DR. VŒLCKER’S EXPERIMENTS ON CLOVER.
In the Journal of the Royal Agricultural Society of England, for 1868,
Dr. Vœlcker, the able chemist of the Society, and formerly Professor
of Agricultural Chemistry, at the Royal Agricultural College at
Cirencester, England, has given us a paper “On the Causes of the
Benefits of Clover, as a preparatory Crop for Wheat.” The paper has been
repeatedly and extensively quoted in this country, but has not been as
critically studied as the importance of the subject demands.
“Never mind all that,” said the Deacon, “tell us what Dr. Vœlcker says.”
“Here is the paper,” said I, “and Charley will read it to us.” Charley
read as follows:
“Agricultural chemists inform us, that in order to maintain the
productive powers of the land unimpaired, we must restore to it the
phosphoric acid, potash, nitrogen, and other substances, which enter
into the composition of our farm crops; the constant removal of organic
and inorganic soil constituents, by the crops usually sold off the farm,
leading, as is well known, to more or less rapid deterioration and
gradual exhaustion of the land. Even the best wheat soils of this
and other countries, become more and more impoverished, and sustain a
loss of wheat-yielding power, when corn-crops are grown in too rapid
succession without manure. Hence, the universal practice of manuring,
and that also of consuming oil-cake, corn, and similar purchased food on
land naturally poor, or partially exhausted by previous cropping.
“Whilst, however, it holds good as a general rule, that no soil can be
cropped for any length of time, without gradually becoming more and more
infertile, if no manure be applied to it, or if the fertilizing elements
removed by the crops grown thereon, be not by some means or other
restored, it is, nevertheless, a fact, that after a heavy crop of clover
carried off as hay, the land, far from being less fertile than before,
is peculiarly well adapted, even without the addition of manure, to bear
a good crop of wheat in the following year, provided the season be
favorable to its growth. This fact, indeed, is so well known, that many
farmers justly regard the growth of clover as one of the best
preparatory operations which the land can undergo, in order to its
producing an abundant crop of wheat in the following year. It has
further been noticed, that clover mown twice, leaves the land in a
better condition, as regards its wheat-producing capabilities, than when
mown once only for hay, and the second crop fed off on the land by
sheep; for, notwithstanding that in the latter instance the fertilizing
elements in the clover-crop are in part restored in the sheep
excrements, yet, contrary to expectation, this partial restoration of
the elements of fertility to the land has not the effect of producing
more or better wheat in the following year, than is reaped on land from
off which the whole clover-crop has been carried, and to which no manure
whatever has been applied.
“Again, in the opinion of several good, practical agriculturists, with
whom I have conversed on the subject, land whereon clover has been grown
for seed in the preceding year, yields a better crop of wheat than it
does when the clover is mown twice for hay, or even only once, and
afterwards fed off by sheep.”
“I do not think,” said the Deacon, “that this agrees with our experience
here. A good crop of clover-seed is profitable, but it is thought to be
rather hard on land.”
“Such,” said I, “is the opinion of John Johnston. He thinks allowing
clover to go to seed, impoverishes the soil.”
Charley, continued to read:
“Whatever may be the true explanation of the apparent anomalies
connected with the growth and chemical history of the clover-plant, the
facts just mentioned, having been noticed, not once or twice only, or by
a solitary observer, but repeatedly, and by numbers of intelligent
farmers, are certainly entitled to credit; and little wisdom, as it
strikes me, is displayed by calling them into question, because they
happen to contradict the prevailing theory, according to which a soil is
said to become more or less impoverished, in proportion to the large or
small amount of organic and mineral soil constituents carried off in the
produce.”
“That is well said,” I remarked, “and very truly; but I will not
interrupt the reading.”
“In the course of a long residence,” continues Dr. Vœlcker, “in a purely
agricultural district, I have often been struck with the remarkably
healthy appearance and good yield of wheat, on land from which a heavy
crop of clover-hay was obtained in the preceding year. I have likewise
had frequent opportunities of observing, that, as a rule, wheat grown on
part of a field whereon clover has been twice mown for hay, is better
than the produce of that on the part of the same field on which the
clover has been mown only once for hay, and afterwards fed off by sheep.
