The physical and chemical analyses of soils are long and tedious
processes and are entirely too costly to be applied to samples which
represent nothing but themselves.
The particular place selected for taking the samples as well as the
method employed are also largely determined by the point of view of the
investigations. The collection of samples to illustrate the geologic or
mineralogical relations of soils is quite a different matter from
gathering portions to represent their agricultural possibilities. In a
given area the sum of plant food in the soil would only be determined by
the analyses of samples from that particular field, while samples
illustrating geologic relations could or should be taken at widely
distant points. Again the chemist is content with a sample of a few
grams in weight while the physicist would require a much larger
quantity. Much popular ignorance exists respecting the importance of the
collection of soil samples. As an illustration of this may be cited a
recent instance in which a sample of soil was received by the author
with a request for a complete analysis and a statement of the kinds of
crops it was suited to grow. No data relating to the locality in which
the sample was taken accompanied this request. The sample itself, which
weighed a little less than 3.6 grams, was not a soil at all in an
agricultural sense but a highly ferruginous sand.
The collector of samples who understands the purpose for which he is
working will find among the approved methods which follow some one or
some combination of methods, by means of which his work can be made
successful. In these cases it is the collector rather than the method on
which reliance must be placed to secure properly representative samples.
=55. General Directions for Sampling.=—The locality having been selected
which presents as nearly as possible the mean composition of the field a
square hole is dug with a sharp spade to the depth of eighteen inches.
The walls of this hole should be smooth and perpendicular. The soil to
the depth of six to nine inches is then removed from the sides of the
hole in a slice about four inches thick; or the sample of soil may be
taken to the depth indicated by a change of color. Any particles which
fall into the bottom of the hole are carefully collected and added to
the parts adhering to the spade. The whole is thrown into a suitable
vessel for removal to the laboratory. The sample of soil having been
thus secured, the subsoil is taken in the same way. To insure uniformity
in the samples, it is well to take several of them from the same field.
Where more than one sample is taken it is advisable to mix all the
sub-samples in the field, remove large sticks, stones, roots, etc., and
take a general sample of from three to five kilograms. The character of
the débris, etc., removed should be carefully noted.
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