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                    SWEET CLOVER: GROWING THE CROP


                               H. S. COE

            Assistant, Office of Forage Crop Investigations

                            [Illustration]

                         FARMERS' BULLETIN 797

                UNITED STATES DEPARTMENT OF AGRICULTURE


            Contribution from the Bureau of Plant Industry

                         WM. A. TAYLOR, chief


                           Washington, D. C.

                              April, 1917


THE cultivation of sweet clover should be preceded by a through
knowledge of the requirements for obtaining a stand.

The white species comprises a very large percentage of the present
acreage of sweet clover.

Annual yellow sweet clover should be sown in no portion of the United
States except the South and Southwest, and then only as a cover of
green-manure crop.

Sweet clover is being cultivated in practically every State in the
Union. At the present time the largest acreage is found in The western
North-Central States and in the Mountain States.

Sweet clover is adapted to a wider range of climatic conditions than
any of the true clovers, and possibly alfalfa.

Sweet clover will grow on practically all soil types to be found in
this country, provided the soil is not acid and is well inoculated.

Sweet clover is more drought resistant than alfalfa or red clover. It
is quite resistant to alkali.

The lime requirement of sweet clover is as high as that of red clover
or alfalfa. Maximum growth is obtained only on soils that are not acid.

Sweet clover usually will respond to applications of fertilizers and
manure.

In the move humid sections of the country good stands usually are
obtained by seeding with a nurse crop.

Only seed which germinates 75 per cent or more should be sown in the
spring of the year unless the rate of seeding is increased to make up
for poor germination.

Sweet clover does best when seeded on a well-firmed seed bed which has
only sufficient loose soil on the surface to cover the seed.

It is very essential that inoculation be provided in some form if
success is to be expected.

The large number of failures in obtaining a stand of sweet clover
are due primarily to acid soils, lack of inoculation, and seed which
germinates poorly.

Spring seedings in general are satisfactory, but in the South excellent
stands are obtained from midwinter seedings also Fall seedings are
usually successful south of the latitude of southern Ohio.

A Farmers' Bulletin (No. 820) on the utilization of sweet clover for
pasture, hay, and as a green-manure is about to be issued.




SWEET CLOVER: GROWING THE CROP.



CONTENTS.



                                      Page.

  Introduction                           3

  Species of sweet clover                4
    White sweet clover                   5
    Biennial yellow sweet clover         8
    Annual yellow sweet clover           9
    Other species of sweet clover        9

  History                               10

  Distribution                          10

  Climatic adaptations                  12

  Requirements for obtaining a stand    12
    Soils suitable for sweet clover     13
    Resistance to alkali                13
    Need of lime on acid soils          14
    Fertilizers                         17
    Use of a nurse crop                 18
    Choice of seed                      19
    Preparation of the seed bed         21

  Seeding                               22
    Hulled sweet-clover seed            23
    Unhulled sweet-clover seed          24
    Rate of seeding                     25
    Methods of seeding                  25

  Inoculation                           27
    The soil-transfer method            28
    The pure-culture method             29

  Treatment of the stand                30
    Treatment the first season          30
    Treatment the second season         32

  Sweet clover in mixtures              32

  Eradication of sweet clover           33




INTRODUCTION.


Sweet clover is an important forage crop in many regions. Although
one of the oldest of known plants, not until very recently has it
been considered seriously as a forage plant in this country. The
principal causes for not utilizing this crop were its aggressiveness
on uncultivated land in many localities, the tendency of the stems to
become woody as they mature, and the refusal of stock to eat sweet
clover before they had become accustomed to the bitter taste. Another
reason was the fact that until recently red clover could be grown in
the eastern half of the United States without difficulty. In northern
Kentucky the continuous growing of tobacco or of tobacco and wheat
impoverished the soil to such an extent that crops no longer could be
grown successfully. Upon the abandoned farms in this section sweet
clover was introduced as a honey plant. Owing to the remarkable yields
of tobacco that were obtained on such farms after sweet clover had been
grown for a few years the acreage of this plant increased very rapidly.
For a number of years sweet clover has been grown on the Selma chalk
(rotten-limestone) soils of Alabama and Mississippi as a soil-improving
crop. At the present time it is being cultivated in practically every
State, and the acreage is increasing very rapidly.

