that we
would lose 960,000 lbs of soil over that time period which would
represent about half of an acre furrow slice or about 3 inches of
soil. In the geological perspective of time this presents problems!
Finally, Johnson makes the statement "some may argue that this
futuristic scenario represents an impossible dream; that the need for
maximum grain production and monetary profit in the near term is so
compelling that reducing soil erosion to anywhere the "normal" rate
cannot be contemplated seriously, much less acheived in the
WHAT SAY YE?
Leonard C. Johnson. 1987. Soil Loss Tolerance: Fact or Myth?
Thanks for your contributions!
Dr. Chris Goedhart e-mail: firstname.lastname@example.org
Agriculture Dept phone: (712)722-6276
Dordt College FAX: (712)722-1198
Sioux Center,IA 51250