Book: Clovers and How to Grow Them

T >> Thomas Shaw >> Clovers and How to Grow Them




=Bacteria and Clovers.=--The fact has long been known, even as long ago
as the days of Pliny, and probably much before those days, that clover,
when grown in the rotation, had the power to bring fertility to the
soil. This fact was generally recognized in modern agriculture and to
the extent, in some instances, of giving it a place even in the short
rotations. But until recent decades, it was only partially known how
clover accomplished such fertilization. It was thought it thus gathered
fertility by feeding deeply in the subsoil, and through the plant food
thus gathered, the root system of the plants were so strengthened in the
cultivated surface section of soil as to account for the increased
production in the plants that followed clover. According to this view,
the stems and leaves of the plants were thus equally benefited and,
consequently, when these were plowed under where they had grown these
also added plant food to the cultivated portion of the soil, in addition
to what it possessed when the clover seed which produced the plants was
sown upon it. In brief, this theory claimed that fertility was added by
the clover plants gathering fertility in the subsoil and depositing it
so near the surface that it became easily accessible to the roots of
other plants sown after the clover and which had not the same power of
feeding so deeply. This theory was true in part. The three important
elements of plant food, nitrogen, phosphoric acid and potash, were and
are thus increased in the soil, but this does not account for the source
from which the greater portion of the nitrogen thus deposited in the
soil was drawn, as will be shown below.

It was also noticed that when the seed of any variety of clover was sown
on certain soils, the plants would grow with more or less vigor for a
time and then they would fail to make progress, and in some instances
would perish. It was further noticed that if farmyard manure was applied
freely to such land, the growth made was more vigorous. Yet, again, it
was noticed that by sowing clover at short intervals on such soils, the
improvement in the growth of the plants was constant. But it was not
understood why clover plants behaved thus under the conditions named. It
is now known that ill success at the first was owing to the lack of
certain micro-organisms, more commonly termed bacteria, in the soil,
the presence of which are essential to enable clover plants to secure
additional nitrogen to that found in the soil and subsoil on which to
feed. When manure was applied, as stated above, the clover plants
secured much or all of their nitrogen from the manure. Bacteria were
introduced in very limited numbers at first, it may be through the
medium of the seed or in some other way, and because of an inherent
power which they possess to increase rapidly in connection with
continued sowing of clover at short intervals, they came at length to be
so numerous in the soil as to make possible the growth of good crops of
clover where these could not be thus grown a few years previously.

Careful observers had noticed that certain warty-like substances were
found attached to the roots of clover plants, and that the more
vigorously the plants grew, the larger and more numerous were these
substances, as a rule. It was thought by many that these warty
substances, now spoken of as nodules, were caused by worms biting the
roots or because of some unfavorable climatic influence or abnormal
condition of soil. It is now known that they are owing to the presence
of bacteria, whose special function is the assimilation of free nitrogen
obtained in the air found in the interstices; that is, the air spaces
between the particles of soil. This they store up in the nodules for the
use of the clover plants and also the crops that shall follow them.

The nodules in clover plants vary in size, from a pin head to that of a
pea, and they are frequently present in large numbers. Bacteria are
present within them in countless myriads. They gain an entrance into
the plant through the root hairs. The exact way in which benefit thus
comes to the clover plants is not fully understood, but it is now quite
generally conceded that the nitrogen taken in by these minute forms of
life is converted into soluble compounds, which are stored in the
tissues of the roots, stems and leaves of the plants, thus furnishing an
explanation to the increased vigor. It cannot be definitely ascertained
at present, if, indeed, ever, what proportion of the nitrogen in clover
is taken from the air and from the soil, respectively, since it will
vary with conditions, but when these are normal, it is almost certain
that by far the larger proportion comes from the air. But it has been
noticed that when soil is freely supplied with nitrogen, as in liberal
applications of farmyard manure, the plants do not form nodules so
freely as when nitrogen is less plentiful in the soil. The inference
would, therefore, seem to be correct, that when plants are well supplied
with nitrogen in the soil they are less diligent, so to speak, in
gathering it from the air. In other words, clover plants will take more
nitrogen from the air when the soil is more or less nitrogen hungry than
when nitrogen abounds in the soil. And yet the plants should be able to
get some nitrogen from the soil in addition to what the seed furnishes
to give them a vigorous start.