After it had been demonstrated that sweet clover would grow
successfully on soils too depleted for other crops, many experiments
were conducted to determine its value as forage. It was found that
it was not only a valuable soil-improving crop, but that it made an
excellent pasture and hay plant, quite palatable and rich in protein.

White sweet clover comprises a very large percentage of the acreage
seeded to sweet clover at the present time. On this account this
species ordinarily is referred to simply as "sweat clover." The yellow
biennial species is designated as yellow sweet clover, and the annual
yellow species as bitter clover, sour clover, or annual yellow sweet
clover. This usage has been adopted in this bulletin.

[Illustration: Fig. 1.--Seeds and seed pods of three species of
Melilotus and seeds of alfalfa: 1. White sweet clover; 2, biennial
yellow sweet clover; 3, annual yellow sweet clover, or sour clover; 4,
alfalfa. The small figures in each drawing show the natural size of the
seed. The venation and shape of the seed pods are important characters
in distinguishing the different species of sweet clover.]

The cultivation of sweet clover should be preceded by a thorough
understanding of the requirements for obtaining a stand. It can not be
grown successfully on all soils, as many assume from seeing it growing
in uncultivated places. Neither will it thrive in many sections of the
country without careful preparation of the seed bed. Sweet clover will
not grow successfully in acid soils unless lime is applied, but it
will make a good growth in soils too low in humus to grow red clover,
provided the soil is neutral or alkaline.

Sweet clover is an excellent plant to precede alfalfa, as the large
roots do much toward breaking up and aerating the subsoil. Contrary to
the belief of many, it will not inoculate the soil for alfalfa unless
inoculation is applied to the sweet clover. If, however, the soil
contains but few inoculating germs, the sweet clover will serve as a
medium to inoculate it thoroughly.




SPECIES OF SWEET CLOVER.


A number of species of sweet clover are found throughout the world, and
most of them are native to temperate Europe and Asia as far east as
Tibet.

White sweet clover,[1] yellow biennial sweet clover,[2] and yellow
annual sweet clover[3] are the only species which have given sufficient
promise as forage and green-manure crops in this country to warrant
growing them under cultivation.

[1] _Melilotus alba_ Dear.

[2] _Melilotus officinalis_ (L.) Lam.

[3] _Melilotus indica_ (L.) All.

It is difficult for the average person to distinguish between the
different species of sweet clover from an examination of the seeds
or seed pods only. The differences are indicated in figure 1. Where
there is a question as to the identity of a sample of seed it should
be sent to a State agricultural experiment station or to one of the
seed laboratories of the United States Department of Agriculture for
identification.


WHITE SWEET CLOVER.

White sweet clover (fig. 2) is ordinarily referred to as melilotus
or meliot in the South and merely as sweet clover in other portions
of the country. When soil conditions are favorable for germination,
sweet-clover seedlings will appear from one to two weeks after seeding.
On account of the biennial nature of the plants, they do not seem
to make much growth above ground the first month or six weeks after
germination, but during this time they are developing root systems
rapidly and thus becoming established, so to be able to withstand
adverse conditions. Plants which have made no more than 2 inches of top
growth very often have produced roots 6 inches or more in length (fig.
3). The tap-root continues to develop rapidly throughout the growing
season the first year, and by autumn often reaches a length of 24 to 36
inches and a diameter of three-fourths to 1 inch at the crown.

[Illustration: Fig. 2.--A branch of white sweet clover, showing the
long, loose racemes which bear white flowers.]

After the root system becomes established the plants produce an
upright, branching, leafy growth, which under ideal growing conditions
may reach a height of 48 inches the first season, but more often 18 to
30 inches. A large quantity of reserve food is stored in the tap-root
the first season; this reserve food enables the plants to make a rapid
and vigorous growth early the following spring.