These observations, extending over a number of years, led me to inquire
into the reasons why clover is specially well fitted to prepare land for
wheat; and in this paper, I shall endeavor, as the result of my
experiments on the subject, to give an intelligible explanation of the
fact, that clover is so excellent a preparatory crop for wheat, as it is
practically known to be.
“By those taking a superficial view of the subject, it may be suggested
that any injury likely to be caused by the removal of a certain amount
of fertilizing matter, is altogether insignificant, and more than
compensated for, by the benefit which results from the abundant growth
of clover-roots, and the physical improvement in the soil, which takes
place in their decomposition. Looking, however, more closely into the
matter, it will be found that in a good crop of clover-hay, a very
considerable amount of both mineral and organic substances is carried
off the land, and that, if the total amount of such constituents in a
crop had to be regarded exclusively as a measure for determining the
relative degrees in which different farm crops exhaust the soil, clover
would have to be described as about the most exhausting crop in the
entire rotation.
“Clover-hay, on an average, and in round numbers, contains in 100 parts:
Water 17.0
Nitrogenous substances,
(flesh-forming matters)* 15.6
Non-nitrogenous compounds 59.9
Mineral matter, (ash) 7.5
-----
100.0
=====
* Containing nitrogen 2.5
“The mineral portion, or ash, in 100 parts of clover-hay, consists of:
Phosphoric acid 7.5
Sulphuric acid 4.3
Carbonic acid 18.0
Silica 3.0
Lime 30.0
Magnesia 8.5
Potash 20.0
Soda, chloride of sodium,
oxide of iron, sand, loss, etc. 8.7
-----
100.0
=====
“Let us suppose the land to have yielded four tons of clover-hay per
acre. According to the preceding data, we find that such a crop includes
224 lbs. of nitrogen, equal to 272 lbs. of ammonia, and 672 lbs. of
mineral matter or ash constituents.
”In 672 lbs. of clover-ash, we find:
Phosphoric acid 51½ lbs.
Sulphuric acid 29 ”
Carbonic acid 121 ”
Silica 20 ”
Lime 201 ”
Magnesia 57 ”
Potash 134½ ”
Soda, chloride of sodium,
oxide of iron, sand, etc. 58 ”
------------
672 lbs.
============
“Four tons of clover-hay, the produce of one acre, thus contain a large
amount of nitrogen, and remove from the soil an enormous quantity of
mineral matters, abounding in lime and potash, and containing also a
good deal of phosphoric acid.
“Leaving for a moment the question untouched, whether the nitrogen
contained in the clover, is derived from the soil, or from the
atmosphere, or partly from the one, and partly from the other, no
question can arise as to the original source from which the mineral
matters in the clover produce are derived. In relation, therefore, to
the ash-constituents, clover must be regarded as one of the most
exhausting crops usually cultivated in this country. This appears
strikingly to be the case, when we compare the preceding figures with
the quantity of mineral matters which an average crop of wheat removes
from an acre of land.
“The grain and straw of wheat contain, in round numbers, in 100 parts:
Grains of
Wheat. Straw.
Water 15.0 16.0
Nitrogenous substances,
(flesh-forming matter)* 11.1 4.0
Non-nitrogenous substances 72.2 74.9
Mineral matter, (ash) 1.7 5.1
----- ------
100.0 100.0
===== ======
* Containing nitrogen 1.78 .64
“The ash of wheat contains, in 100 parts:
Grain. Straw.
Phosphoric acid 50.0 5.0
Sulphuric acid 0.5 2.7
Carbonic acid
Silica 2.5 67.0
Lime 3.5 5.5
Magnesia 11.5 2.9
Potash 30.0 13.0
Soda, chloride of sodium,
oxide of iron, sand, etc. 2.0 4.8
----- -----
Total 100.0 100.0
===== =====
“The mean produce of wheat, per acre, may be estimated at 25 bushels,
which, at 60 lbs. per bushel, gives 1,500 lbs.; and as the weight of the
straw is generally twice that of the grain, its produce will be 3,000
lbs. According, therefore, to the preceding data, there will be carried
away from the soil:
In 1,500 lbs. of the grain 25 lbs. of mineral food,
(in round numbers).
