MORE PROBLEMS
"NOW let us give Mr. Johnston a chance to tell us about the nitrogen
problem," said Mr. Thornton. "I'm pretty well satisfied with the
natural circulation of carbon, oxygen, and hydrogen; but I want to
understand all I can of the practical methods of securing and
utilizing nitrogen; and we have heard almost nothing about the other
six essential elements which the soil must furnish. Let me see.--I
think you said that iron, calcium, magnesium and potassium are
usually abundant in the soil, while phosphorus and sulfur are very
limited."
"Yes, that is the rule under general or average conditions, but it
should be stated that the amount of sulfur required by plants is
very small as compared with phosphorus, a difference which places a
great distinction between them. Besides considerable quantities of
sulfur are returned to the air in the combustion of coal and organic
matter, and this returns to the soil in rain. The information thus
far secured shows that sulfur rarely if ever limits the crop yields
under field conditions; and the same may be said of iron, which is
required by plants in very small amount and is contained in
practically all soils in enormous quantities.
"While normal soils contain abundance of potassium, with about half
as much calcium and one-fourth as much magnesium; yet, when measured
by crop requirements for plant food, the supplies of these three
elements are not markedly different. On the other hand, about 300
pounds of calcium are lost per acre per annum by leaching from good
soils in humid climates, compared with about 10 pounds of potasssium
and intermediate amounts of magnesium; so that, of these three
elements, calcium requires by far the most consideration and
potassium the least, even aside from the use of limestone to correct
or prevent soil acidity.
"Among the conditions essential for nitrification may be mentioned
the presence of free oxygen and limestone; and of course all
bacteria require certain food materials, resembling other plants in
this respect."
"Are they plants?" asked Mrs. Thornton. "I thought they were tiny
little animals."
"No, they are classified as plants," replied Percy; "but the
scientists have difficulty with some of the lower organism to decide
whether they are plants or animals. The college boys used to say
that some animals were plants in the botanical department and
animals again when they studied zoology. Orton says it is easy to
tell a cow from a cabbage, but impossible to assign any absolute,
distinctive character which will divide animal life from plant life.
"The oxygen is essential for nitrification, because that is an
oxidation process. That is, it is a kind of combustion, so to speak.
The organic matter is oxidized or converted into substances
containing more oxygen than in the original form. In ammonification
the carbon is separated or divorced from the nitrogen and united
with oxygen. Some of the hydrogen of the organic matter remains
temporarily with the carbon, and some is held temporarily with the
nitrogen in the form of ammonia.
"The nitrite bacteria replace two of the hydrogen atoms in ammonia
with one of oxygen, and insert another oxygen atom between the
nitrogen and the remaining hydrogen, thus forming nitrous acid;
H-O-N=O, or HNO2.
"The nitrate bacteria then cause the direct addition of another
oxygen atom, which is held by the two extra bonds of the nitrogen
atom, which you will remember is a five-handed atom.
"Thus you will see the absolute need of free oxygen in the
nitrification process; and we can control the rate of nitrification
to a considerable extent by our methods of tillage. In soils
deficient in organic matter, excessive cultivation may still
liberate sufficient nitrogen for a fairly satisfactory crop; and the
benefits of such excessive cultivation for potatoes and other
vegetables is more often due to increased nitrification than to the
conservation of moisture, to which it is frequently ascribed by
agricultural writers.
"Thus the more we cultivate, the more we hasten the nitrification,
oxidation, or destruction of the organic matter or humus of the
soil. Where the soil is well supplied with decaying organic matter,
we rarely need to cultivate in a humid section like this, except for
the purpose of killing weeds.
"The presence of carbonates in the soil is essential for
nitrification, because the bacteria will not continue the process in
the presence of their own product. Nitrification ceases if the
nitrous or nitric acid remains as such; but, in the presence of
carbonates such as calcium carbonate (ordinary limestone) or the
double carbonate of magnesium and calcium (magnesian limestone, or
dolomite), the nitrous acid or nitric acid is converted into a
neutral salt of calcium or magnesium, one of these atoms taking the
place of two hydrogen atoms and forming, say, calcium nitrate:
Ca(NO3)2. At the same time the hydrogen atoms take the place of the
calcium in limestone ( CaC03), and form carbonic acid (H2CO3), which
at once decomposes into water (H2O) and carbon dioxid (CO2), which
thus escapes as a gas into the air or remains in the pores of the
soil.