[Illustration: Fig. 3.--White sweet-clover plants collected from a plat
six weeks from the date of seeding. An extensive root system such as is
shown here is often developed before much growth is made above ground.]

Toward the end of the growing season of the first year a number of
buds, which serve to produce the second year's growth (fig. 4), are
formed on the crowns of the plants. After these buds are formed the
plants may be clipped quite close to the ground, as the buds are not
developed until the plants have made sufficient growth to live through
the winter.

During the second season sweet clover makes a rapid, erect, stemmy,
branching growth from 5 to 10 feet in height, the plants producing
only a moderate number of leaves, which drop as the seed matures. A
large number of loose racemes bearing white flowers (see fig. 2) are
produced during the flowering period, which usually lasts from three to
five weeks.

Before sweet clover has made a growth of 12 to 18 inches it closely
resembles alfalfa. The plants may be distinguished from alfalfa by the
absence of pubescence on the under side of the leaves and by their
bitter taste. When they are in bloom they may be identified easily
by their long, loose racemes of white flowers and their open, coarse
growth. Unlike alfalfa, the seeds are ordinarily found singly in the
pods. Two seeds may occasionally be found, and very rarely three, in a
single pod.

STRAINS OF WHITE SWEET CLOVER.

A number of different strains of white sweet clover are to be found in
the average field, but most of them are not as marked or as conspicuous
as the different strains of red clover. The principal differences
between strains of sweet clover are in leafiness, habit of growth, and
date of blooming.

[Illustration: Fig. 4.--Buds produced on the crown of a sweet-clover
plant at the end of the first season's growth. These buds will produce
the first crop the second season.]

Occasional plants are especially heavy seed producers and bear many
pods containing more than one seed. Other plants bloom earlier than
the average date for white sweet clover, and it may be possible by
selecting such strains to find one which matures early enough to
produce two crops a season at high altitudes in the northern sections
of the United States.

Fields of an exceptionally early blooming strain were found in
Illinois, Iowa, and North Dakota in the summer of 1916. The plants
were different in type of growth from the ordinary white sweet clover,
being most conspicuous from the fact that they were in bloom during
the first week of June, which is at least three weeks earlier than the
ordinary species should bloom in these localities.

[Illustration: Fig. 5.--Root of white sweet clover (on the left)
and of biennial yellow sweet clover (on the right). These roots were
collected on October 28, 1915, at Arlington, Va., from adjacent plats
seeded to cuts and sweet clover on April 10, 1915. Note the difference
in the size of the roots. Tubercles are present on the right-hand side
of each root.]

An annual white-flowered sweet clover was found in several localities
in the fall of 1916. The seed which produced these plants was grown
in Alabama. These plants resembled _Melilotus alba_ in most respects
except that they were strictly annual. They flowered and matured
seed abundantly in South Dakota and North Dakota. It has not been
determined whether this is a distinct species or merely an annual
strain of the species mentioned.


BIENNIAL YELLOW SWEET CLOVER.

Biennial yellow sweet clover ordinarily is referred to in the seed
trade and among farmers in regions where it is grown simply as yellow
sweet clover. The plants of this species are somewhat more decumbent
the first year, and ordinarily with more deeply notched leaves than the
white-flowering species. Yellow sweet clover usually grows from 3 to 5
feet in height. This plant blooms from 10 to 14 days earlier than the
white species, and for this reason it is advisable to sow seed of both
plants when they are to be used for bee pasturage. On account of the
finer stems of yellow sweet clover it is preferred in some localities
for hay, but since it does not produce as much forage as white sweet
clover and there is much less demand for the seed, it constitutes only
a very small percentage of the total acreage. The much larger root
growth of the white species, as illustrated in figure 5, is desirable
because of the additional quantity of hummus added to the soil.

The seeds of the yellow species may usually be distinguished from those
of other species, as some of them are slightly mottled with purple. The
shape of the calyx, which is generally present on unhulled seed, and
the venation of the seed pods also distinguish it. (See fig, 1.)


ANNUAL YELLOW SWEET CLOVER.