This power to form tubercles, and thus to store up nitrogen, is by no
means confined to clovers. It is possessed by all legumes, as peas,
beans and vetches. It is claimed that some of these, as soy beans, cow
peas and velvet beans, have even greater power to gather nitrogen from
the air and store it in the soil than clover, since the nodules formed
on the roots of these are frequently larger. In some instances, on the
roots of the velvet bean they grow in clusters as large as an ordinary
potato. With reference to all these leguminous plants it has been
demonstrated that under proper conditions good crops may be grown and
removed from the soil and leave it much richer in nitrogen than when the
seed was sown. It is thus possible by sowing these crops at suitable
intervals to keep the soil sufficiently supplied with nitrogen to grow
good crops other than legumes, adapted to the locality, without the
necessity for purchasing the nitrogen of commerce in any of its forms.
They may be made to more than maintain the supply of nitrogen,
notwithstanding the constant loss of the same by leeching down into the
subsoil in the form of nitrates, and through the more or less constant
escape of the same into the air in the form of ammonia, during those
portions of the year when the ground is not frozen.

They will do this in addition to the food supplies which they furnish,
hence they may be made to supply this most important element of
fertility, and by far the most costly when purchased in the market,
virtually without cost. The favorable influences which these plants thus
exert upon crop production is invaluable to the farmer. They make it
possible for him to be almost entirely independent of the nitrogen of
commerce, which, at the rate of consumption during recent years, will
soon be so far reduced as to be a comparatively insignificant factor in
its relation to crop production. It is possible, however, and not
altogether improbable, that by the aid of electricity a manufactured
nitrate of soda or of potash may be put upon the market at a price which
will put it within reach of the farmer. The power of legumes to increase
the nitrogen content in the soil should allay apprehension with
reference to the possible exhaustion of the world's supply of nitrogen,
notwithstanding the enormous waste of the same in various ways.

The more common sources of loss in nitrogen are, first, through the
leeching of nitrates into the drainage water; second, through oxidation;
third, through the use of explosives in war; and fourth, through the
waste of the sewerage of cities. When plant and animal products are
changed into soluble nitrates, they are usually soon lost to the soil,
unless taken up by the roots of plants. When vegetable matter on or near
the surface of the ground is broken down and decomposed, in the process
of oxidation, there is frequently much loss of nitrogen, as in the rapid
decomposition of farmyard manure in the absence of some material, as
land plaster, to arrest and hold the escaping ammonia. Through
explosives used in war there is an enormous vegetable loss of nitrogen,
as nitrate salts, which should rather be used to preserve and sustain
life than to destroy it. The waste of nitrogen through the loss of
sewerage is enormous, nor does there seem to be any practicable way of
saving the bulk of it.

In many soils the germs which produce nodules are present when clovers
are first grown on them. But where they are not present, the clover
plants have no more power to gather nitrogen than wheat or other
non-leguminous crops. But since in other soils they are almost entirely
absent, how shall they be introduced? The process of introducing them is
generally referred to as a process of inoculation, and soils when
treated successfully are said to be inoculated.

Three methods have been adopted. By the first, as previously indicated,
the grower perseveres in sowing clover at short intervals in the
rotation. He may also add farmyard manure occasionally, and thus,
through the inherent power of multiplication in the bacteria, they
increase sufficiently to enable the land to grow good crops. By the
second method, inoculating is effected through soil which is possessed
of the requisite bacteria; and by the third, it is effected through the
aid of a prepared product named nitragin.

When fields are to be inoculated by using soil it is obtained from areas
which have grown clovers successfully quite recently, and which are,
therefore, likely to be well filled with the desired bacteria. In some
instances the seed is mixed with the soil and these are sown together.
To thus mix the seed with the soil and then sow both together broadcast
or with a seed drill is usually effective, and it is practicable when
minimum quantities of soil well laden with germs are used. In other
instances the soil containing germs is scattered broadcast before or
soon after the seed is sown. Considerable quantities of earth must needs
be applied by this method.

