A LESSON IN FARM SCIENCE
"THE subject is somewhat complicated," Percy replied, "yet it
involves no more difficult problems than have been solved in many
other lines. The chief trouble is that we have done too little
thinking about our own real problems. Even in the country schools we
have learned something of banking and various other lines of
business, something of the history and politics of this and other
countries, something of the great achievements in war, in discovery
and exploration, in art, literature, and invention; but we have not
learned what our soils contain nor what our crops require. Not one
farmer in a hundred knows what chemical elements are absolutely
required for the production of our agricultural plants, and one may
work hard on the farm from four o'clock in the morning till nine
o'clock at night for forty years and still not learn what corn is
made of.
"All agricultural plants are composed of ten chemical elements, and
the growth of any crop is absolutely dependent upon the supply of
these plant food elements. If the supply of any one of these plant
food elements is limited, the crop yield will also be limited. The
grain and grass crops, such as corn, oats, wheat, and timothy, also
the root crops and potatoes, secure two elements from the air, one
from water, and seven from the soil.
"The supply of some elements is constantly renewed by natural
processes, and iron, one of the ten, is contained in all normal
soils in absolutely inexhaustible amount; while other elements
become deficient and the supply must be renewed by man, or crop
yields decrease and farming becomes unprofitable.
"Matter is absolutely indestructible. It may change its form, but
not a pound of material substance can be destroyed. Matter moves in
cycles, and the key to the problem of successful permanent
agriculture is the circulation of plant food. While some elements
have a natural cycle which is amply sufficient to meet all
requirements for these elements as plant food, other elements have
no such cycle, and it is the chief business of the farmer to make
these elements circulate.
"Take carbon, for example. This element is well represented by hard
coal. Soft coal and charcoal are chiefly carbon. The diamond is pure
crystallized carbon, and charcoal made from pure sugar is pure,
uncrystallized carbon. This can easily be made by heating a lump of
sugar on a red hot stove until only a black coal remains. Now these
different solid materials represent carbon in the elemental form or
free state. But carbon may unite with other elements to form
chemical compounds, and these may be solids, liquids, gases.
"Thus carbon and sulfur are both solid elements, one black and the
other yellow, as generally found. If these two elements are mixed
together under ordinary conditions no change occurs. The result is
simply a mixture of carbon and sulfur. But, if this mixture is
heated in a retort which excludes the air, the carbon and sulfur
unite into a chemical compound called carbon disulfid. This compound
is neither black, yellow, nor solid; but it is a colorless, limpid
liquid; and yet it contains absolutely nothing except carbon and
sulfur."
"That seems strange," remarked Mr. Thornton. "Yes, but similar
changes are going on about us all the time," replied Percy. "We put
ten pounds of solid black coal in the stove and an hour later we
find nothing there, except a few ounces of ashes which represent the
impurities in the coal."
"Well, the coal is burned up and destroyed, is it not?"
"The carbon is burned and changed, but not destroyed. In this case,
the heat has caused the carbon to unite with the element oxygen
which exists in the air in the form of a gas, and a chemical
compound is formed which we call carbon dioxid. This compound is a
colorless gas. This element oxygen enters the vent of the stove and
the compound carbon dioxid passes off through the chimney. If there
is any smoke, it is due to small particles of unburned carbon or
other colored substances.
"As a rule more or less sulfur is contained in coal, wood, and other
organic matter, and this also is burned to sulfur dioxid and carried
into the air, from which it is brought back to the soil in rain in
ample amounts to supply all of the sulfur required by plants.
"Everywhere over the earth the atmosphere contains some carbon
dioxid and this compound furnishes all agricultural plants their
necessary supply of both carbon and oxygen. In other words, these
are the two elements that plants secure from the air. The gas,
carbon dioxid, passes into the plant through the breathing pores on
the under side of the leaves. These are microscopic openings but
very numerous. A square inch of a corn leaf may have a hundred
thousand breathing pores."
