MANURING OF THE COMMON FARM CROPS.
In this chapter we shall attempt to summarise briefly the results of
experiments on the manuring of some of the commoner crops, and we shall
start with the manuring of cereals.
CEREALS.
As we have already pointed out, a certain similarity in the manurial
requirements of the different members of this class exists. They are
characterised, for one thing, by the comparatively small quantity of
nitrogen they remove from the soil--less than either leguminous or root
crops. Of this nitrogen the larger proportion--amounting to
two-thirds--is contained in the grain, the straw only containing about a
quarter of the total amount of nitrogen in the plant. The amount of
phosphoric acid they remove from the soil is not much less than that
removed by the other two classes of crops; but this, again, is also
chiefly in the grain. It is on this account that the cereals may be
regarded, in a sense, as exhaustive crops, seeing that the grain is
almost invariably sold off the farm. But, on the other hand, owing to
the comparatively small demands they make on fertilising ingredients,
cereals will continue to grow on poor land for a longer period than most
crops,--a fact of very great importance for mankind.
_Especially benefited by Nitrogenous Manures._
Despite the fact that cereals remove comparatively little nitrogen from
the soil, it is somewhat striking to find that they are chiefly
benefited by the application of nitrogenous manures. This fact may be
explained by the shortness of the period of their growth, and the fact
that they assimilate their nitrogen in spring and early summer, and are
thus unable to utilise to the full the nitrates which accumulate in the
soil during later summer and autumn. As they seem to absorb their
nitrogen almost exclusively in the form of nitrates, they are especially
benefited by the application of nitrate of soda.
_Power of absorbing Silicates._
A characteristic feature in the composition of cereals is the large
amount of silica they contain. In common with the grasses, they seem to
possess a power, not possessed by other crops, of feeding upon
silicates.
The special manure, therefore, required for cereals is a nitrogenous
manure, and that, as a rule, of a speedily available character, such as
nitrate of soda or sulphate of ammonia. Furthermore, certain members of
the group are also specially benefited by phosphatic manures.
We shall now consider individually a few of the more important cereal
crops.
BARLEY.
Of cereal crops barley deserves to be considered first, owing to the
fact that it is, of all grain crops, the most widely distributed. In
England, in amount, it comes next to wheat among cereals. Its habits
have also been studied in a very elaborate and careful manner, and have
been made the subject of many experiments, both in this country and
abroad.
_Period of Growth._
The first point to notice about barley is the fact that its period of
growth is a short one. This has a most important bearing on its
treatment with manure. It may be said to ripen, on an average, in
thirteen or fourteen weeks in this country; although in Norway and
Sweden its period of growth is much less--viz., from six to seven weeks.
Indeed no fewer than three crops have been obtained in one year in
certain districts in these countries, and two crops are common. With
regard to the period of its growth, it differs from wheat, which in its
general manurial requirements it resembles. Wheat, which is largely sown
in autumn, has four or five months' start of barley. From the fact that
it is a short-lived crop, and that its roots are shallower than wheat,
and draw their nourishment chiefly from the surface-soil, it benefits to
a greater extent from liberal manuring than wheat, which is more
independent of artificial supplies of fertilisers.
_Most suitable Soil._
Again, while wheat does well on a heavy soil, and does not require a
fine surface-tilth, barley does best on a light, rich, friable soil. It
has, however, been very successfully grown on a heavy soil after wheat.
Barley benefits more than wheat does from the application of
superphosphate of lime, or some other readily available phosphatic
manure. This may be accounted for by its shorter period of growth and
shallower root system, which thus prevent it drawing much mineral
sustenance from the subsoil. In fact, spring-sown crops, as a rule,
benefit more from superphosphate than autumn-sown crops. The exhaustion
of a soil under barley is essentially, as in the case of wheat, one of
nitrogen, as Sir J. Henry Gilbert has pointed out.[244]
_Farmyard Manure not suitable._
It has been urged, with some show of reason, that farmyard manure is not
suitable for barley, as its action is too slow to have much influence on
so short-lived a plant, and that only quick-acting manures should be
used. Where farmyard manure is applied, it should be to the preceding
crop; and this is advisable for more reasons than one.
_Importance of uniform Manuring of Barley._
The use to which barley is put--viz., for malting purposes--renders the
uniformity of its composition a point of great importance. Since its
quality is very largely influenced by its treatment with manures,
special care has to be exercised in their application. Grown as it
generally is after roots, fed off with sheep, its quality, it is
alleged, is apt to suffer from the unequal distribution of the manure
applied in this way. It has consequently been recommended, in order to
avoid this inequality, rather to grow a wheat crop immediately preceding
the barley.
_Norfolk Experiments on Barley._
Mr Cooke, in summing up the results of the interesting Norfolk
experiments on barley, points out that in these experiments barley
always was benefited by nitrogenous manures, sometimes by superphosphate
of lime, and more rarely by potash; that of nitrogenous manures those
of quickest action exerted the best influence. On an average it was
found that 1 cwt. nitrate of soda per acre gave an increase of 8 bushels
of barley, and 2 cwt. gave 14 bushels; while 3/4 cwt. sulphate of
ammonia (_i.e._, the amount containing the same quantity of nitrogen as
1 cwt. nitrate of soda) gave only 5-1/2 bushels of an increase, and
1-1/2 cwt. (= 2 cwt. nitrate of soda) gave 10 bushels.