Annual yellow sweet clover, more commonly known as sour clover or
bitter clover, is found chiefly in the South and Southwest. This plant
is considered a noxious weed in grain fields throughout the Southwest.
It is claimed that the flavor of the seed which is imparted to wheat
can not be removed. Bakers decidedly object to this flavor, stating
that it injures bread. Sour clover is grown rather extensively as a
green-manure crop in orchards in portions of Arizona and southern
California and when properly handled in these regions it has given
profitable results. As the seed is obtained from the screenings of
wheat, it is offered on the market at a very low price. Occasionally it
is sold for the yellow biennial sweet clover. Seed of this plant should
not be sown in any part of the United States except the extreme South
or Southwest, and then only as a green hay manure crop. Where it is
desired to plant sweet clover for pasturage or for the biennial white
or biennial yellow species should be used.


OTHER SPECIES OF SWEET CLOVER.

Thirteen species of sweet clover have been tested by the Office of
Forage-Crop Investigations to determine their economic value. With
the exception of white sweet clover, yellow biennial sweet clover, and
yellow annual sweet clover, but four species in the somewhat limited
tests have given sufficiently good results to merit special attention,
and none have so far proved superior to white sweet clover, which is
now extensively grown in many States.

A species of Trigonella[4] is often referred to as blue-flowered
melilotus or blue-flowered sweet clover. While this plant is closely
related to the plants belonging to the genus Melilotus, it does not
belong to this genus and therefore should not be called sweet clover.
It is an erect, quite leafy, very fragrant annual, which produces a
fair growth. It may prove of value as a green-manure crop or as a catch
crop under certain conditions, but at the present time it is not to be
recommended where sweet clover can be grown successfully. In most tests
Trigonella has produced less forage than the better species of sweet
clover.

[4] _Trigonella caerulea_.




HISTORY.


Sweet clover has been used as a honey plant and for forage and
green-manure for more than 2,000 years in the Mediterranean region,
although it has never been considered of much importance.

The first authentic report of sweet clover in the United States was
in 1739, when Gronovius stated in his Flora Virginica that it was
collected by Clayton. Cutler reported its presence in New England
as early as 1785, and Pursh in 1814 stated in his Flora Americæ
Septentrionulis that it is found on the gravelly shores of rivers from
Pennsylvania to Virginia. Elliott reported the presence of yellow
biennial sweet clover in his Sketch of the Botany of South Carolina and
Georgia in 1824, and Beck found the species _Melilotus leucantha_[5] in
the Northern States in 1833.

[5] Undoubtedly meaning _Melilotus alba_.

In 1856 Prof. Tutwiller, of Green Springs Academy, Ala., received a
small quantity of white sweet-clover seed from the secretary to the
United States consul in Chile. Part of this seed was planted by a young
man named Stendwick on his father's plantation on the prairie limestone
belt, where it flourished. This plantation later became the property
of J. T. Collins who, realizing the value of this plant, sold seed to
persons in many States. Not until recently has sweet clover been grown
to any extent as a cultivated crop in this country.




DISTRIBUTION.


While sweet clover is to be found growing in many countries and on all
the continents of the world, it is native to temperate Europe and Asia
as far east as Tibet. It is grown to a limited extent in England,
while in the eastern part of Scotland a small quantity is considered
valuable in hay on account of its agreeable odor. The famous Cruyere
cheese of Switzerland owes its flavor to yellow sweet clover. In
Germany it has given very good results when used as a green-manure,
while in parts of Russian Poland and Austria-Hungary it is grown as
a green-manure, pasturage, and hay crop on poor soils. This plant is
used for forage and as a soil-improving crop in the central provinces
of India, while sour clover, commonly referred to as _Melilotus
parviflora_, is credited with furnishing 75 per cent of the feed for
the cattle of King Island, Tasmania, which produce the best beef and
butter sold on the Tasmania market.

[Illustration: Fig. 6.--Outline map of the United States, showing the
localities where sweet clover is grown for forage or for green-manure.
Each dot or circle indicates a county where 50 acres or more is grown
under cultivation. The solid dots represent white or yellow sweet
clover; the circles represent annual yellow sweet clover.]

