MATHEMATICS APPLIED TO AGRICULTURE
PERCY left the Bureau of Soils with a feeling of deep appreciation
for the uniform courtesy and kindness that had been accorded him,
but with a firm conviction that the laboratory scientists were too
far removed from the actual conditions existing in the cultivated
field. He sought the quiet of his room at the hotel in order to
study the bulletins he had received.
Even with his college training he found it difficult to form clear
mental conceptions of the results of investigations reported in the
bulletins. Sometimes the data were reported in percentages and
sometimes in parts per million. No reports gave the amounts of the
element phosphorus; but PO4 was given in some places and P2O5 in
others. In Bulletin No. 22, the potassium and calcium were reported
as the elements and the nitrogen in terms of NO3, while potash
(K20), quicklime (CaO), and magnesia (MgO) were reported in Bulletin
54.
By a somewhat complicated mathematical process, he finally succeeded
in making computations from the percentages of the various compounds
reported in the soil separates and from the percentages of these
different separates contained in the soils themselves and from the
known weights of normal soils, until he reduced the data to amounts
per acre of plowed soil.
He was especially pleased to find that the essential data were at
hand not only for both the Leonardtown loam and the Porter's black
loam, but also for the Norfolk loam, which he had learned from one
of the soil maps was the principal type of soil southwest of
Blairville on Mr. Thornton's farm; and, furthermore, the Miami black
clay loam of Illinois was included. Percy knew the black clay loam
was a rich soil, for the teacher in college had said that the more
common prairie land and most timber lands were much less durable and
needed thorough investigation at once, while the flat recently
drained heavy black land could wait a few years if necessary.
Percy first worked out the data for the Miami black clay loam. The
chemist had analyzed the soil separates for only four constituents,
and they showed the following amounts per acre of plowed soil to a
depth of six and two-thirds inches, averaging two million pounds in
weight:
2,970 pounds of phosphorus
38,500 pounds of potassium
18,440 pounds of magnesium
46,200 pounds of calcium
He then made the computations for the average of the Leonardtown
loam of St. Mary County, Maryland, with results as follows:
160 pounds of phosphorus
18,500 pounds of potassium
3,480 pounds of magnesium
1,000 pounds of calcium
Percy stared at these figures when he brought them together for
comparison. He then checked up his computations to be sure they were
right.
"Almost twenty times as much phosphorus!" he said to himself. "Is it
possible? And more than forty times as much calcium! Let me see! It
takes one hundred and seventeen pounds of calcium for four tons of
clover hay. The total amount in the plowed soil of the Leonardtown
loam would not be sufficient for eight such crops; and six crops of
corn such as we raised one year on our sixteen acres would take more
phosphorus from the land than is now left in the plowed soil of this
Leonardtown loam. The magnesium is not quite so bad--about one-fifth
as much as in our black soil, and the potassium is almost one-half
as much as we have."
Percy next turned to the Porters black loam, which he had noticed
was to be found not many miles from Montplain. He thought he might
induce Mr. West to drive with him to the upper mountain slope in
order that they might see that land. His computations for the
Porters black loam gave the following results:
4,630 pounds of phosphorus
48,300 pounds of potassium
12,360 pounds of magnesium
23,700 pounds of calcium
He viewed these figures a moment with evident satisfaction.
"Plenty of everything in this wonderful 'pippin land,'" he thought.
"Big yields reported for everything suited to that altitude. 'Can be
worked year after year without apparent impairment of its
fertility,' so the Report stated. I should think it might,
especially since clover is one of the crops grown. Both phosphorus
and potassium are way above our best black land. Magnesium
two-thirds and calcium one-half of our flat land, but still greater
than our common prairie, according to the average they gave us at
college. And no doubt there is plenty of magnesian limestone in
these mountains which could be had if ever needed. The soil surveyor
certainly did not say too much in praise of the Porters black loam,
considering that its physical composition is also all right."
He worked out the Norfolk loam to see what he would get if he
accepted Miss Russell's dare. The following are the figures:
610 pounds of phosphorus
13,200 pounds of potassium
1,200 pounds of magnesium
3,430 pounds of calcium
"Rather low in everything," said Percy, "compared with any soil I
know that has a good reputation. More uniformly poor but not so
extremely poor as the Leonardtown loam."
He wished that the nitrogen had been determined by the chemist, even
though he knew the organic matter and the nitrogen must be very low
in the poor soils, but nowhere was any such record to be found in
the bulletin. He found the statement, however, that all data were
reported on the basis of ignited soil.
"That will reduce some of these amounts about one-tenth," he said to
himself. "In our physics work in college, good soils generally lost
about ten per cent. in weight by ignition, even after all
hygroscopic moisture had been expelled; but these very poor soils
haven't much to lose, I guess. They surely contain no carbonates and
very little organic matter, although they may contain some combined
water."