Mr Cooke recommends the following manures for the barley crop. From 1/4
to 1 cwt. of nitrate of soda, according to previous treatment of soil;
from 1 to 2 cwt. super; and where it is required, from 1/2 to 1 cwt.
muriate of potash.
_Proportion of Grain to Straw._
Professor Hellriegel, the distinguished German investigator, has carried
out most elaborate experiments on a small scale, with a view to
investigating the habits of the barley plant. In the most perfectly
developed of these plants, grown under the most favourable conditions,
he found that the grain and straw were about equal in weight. Such a
proportion of grain is, however, never realised in practice, the
proportion of 2 of grain to 3 of straw being probably the common one.
WHEAT.
Wheat occupies the first position amongst cereals, in respect of extent
of cultivation, in England. As a rule it is sown in autumn, although it
is also sown in spring. It is generally taken after rotation grasses or
a leguminous crop, such as peas or beans, or after potatoes or roots.
Unlike barley, it does best on a clay soil, or at any rate on a firm
soil, and requires a moist seed-bed. From the fact that wheat is often
sown after such a crop as potatoes or a root crop to which a liberal
application of manure has been given, it is not so necessary to manure
it except with a top-dressing of nitrate of soda. In short, it is
usually considered highly desirable to get land into "good heart" before
wheat, so that the wheat may obtain its nourishment from the residue of
the previous crop and the farmyard manure previously applied.
Although, therefore, as a rule, the only manure it will be found
necessary to add to wheat is a nitrogenous manure, such as nitrate of
soda or sulphate of ammonia, still there are circumstances in which it
will be well to supplement these by phosphatic or even potassic manures.
On a light soil it may be advisable to add superphosphate of lime,
guano, or bone-meal, in quantities of 2 to 3 cwt. per acre, in addition
to a nitrogenous manure.
_Rothamsted Experiments on Wheat._
Of experiments carried out on the growth of wheat, those which have now
been in progress for over half a century at Rothamsted are the most
valuable and famous. In these experiments the comparative value of
nitrogen and mineral manures on this crop was strikingly exemplified.
The former gave a most marked increase in the crop, while with the
latter little or no increase was obtained. A combination of nitrogenous
and mineral manures, on the other hand, gave the most striking results.
An explanation of these results may be afforded by the fact that in
ordinary farming an excess of mineral matter, as compared with nitrates,
is returned to the soil in the crop residues and in the straw of the
farmyard manure.
Of nitrogenous manures, nitrate of soda, on the whole, showed better
results than sulphate of ammonia.
_Continuous Growth of Wheat._
The possibility of growing fair crops of wheat year after year for fifty
years on the same land, and that without any manure whatever, is among
the most striking of the results of these famous Rothamsted wheat
experiments.
_Flitcham Experiments._
In conclusion, we may refer to Mr Cooke's Flitcham experiments. These
were carried out for the purpose of ascertaining the most suitable
manure for the wheat crop under different conditions.
It will be sufficient here to give the recommendations made by Mr Cooke
as the practical outcome of these experiments.
He recommends the application of 10 tons of farmyard manure on light or
mixed soils, after rotation seeds, ploughed in in the autumn, with from
1/4 to 1 cwt. of nitrate of soda, sown in the spring. In certain cases
farmyard manure will be sufficient without the nitrate of soda. When
farmyard manure is not available, the most effective and economical
substitute is 4 cwt. per acre of rape-cake, ploughed in in the autumn,
or 1 cwt. of sulphate of ammonia, sown in the spring, with, in either
case, 1 cwt. of nitrate of soda as a spring top-dressing. In addition to
the above, on land in doubtful agricultural condition, or exceptionally
deficient in one or other of these ingredients, Mr Cooke recommends the
addition of 2 cwt. superphosphate, or 1 cwt. muriate of potash, or both
of these manures, ploughed or harrowed in in autumn.
OATS.
Like barley, oats are generally sown in spring, and, like barley, may be
described as a shallow-rooted crop. They require, therefore, manures
which are readily available, and their demands on the different
fertilising ingredients are very similar to barley. The manures which
will pay best, consequently, for oats, are nitrate of soda, used as a
top-dressing, and superphosphate of lime, applied along with the seed.
Probably upon no other crop is nitrate of soda so safe and so effective
as upon oats. In some respects, however, oats differ strikingly from
barley.
_A very hardy Crop._
In the first place, oats are a much hardier crop than barley or wheat.
They can grow on a wonderfully wide range of soil, and under
comparatively adverse circumstances, both of climate and situation. They
are better suited for a damp climate such as our own than a warm
climate. They may be described as of all crops the least fastidious, and
will flourish on sandy, peaty, or clayey soils. While this is so, they
show a preference for soils rich in decayed vegetable matter. It is for
this reason that they flourish so well on soils freshly broken up from
pasture, and are often the first crop to be grown on such soils.