"The fact that nitrification will not proceed in the presence of
acid reminds us that only a certain degree of acidity can be
developed in sour milk. Here the lactic acid bacteria produce the
acid from milk sugar, but the process stops when about seven-tenths
of one per cent. of lactic acid has developed. If some basic
substance, such as lime, is then added, the acid is neutralized and
the fermentation again proceeds.
"In the general process of decay and oxidation of the organic matter
of the soil, the nitrogen thus passes through the forms of ammonia,
nitrous acid, and nitric acid, and at the same time the carbon
passes into various acid compounds, including the complex humic and
ulmic acids, and smaller amounts of acetic acid (found in vinegar),
lactic acid, oxalic acid (found in oxalic), and tartaric acid (found
in grapes). The final oxidation products of the carbon and hydrogen
are carbon dioxid and water, which result from the decomposition of
the carbonic acid.
"Now the various acids of carbon and nitrogen constitute one of the
most important factors in soil fertility. They are the means by
which the farmer can dissolve and make available for the growing
crops the otherwise insoluble mineral elements, such as iron,
calcium, magnesium, and potassium, all of which are contained in
most soils in great abundance. These elements exist in the soil
chiefly in the form of insoluble silicates. Silicon itself is a
four-handed element which bears somewhat the same relation to the
mineral matter of the soil as carbon bears to the organic matter.
Quartz sand is silicon dioxid (SiO2). Oxygen, which is present in
nearly all substances, including air, water, and most solids,
constitutes about one-half of all known matter. Silicon is next in
abundance, amounting to more than one-fourth of the solid crust of
the earth. Aluminum is third in abundance (about seven per cent),
aluminum silicate being common clay. Iron, calcium, potassium,
sodium, and magnesium, in this order, complete the eight abundant
elements, which aggregate about ninety-eight per cent. of the solid
crust of the earth.
"It is worth while to know that about two and one-half per cent. of
the earth's crust is potassium, while about one-tenth of one per
cent. is phosphorus; also that when a hundred bushels of corn are
sold from the farm, seventeen pounds of phosphorus, nineteen of
potassium, and seven of magnesium are carried away.
"The acids formed from the decaying organic matter not only liberate
for the use of crops the mineral elements contained in the soil in
abundance, but they also help to make available the phosphorus of
raw phosphate, when naturally contained in the soil, as it is to
some extent in all soils, or when applied to the soil in the
fine-ground natural phosphate from the mines.
"Now the increase or decrease of organic matter in the soil is
measured with a very good degree of satisfaction by the element
nitrogen, which is a regular constituent of the organic matter of
the soil; and you are already familiar, Mr. Thornton, with the
amounts of nitrogen contained in average farm manure and in some of
our most common crops."
"Yes, Sir, I have some of the figures in my note book and I mean to
have them in my head very soon. But, say, that organic matter seems
to be a thing of tremendous importance, and I'm sure we've got
mighty little of it. I think about the only thing we'll need to do
to make this old farm productive again is to grow the vegetation and
plow it under. As it decays, it will furnish the nitrogen, and
liberate the phosphorus, potassium, calcium, and magnesium; and we
may have plenty of all of them just waiting to be liberated."
"That is altogether possible," said Percy; "but it must be
remembered that your soil is acid and consequently will not grow
clover or alfalfa successfully, or even cowpeas very satisfactorily.
A liberal use of ground limestone and large use of clover may be
sufficient to greatly improve your soil; but if I am permitted to
separate Miss Russell and the Thorntons "--Mr. Thornton's hilarious
"Ha, ha" cut Percy short. He crimsoned and the ladies smiled at each
other with expressions that revealed nothing whatever.
"Now let me finish," Percy continued, when Mr. Thornton had somewhat
subsided. "I say, if I am permitted to separate Miss Russell and the
Thorntons from about three hundred acres of their land, I shall
certainly wish to know its total content of phosphorus, potassium,
magnesium, and calcium, before I make any purchase; and, if you will
remember the pot cultures and the peaty swamp land, I think you'd
agree with me.
"Well, I shall be mighty glad to know that myself," said Mr.
Thornton, "and we shall much appreciate it if you can tell us how
to secure that information."
"We can collect some soil to-morrow," Percy replied, "and send it to
a chemist for analysis."
"Good," said Mr. Thornton; "now just one more question, and I think
I shall sleep better if I have it answered to-night. Just what is
meant by potash and phosphoric acid?"