In 3,000 lbs. of the straw 150 lbs. of mineral food,
(in round numbers).
---
Total 175 lbs.
“On the average of the analyses, it will be found that the composition
of these 175 lbs. is as follows:
------------------------------+-----------+-----------+----------
| In the | In the |
| grain. | straw. | Total.
+-----------+-----------+----------
Phosphoric acid | 12.5 lbs. | 7.5 lbs. | 20.0 lbs.
Sulphuric acid | 0.1 ” | 4.0 ” | 4.1 ”
Carbonic acid | | |
Silica | 0.6 ” |100.5 ” |101.1 ”
Lime | 0.9 ” | 8.2 ” | 9.1 ”
Magnesia | 2.9 ” | 3.0 ” | 5.9 ”
Potash | 7.5 ” | 19.5 ” | 27.0 ”
Soda, chloride of sodium, | | |
oxide of iron, sand, etc. | 0.5 ” | 7.3 ” | 7.8 ”
+-----------+-----------+----------
| 25. lbs. |150. lbs. |175. lbs.
------------------------------+-----------+-----------+----------
“The total quantity of ash constituents carried off the land, in an
average crop of wheat, thus amounts to only 175 lbs. per acre, whilst a
good crop of clover removes as much as 672 lbs.
“Nearly two-thirds of the total amount of mineral in the grain and straw
of one acre of wheat, consists of silica, of which there is an ample
supply in almost every soil. The restoration of silica, therefore, need
not trouble us in any way, especially as there is not a single instance
on record, proving that silica, even in a soluble condition, has ever
been applied to land, with the slightest advantage to corn, or
grass-crops, which are rich in silica, and which, for this reason, may
be assumed to be particularly grateful for it in a soluble state.
Silica, indeed, if at all capable of producing a beneficial effect,
ought to be useful to these crops, either by strengthening the straw, or
stems of graminaceous plants, or otherwise benefiting them; but, after
deducting the amount of silica from the total amount of mineral matters
in the wheat produced from one acre, only a trifling quantity of other
and more valuable fertilizing ash constituents of plants will be left.
On comparing the relative amounts of phosphoric acid, and potash, in an
average crop of wheat, and a good crop of clover-hay, it will be seen
that one acre of clover-hay contains as much phosphoric acid, as two and
one-half acres of wheat, and as much potash as the produce from five
acres of the same crop. Clover thus unquestionably removes from the land
very much more mineral matter than does wheat; wheat, notwithstanding,
succeeds remarkably well after clover.
“Four tons of clover-hay, or the produce of an acre, contains, as
already stated, 224 lbs. of nitrogen, or calculated as ammonia, 272 lbs.
“Assuming the grain of wheat to furnish 1.78 per cent of nitrogen, and
wheat-straw, .64 per cent, and assuming also that 1,500 lbs. of corn,
and 3,000 lbs. of straw, represent the average produce per acre, there
will be in the grain of wheat, per acre, 26.7 lbs. of nitrogen, and in
the straw, 19.2 lbs., or in both together, 46 lbs. of nitrogen; in round
numbers, equal to about 55 lbs. of ammonia, which is only about
one-fifth the quantity of nitrogen in the produce of an acre of clover.
Wheat, it is well known, is specially benefited by the application of
nitrogenous manures, and as clover carries off so large a quantity of
nitrogen, it is natural to expect the yield of wheat, after clover, to
fall short of what the land might be presumed to produce without manure,
before a crop of clover was taken from it. Experience, however, has
proved the fallacy of this presumption, for the result is exactly the
opposite, inasmuch as a better and heavier crop of wheat is produced
than without the intercalation of clover. What, it may be asked, is the
explanation of this apparent anomaly?
“In taking up this inquiry, I was led to pass in review the celebrated
and highly important experiments, undertaken by Mr. Lawes and Dr.