_Require mixed Nitrogenous Manuring._
Stoeckhardt has found, in experiments on the manuring of the oat crop,
that they greedily absorb nitrogen during nearly the whole period of
their growth, and that, consequently, it is desirable to manure them
with a mixed nitrogenous manure which shall contain nitrogen, both in a
readily available form to supply the plant during the early stages of
its growth, and in a less available form for the later stages of
growth. He was of the opinion that in this way a continuous and
satisfactory growth of the crop would be promoted.
_Arendt's Experiments._
The oat-plant has been made the subject of many elaborate
investigations. Of these, those carried out by Arendt are the most
elaborate and best known. In these experiments the composition of the
oat-plant at different stages of growth was investigated. It was found
that the oat-plant increased during the whole period of its life, and
that two-thirds of the nitrogen absorbed was absorbed during the later
period of growth. It has since been shown, however, that the absorption
of nitrogen is very much influenced by circumstances. Indeed its
composition is peculiarly susceptible to the influence of manures, and
especially the influence of weather. Thus Arendt found that the
assimilation of nitrogen is checked by cold wet weather; while, on the
other hand, it is promoted by warm dry weather. The grain of oats grown
in warm seasons is better developed, and in composition more nutritious
(_i.e._, contains more nitrogen), than that of oats grown in wet
seasons, while the reverse is the case with the straw.
"_Avenine._"
A point of considerable interest in connection with the composition of
oats is the fact that it contains a body which exerts a strikingly
stimulating effect on the nervous system of the animal, and to which the
name "avenine" has been given.
_Quantities of Manures._
The quantities of manures which may be applied to the oat crop are
similar in amount to those which ought to be applied to barley--from 1/2
to 1 cwt. of nitrate of soda, and from 2 to 3 cwt. superphosphate of
lime. Very often, however, the oat crop receives directly little or no
manure. In the Highland and Agricultural Society of Scotland's
experiments, sulphate of ammonia was found to be of very much less value
than nitrate of soda as a manure for oats. Potash manures, especially
muriate of potash, had a very beneficial effect. The general conclusions
drawn from these experiments were, that the treatment of the land should
be such as to accumulate organic matter in it, to prevent too great a
loss of moisture, and to provide the young plant with manures that come
speedily into operation.
GRASS.
The manuring of grass is a question of very great interest and
importance, but is, at the same time, beset with peculiar difficulties.
Grass is grown under two conditions--first, that grown on soils
exclusively set apart for its continuous growth (permanent pasture);
and secondly, that grown for the purpose of being converted into hay and
of providing pasture in the ordinary rotation of crops (rotation seeds).
The manuring of the former is somewhat different from the manuring of
the latter.
_Effect of Manure on Herbage of Pastures._
The nature of the herbage growing on pasture is very much influenced by
the manure applied. This, indeed, is one of the most noteworthy features
connected with the manuring of grass, and has been especially observed
in the Rothamsted experiments, where the influence of the different
manures on the various kinds of herbage has been investigated with great
care. The herbage constituting pasture is, as every farmer knows, of a
varied description. We have in pastures a mixture of plants belonging
both to the gramineous and leguminous classes, as well as a variety of
weeds. Now the result of the application of different manures tends
respectively to foster the different kinds of grasses. Thus when one
kind of manure is applied, grasses of one kind tend to predominate and
crowd out grasses of another. It has been found that _the more highly
pasture-land is manured the simpler is the nature of its herbage_ (that
is, the fewer are the different kinds of herbage growing on it).
_Unmanured pasture, on the other hand, is more complex in its herbage._
The result is, that the application of manure to pasture-land is
attended with certain dangers. To maintain good pasture it is desirable
to effect a proper balance between the different kinds of grasses. For
this reason permanent pasture may be said to be, of all crops, the least
commonly manured. As a rule it is only manured by the droppings of the
cattle and sheep feeding upon it.
_Influence of Farmyard Manure._
It is found that the influence of farmyard manure upon the composition
of the pasture does not tend, to the same extent, to the undue
development of one type of herbage over another; and in this respect it
is probably to be preferred to artificial manures.
The same reasons, however, do not hold with regard to rotation seeds,
where an abundant growth is desired, and complexity of herbage is not so
important. A further reason which exists for the manuring of meadow-land
is the greater impoverishment of the soil taking place under such
conditions. As illustrating the influence of different manures on
different kinds of herbage, it may be mentioned that in New England
wood-ashes, a manure commonly used there, have been observed, when
applied to pasture, to bring in white clover, and that the application
of gypsum had the same effect. An explanation of this fact may be found
in the influence of potash on leguminous crops. The chief value of
wood-ashes as a manure is due to the large percentage of potash they
contain, while the value of gypsum is probably to be accounted for by
the fact that it has an indirect action, and sets free potash from its
inert compounds in the soil. In the Rothamsted experiments this point
has been verified, and potash has been shown to increase the proportion
of leguminous plants on a grass-field. Nitrogenous manures, on the other
hand, more especially sulphate of ammonia, have been found to increase
the proportion of grasses proper, and to diminish the proportion of
leguminous plants. The effect of farmyard manure, while less marked in
inducing simplicity of herbage, has a similar effect to sulphate of
ammonia; while phosphates and other mineral manures exercise an
influence similar to that of potash. Mixtures of mineral and nitrogenous
manures gave the largest returns obtained, but their influence was to
increase the proportion of grasses proper. Sewage irrigation also tends
chiefly to develop grasses.