"Now, as we go on, I am especially anxious to get at this question
of supply and demand," said Mr. Thornton. "I think I understand
about iron and sulfur, and also that these two elements, carbon and
oxygen, are both contained in the air in the compound called carbon
dioxid, and that this must supply our crops with those two elements
of plant food. I'd like to know about the supply. How much is there
in the air and how much do the crops require?"
"As you know," said Percy, "the atmospheric pressure is about
fifteen pounds to the square inch."
"Yes, I've heard that, I know."
"Well, that means, of course, that there are fifteen pounds of air
resting on every square inch of the earth's surface; in other words,
that a column of air one inch square and as high as the air goes,
perhaps fifty miles or more, weighs fifteen pounds."
"Yes, that is very clear."
"There is only one pound of carbon in ten thousand pounds of
ordinary country air. Now, there are one hundred and sixty square
rods in an acre, and since there are twelve inches in a foot and
sixteen and one-half feet in a rod, it is easy to compute that there
are nearly a hundred million pounds of air on an acre, and that the
carbon in this amounts to only five tons. A three-ton crop of corn
or hay contains one and one-fourth tons of the element carbon; so
that the total amount of the carbon in the air over an acre of land
is sufficient for only four such crops; while a single crop of corn
yielding a hundred bushels to the acre, such as we often raise in
Illinois on old feed-lots or other pieces of well treated land would
require half of the total supply of carbon contained in the air over
an acre. However, the largest crop of corn ever grown, of which
there is an established authentic record, was not raised in
Illinois, but in the state of South Carolina, in the county of
Marlborough, in the year 1898, by Z. J. Drake; and, according to the
authentic report of the official committee that measured the land
and saw the crop harvested and weighed, and awarded Drake a prize of
five hundred dollars given by the Orange Judd Publishing
Company,--according to this very creditable evidence, that acre of
land yielded 239 bushels of thoroughly aid-dried corn; and such a
crop, Mr. Thornton, would require as much carbon as the total amount
contained in the air over an acre of land."
"Well, that is astonishing! Then there must be some other source of
supply besides the air."
"There is no other direct source from which plants secure carbon;
but of course the air is in constant motion. Only one-fourth of the
earth's surface is land, and perhaps only one-fourth of this land is
cropped, and the average crop is about one-fourth of three tons; so
that the total present supply of carbon in the air would be
sufficient for about two hundred and fifty years. But as a matter of
fact the supply is permanently maintained by the carbon cycle. Thus
the carbon of coal that is burned in the stove returns to the air in
carbon dioxid; and all combustion of coal and wood, grass and weeds,
and all other vegetable matter returns carbon to the atmosphere. All
decay of organic matter, as in the fermentation of manure in the
pile and the rotting of vegetable matter in the soil, is a form of
slow combustion and carbon dioxid is the chief produce of such
decay. Sometimes an appreciable amount of heat is developed, as in
the steaming pile of stable refuse lying in the barnyard, while the
heat evolved in the soil is too quickly disseminated to be apparent.
"In addition to all this, every animal exhales carbon dioxid. The
body heat and the animal force or energy are supplied by the
combustion of organic food within the body, and here, too, carbon
dioxid is the chief product of combustion.
"Thus, as a general average, the amount of carbon removed from the
atmosphere by growing plants is no greater than the amount returned
to the air by these various forms of combustion or decay. In like
manner the supply of combined oxygen is maintained, both carbon and
oxygen being furnished to the plant m the carbon dioxid.
"As a matter of fact, the air consists very largely of oxygen and
nitrogen, both in the free state, but in this form these elements
cannot be utilized in the growth of agricultural plants. The only
apparent exception to this is in case of legume crops, such as
clover, alfalfa, peas, beans, and vetch, which have power to utilize
the free nitrogen by means of their symbiotic relationship with
certain nitrogen-fixing bacteria which live, or may live, in
tubercles on their roots.
"Carbon and oxygen constitute about ninety per cent. of the dry
matter of ordinary farm crops, and with the addition of hydrogen
very important plant constituents are produced; such as starch,
sugar, fiber, or cellulose, which constitute the carbohydrate group.
As the name indicates, this group contains carbon, hydrogen, and
oxygen, the last two being present in the same proportion as in
water.