Gilbert, on the continued growth of wheat on the same soil, for a long
succession of years, and to examine, likewise carefully, many points, to
which attention is drawn, by the same authors in their memoirs on the
growth of red clover by different manures, and on the Lois Weedon plan
of growing wheat. Abundant and most convincing evidence is supplied by
these indefatigable experimenters, that the wheat-producing powers of a
soil are not increased in any sensible degree by the liberal supply of
all the mineral matters, which enter into the composition of the ash of
wheat, and that the abstraction of these mineral matters from the soil,
in any much larger proportions than can possibly take place under
ordinary cultivation, in no wise affects the yield of wheat, provided
there be at the same time a liberal supply of available nitrogen within
the soil itself. The amount of the latter, therefore, is regarded by
Messrs. Lawes and Gilbert, as the measure of the increased produce of
grain which a soil furnishes.
“In conformity with these views, the farmer, when he wishes to increase
the yield of his wheat, finds it to his advantage to have recourse to
ammoniacal, or other nitrogenous manures, and depends more or less
entirely upon the soil, for the supply of the necessary mineral or
ash-constituents of wheat, having found such a supply to be amply
sufficient for his requirements. As far, therefore, as the removal from
the soil of a large amount of mineral soil-constituents, by the
clover-crop, is concerned, the fact viewed in the light of the
Rothamsted experiments, becomes at once intelligible; for,
notwithstanding the abstraction of over 600 lbs. of mineral matter by a
crop of clover, the succeeding wheat-crop does not suffer. Inasmuch,
however, as we have seen, that not only much mineral matter is carried
off the land in a crop of clover, but also much nitrogen, we might, in
the absence of direct evidence to the contrary, be led to suspect that
wheat, after clover, would not be a good crop; whereas, the fact is
exactly the reverse.
“It is worthy of notice, that nitrogenous manures, which have such a
marked and beneficial effect upon wheat, do no good, but in certain
combinations, in some seasons, do positive harm to clover. Thus, Messrs.
Lawes and Gilbert, in a series of experiments on the growth of
red-clover, by different manures, obtained 14 tons of fresh green
produce, equal to about three and three-fourths tons of clover hay, from
the unmanured portion of the experimental field; and where sulphates of
potash, soda, and magnesia, or sulphate of potash and superphosphate of
lime were employed, 17 to 18 tons, (equal to from about four and
one-half to nearly five tons of hay), were obtained. When salts of
ammonia were added to the mineral manures, the produce of clover-hay
was, upon the whole, less than where the mineral manures were used
alone. The wheat, grown after the clover, on the unmanured plot, gave,
however, 29½ bushels of corn, whilst in the adjoining field, where wheat
was grown after wheat, without manure, only 15½ bushels of corn per acre
were obtained. Messrs. Lawes and Gilbert notice especially, that in the
clover-crop of the preceding year, very much larger quantities, both of
mineral matters and of nitrogen, were taken from the land, than were
removed in the unmanured wheat-crop in the same year, in the adjoining
field. Notwithstanding this, the soil from which the clover had been
taken, was in a condition to yield 14 bushels more wheat, per acre, than
that upon which wheat had been previously grown; the yield of wheat,
after clover, in these experiments, being fully equal to that in another
field, where large quantities of manure were used.
“Taking all these circumstances into account, is there not presumptive
evidence, that, notwithstanding the removal of a large amount of
nitrogen in the clover-hay, an abundant store of available nitrogen is
left in the soil, and also that in its relations towards nitrogen in the
soil, clover differs essentially from wheat? The results of our
experience in the growth of the two crops, appear to indicate that,
whereas the growth of the wheat rapidly exhausts the land of its
available nitrogen, that of clover, on the contrary, tends somehow or
other to accumulate nitrogen within the soil itself. If this can be
shown to be the case, an intelligible explanation of the fact that
clover is so useful as a preparatory crop for wheat, will be found in
the circumstance, that, during the growth of clover, nitrogenous food,
for which wheat is particularly grateful, is either stored up or
rendered available in the soil.