_Influence of Soil and Season on Pastures._
Manures are not the only factors influencing the quality of pastures.
The nature of the soil, as well as the age of the pasture and the
character of the season, exert a very considerable influence. Grass
growing on damp or badly drained soil is invariably of poor quality, the
coarser grasses predominating. Old pastures, again, are generally of
better quality than new ones.
MANURING OF MEADOW-LAND.
Nitrate of soda is a common manure for grass grown for hay. It is often
applied at the rate of 2 or 3 cwt. per acre. It is best, however, to
apply it in smaller doses. On soils where lime is abundant,
superphosphate may be applied, if necessary, at the rate of 2 or 3 cwt.
per acre, or bones at a similar rate. Basic slag has been found to meet
with good results as a manure for grass-land, especially where the soil
is rich in organic matter.
_Bangor Experiments._
Mr Gilchrist of University College, Bangor, as a result of numerous
experiments carried out in different parts of Wales, recommends for
rye-grass and clover hay on land in good condition 1 cwt. of nitrate of
soda or sulphate of ammonia per acre, the former being applied about the
middle of April, the latter during March. For land in poor condition,
the addition of 2 cwt. of superphosphate is recommended--this to be
applied some time between December and March. Farmyard manure may be
usefully applied to young grass and clover seeds in the autumn, more
especially on light soils. For meadow-land which is growing hay every
year, Mr Gilchrist further recommends the following 4-course rotation of
manuring:--
First year, 15 tons farmyard manure, applied in the autumn.
Second year, 1 cwt. nitrate of soda.
Third year, 4 cwt. basic slag or 3 cwt. superphosphate and 1 cwt.
nitrate of soda.
Fourth year, 1 cwt. nitrate of soda.
_Norfolk Experiments._
Mr Cooke, from his Norfolk experiments, recommends the following manures
for rotation seeds:--
One to 1-1/2 cwt. nitrate of soda as a top-dressing in early spring.
Where the clover plant is a good one, and it is particularly desired to
cultivate it, he recommends as a dressing 1 cwt. of muriate of potash
per acre, to be applied immediately after the clover is sown. The
practice of dressing growing seeds in their first winter has, so far as
the experiments in Norfolk go, less to recommend it than the earlier
dressing.
MANURING OF PERMANENT PASTURES.
In this case the manure should be applied so as not to impair the
quality of the herbage. Slow-acting manures are consequently best, such
as basic slag or bones, which have been found to be of special value. On
wet or marshy land after draining, lime is perhaps one of the best
manures to apply in the first instance. As we have already said,
farmyard manure will do more to maintain the quality of pasture than any
kind of artificial manure. Mr Cooke is of opinion that no system of
manuring yet discovered will both thicken and improve the herbage at
all equally in success to the careful and regular feeding upon the grass
of cattle or sheep, the animals having a good allowance of decorticated
cotton-cake, or even of linseed-cake.
ROOTS.
Of all crops roots may be said to require the most liberal application
of manure, and to respond most freely to it. They contain large
quantities of the fertilising ingredients--nitrogen, phosphates, and
potash--and may be regarded as exceedingly exhaustive crops. This is
especially the case with regard to mangels, which make particularly
large demands on a soil's fertilising ingredients.
Turnips are characterised by the large amount of sulphur they contain;
and, according to some, this explains the beneficial effect which gypsum
has when applied to them as a manure. This, however, is more probably to
be explained by the indirect action of gypsum in setting free the potash
of the soil. The fact that the successful cultivation of root crops
depends on the application of large quantities of manure, is recognised
in practice, as they receive the most manure of any crop of the
rotation. Roots flourish best on a light soil which is neither too wet
nor too dry; but with liberal manuring and careful tillage, they may be
said to do well on any soil. Mangels are generally more benefited by
the application of nitrogenous manures than are turnips or swedes,
which, it would seem, have a greater power of absorbing nitrogen from
the soil than the first-named crop; but it is a mistake to suppose that
any of the root crops are not dependent on a ready supply of nitrogen;
and the fact that large crops of turnips can often be grown by the
application of superphosphate alone, may be taken as a proof that the
soil contains plenty of nitrogen. Mangels are, from their deeper roots,
more capable of drawing their supply of phosphoric acid from the soil
than turnips. They respond, therefore, as a rule, less freely than
turnips or swedes to an application of superphosphate. Generally
speaking, we may say that the characteristic manure for turnips is
superphosphate, and that for mangels is a nitrogenous manure such as
nitrate of soda or sulphate of ammonia.