"Water is composed of the two elements, hydrogen and oxygen, both of
which are gases in the free state. Water is taken into the plant
through the roots and decomposed in the leaves in contact with the
carbon dioxid under the influence of sunlight and the life
principle. The oxygen from the water and part of that from the
carbon dioxid is given off into the air through the breathing pores,
while the carbon, hydrogen, and part of the oxygen, unite to form
the carbohydrates. These three elements constitute about ninety-five
per cent. of our farm crops, and yet every one of the other seven
plant food elements is just as essential to the growth and full
development of the plant as are these three."
"Then so long as we have air above and moisture below, our crops
will not lack for carbon, oxygen, and hydrogen. Is that the summing
up of the matter?"
"Yes, Sir," Percy replied.
"And those three elements make up ninety-five per cent. of our farm
crops. Is that correct?"
"Yes, Sir, as an average."
"Well, now it seems to me, if nature thus provides ninety-five per
cent. of all we need, we ought to find some way of furnishing the
other five per cent. It makes me think of the young wife who told
her husband she could live on bread and water, with his love, and he
told her that if she would furnish the bread he'd skirmish around
and get the water. But, say, did that South Carolina man use any
fertilizer for that immense crop of corn?"
"Some fertilizer, yes. He applied manure and fertilizer from
February till June. In all he applied 1000 bushels (about 30 tons)
of farm manure, 600 bushels of whole cotton seed, 900 pounds of
cotton seed meal, 900 pounds of kainit, 1100 pounds of guano, 200
pounds of bone meal, 200 pounds of acid phosphate, and 400 pounds of
sodium nitrate."
"I would also like to know the facts about this nitrogen business,"
said Mr. Thornton. "I've understood that one could get some of it
from the air, and I would much rather get it that way than to buy it
from the fertilizer agent at twenty cents a pound. Cowpeas don't
seem to help much, and we don't have the cotton seed, and we never
have sufficient manure to cover much land."
"It is a remarkable fact," said Percy, "that of the ten essential
elements of plant food, nitrogen is the most abundant, measured by
crop requirements, and at the same time the most expensive. The air
above an acre of land contains enough carbon for a hundred bushels
of corn per acre for two years, and enough nitrogen for five hundred
thousand years; and yet the nitrogen in commercial fertilizers costs
from fifteen to twenty cents a pound. At commercial prices for
nitrogen, every man who owns an acre of land is a millionaire.
"You mean he has millions in the air," amended Mr. Thornton.
"Yes, that is the better way to put it," Percy admitted, "but the
fact is he can not only get this nitrogen for nothing by means of
legume crops, but he is paid for getting it, because those crops are
profitable to raise for their own value. Clover, alfalfa, cowpeas,
and soy beans are all profitable crops, and they all have power to
use the free nitrogen of the air.
"There are a few important facts to be kept in mind regarding
nitrogen:
"A fifty-bushel crop of corn takes 75 pounds of nitrogen from the
soil. Of this amount about 50 pounds are in the grain, 24 pounds are
in the stalks, and 1 pound in the cobs. A fifty-bushel crop of oats
takes 48 pounds of nitrogen from the soil, 33 pounds in the grain,
and 15 in the straw. A twenty-five bushel crop of wheat also takes
48 pounds of nitrogen from the soil, 36 pounds in the grain and 12
in the straw.
"These amounts will vary to some extent with the quality of the
crops, just as the weight of a bushel of wheat varies from perhaps
56 to 64 pounds, although as an average wheat weighs 60 pounds to
the bushel."
"You surely remember figures well," remarked Mr. Thornton as he made
some notations.
"It is easy to remember what we think about much and often," said
Percy; "as easy to remember that a ton of cowpea hay contains 43
pounds of nitrogen as that Blairville is 53 miles from Richmond."
"I have added those figures together," continued Mr. Thornton, "and
I find that the three crops, corn, oats, and wheat, would require
171 pounds of nitrogen. Now suppose we raise a crop of cowpeas the
fourth year, how much nitrogen would be added to the soil in the
roots and stubble?"
"Not any."