“An explanation, however plausible, can hardly be accepted as correct,
if based mainly on data, which, although highly probable, are not proved
to be based on fact. In chemical inquiries, especially, nothing must be
taken for granted, that has not been proved by direct experiment. The
following questions naturally suggest themselves in reference to this
subject: What is the amount of nitrogen in soils of different
characters? What is the amount more particularly after a good, and after
an indifferent crop of clover? Why is the amount of nitrogen in soils,
larger after clover, than after wheat and other crops? Is the nitrogen
present in a condition in which it is available and useful to wheat? And
lastly, are there any other circumstances, apart from the supply of
nitrogenous matter in the soil, which help to account for the beneficial
effects of clover as a preparatory crop for wheat?
“In order to throw some light on these questions, and, if possible, to
give distinct answers to at least some of them, I, years ago, when
residing at Cirencester, began a series of experiments; and more
recently, I have been fortunate enough to obtain the co-operation of Mr.
Robert Valentine, of Leighton Buzzard, who kindly undertook to supply me
with materials for my analysis.
“My first experiments were made on a thin, calcareous, clay soil,
resting on oolitic limestone, and producing generally a fair crop of
red-clover. The clover-field formed the slope of a rather steep hillock,
and varied much in depth. At the top of the hill, the soil became very
stony at a depth of four inches, so that it could only with difficulty
be excavated to a depth of six inches, when the bare limestone-rock made
its appearance. At the bottom of the field the soil was much deeper, and
the clover stronger, than at the upper part. On the brow of the hill,
where the clover appeared to be strong, a square yard was measured out;
and at a little distance off, where the clover was very bad, a second
square yard was measured; in both plots, the soil being taken up to a
depth of six inches. The soil, where the clover was good, may be
distinguished from the other, by being marked as No. 1, and that where
it was bad, as No. 2.
CLOVER-SOIL NO. 1. (GOOD CLOVER).
“The roots having first been shaken out to free them as much as possible
from the soil, were then washed once or twice with cold distilled water,
and, after having been dried for a little while in the sun, were
weighed, when the square yard produced 1 lb. 10½ oz. of cleaned
clover-roots, in an air-dry state; an acre of land, or 4,840 square
yards, accordingly yielded, in a depth of six inches, 3.44 tons, or 3½
tons in round numbers, of clover-roots.
“Fully dried in a water-bath, the roots were found to contain altogether
44.67 per cent of water, and on being burnt in a platinum capsule,
yielded 6.089 of ash. A portion of the dried, finely powdered and well
mixed roots, was burned with soda lime, in a combustion tube, and the
nitrogen contained in the roots otherwise determined in the usual way.
Accordingly, the following is the general composition of the roots from
the soil No. 1:
Water 44.675
Organic matter* 49.236
Mineral matter 6.089
-------
100.000
=======
* Containing nitrogen 1.297
Equal to ammonia 1.575
“Assuming the whole field to have produced 3½ tons of clover-roots, per
acre, there will be 99.636 lbs., or in round numbers, 100 lbs. of
nitrogen in the clover-roots from one acre; or, about twice as much
nitrogen as is present in the average produce of an acre of wheat.”
“That is a remarkable fact,” said the Deacon, “as I understand nitrogen
is the great thing needed by wheat, and yet the _roots_ alone of the
clover, contain twice as much nitrogen as an average crop of wheat. Go
on Charley, it is quite interesting.”
“The soil,” continues Dr. Vœlcker, “which had been separated from the
roots, was passed through a sieve to deprive it of any stones it might
contain. It was then partially dried, and the nitrogen in it determined
in the usual manner, by combustion with soda-lime, when it yielded .313
per cent of nitrogen, equal to .38 of ammonia, in one combustion; and
.373 per cent of nitrogen, equal to .46 of ammonia, in a second
determination.
“That the reader may have some idea of the character of this soil, it
may be stated, that it was further submitted to a general analysis,
according to which, it was found to have the following composition:
General Composition of Soil, No. 1. (Good Clover).
Moisture 18.73
Organic matter* 9.72
Oxide of iron and alumina 13.24
Carbonate of lime 8.82
Magnesia, alkalies, etc. 1.72
Insoluble silicious matter, (chiefly clay) 47.77
-------
100.00
=======
* Containing nitrogen .313
Equal to ammonia .380
“The second square yard from the brow of the hill, where the clover was
bad, produced 13 ounces of air-dry, and partially clean roots, or 1.75
tons per acre. On analysis, they were found to have the following
composition:
Clover-Roots, No. 2. (Bad Clover).