A special reason for manuring root crops is the fact that they are more
liable to disease than other crops; and this is especially the case in
the early stages of their growth. One of the great benefits conferred on
the turnip crop by an application of superphosphate, is the help it
gives the crop to pass safely the critical period of its growth. The
superphosphate is best drilled in with the seed, in quantities varying
from 3 to 5 cwt. In Scotland, it may be well to point out, the manure
applied to this crop is very much in excess of the amount customarily
applied in England; for in the former country larger applications of
manure may be profitably employed. Roots generally receive a large
dressing of farmyard manure. Salt has been found in some districts to
have a very good effect on the mangel crop, and potash is often found to
amply repay application.
_Influence of Manure on Composition._
A most interesting point in connection with the manuring of roots is the
effect of manure on their composition. This has been most elaborately
investigated at Rothamsted and elsewhere. Thus it has been found that
the effect of the application of excessive quantities of nitrogenous
manures is to produce too great a development of leaves at the expense
of the roots.
_Nitrogenous Manures increase Sugar in Roots._
Nitrogenous manures also tend to increase the proportion of sugar and
diminish the proportion of nitrogenous matter in roots. This has an
important bearing on the treatment of roots which are cultivated for
their sugar, such as beets, in the growth of which nitrate of soda is
the chief artificial manure applied.[245]
The leaf, it may be pointed out, contains a larger percentage of dry
matter, both in swedes and in turnips, than the root.
_Amount of Nitrogen recovered in Increase of Crop._
With regard to the amount of nitrogen recovered in the increased crop of
mangel and roots when manured with different nitrogenous manures, it was
found at Rothamsted, as an average of six years, that the following
percentages of nitrogen were recovered: When nitrate of soda was
applied, 60 per cent of the nitrogen it contained was recovered in the
increased crop; when ammonia salts were applied, 52 per cent; when
rape-cake was used, 50 per cent; and when a mixture of rape-cake and
ammonia salts was used, 46 per cent.
It may be pointed out that the influence of season and climate on the
composition of root crops is very great--greater, indeed, than on any
other crop. Like oats, turnips grow better in Scotland than in England,
the moister climate of the former country being more suitable for their
maximum development, and hence the economy of maximum dressings in
Scotland.
_Norfolk Experiments._
In conclusion, a few words may be said on the Norfolk experiments,
carried out under the direction of Mr Cooke for the purpose of
ascertaining the best and most economical manure for mangels and swedes
on different Norfolk soils. In most of these experiments it was found
that superphosphate had not much effect in producing increase of crop in
the case of mangels; that the best nitrogenous manure was nitrate of
soda; and that on the whole it was not economical to apply farmyard
manure at the rate of more than 10 tons per acre. It was further found
that, although either potash or common salt gave a decided increase in
weight of roots, it was not necessary to give both these manures at
once, either of them being about as effective as the other.
Mr Cooke recommends the following manures as best suited for
mangels--viz., 2 cwt. nitrate, 3 cwt. common salt, and 2 cwt.
superphosphate. Upon certain soils peculiarly adapted to mangels, and in
warm localities where larger crops than 25 to 30 tons per acre are
habitually grown, it would probably pay to increase or to double the
above quantity of nitrate of soda. Ten tons of farmyard manure may, if
preferred, be substituted for all or a part of the nitrate of soda, or
may even be used in addition to it, according to the resources of the
farmer in respect of it, and the return he desires to get from the dung
in the first year of application or in future ones. It is best to apply
the nitrate of soda in two instalments--half at the time of seeding, and
half as a top-dressing immediately after the first hand-hoeing of the
roots. A third dressing may often be given with advantage a month later.
_Manure for Swedes._
As a complete and economical dressing for swedes in Norfolk, Mr Cooke
recommends 3 to 4 cwt. superphosphate, 1 cwt. sulphate of ammonia, and
1/2 cwt. of muriate of potash. Occasionally it may be found advisable to
reduce the quantity of sulphate of ammonia, or to leave it out
altogether; and in other cases the potash may be judiciously omitted.
The entire mixture should be sown at the time of drilling the turnips.
If farmyard manure is used--and if used it should be applied in a
well-decomposed state--no other manure than 3 cwt. of superphosphate
will be required.
_Highland Society's Experiments._
Valuable experiments have been carried out on the subject of manuring of
turnips by Dr A. P. Aitken, for the Highland and Agricultural Society of
Scotland. The following are some of the results to be gathered from
these experiments. The effect of a dissolved phosphate as compared with
a ground phosphate is to produce a turnip of less feeding value.
Superphosphate had a better effect when applied in April than when
applied with the seed in June. It was further found that when the
nitrogenous manure was given entirely in the form of nitrate of soda or
sulphate of ammonia, the latter produced a denser and sounder turnip.
Lastly, with regard to the application of potash, it was found that the
best way was to apply it several months before sowing. The effect of
potash manures is to increase the amount of turnips, but to retard the
ripening of the bulbs. The effect of excessive potash manuring is to
greatly injure the crop.