It should be remembered that each class of legumes has its own proper
bacteria. Because of this, inoculation can only, or at least chiefly, be
effected through the use of soils on which that particular class of
legumes have grown, or which are possessed of bacteria proper to that
particular species. In other words, bacteria necessary to the growth of
vetches will not answer for the growth of clovers, and _vice versa_. Nor
will the bacteria requisite to grow medium red clover answer for growing
alfalfa. In other words, the bacteria proper to the growth of one member
of even a family of plants will not always answer for the growth of
another member of the same. But in some instances it is thought that it
will answer. The study of this phase of the question has not yet
progressed far enough to reflect as much light upon it as could be
desired. It is certainly known, however, that alfalfa will grow on soils
that grow burr clover (_Medicago maculata_) and sweet clover (_Melilotus
alba_), hence the inference that soil from fields of either will
inoculate for alfalfa.

Nitragin is the name given by certain German investigators to a
commercial product put upon the market, which claims to be a pure
culture of the root tubercle organism. These cultures were sold in the
liquid form, and it was customary when using them to treat the seed with
them before it was planted. Their use has been largely abandoned,
because of the few successes which followed their use compared with the
many failures. But it is now believed that these cultures can be
prepared and used so as to be generally effective and without excessive
cost to the grower.

In preparing cultures it has been found that by gradually reducing the
amount of nitrogen in the culture of media, it is possible to increase
the nitrogen fixing power in these germs from five to ten times as much
as usually occurs in nature. It is now known that the bacteria thus
grown upon nitrogen free media retain high activity if carefully dried
and then revived in liquid media at the end of the varying lengths of
time. Some absorbent is used to soak up the tubercle-forming organisms.
The cultures are then allowed to dry, and when in that condition they
can be safely sent to any part of the country without losing their
efficacy. It is necessary to revive the dry germs by immersing them in
water. By adding certain nutrient salts the bacteria are greatly
increased if allowed to stand for a limited time--as short, in some
instances, as 24 hours. The culture thus sent out in a dry form, and no
larger than a yeast cake, may thus be made to furnish bacteria
sufficient to inoculate not less than an acre of land. It is stated that
the amount of inoculating material thus obtained is only limited by the
quantity of the nutrient water solution used in increasing the germs, so
that the cost of inoculating land by this process is not large. The
culture may be applied by simply soaking the seed in it, by spraying the
soil, or by first mixing the culture into earth, spreading it over the
field and then harrowing it. Inoculations thus tried under the
supervision of the United States Department of Agriculture have proved
quite successful.

Where any legume is extensively grown surrounding soils come to be
inoculated through the agency of winds and water. The increase brought
to the yield of plants on various soils runs all the way from a slight
gain to 1000-fold. And when soil is once inoculated it remains so for a
long time, even though the proper legume should not be grown again on
the same soil.

The amount of nitrogen that may thus be brought to many soils by growing
clover and other legumes upon them is only hedged in practically by the
nature of the rotation fixed upon. An acre of clover when matured will
sometimes add 200 to 300 pounds of nitrogen to the soil under favorable
conditions. Where the soil contains the requisite bacteria, the young
plants begin to form tubercles when but a few weeks old, and continue to
do so while the plant is active until mature. That the plants use much
of the nitrogen while growing would seem to be clear, from the fact that
toward the close of the growing season the tubercles become more or less
broken down and shrunken.




CHAPTER III

MEDIUM RED CLOVER


Medium Red Clover (_Trifolium pratense_) is also known by the names
Common Red Clover, Broad-Leaved Clover and Meadow Trefoil. The term
medium has doubtless come to be applied to it because the plants are in
size intermediate between the Mammoth variety (_Trifolium magnum_) and
the smaller varieties, as the Alsike (_Trifolium hybridum_) and the
small white (_Trifolium repens_). But by no designation is it so
frequently referred to as that of Red Clover.