"Do you mean to say that the roots and stubble of the cowpeas would
add no nitrogen to the soil? Surely that does not agree with the
common talk."
"It is even worse than that," said Percy. "The cowpea roots and
stubble would contain less nitrogen than the cowpea crop takes from
a soil capable of yielding thirty bushels of corn or oats. Only
about one-tenth of the nitrogen contained in the cowpea plant is
left in the roots and stubble when the crop is harvested. Suppose
the yield is two tons per acre of cowpea hay! Such a crop would
contain about 86 pounds of nitrogen, and about 10 pounds of nitrogen
per acre would be left in the roots and stubble."
"Well, that wouldn't go far toward replacing the 171 pounds removed
from the soil by the corn, oats, and wheat, that's sure," was Mr.
Thornton's comment.
"It is worse than that," Percy repeated. "Land that will furnish 48
pounds of nitrogen for a crop of oats or wheat will furnish more
than 10 pounds for a crop of cowpeas. At the end of such a four-year
rotation such a soil would be about 200 pounds poorer in nitrogen
per acre than at the beginning, if all crops were removed and
nothing returned."
"How much would it cost to put that nitrogen back in commercial
fertilizer?" asked Mr. Thornton.
"That depends, of course, upon what kind of fertilizer is used."
"Well, most people around here who use fertilizer buy what the agent
calls two-eight-two, and its costs about one dollar and fifty cents
a hundred pounds; but it can be bought by the ton for about
twenty-five dollars."
"'Two-eight-two' means that the fertilizer is guaranteed to contain
two per cent. of ammonia, eight per cent. of available 'phosphoric
acid,' and two per cent. of potash."
"Ammonia is the same as nitrogen, is it not?"
"No, it is not the same," replied Percy. "Ammonia is a compound of
nitrogen and hydrogen. In order to have a clear understanding of the
relation between ammonia and nitrogen we only need to know the
combining weights of the elements. The smallest particle of an
element is called an atom. Hydrogen is the lightest of all the
elements and the weight of the hydrogen atom is used as the standard
or unit for the measure of all other atomic weights; thus the atom
of hydrogen weighs one."
"One what?" interrupted Mr. Thornton.
"No one knows," replied Percy. "The atom is extremely small, much
too small to be seen with the most powerful microscope; but you know
all things are relative and we always measure one thing in terms of
another. We say a foot is twelve inches and an inch is one-twelfth
of a foot, and there we stop with a definition of each expressed in
terms of the other, and both depending upon an arbitrary standard
that somebody once adopted; and yet, while the foot is known in most
countries, it is rare that two countries have exactly the same
standard for this measure of length.
"We do not know the exact weight of the hydrogen atom, but we do
know its relative weight. If the hydrogen atom weighs one then other
atomic weights are as follows:
12 for carbon
14 for nitrogen
16 for oxygen
24 for magnesium
31 for phosphorus
32 for sulfur
39 for potassium
40 for calcium
56 for iron
"This means that the iron atom is fifty-six times as heavy as the
hydrogen atom. These atomic weights are absolutely necessary to a
clear understanding of the compounds formed by the union or
combination of two or more elements.
"One other thing is also necessary. That is to keep in mind the
number of bonds, or hands, possessed by each atom. The atom of
hydrogen has only one hand, and the same is true of potassium. Each
atom of oxygen has two hands; so that one oxygen atom can hold two
hydrogen atoms in the chemical compound called water (H-O-H or H20).
Other elements having two-handed atoms are magnesium and calcium.
Strange to say, the sulfur atom has six hands but sometimes uses
only two, the others seemingly being clasped together in pairs. I
will write it out for you, thus:
Hydrogen sulfid: H-S-H or H2S
Sulfur dioxid: O=S=0 or S02
"The carbon atom has four hands, and atoms of nitrogen and
phosphorus have five hands, but sometimes use only three. Thus, in
the compound called ammonia, one atom of nitrogen always holds three
atoms of hydrogen; so, if you buy seventeen pounds of ammonia you
would get only fourteen pounds of nitrogen and three pounds of
hydrogen. This means that, if the two-eight-two fertilizer contains
two per cent. of ammonia, it contains only one and two-thirds per
cent. of the actual element nitrogen, and a ton of such fertilizer
would contain thirty-three pounds of nitrogen. In other words it
would take six tons of such fertilizer to replace the nitrogen
removed from one acre of land in four years if the crop yields were
fifty bushels of corn and oats, twenty-five bushels of wheat, and
two tons of cowpea hay."