_Manuring for rich Crops of Turnips._
In Dr Aitken's own words: "In order to grow a large and at the same time
a healthy and nutritious crop of turnips, such a system of manuring or
treatment of the soil, by feeding or otherwise, should be practised as
will result in the general enriching and raising of the condition of the
land, so that the crop may grow naturally and gradually to maturity. For
that purpose a larger application of slowly acting manures, of which
bone-meal may be taken as the type, is much better suited than smaller
applications of the more quickly acting kind. A certain amount of
quickly acting manure is very beneficial to the crop, especially in its
youth; but the great bulk of the nourishment which the crop requires
should be of the slowly rotting or dissolving kind, as uniformly
distributed through the soil as possible."
_Experiments by the Author._
Experiments by the author on turnip-manuring, carried out in different
parts of the South and West of Scotland, showed that while farmyard
manure is valuable in giving the crop a good start and bringing it well
forward during the period of germination and early growth, by supplying
a certain amount of easily assimilable plant-food, and in the case of
dry weather attracting a quantity of moisture, its application in
quantities of 20 or even 10 tons per acre can scarcely be regarded as
profitable, giving to farmyard manure a nominal value of a few shillings
a ton. In these experiments slag proved itself a most valuable manure,
indeed one of the most economical of all the manures experimented with.
They further showed that heavy dressings with superphosphate, amounting
to as much as 8 cwt. per acre, are, from an economical point of view, as
a rule justifiable in Scotland; and that nitrate of soda and sulphate of
ammonia possess practically equal value as a manure for turnips. In
almost every one of the experiments the benefit of supplementing
superphosphate with nitrogenous manure was shown. Potash was also found
in many cases to be a thoroughly paying manure for the turnip crop, when
it was applied along with nitrogen and phosphates; but when applied
alone, far from exercising any appreciable benefit, it seemed to exert
an injurious action.
POTATOES.
Potatoes are often classed along with the root crops, and in their
manurial requirements they offer many points of similarity. Next to root
crops, they may be said to make the most exhaustive demands on the soil,
and therefore require a liberal general manuring. A point of importance
in the manuring of potatoes is a good tilth in the soil, so as to enable
a free expansion of the tubers to take place. They may be said to grow
best on deep warm soils; but, like roots, if liberally manured, they may
be successfully grown on any kind of soil. Farmyard manure has long been
regarded as specially valuable for the potato crop. In many parts of
Scotland it is applied in enormous quantities, ranging from 20 to even
40 tons per acre. There can be little doubt that the value of farmyard
manure, as well as other bulky manures, for the potato crop, is partly
due to their mechanical influence on the soil. Potatoes are
surface-feeders, and require their food in a readily available
condition. It is found desirable, therefore, to supplement farmyard
manure by readily available artificial manures. Potatoes repay the
application of a mixed manure containing all the fertilising
ingredients--nitrogen, phosphoric acid, and potash--better than most
crops.
_Highland Society's Experiments on Potatoes._
The nitrogen is, according to the Highland Society's experiments, best
applied in the form of nitrate of soda. Sulphate of ammonia does not
seem, when farmyard manure is also applied, to have an equally valuable
effect, as it influences the size of the tuber, producing an undue
proportion of small potatoes. When no farmyard manure is applied,
however, sulphate of ammonia seems to have a good effect, especially in
wet seasons.
With regard to the nature of the phosphatic manure to be applied,
superphosphate is to be preferred. Potatoes make large demands on
potash, and consequently require potassic manures. In consequence of the
fact that they receive large applications of farmyard manure, the
necessity for adding potash in the form of artificial manures does not
generally exist. Potash, if applied in too large quantities, has been
found to exert a deleterious effect. We have already pointed out that
muriate of potash tends to produce a waxy potato.
_The Rothamsted Experiments with Potatoes._
The Rothamsted experimenters have very fully investigated the conditions
of the manurial requirements of potatoes. In these experiments potatoes
were grown year after year in the same field. It was found that the
effect of mineral manures alone was greater than the effect of
nitrogenous manures alone, and that of mineral manures phosphates, as a
rule, had a better effect than potash; that under the action of the
growth of potatoes a greater exhaustion of phosphates than of potash
takes place in the soil; and lastly, that it is essential to have an
abundant supply of the different fertilising ingredients in order to
grow successful crops. In the Rothamsted experiments, the slow action of
farmyard manure in supplying fertilising ingredients to the potatoes is
strikingly demonstrated. Thus, although farmyard manure was applied at
such a rate that more than 200 lb. of nitrogen were added to the soil,
the result was inferior to that obtained from the application of 86 lb.
of nitrogen applied in the form of readily available artificial manure.
_Effect of Farmyard Manure on Potatoes._
It may be said, in this respect, that the potato is less able to utilise
the fertilising ingredients of farmyard manure than any other of the
farm crops. Yet, despite this fact, farmyard manure has been found to be
one of the best manures to apply. The reconciliation of these seemingly
contradictory statements depends on the influence exerted by the
farmyard manure on the mechanical condition of the soil, rendering it
more porous and easily permeable to the surface-roots, upon the
development of which the success of the crop so much depends. The
beneficial effect of farmyard manure is also doubtless due to the
increased temperature which large applications of it produce in a soil.
