CHEMICAL REPORT.



  Because of the very small proportion of the essential ingre-
dients of the soil, which are carried off in crops, as compared
with the whole amount of the earth, taken to the depth through
which the roots of plants absorb nourishment, it has been
denied that it is possible by chemical analysis to show their
diminution in the old field soil, as compared with the virgin
soil. Indeed it has been logically demonstrated to be impos-
sible. But, it should be recollected that when, by the acid
digestion, we separate these essential soluble ingredients from
the greater mass of the soil, left as sand and insoluble silicates,
which amount to from about seventy-five to ninety-two per cent.
of the whole, the probabilities of error in the determination
of these minuter ingredients must not be calculated into the
whole weight of the soil, but into that smaller part which we
have thus extracted from it.
  Logic apart, the fact still remains, that in one hundred and
forty-nine duplicate analyses, made by the writer for the Ken-
tucky, Arkansas, and Indiana Surveys, in which the chemical
composition of the virgin soil was compared, under similar
conditions of treatment, with soil of a neighboring old field in
the same locality, one hundred and twenty-two out of the one
hundred and forty-nine showed a marked diminution of most
of the essential ingredients of the soil in that of the old field
as compared with the virgin soil. This certainly is not an
accidental result.
  In the soil analyses at present reported the results are not
so striking in this relation. Partly because the samples had
not, in several cases, been collected with special reference to
this investigation, and partly because of greater local variations
of the soil in the regions in which they were obtained.
  In calculating the probable amount of exhaustion of the
essential soil ingredients, it should be recollected that as
much, and sometimes more, may be alienated from the soil
by the solvent action of the atmospheric agents, while the
surface is much exposed in the cultivation of hoed crops,
than is absorbed and removed by the products. Hence the
exhaustion of the soil is much more rapid under these cir-
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