At the present time sweet clover is grown rather extensively as a field
crop in the limestone regions of Alabama, Mississippi, and Kentucky,
in northern Illinois, and throughout the western North-Central and
Mountain States (fig. 6): in fact, it is grown as a cultivated crop to
some extent in nearly every State in the Union. Comparatively little
sweet-clover seed is sown in the Atlantic Coast States, since there
the soils are for the most part acid, and heavy applications of lime
will be necessary before sweet clover can be grown successfully. It
is questionable whether this plant will ever be of much importance in
the South Atlantic States, as cowpeas, soy beans, and crimson clover
will make a fair growth on those soils in their present condition.
The acreage of sweet clover probably will increase in the New
England States, where it should prove of value as pasturage and as a
soil-improving crop on soils where red clover no longer can be grown.
Sweet clover grows abundantly in the limestone regions of northwestern
New York.

A much larger acreage of sweet clover is grown in northern Illinois
than in any other of the eastern North-Central States. The conditions
in the western North-Central States and in the Mountain States appear
to be particularly adapted to this crop. It is in that part of the
country that the largest acreage is found, and, with the exception
of the limestone regions of the South, that the least difficulty is
experienced in obtaining a stand.

In those parts of the Mountain and Pacific Coast States, especially
Utah, where it has not been tested carefully or where red clover or
alfalfa can be grown successfully, sweet clover is looked upon as a
weed. It may rightly be considered a weed in the irrigated regions of
the West and Northwest, where it grows luxuriantly on ditch Banks.
The dissemination of this plant in all parts of the country has been
hastened by beekeepers who have seeded it in waste places for the
production of honey.




CLIMATIC ADAPTATIONS.


Sweet clover is adapted to a wider range of climatic conditions than
any of the true clovers and possibly alfalfa; in fact, it may be grown
successfully in any portion of the United States except, perhaps,
Florida, and in Florida trials with biennial yellow sweet clover,
annual sweet clover, and _Melilotus suaveolens_ have been successful.
Apparently neither the high temperatures of the South nor the cold
winters of the North severely affect the plants, provided there is
sufficient moisture in the soil. Comparatively little winterkilling
is experienced in Montana, Wyoming, Idaho, and North Dakota when the
seed is sown in close drills or broadcasted. Although approximately 50
per cent of the sweet clover seeded in rows 3 feet apart at Moccasin,
Mont., was killed by the unusually severe winter of 1915-16, no
winterkilling was noted in plats seeded in close drills.

Sweet clover thrives in the more humid parts of the country, as well
as in the semiarid regions where the rainfall is but three-fifths of
that required for the normal growth of such crops as red clover and
timothy. In the semiarid regions of the West sweet clover has proved to
be somewhat more drought resistant than alfalfa.




REQUIREMENTS FOR OBTAINING A STAND.


The requirements for obtaining a stand of sweet clover are somewhat
exacting. It is for this reason that so many failures have been
experienced. It must not be assumed, because sweet clover is found
growing luxuriantly in many waste places and on uncultivated land, that
a stand may be obtained by planting it at any time of the year, in any
manner, and under all conditions. Throughout the eastern and southern
portions of the country, with the exception of a few regions rich in
limestone, much care must be used in the preparation of the seed bed,
the selection of seed, and the manner of seeding if success is to be
expected. For this reason it is necessary to understand fully the
requirements for obtaining and maintaining a successful stand.


SOILS SUITABLE FOR SWEET CLOVER.