"Six tons! Why, that would cost a hundred and fifty dollars! Well,
well, I thought I knew we couldn't afford to keep up our land with
commercial fertilizer; but I didn't think it was that bad. Almost
forty dollars an acre a year!"
"It need not be quite that bad," said Percy. "You see this
two-eight-two fertilizer contains eight per cent. of so-called
'phosphoric acid' and two per cent. of potash, and those
constituents may be worth much more than the nitrogen; but, so far
as nitrogen is concerned, the two hundred pounds would cost from
thirty to forty dollars in the best nitrogen fertilizers in the
market, such as dried blood or sodium nitrate."
"Well, even that would be eight or ten dollars a year per acre, and
that is as much as the land is worth, and this wouldn't include any
other plant food elements, such as 'phosphoric acid' and potash."
"No, that much would be required for the nitrogen alone if bought in
commercial form. I understand that the farmers who use this common
commercial fertilizer, apply about three hundred pounds of it to the
acre perhaps twice in four years. That would cost about eight
dollars for the four years, and the total nitrogen applied in the
two applications would amount to 10 pounds per acre."
"It is not quite correct to call 'phosphoric acid' and potash plant
food elements. They are not elements but compounds."
"Like ammonia, which is part nitrogen and part hydrogen?"
"The problem is somewhat similar, but not just the same," Percy
replied. "These compounds contain oxygen and not hydrogen."
"Well, I understand that both oxygen and hydrogen are furnished by
natural processes, the oxygen from carbon dioxid in the carbon
cycle, and the hydrogen from the water which falls in rain."
"That is all true, but you really do not buy the hydrogen or oxygen.
While they are included in the two-eight-two guarantee, the price is
adjusted for that. Thus the cost of nitrogen would be just the same
whether you purchase the fertilizer on the basis of seventeen cents
a pound for the actual element nitrogen, or fourteen cents a pound
for the ammonia."
"Yes, I see how that might be, but I don't see why the guarantee
should be two per cent. of ammonia instead of one and two-thirds per
cent. of nitrogen, when the nitrogen is all that gives it value."
"There is no good reason for it," said Percy. "It is one of those
customs that are conceived in ignorance and continued in
selfishness. It is very much simpler to consider the whole subject
on the basis of actual plant food elements, and I am glad to say
that many of the state laws already require the nitrogen to be
guaranteed in terms of the actual element, a few states now require
the phosphorus and potassium also to be reported on the element
basis."
"That is hopeful, at least," said Mr. Thornton. "Now, if I am not
asking too many questions or keeping you here too long, I shall be
glad to have you explain two more points that come to my mind:
First, how much of that two hundred pounds of nitrogen can I put
back in the manure produced on the farm; and, second, just what is
meant by potash and phosphoric acid?"
Percy made a few computations and then replied: "If you sell the
wheat; feed all the corn, oats, and cowpea hay and half of the straw
and corn fodder, and use the other half for bedding; and, if you
save absolutely all of the manure produced, including both the solid
and liquid excrement; then it would be possible to recover and
return to the land about 173 pounds of nitrogen during the four
years, compared with the 200 pounds taken from the soil."
"I can't understand that," said Mr. Thornton. "How can that be when
one of the crops is cowpeas?"
"In average live-stock and dairy farming," Percy continued, "about
one-fourth of the nitrogen contained in the food consumed is
retained in the milk and animal growth, and you can make the
computations for yourself. It should be kept in mind, moreover, that
much of the manure produced on the average farm is wasted. More than
half of the nitrogen is in the liquid excrement, and it is extremely
difficult to prevent loss of the liquid manure. There is also large
loss of nitrogen from the fermentation of manure in piles; and when
you smell ammonia in the stable, see the manure pile steaming, or
colored liquid soaking into the ground beneath, or flowing away in
rainy weather, you may know that nitrogen is being lost. How many
tons of manure can you apply to your land under such a system of
farming as we have been discussing?"