Sir J. Henry Gilbert, in his well-known Cirencester Lecture on the
Growth of Potatoes, cites several examples of the manurial treatment of
potatoes in different parts of the country. In Forfarshire, farmyard
manure or stable manure is largely employed (at the rate of 12 to 14
tons, and in some cases even 20 tons per acre), and it is also largely
supplemented by artificial manures. These latter are applied to the
extent of about 10 cwt., and consist of superphosphate, dissolved bones,
and potash salts. Six tons of potatoes are considered a fair crop. In
East Lothian the manuring is similar, with the exception that farmyard
manure is applied in even larger quantities--30 to 40 tons being often
used. Sometimes potatoes are grown with artificial manures alone. It
would seem that the usual crop of potatoes ranges from 4 to 8 tons per
acre.
_Manuring of Potatoes in Jersey._
The manuring of the potato crop, so largely grown in Jersey in the
Channel Islands, is of interest. Potatoes are there grown two or three
years, then corn, then grass for a few years, then potatoes again, no
special rotation of crops being followed. Either farmyard manure or
sea-weed is applied at the rate of 25 to 30 tons per acre, supplemented
by 8 to 12 cwt. of artificial manures.
These statements show how prevalent the practice of heavily manuring the
potato crop is.
_The Influence of Manure on the Composition of the Potato._
The influence of manure on the composition of the potato crop is of much
interest. Potatoes grown without manure, just as in the case of roots,
are found to have a larger percentage of nitrogen than potatoes grown
with manure. The effect of manuring, therefore, is to increase the
proportion of starch, which is the most important constituent of the
potato. Mineral manures have a greater effect in increasing the
percentage of starch than purely nitrogenous manures; but when used
together, a still greater increase is obtained than when used singly.
The effect of nitrogenous manures on the composition of roots and
potatoes is thus seen to be similar. In the case of both crops the
effect is to increase the proportion of the characteristic carbohydrate
constituent, which in roots is sugar, and in potatoes starch. Potatoes,
like roots, are also much influenced by the season. The effect of season
and manuring on the potato disease is worthy of notice. Wet seasons are
favourable to the development of the disease. It has been found that in
a highly nitrogenous manured crop the proportion of diseased tubers is
greater than in a non-manured crop.
LEGUMINOUS CROPS.
We have already referred to the manuring of crops of the leguminous
class in discussing the manuring of meadows and permanent pasture. It
was there pointed out that the tendency of certain manures was to
encourage the growth of the leguminous plants of the herbage, while
other manures had the effect of encouraging those of the gramineous
class. It was pointed out that a manure which had this effect was
potash, or any manure which owed its characteristic action to the fact
that it supplied potash to the soil or set it free in the soil.
_Leguminous Plants benefit by Potash._
This is one of the most important points to notice in manuring
leguminous plants. Just as we can say that nitrogenous manures are
specially beneficial to cereals, and phosphatic manures to roots, so
potash is the special manure for leguminous crops.
_Nitrogenous Manures may actually be hurtful._
But we have, further, an even more striking characteristic of leguminous
crops to notice. We have seen that, with regard to the crops already
discussed, while there are cases in which a fertilising ingredient may
be of no value, or may positively exert a hurtful action on the crops,
such cases are only exceptional. With regard to leguminous crops,
however, we find that almost invariably they derive little or no benefit
from the use of artificial nitrogenous manures. And this is all the more
striking since they contain large quantities of nitrogen in their
composition--twice as much as the cereals. The fact, which has long been
noticed with regard to certain members of this class of plants, such as
clover, that not only do they contain a large amount of nitrogen, but
that by growing them on a soil the soil is largely enriched in this
valuable fertilising constituent, has long waited for a satisfactory
explanation, which at last has been forthcoming. The discovery that
leguminous crops can draw on the boundless store of nitrogen present in
the air has done much to clear up the mystery. There are, however, other
problems with regard to the growth of leguminous plants which still
await solution.
_Clover-sickness._
One of these is the fact that land on which a leguminous crop like
clover has been growing for a number of years becomes unfit to support
its growth any longer. Such a soil is termed "clover-sick"; and many
have been the theories put forward to explain the phenomenon, but none
of them can be regarded as satisfactory.
The knowledge that leguminous plants have the power of deriving their
nitrogen from the air, furnishes us with an economical means of
enriching our soils in nitrogen. By growing leguminous crops alternately
with cereals, for example, the air should be made to furnish the
necessary nitrogenous manure. As a matter of fact, modified forms of
such a practice have long been in use--indeed the ordinary rotations of
crops are, to a certain extent, adaptations of this practice.
_Alternate Wheat and Beans Rotation._
An interesting experiment carried out at Rothamsted may be here cited
which illustrates in a striking manner the truth of the above statement.
Wheat and the leguminous crop beans were grown alternately. It was
found that almost as much wheat (containing nearly as much nitrogen) was
yielded in eight crops of wheat so grown as was yielded by sixteen crops
of wheat grown consecutively in an adjoining field.
The most commonly cultivated leguminous crops are clover, beans, and
peas. Clover having been already discussed, we need only say a word or
two on the manuring of beans and peas.
BEANS.