Sweet clover thrives on the adobe and granitic soils of the Pacific
coast; upon the gumbo, hardpan, prairie, and sandy soils of the western
North-Central States; and upon the heavy clay, loam, limestone,
and sandy soils of the South and East. In fact, it has been grown
successfully on all the principal soil types of the United States where
the soils were not acid and were well inoculated. It grows luxuriantly
on the Selma chalk (rotten-limestone) soils of Alabama and upon soils
rich in calcium carbonate in many parts of the country where the
lack of nitrogen and humus has caused large numbers of farms to be
abandoned. The plants thrive on newly exposed heavy clay soils and
upon steep embankments where little else will grow. Sweet clover is
more tolerant of poor drainage, overflow, and seepage conditions than
alfalfa. In irrigated sections, especially where the reservoir system
is in use, large bodies of land are likely to become useless for the
growth of alfalfa because of the rising of the water table. On such
areas sweet clover will make a vigorous growth. However, maximum growth
is to be expected only on well-drained soil.

Sweet clover will do well on many soils which are not fertile enough
to grow red clover or alfalfa, and it is on these soils that it will
prove most valuable. Like many other plants, it makes its best growth
on fertile soils rich in calcium carbonate, although it will make
sufficient growth on poor soils which are not acid to warrant planting
it on them. Many hilly pastures may profitably be seeded to sweet
clover. It will not only make a valuable addition to the forage of
these pastures but will improve the soil so that grasses will grow more
abundantly. Some of the best pastures in the Middle West are composed
of bluegrass, timothy, and sweet clover.


RESISTANCE TO ALKALI.

Sweet clover grows successfully on soils in the West which apparently
are too alkaline for grains or alfalfa. The Wyoming Agricultural
Experiment Station reports that it has obtained good yields of sweet
clover on seepage land which is so strongly alkaline that no other
plants except some of the native grasses will survive, while the
California Agricultural Experiment Station found that sweet clover will
withstand alkali to a remarkable degree. Prof. F. S. Harris, agronomist
of the Utah Agricultural Experiment Station at Logan, claims that it is
one of the most alkali-resistant crops grown in Utah, and that in and
1913 and 1914 quite an industry developed in some parts of that State
in growing sweet clover for hay and seed on land too alkaline for other
crops.

In reply to a circular letter on the culture of sweet clover,
approximately 100 county agents and extensive growers of this crop
located in many parts of the West state that this plant is one of the
most alkali-resistant plants grown in their respective districts. In
Crook County, Oreg., a good stand was obtained from April seeding in
1915 on a 20-acre demonstration field of sandy loam bottom land so
strongly alkaline from black alkali that only salt grass was growing on
it before it was planted to sweet clover. This field pastured from 18
to 28 head of calves, cows, and horses from June 1 to October 1 without
being irrigated. Sweet clover generally will grow on soils where salt
grass[6] will survive, and it is very much superior to this grass as
pasture. After the drainage of water-logged land on which there is a
surface accumulation of alkali, it is the common practice in parts of
Utah to grow sweet clover for several years before planting alfalfa. It
is often stated that alkali land will grow less tolerant crops after
sweet clover has been grown on it for a few years. The long roots
will open up the subsoil and cause better drainage, thereby affording
an excellent means for removing the salts from the soil, as they are
readily soluble in water.

[6] _Distichlis spicata_.


NEED OF LIME ON ACID SOILS.

Sweet clover, like many other legumes, requires a soil containing
an abundance of limestone if a maximum growth is to be expected.
Throughout the world it makes a luxuriant growth only on calcareous
soils. On the black prairie limestone soils of Alabama and Mississippi
it grows luxuriantly, although in this region it is very seldom found
on the outcroppings of red clay, which are acid. The distribution
corresponds sharply with the line of demarcation between the black
prairie soils and other soil types. In some places sweet clover makes a
vigorous growth on the Selma chalk (rotten-limestone) soils, while none
is to be found on red post-oak clay but a few yards away; yet sweet
clover will grow on the red post-oak clay after the soil has received
an application of lime. It will thrive on the bald lime-rock spots
and rotten-limestone hills of Mississippi, which are so barren that
practically no other plants will survive. Thus it appears that lime is
essential for the maximum growth of sweet clover in this Region.

The reason for the exceptional growth of sweet clover in north-central
Kentucky is undoubtedly the fact that these soils contain an abundant
supply of limestone. The Kentucky Agricultural Experiment Station
states that this area is the only portion of the State where sweet
clover is being grown with general success without applying lime.