"Well, I've figured a good deal on manure," was the reply, "and I
think with four fields producing such crops as you counted on, that
I could possibly put ten or twelve tons to the acre on one field
every year."
"That would return from 100 to 120 pounds of nitrogen;" said Percy,
"instead of the 173 pounds possible to be returned if there is no
loss. There are three methods that may be used to reduce the loss of
manure: One of these is to do the feeding on the fields. Another is
to haul the manure from the stable every day or two and spread it on
the land. The third is to allow the manure to accumulate in deep
stalls for several weeks, using plenty of bedding to absorb the
liquid and keep the animals clean, and then haul and spread it when
convenient."
"I'm afraid that last method would not do at all for the dairy
farmer," said Mr. Thornton. "You see we have to keep things very
clean and in sanitary condition."
"Most often the cleanest and most sanitary method the average farmer
has of handling the manure in dairying," said Percy, "is to keep it
buried as much as possible under plenty of clean bedding; and one of
the worst methods is to overhaul it every day by 'cleaning' the
stable, unless you could have concrete floors throughout, and flush
them well once or twice a day, thus losing a considerable part of
the valuable excrement. If you allow the manure to accumulate for
several weeks at a time, it is best to have sufficient room in the
stable or shed so that the cows need not be tied. If allowed to run
loose they will find clean places to lie down even during the night.
"In case of horses, the manure can be kept buried for several weeks
if some means are used to prevent the escape of ammonia. Cattle
produce what is called a 'cold' manure, while it is called 'hot'
from horses because it decomposes so readily. One of the best
substances to use for the prevention of loss of ammonia in horse
stables is acid phosphate, which has power to unite with ammonia and
hold it in a fixed compound. About one pound of acid phosphate per
day for each horse should be sprinkled over the manure. Of course
the phosphorus contained in the acid phosphate has considerable
value for its own sake, and care should be taken that you do not
lose more phosphorus from the acid phosphate applied than the value
of all the ammonia saved by this means. Porous earth floors may
absorb very considerable amounts of liquid from wet manure lying
underneath the dry bedding, and the acid phosphate sometimes injures
the horses' feet; so that, as a rule, it is better to clean the
horse stables every day and supply phosphorus in raw phosphate at
one-fourth of its cost in acid phosphate."
"Before we leave the nitrogen question," said Mr. Thornton, "I want
to ask if you can suggest how we can get enough of the several
million dollars' worth we have in the air to supply the needs of our
crops and build up our land?"
"Grow more legumes, and plow more under, either directly or in
manure."
"That sounds easy, but can you suggest some practical system?"
"I think so. I know too little of your conditions to think I could
suggest the best system for you to adopt; but I can surely suggest
one that will supply nitrogen for such crop yields as we have
considered: Suppose we change the order of the crops and grow wheat,
corn, oats, and cowpeas, and grow clover with the wheat and oats,
plowing the clover under in the spring as green manure for corn and
cowpeas. If necessary to prevent the clover or weeds from producing
seed, the field may be clipped with the mower in the late summer
when the clover has made some growth after the wheat and oats have
been removed. Leave this season's growth lying on the land. As an
average it should amount to more than half a ton of hay per acre.
The next spring the clover is allowed to grow for several weeks. It
should be plowed under for corn on one field early in May and two or
three weeks later the other field is plowed for cowpeas. The spring
growth should average nearly a ton of clover hay per acre. In this
way clover equivalent to about three tons of hay could be plowed
under. Clover hay contains 40 pounds of nitrogen per ton; so this
would supply about 120 pounds of nitrogen in addition to the 173
pounds possible to be supplied in the manure. This would make
possible a total return of 293 pounds, while we figured some 200
pounds removed. Of course if you save only 100 pounds in the manure
the amount returned would be reduced to 220 pounds."