"Potash," said Percy, "is a compound of potassium and oxygen. The
proportions are one atom of oxygen and two atoms of potassium, which
you may remember are single-handed and weigh thirty-nine, so that
seventy-eight of potassium unite with sixteen of oxygen. A better
name for the compound is potassium oxid: K20. The Latin name for
potassium is kalium, and K is the symbol used for an atom of that
element. If you were to purchase potassium in the form of potassium
chlorid, which in the East is often called by the old incorrect name
'muriate of potash,' the salt might be guaranteed to contain a
certain percentage of potash, which, however, consists of
eighty-three per cent. of potassium and seventeen of oxygen."
"Just what is this potassium chlorid, or 'muriate of potash'?"
"Pure potassium chlorid contains only the two elements, potassium
and chlorin."
"But didn't you say that it was guaranteed to contain potash and
that potash is part oxygen? Now you say it contains only potassium
and chlorin."
"Yes, I am sorry to say, that this is one of those blunders of our
semi-scientific ancestors for which we still suffer. The chemist
understands that the meaning of the guarantee of potash is the
amount of potash that the potassium present in the potassium chlorid
could be converted into. The best you can do is to reduce the potash
guarantee to potassium by taking eighty-three per cent. of it; or,
to be more exact, divide by ninety-four and multiply by
seventy-eight, in order to eliminate the sixteen parts of oxygen.
"It may be well to keep in mind that when the druggist says potash
he means potassium hydroxid, KOH, a compound of potassium, hydrogen,
and oxygen, as the name indicates."
"You mentioned the word chlorin," said Mr. Thornton. "That is
another element?"
"Yes, that is a very common element. Ordinary table salt is sodium
chlorid: NaCl. Sodium is called natrium in Latin, and Na is the
symbol used in English to be in harmony with all other languages,
for practically all use the same chemical symbols. Sodium and
potassium are very similar elements in some respects, and in the
free state they are very peculiar, apparently taking fire when
thrown into water. Chlorin in the free state is a poisonous gas.
Thus the change in properties is well illustrated when these two
dangerous elements, sodium and chlorin, unite to form the harmless
compound which we call common salt.
"It is a shame," continued Percy, "that agricultural science has so
long been burdened with such a term as 'phosphoric acid,' which
serves to complicate and confuse what should be made the simplest
subject to every American farmer and landowner. As agriculture is
the fundamental support of America and of all her other great
industries, so the fertility of the soil is the absolute support of
every form of agriculture. Now, if there is any one factor that can
be the most important, where so many are positively essential, then
the most important factor in the problem of adopting and maintaining
permanent systems of profitable agriculture on American soils is the
element phosphorus.
"Phosphorus in very appreciable amount is positively necessary for
the growth of every organism. It is an absolutely essential
constituent of the nucleus of every living cell, whether plant or
animal. Nuclein, itself, which is the substance nearest to the
beginning of a new cell, contains as high as ten per cent. of the
element phosphorus.
"On the other hand, phosphorus is the most limited of all the plant
food elements, measured by supply and demand and circulation.
"What is phosphoric acid? Well, the professor of chemistry says it
is a compound containing three atoms of hydrogen, one of phosphorus,
and four of oxygen. It is a syrupy liquid and one of the strongest
mineral acids. In concentrated form it is as caustic as oil of
vitriol. Why, here you have a Century dictionary. That should tell
what phosphoric acid is. This is what the Century says:
"'It is a colorless, odorless syrup, with an intensely sour taste.
It is tribasic, forming three distinct classes of metallic salts.
The three atoms of hydrogen may in like manner be replaced by
alcohol radicles, forming acid and neutral ethers. Phosphoric acid
is used in medicine as a tonic.'
"That," continued Percy, "is the complete definition as given by the
Century dictionary as to what phosphoric acid is, and I note that
this is the latest edition of the Century, copyrighted in 1902."
"We bought it less than a month ago," said Mrs. Thornton. "We can
have so few books that we thought the Century would be a pretty good
library in itself; Mr. Thornton has had too little time to use it
much as yet."
"Well, even if I had used it," said Mr. Thornton, "you see there are
five volumes before I'd get to the P's. But, joking aside, I don't
get much out of that definition except that phosphoric acid is a
sour liquid and is used in medicine."
"The definition is entirely correct," said Percy "Any text on
chemistry will give you a very similar definition, and your
physician and druggist will give you the same information."
"Well, I know the fertilizer agents claim to sell phosphoric acid in
two-hundred-pound bags which wouldn't hold any kind of liquid."