Soils on which sweet clover is aggressive are almost invariably
alkaline or but slightly acid. This plant is often found in valleys of
streams in localities where the soils are supposedly acid, but such
streams generally have their origin in limestone areas or flow through
limestone regions, and calcium carbonate is thus deposited in these
valleys during flood periods with the sedimentary deposits from flood
waters. Sweet clover often appears in deep cuts along highways or
railroads in localities where the soil is known to be acid and where
sweet clover has not previously grown. In many of these cuts the acid
soil has been removed and neutral or alkaline subsoil exposed, or
limestone has been used in ballasting or road making and the dust has
blown on the exposed soil. It is a very common occurrence to find sweet
clover making an abundant growth along macadamized roads from which the
wind has scattered the finely pulverized limestone.

An application of burnt lime or finely ground limestone has made the
difference between success and failure in most experiments which have
thus far been conducted on decidedly acid soils. (Fig. 7.)

A number of sweet-clover experiments were performed on acid soils and
on adjacent plats or fields of the same type of soil that had received
applications of limestone varying from 1 to 4 tons to the acre. There
was a marked difference in the stands obtained and in the growth of the
plants on the limed and unlimed areas. In some cases the difference in
growth was so marked that the last round of the lime spreader could be
distinguished at some distance from the plats. The stands were much
heavier on the limed areas and the plants made from two to three times
more growth than those on the unlimed plats. Yields of hay were doubled
on soils that received only sufficient limestone to neutralize the
acids in the surface soil, although the yields were further increased
when more limestone was added.

Mr. W. E. Watkins, county agent of Allen County, Kans., made counts of
the number of plants which winterkilled during the winter of 1914-15
on given areas of limed and unlimed soil. It was found that from 15
to 35 per cent more plants winterkilled on the unlimed soil than on
the limed areas. That portion of the unlimed field on which the fewest
plants winterkilled was found to have the lowest lime requirement.
On the unlimed areas with a low lime requirement 15 per cent more
plants winterkilled than on the limed areas; on those with a high lime
requirement the increase in winterkilling was 33 per cent. In the fall
of 1914 the hay cut from the limed areas exceeded that from the areas
with a low lime requirement by 600 pounds per acre and exceeded that
from the areas of high lime requirement by 4,000 pounds per acre. In
July, 1915, the increase in hay yield on the limed areas over that from
the areas with a low and with a high lime requirement was 2,300 and
9,400 pounds per acre, respectively. The area of high lime requirement
returned a small yield in 1914 and no hay in 1915.

In spite of the fact that sweet clover is as sensitive to soil acidity
as red clover or alfalfa, a large percentage of the acreage thus far
seeded in the eastern half of the United States has been composed of
acid soils, and this soil acidity undoubtedly is responsible for a very
large percentage of the failures with sweet clover in this section.
Where sweet clover is to be sown on acid soils a sufficient quantity of
lime should first be applied to at least neutralize the fields in the
soil to a depth of 6 inches. An application of 1 ton of burnt lime or
2 tons of finely ground limestone will usually be sufficient for this
purpose.

[Illustration: Fig. 7.--Sweet-clover plants, showing the effect of lime
upon their growth. The plants at the left represent the average growth
on the unlimed portion of a field; the plants at the right show the
average growth on the limed part of the same field.]

Fields have been noted where sweet clover was making a fair growth
on apparently acid soils. Such fields usually are rich in humus or
phosphorus and are exceptional cases rather than the rule.

Soil types which have slightly acid surface soils and alkaline subsoils
will grow sweet clover successfully, provided the acid soil is not more
than 6 to 12 inches in depth.


FERTILIZERS.

