THE CHEMIST'S LABORATORY
THE Chief showed Percy into the laboratories of the Bureau and
introduced him to the soil physicist and the soil chemist. Percy was
greatly interested in the various lines of work in progress and
gladly accepted an invitation to return after lunch and become
better acquainted with the methods of investigation used.
In the afternoon the physicist showed him how the soil water could
be removed from an ordinary moist soil by centrifugal force, and the
chemist was growing wheat seedlings in small quantities of this
water and in water extracts contained in bottles. The seedlings were
allowed to grow for twenty days and then other seedlings were
started in the same solution and also in fresh solution, and it was
very apparent that in some cases the wheat grew better in the fresh
solutions.
The chemist explained that he also analyzed the soil solutions and
water extracts from different soils and that there was no relation
between the crop yields and the chemical composition of the soils.
"But it seems to me," said Percy, "that your analysis refers to the
plant food dissolved in the soil water only at the time when you
extract it. How long a time does it require to make the extraction?"
"As a rule we shake the soil with water for three minutes and then
it takes twenty minutes to separate the water from the soil. This
gives us the plant food in solution and with the addition of more
water the nitrates, phosphoric acid, and potash in the soil
immediately dissolve sufficiently give us a nutrient solution of the
same concentration as we had before. Thus there is always sufficient
plant food in the soil so long as there is any of the original
stock."
"That is surely quick work," said Percy, "but I wonder if the corn
plant might not get somewhat different results from the soil
analysis which it makes."
"How do you mean?"
"Did you ever plant a field of corn and then cultivate it and watch
it grow with increasing rapidity, until along about the Fourth of
July every leaf seemed to nod its appreciation and thanks as you
stirred the soil; and to show its gratitude, too, by growing about
five inches every twenty-four hours when the nights were warm?"
"No," replied the Chemist, "I have never had any experience of that
sort. I am devoting my life to the more scientific investigations
relating to the fundamental laws which underlie these soil fertility
problems."
"Well, I was only thinking," Percy continued, "that you analyze a
fraction of a pound of soil in a few minutes, while the corn plant
analyzes about a ton of soil by a sort of continuous process, which
covers twenty-four hours every day for about one hundred and twenty
days, and it takes into account every change in temperature and
moisture, the aeration with any variation produced by cultivation,
and also the changes brought about by the nitrifying bacteria and
all other agencies that promote the decomposition of the soil and
the liberation of plant food, including the action upon the
insoluble phosphates and other minerals of the carbonic acid exhaled
by the roots of the corn plants, the nitric acid produced by the
process of nitrification, and the various acids resulting from the
decay of organic matter contained in the soil."
"I am very familiar with the literature of the whole subject of soil
fertility," replied the Chemist, "and our theories are being
accepted everywhere. I have just returned from a lecture tour
extending from Florida to Michigan, and our ideas and methods are
being very generally adopted, not only in this country but also in
Europe."
"The Chief of the Bureau very kindly permitted me to look over the
maps and reports relating to the soils of Maryland and Virginia,"
said Percy, "but in this literature I found no data as to the amount
of plant food contained in the various soil types that have been
found in the surveys. May I ask if the Bureau has made any analyses
to ascertain the total amounts of the different essential plant food
elements contained in these different soils?"
"No," the Chemist replied, "a chemical analysis gives practically no
information concerning the fertility of the soil. We have made no
ultimate analyses of soils, although we have used the same methods
of analysis in a study of the partial composition of the soil
separates, or particles of different grades, such as the sand, the
silt, and the clay."
"And have you also determined the percentages of sand, silt, and
clay in the soils themselves?"
"Oh, yes, the physical composition of the soil is a matter of very
great importance, and this is always determined and reported for
every soil. Did you not see that in the Reports you examined this
morning?"
"I think I did notice it," Percy replied, "but it is so easy for the
farmer himself to tell a sandy soil from a clay soil that I did not
appreciate the value of those physical analyses.
"In any case, I shall be very glad to know what results were
obtained from the chemical analysis of the soil separates to which
you referred."
"Those results are all reported in Bulletin No. 54 of the Bureau of
Soils," said the Chemist, "and I have extra copies right here and
will be glad to present you with one. And let me give you our
Bulletin 22 also. This will enable you to get a clear idea of the
principles we are developing which are solving the soil fertility
problems that have completely baffled the scientists heretofore."