This plant is spreading and upright in its habit of growth. Several
branches rise up from the crown of each plant, and these in turn
frequently become branched more or less in their upward growth. The
heads which produce the flowers are nearly globular in shape, inclining
to ovate, and average about one inch in diameter. Each plant contains
several heads, and frequently a large number when the growth is not too
crowded. When in full flower these are of a beautiful purple crimson,
hence, a field of luxuriant red clover is beautiful to look upon. The
stems of the plants are slightly hairy, and ordinarily they stand at
least fairly erect and reach the height of about one foot or more; but
when the growth is rank, they will grow much higher, even as high as 4
feet in some instances, but when they grow much higher than the average
given, the crop usually lodges. The leaves are numerous, and many of
them have very frequently, if not, indeed, always, a whitish mark in the
center, resembling a horseshoe. The tap roots go down deeply into the
soil. Usually they penetrate the same to about 2 feet, but in some
instances, as when subsoils are open and well stored with accessible
food, they go down to the depth of 5 or 6 feet. The tap roots are
numerously branched, and the branches extend in all directions. When
they are short, as they must needs be in very stiff subsoils and on thin
land underlaid with hard soil, the branches become about as large as the
tap roots. It has been computed that the weight of the roots in the soil
is about equal to the weight of the stem and leaves.

Medium red clover is ordinarily biennial in its habit of growth, but
under some conditions it is perennial. Usually in much of the
Mississippi basin it is biennial, especially on prairie soils. On the
clay loam soils of Ontario, Ohio, Michigan, Wisconsin, Indiana and some
other States, it is essentially biennial, but many of the plants will
survive for a longer period. In the mountain valleys in the Northwestern
States, and on the Pacific slope west of the Cascade Mountains, it is
perennial. Medium red clover meadows in these have been cut for several
successive years without re-seeding the crop. The duration of this plant
is also more or less influenced by pasturing as compared with cutting
for seed. Grazing the plants has the effect of prolonging the period of
their growth, while maturing seed from them has the opposite effect.

Medium red clover is characterized by a rapid growth. Seed sown in the
spring has in certain climates produced a crop of hay in 120 days from
the date of sowing. It is also most persistent in its growth from spring
until fall when sufficient moisture is present. In this property it far
outranks any of the other varieties of clover. It comes into bloom in
the South during the latter half of May and in the North during the
month of June, early or later, according to location, and in about sixty
days from the time that it is cut for hay. Ordinarily, a second cutting
of hay may be taken from it and still later some pasture.

It furnishes excellent pasture, soiling food and hay for nearly all
classes of live stock. While it is much relished by the stock, it is
probably not exceeded in its capacity for quick and prolonged growth
throughout the growing season by any pasture plant, except alfalfa. For
a similar reason it stands high as a soiling food. No other variety of
clover grown in America will furnish as much of either pasture or
soiling food. For animals producing milk and for young animals, the
pasture is particularly excellent. It is also the standard pasture for
swine where it can be grown, and where alfalfa is not a staple crop.
When the hay is well cured, it makes a ration in even balance for cattle
and sheep, and for horses it is equally good. The prejudice which exists
in some quarters against feeding it to horses has arisen, in part, at
least, from feeding it when improperly harvested, when over-ripe, when
damaged by rain, or by overcuring in the sun, or when it may have been
stored so green as to induce molding. It may also be fed with much
advantage to brood sows and other swine in winter.

As a soil improver, medium red clover is probably without a rival,
unless it be in mammoth clover, and in one respect it exceeds the
mammoth variety; that is, in the more prolonged season, during which it
may be plowed under as a green manure. Its quick growth peculiarly
adapts it to soil enrichment. For this reason, it is more sown than any
of the other varieties in the spring of the year, along with the small
cereal grains to be plowed under in the late autumn or in the following
spring, after the clover has made a vigorous start, since it produces
two crops in one season, the first crop may be harvested and the second
plowed under after having made a full growth. This can be said of no
other variety of clover. More enrichment is also obtained from the
falling of the leaves when two crops are grown than from the other
varieties.

The influence of this plant on weed destruction when grown for hay is
greater than with the other varieties of clover. This is owing in part
to the shade resulting from its rapid growth and in part to the two
cuttings which are usually made of the crop. These two cuttings prevent
the maturing of the seeds in nearly all annual weeds, and to a very
great extent in all classes of biennials. The power of this crop to
smother out perennials is also considerable, and when this is linked
with the weakening caused by the two cuttings, it sometimes proves
effective in completely eradicating for the time being this class of
weeds.