"There are two questionable points in this plan," said Mr. Thornton,
" one is the impossibility, or at least the difficulty, of growing
clover on this land. The other point is, How much of that 120 pounds
of nitrogen returned in the clover is taken from the soil itself? I
remember you figured 86 pounds of nitrogen in two tons of cowpea
hay, but you also assumed that about 29 pounds of it would be taken
from the soil."
"Yes, that is true," Percy replied, "at least 29 pounds and
probably more. You see the cowpeas grow during the same months as
corn and on land prepared in about the same manner. If the soil will
furnish 75 pounds of nitrogen to the corn crop, and 48 pounds to the
oats and wheat, it would surely furnish 29 pounds to the cowpeas. Of
course this particular amount has no special significance, but the
other definite amounts removed in corn, oats, and wheat aggregate
171 and the 29 pounds were added to make the round 200 pounds.
Perhaps 210 pounds would be nearer the truth, in which case the soil
would furnish about half as much nitrogen to the cowpea crop as to
the corn crop. This is reasonable considering that corn is the first
crop grown after the manure is applied. You will remember that only
one-tenth of the total nitrogen of the cowpea plant remains in the
roots and stubble?"
"Yes, that's what we figured on."
"The cowpea is an annual plant. It is planted, produces its seed,
and dies the same season. It has no need to store up material in the
roots for future use. Consequently the substance of the root is
largely taken into the tops as the plan approaches maturity. It is
different with the clover plant. This is a biennial with some
tendency toward the perennial plant. It lives long and develops an
extensive root system, and its stores up material in the roots
during part of its life for use at a later period. About one-third
of the total nitrogen content of the clover plant is contained in
the roots and stubble. This means that the roots and stubble of a
two-ton crop of clover would contain about forty pounds of nitrogen,
or more than we assumed was taken from the soil by the cowpeas. But
there is still another point in favor of the clover. The cowpeas
make their growth during the summer months when nitrification is
most active, whereas the clover growth we have counted on occurs
chiefly during the fall and spring when nitrification is much less
active, consequently the clover probably takes even a larger
proportion of its nitrogen from the air than we have counted on."
"That is rather confusing," said Mr. Thornton, "you say the cowpea
grows when nitrification is most active, and yet you say that it
takes less nitrogen from the air than clover. Isn't that somewhat
contradictory?"
"I think not," said Percy." Let me see.--Just what do you understand
by nitrification?"
"Getting nitrogen from the air, is it not?"
"No, no. That explains it. Getting nitrogen from the air is called
nitrogen fixation. This action is carried on by the nitrogen-fixing
bacteria, such as the clover bacteria, the soy bean bacteria, the
alfalfa bacteria, which, by the way, are evidently the same as the
bacteria of sweet clover, or mellilotus. Then we also have the
cowpea bacteria, and these seem to be the same as the bacteria of
the wild partridge pea, a kind of sensitive plant with yellow
flowers, and a tiny goblet standing upright at the base of each
compound leaf,--the plant called Cassia Chamaecrista by the
botanist."
"Nitrification is an altogether--"
"Well, I declare! Excuse me, Sir, but that's Charlie calling the
cows. Scotts, I don't see where the time has gone! You'll excuse me,
Sir, but I must look after separating the cream. You will greatly
oblige me, Mr. Johnston, if you will have dinner with us and share
our home to-night. In addition to the pleasure of your company, I
confess that I am mightily interested in this subject; and I would
like especially to get a clear understanding of that nitrification
process, and we've not had time to discuss the potash and
'phosphoric acid,' which I know cost some of our farmers a good part
of all they get for their crops, and still their lands are as poor
as ever."
"I appreciate very much your kind invitation, Mr. Thornton. I came
to you for correct information regarding the agricultural conditions
here, and you were very kind and indulgent to answer my blunt
questions, even concerning your own farm practice and experience. I
feel, Sir, that I am already greatly indebted to you, but it will
certainly be a great pleasure to me to remain with you to-night."
For more than two hours they had been standing, leaning, or sitting
in a field beside a shock of cowpea hay, Percy toying with his soil
auger, and Mr. Thornton making records now and then in his pocket
note book.