Water 55.732
Organic matter* 39.408
Mineral matter, (ash) 4.860
-------
100.000
=======
* Containing nitrogen .792
Equal to ammonia .901
“The roots on the spot where the clover was very bad, yielded only 31
lbs. of nitrogen per acre, or scarcely one-third of the quantity which
was obtained from the roots where the clover was good.
“The soil from the second square yard, on analysis, was found, when
freed from stones by sifting, to contain in 100 parts:
Composition of Soil, No. 2. (Bad Clover).
Water 17.24
Organic matter* 9.64
Oxide of iron and alumina 11.89
Carbonate of lime 14.50
Magnesia, alkalies, etc. 1.53
Insoluble silicious matter 45.20
-------
100.00
=======
2d
determination.
* Containing nitrogen .306 .380
Equal to ammonia .370 .470
“Both portions of the clover-soil thus contained about the same
percentage of organic matter, and yielded nearly the same amount of
nitrogen.
“In addition, however, to the nitrogen in the clover-roots, a good deal
of nitrogen, in the shape of root-fibres, decayed leaves, and similar
organic matters, was disseminated throughout the fine soil in which it
occurred, and from which it could not be separated; but unfortunately,
I neglected to weigh the soil from a square yard, and am, therefore,
unable to state how much nitrogen per acre was present in the shape of
small root-fibres and other organic matters.
“Before mentioning the details of the experiments made in the next
season, I will here give the composition of the ash of the partially
cleaned clover-roots:
Composition Of Ash Of Clover-Roots, (Partially Cleaned).
Oxide of iron and alumina 11.73
Lime 18.49
Magnesia 3.03
Potash 6.88
Soda 1.93
Phosphoric acid 3.61
Sulphuric acid 2.24
Soluble silica 19.01
Insoluble silicious matter 24.83
Carbonic acid, chlorine, and loss 8.25
------
100.00
======
“This ash was obtained from clover-roots, which yielded, when perfectly
dry, in round numbers, eight per cent of ash. Clover-roots, washed quite
clean, and separated from all soil, yield about five per cent of ash;
but it is extremely difficult to clean a large quantity of fibrous roots
from all dirt, and the preceding analysis distinctly shows, that the ash
of the clover-roots, analyzed by me, was mechanically mixed with a good
deal of fine soil, for oxide of iron, and alumina, and insoluble
silicious matter in any quantity, are not normal constituents of
plant-ashes. Making allowance for soil contamination, the ash of
clover-roots, it will be noticed, contains much lime and potash, as well
as an appreciable amount of phosphoric and sulphuric acid. On the decay
of the clover-roots, these and other mineral fertilizing matters are
left in the surface-soil in a readily available condition, and in
considerable proportions, when the clover stands well. Although a crop
of clover removes much mineral matter from the soil, it must be borne in
mind, that its roots extract from the land, soluble mineral fertilizing
matters, which, on the decay of the roots, remain in the land in a
prepared and more readily available form, than that in which they
originally occur. The benefits arising to wheat, from the growth of
clover, may thus be due partly to this preparation and concentration of
mineral food in the surface-soil.
“The clover on the hillside field, on the whole, turned out a very good
crop; and, as the plant stood the winter well, and this field was left
another season in clover, without being plowed up, I availed myself of
the opportunity of making, during the following season, a number of
experiments similar to those of the preceding year. This time, however,
I selected for examination, a square yard of soil, from a spot on the
brow of the hill, where the clover was thin, and the soil itself stony
at a depth of four inches; and another plot of one square yard at the
bottom of the hill, from a place where the clover was stronger than that
on the brow of the hill, and the soil at a depth of six inches contained
no large stones.
SOIL NO. 1. (CLOVER THIN), ON THE BROW OF THE HILL.
“The roots in a square yard, six inches deep, when picked out by hand,
and cleaned as much as possible, weighed, in their natural state, 2 lbs.
11 oz.; and when dried on the top of a water-bath, for the purpose of
getting them brittle and fit for reduction into fine powder, 1 lb. 12
oz. 31 grains. In this state they were submitted as before to analysis,
when they yielded in 100 parts:
Composition Of Clover-Roots, No. 1, (From Brow Of Hill).