Beans do best on strong land, and, unlike some of the crops considered,
do not require a particularly fine tilth. They are generally grown after
cereals, and as a rule are sown in spring. More rarely, however, they
are sown in autumn. Spring-sown beans take about seven months to come to
maturity. They are much affected, like other crops, but to a greater
extent, by the nature of the season--a wet season inducing an undue
development of straw.
_Manure for Beans._
In common practice the manure used for the bean crop is farmyard manure,
applied to the soil in autumn after the harvest of the wheat, barley, or
other cereal crop grown. So common is this practice, that the belief
commonly exists that farmyard manure is necessary for a successful bean
crop. But experiments conducted at the Highland Society's Experiment
Station at Pumpherston show that full crops of beans may be grown with
the aid of artificial manures on soils which have received no
application of farmyard manure for ten years.
_Relative Value of Manurial Ingredients._
In the Appendix[246] will be found a table giving the results of
manurial experiments with the nitrogenous, phosphatic, and potash
manures on beans, carried out by Dr A. P. Aitken at the Highland
Society's Experiment Station. From these experiments it will be seen
that the application of phosphates and nitrogenous manures, either alone
or together, exerted a comparatively small effect in increasing the
yield of beans compared with that obtained with potash, either alone or
combined with phosphates. As Dr Aitken says, "Without potash in the
manure, the other two ingredients are of very little use, unless,
indeed, the land be very rich in potash."
_Gypsum._
Gypsum has a good effect on the bean crop, both on account of the lime
it contains, and of its indirect action in setting free potash.
Superphosphate is a much better manure than insoluble phosphates, and
similarly, in the few cases where nitrogenous manures are beneficial,
the speediest acting are best. Hence nitrate of soda is to be preferred
to other nitrogenous manures. When it is applied, it should be applied
in small quantities. A slow-acting nitrogenous manure is positively
injurious; so also, according to Dr Aitken, is nitrate of soda, applied
as a top-dressing to the crop.
Of potash manures, the muriate seems to be more effective than the
sulphate.
_Effect of Manure on Composition of Crop._
Lastly, we may refer to the effect of manures on the composition of the
crop. This is, on the whole, very slight, especially when compared with
the effect manures exert on the composition of such crops as turnips or
potatoes. It is the quantity and not the quality of the crop which the
manure affects in the case of beans.
PEAS.
Peas are not grown to anything like the same extent as beans. As a rule,
when they are cultivated it is along with beans, when they are
necessarily manured in a similar manner. If grown alone, however, it may
be well to point out that peas do best, unlike beans, on light, friable,
chalky loam. When grown in clay they tend to develop an undue amount of
straw. The effect of season on the crop is similar to that exerted on
the bean crop. In conclusion, it may be pointed out that it is alleged
that the effect of farmyard manure on peas is to force the straw.
In concluding this chapter a word or two may be said on the manuring of
two other crops which are cultivated to a considerable extent in this
country--viz., hops and cabbages.
HOPS.
The requirements of the hop crop in the matter of manures are rather
singular. It has been pointed out that in the case of most crops
quick-acting manures are to be preferred to slow-acting manures. With
hops, however, the case is very different; for they require, and cannot
be successfully cultivated without, slow-acting manures. Hops are
especially benefited by bulky nitrogenous manures--such as shoddy,
horn-meal, hide-scraps, hoofs, rape-dust, &c.; and it is only when
quick-acting manures are applied along with such slow-acting manures
that they will exercise their full influence. It is best to manure hops
twice a-year,--in spring with farmyard manure, supplemented by a
slow-acting nitrogenous manure, such as shoddy; and again in summer with
a more quickly acting manure. The dressings applied to hops are enormous
relatively to those used on other farm crops.
CABBAGES.
Cabbages belong to that class of crops known as gross feeders, to which
any sort of manure, applied in almost any quantities, does not come
amiss. Cabbages grow best on good loams with a well-drained porous
subsoil, although they also do well on clay soils. The quantity of
fertilising ingredients, especially potash, which a large crop of
cabbage removes from the soil is very great. They consequently require
large quantities of manure, and are especially benefited by saline
manures--such as kainit and common salt--and liberal doses of nitrate of
soda, which may be regarded as the most effective of manures for all the
cabbage tribe. Farmyard manure may be applied with benefit in larger
quantities than it would be applied to any other crop.
FOOTNOTES:
[244] See his Lecture on the Growth of Barley.
[245] Small roots are found to contain a larger proportion of sugar than
large roots.
[246] See Note I., p. 530.
APPENDIX TO CHAPTER XXIII.
NOTE I. (p. 526).
EXPERIMENTS ON THE MANURING OF BEANS.
Experiments with beans carried out at the Highland and Agricultural
Society's Experiment Station at Pumpherston, showing the effect of
potash:--
No. of Bushels dressed
plots. Kind of manure. grain, per acre.
27. No manure 2-1/2
12. Phosphate (bone-ash) 5-1/6
18. Nitrate 6-1/4
21. Phosphate and nitrate 5-1/3
22. _Potash_ 26-1/2
17. _Potash_ and phosphate 42-1/3
10. _Potash_, phosphate, and nitrate 45-1/2
38. _Potash_, phosphate, nitrate, and gypsum 51