[Illustration: Fig. 2. Medium Red Clover (_Trifolium pratense_)
Oregon Experiment Station]

=Distribution.=--Medium red clover is thought to be native to Europe. It
was probably introduced into England some time early in the seventeenth
century. That it was attracting attention about the middle of the
century or a little later, is rendered probable by the fact that it is
discussed at considerable length in the third edition of Blyth's
"Improver Improved," published in 1662, while it is not mentioned in the
first edition, published in 1650. It was doubtless introduced into the
United States by the early colonists and at sundry times.

Medium red clover will grow in good form only in the temperate zone,
since it cannot stand excessive heat or excessive cold. The northerly
limit of its successful growth in North America is somewhere about 50 deg.
north latitude on the wind-swept prairies, but on suitable soils, and
protected somewhat by trees and winter snows, it will probably grow 10
degrees further to the north. In British Columbia, on the Pacific slope,
it will probably grow as far north as Alaska. But on prairies eastward
from the Rocky Mountains, it has not been grown with much success much
further north than 48 deg., unless under the eastern shadow of the Rocky
Mountains. Low temperatures in winter, where there is only a moderate
covering of snow, are far less fatal to clover plants than exposure to
the sweep of the cold winds. Even where the thermometer is not so low as
in the areas just referred to, such winds are particularly damaging to
the plants when they blow fiercely just after a thaw which has removed a
previous covering of snow. In some instances, one cold wave under the
conditions named has proved fatal to promising crops of clover over
extended areas.

In a general way, the southerly limit of vigorous and reliable growth
may be put at about 37 deg.. But in some localities good crops may be grown
further South, especially in some parts of Tennessee. Nor would it be
correct to say that medium red clover grows at its best in many
localities much south of 38 deg.. On the plateaus it can be grown further
South, where the soil is suitable.

This plant flourishes best in a moist climate. In fact, the abundance
and continuance of the growth for the season are largely dependent on
the amount of the precipitation, and on the distribution of the same
throughout the season. In climates in which it is usual for a long spell
of dry weather to occur in mid-summer, the plants will not make rapid
growth after the first cutting of the season; but under conditions the
opposite, they will grow continuously from spring until fall. Continuous
growth may be secured through all the season on irrigated land. Although
the plants root deeply, they will succumb under drought beyond a certain
degree, and in some soils the end comes much more quickly than on
others; on porous and sandy soils, it comes much sooner than on clays.
On the latter, drought must be excessive to destroy clover plants that
have been well rooted. White clover can withstand much heat when
supplied with moisture. Moderate temperatures are much more favorable to
its growth.

Spring weather, characterized by prolonged periods of alternate freezing
and thawing, is disastrous to the plants on dry soils, possessed of an
excess of moisture, when not covered with snow. They are gradually drawn
up out of the soil and left to die on the surface. In some instances,
the destruction of an otherwise fine stand is complete. In other
instances, it is partial, and when it is, a heavy roller run over the
land is helpful in firming the soil around the roots that have been thus
disturbed.

Medium red clover can be grown with some success in certain parts of
almost every State in the Union. But in paying crops it is not much
grown south of parallel 37 deg.. With irrigation it grows most vigorously in
the mountain valleys between the Rocky and Cascade mountains, and
between about 37 deg. and 50 deg. north latitude. In these valleys its habit of
growth is perennial. Without irrigation, the highest adaptation, all
things considered, is found in Washington and Oregon, west of the
Cascades, except where shallow soils lying on gravels exist. East of the
mountains, the best crops are in the States of Michigan, Ohio, Indiana,
Kentucky, Illinois, Missouri, Iowa, Wisconsin and Minnesota. The soils
of Northern Minnesota, Wisconsin and Michigan, that have produced
hardwood timber, have unusually high adaptation to the growth of this
plant, and as the snow usually covers the ground in these areas in
winter, the crop may be relied upon with much certainty. But on the
sandy soils, which more or less abound in these areas, it does not
succeed so well. It has not yet proved a marked success in Western
Minnesota or in the Dakotas, owing in part probably to the lack of the
proper bacteria in the soil. Its growth in these localities, however, is
extending from year to year. Indiana and Ohio are great clover States,
and the same is true of much of Illinois and Iowa; but southward in
these States there is some hazard to the young plants from drought and
heat in summer, and to an occasional frost in winter when the ground is
bare.

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