Moisture 4.34
Organic matter* 26.53
Mineral matter 69.13
-------
100.00
=======
* Containing nitrogen .816
Equal to ammonia .991
“According to these data, an acre of land will yield three tons 12 cwts.
of nearly dry clover-roots, and in this quantity there will be about 66
lbs. of nitrogen. The whole of the soil from which the roots have been
picked out, was passed through a half-inch sieve. The stones left in the
sieve weighed 141 lbs.; the soil which passed through weighing 218 lbs.
“The soil was next dried by artificial heat, when the 218 lbs. became
reduced to 185.487 lbs.
“In this partially dried state it contained:
Moisture 4.21
Organic matter* 9.78
Mineral matter† 86.01
-------
100.00
=======
* Containing nitrogen .391
Equal to ammonia .475
† Including phosphoric acid .264
“I also determined the phosphoric acid in the ash of the clover-roots.
Calculated for the roots in a nearly dry state, the phosphoric acid
amounts to .287 per cent.
“An acre of soil, according to the data, furnished by the six inches on
the spot where the clover was thin, produced the following quantity of
nitrogen:
Ton. Cwts. Lbs.
In the fine soil 1 11 33
In the clover-roots 0 0 66
-- -- --
Total quantity of nitrogen per acre 1 11 99
== == ==
“The organic matter in an acre of this soil, which can not be picked out
by hand, it will be seen, contains an enormous quantity of nitrogen; and
although, probably, the greater part of the roots and other remains from
the clover-crop may not be decomposed so thoroughly as to yield
nitrogenous food to the succeeding wheat-crop, it can scarcely be
doubted that a considerable quantity of nitrogen will become available
by the time the wheat is sown, and that one of the chief reasons why
clover benefits the succeeding wheat-crop, is to be found in the
abundant supply of available nitrogenous food furnished by the decaying
clover-roots and leaves.
CLOVER-SOIL NO. 2, FROM THE BOTTOM OF THE HILL. (GOOD CLOVER.)
“A square yard of the soil from the bottom of the hill, where the clover
was stronger than on the brow of the hill, produced 2 lbs. 8 oz. of
fresh clover-roots; or 1 lb. 11 oz. 47 grains of partially dried roots;
61 lbs. 9 oz. of limestones, and 239.96 lbs. of nearly dry soil.
“The partially dried roots contained:
Moisture 5.06
Organic matter* 31.94
Mineral matter 63.00
-------
100.00
=======
* Containing nitrogen .804
“An acre of this soil, six inches deep, produced 3 tons, 7 cwts. 65 lbs.
of clover-roots, containing 61 lbs. of nitrogen; that is, there was very
nearly the same quantity of roots and nitrogen in them, as that
furnished in the soil from the brow of the hill.
“The roots, moreover, yielded .365 per cent of phosphoric acid; or,
calculated per acre, 27 lbs.
“In the partially dried soil, I found:
Moisture 4.70
Organic matter* 10.87
Mineral matter† 84.43
-------
100.00
=======
* Containing nitrogen .405
Equal to ammonia .491
† Including phosphoric acid .321
“According to these determinations, an acre of soil from the bottom of
the hill, contains:
Tons Cwts. Lbs.
Nitrogen in the organic matter of the soil 2 2 0
Nitrogen in clover-roots of the soil 0 0 61
--- --- ---
Total amount of nitrogen per acre 2 2 61
=== === ===
“Compared with the amount of nitrogen in the soil from the brow of the
hill, about 11 cwt. more nitrogen was obtained in the soil and roots
from the bottom of the hill, where the clover was more luxuriant.
“The increased amount of nitrogen occurred in fine root-fibres and other
organic matters of the soil, and not in the coarser bits of roots which
were picked out by the hand. It may be assumed that the finer particles
of organic matter are more readily decomposed than the coarser roots;
and as there was a larger amount of nitrogen in this than in the
preceding soil, it may be expected that the land at the bottom of the
hill, after removal of the clover, was in a better agricultural
condition for wheat, than that on the brow of the hill.”