"True," replied Percy, "and I consider it a shame that the farm boy
who goes to the high school or college and is there taught exactly
what phosphoric acid is, must. when he returns to the farm, try to
read bulletins from his agricultural experiment station in which the
term 'phosphoric acid' is used for what it is not. At the state
agricultural college, the professor of chemistry correctly teaches
the farm boy that phosphoric acid is a liquid compound containing
three atoms of hydrogen, one of phosphorus, and four of oxygen in
the molecule; and then the same professor, as an experiment station
investigator, goes to the farmers' institutes and incorrectly
teaches the same boy's father that phosphoric acid is a solid
compound pound containing two atoms of phosphorus and five atoms of
oxygen in the molecule."
"But why do they continue to teach such confusion?"
"Well, Sir, if they know, they never tell. In some manner this
misuse of the name was begun, and every year doubles the difficulty
of stopping it."
"Like the man that was too lazy to stop work when he had once
begun," remarked Mr. Thornton.
"Yes," said Percy, "but it is true that some of the States have
adopted the practice of reporting analyses of soils and fertilizers
on the basis of nitrogen instead of ammonia; and in the Corn Belt
States, phosphorus and potassium are the terms used to a large
extent instead of 'phosphoric acid,' and potash. The agricultural
press is greatly assisting in bringing about the adoption of the
simpler system, and the laws of some States now require that the
percentages of the actual plant food elements, as nitrogen,
phosphorus, and potassium, shall be guaranteed in fertilizers
offered for sale. It is one of those questions that are never
settled until they are settled right; and it is only a question of
time until the simple element basis will be used throughout the
United States, or at least in the Central and Western States."
"The so-called 'phosphoric acid' of the fertilizer agent is a
compound whose molecule contains two atoms of phosphorus and five
atoms of oxygen; and, since the atomic weight of phosphorus is
thirty-one and that of oxygen sixteen, this compound contains
sixty-two parts of phosphorus and eighty parts of oxygen. In other
words, this phosphoric acid, falsely so-called, contains a trifle
less than forty-four per cent. of the actual element phosphorus."
"Is the bone phosphate of lime that the agents talk about the same
as the 'phosphoric acid'?" asked Mr. Thornton.
"No, by 'bone phosphate of lime,' which is often abbreviated B. P.
L., is meant tricalcium phosphate, a compound which contains exactly
twenty per cent. of phosphorus. Thus, you can always divide the
guaranteed percentage of 'bone phosphate of lime' by five, and the
result will be the per cent. of phosphorus.
"As stated in your Century dictionary, true phosphoric acid forms
three distinct classes of salts, because either one, two, or all of
the three hydrogen atoms may be replaced by a metallic element.
Thus, we have phosphoric acid itself containing the three hydrogen
atoms, one phosphorus atom, and four oxygen atoms. This might be
called trihydrogen phosphate (H3PO4). Now if one of the hydrogen
atoms is replaced by one potassium atom, we have potassium
dihydrogen phosphate (KH2PO4); with two potassium atoms and one
hydrogen, we have dipotassium hydrogen phosphate (K2HPO4); and if
all hydrogen is replaced by potassium the compound is tripotassium
phosphate (K3PO4). To make similar salts with two-handed metallic
elements, like calcium or magnesium, we need to start with two
molecules of phosphoric acid H6(PO4)2; because each atom of calcium
will replace two hydrogen atoms. Thus we have mono calcium
phosphate, CaH4(PO4)2, dicalcium phosphate, Ca2H2(PO4)2, and
tricalcium phosphate, Ca3(PO4)2. It goes without saying that
monocalcium phosphate contains four atoms of hydrogen and that
dicalcium phosphate contains two hydrogen atoms. By knowing the
atomic weights (40 for calcium, 31 for phosphorus, and 16 for
oxygen), it is easy to compute that the molecule of tricalcium
phosphate weighs 310 of which 62 is phosphorus. This is exactly
one-fifth, or twenty per cent. This compound you will remember is
sometimes called 'bone phosphate of lime'. It is also called simply
'bone phosphate'; because it is the phosphorus compound contained in
bones. It is sometimes called lime phosphate, although it contains
no lime in the true sense, for it has no power to neutralize acid
soils, except when the phosphorus is taken up by plants more rapidly
than the calcium, which in such case might remain in the soil to act
as a base to neutralize soil acids; but even then the effect of the
small amount of calcium thus liberated from the phosphate would be
very insignificant compared with a liberal application of ground
limestone."
"Well," said Mr. Thornton, stretching himself, "orange phosphate is
my favorite drink but I fear some of these phosphate you have just
been giving me are too concentrated. I ought to have the dose
diluted; but I like the taste of it, and if you'll write a book
along this line, in this plain way just about as you have been
giving it to me straight for almost twelve hours, I tell you I'll
read it over till I learn to understand it a heap better than I do
now."