Owing to the fact that sweet clover thrives on the barren Selma
chalk (rotten-limestone) hills of Alabama and Mississippi and grows
abundantly on worn-out, abandoned land in north-central Kentucky, it
is often assumed that it will grow on soils too depleted in plant
food to produce other crops. These regions represent soils which have
become exhausted primarily in nitrogen and humus as the result of
continuous cropping with nonleguminous plants. Some of these soils
contain sufficient phosphorus and potassium for fair crop production,
although this supply may be in such a condition that it will not
become available fast enough to supply the needs of most crops. Sweet
clover, like all legumes, has the power to extract nitrogen from the
atmosphere, and on account of its extensive root system it is able to
obtain phosphorus and potassium from a larger area than most plants.
The large roots not only add a quantity of humus and nitrogen to the
soil but they also open it up to a considerable depth, thus providing
better aeration and improving its physical condition. Improved physical
condition causes the bacterial flora to increase and thereby indirectly
causes a larger quantity of unavailable phosphorus and potassium to be
made available for plant use.

On soils which are known to be low in phosphorus or potassium an
application of fertilizer containing the necessary element should be
made when sweet clover is sown without a nurse crop. However, when
it is sown with a nurse crop or in the late summer or early fall on
grain stubble, the residues left in the soil from fertilizers applied
to the nurse crop will, under ordinary conditions, be sufficient for
the plants. That sweet clover will respond readily to applications of
phosphorus on soils low in this element has been well demonstrated by
the farmers of Livingston County, Ill. In this county finely ground
rock phosphate was applied to a portion of a number of fields at the
rate of 1,500 to 2,000 pounds per acre. The phosphate was thoroughly
incorporated with the soil just before seeding oats and sweet clover.
In the growth of sweet clover there was a marked difference the
following year between the treated and untreated portions of the
fields. Those portions of the fields which received an application of
phosphate not only contained many more plants on a given area, but the
vigor and growth of the plants were most marked. On June 1 the plants
on the treated areas were 12 to 15 inches taller than those on the
untreated parts of the fields. This difference in the thickness of
stand and the height of plants was so striking that the last round of
the phosphate spreader was plainly distinguishable.

Yields of sweet-clover hay have been increased as much as 2 tons per
acre from applications of barnyard manure. Such an increased yield
would be equal approximately to 8 tons of green-manure. Some people
may consider it poor farm practice to apply manure to such crops as
sweet clover, but it is very probable that the cumulative effect of the
increased yields of the following crops, especially on soils low in
organic matter, will be greater than if the manure is applied to other
crops. Heavy applications of manure to the preceding crop should also
greatly benefit sweet clover.


USE OF A NURSE CROP.

If sweet clover is to become an important crop throughout the
North-Central States it must necessarily be seeded with grain. Good
success has been obtained by seeding sweet clover in the spring on
winter grain or with spring grain on soil that was inoculated and not
acid. Seed may be broadcasted in the early spring on winter grain when
the ground is in a honeycombed condition, or it may be sown later when
the ground may be cultivated. A large acreage of sweet clover is sown
in the western North-Central States and in Illinois in the spring with
oats, barley, or wheat as a nurse crop. Early varieties of oats and
spring wheat have given somewhat better results in portions of the
Northwest than barley. In Illinois oats are used almost entirely. Only
a few fields were noted where flax had been used as a nurse crop, but
in these fields it was successful. In wet seasons the sweet clover may
make a growth sufficiently large to interfere seriously with harvesting
the flax. On this account this combination should be tested thoroughly
in an experimental way before being recommended for general field
practice.

In those sections of the country where the moisture supply is limited,
sweet clover should be sown without a nurse crop. Failure to obtain a
stand is more likely to occur when the seed is sown with grain than
when it is sown alone, because during dry weather, which is likely to
occur when the grain is maturing, the supply of moisture in the soil is
apt to be insufficient for both crops. When this condition prevails the
clover will suffer badly and in some cases be killed. When sweet clover
is sown with a nurse crop it is strongly recommended that the grain be
seeded at not more than two-thirds the usual rate. This will give the
sweet clover a much better chance than when a full seeding is made.
When severe droughts occur it may be necessary to cut the grain for hay
if the stand is to be saved.


CHOICE OF SEED.

On account of the low germination of much of the sweet-clover seed
offered for sale it is very important that seed be tested for
germination before planting. Low germination usually is due to the
fact that many of the seeds remain hard after they have been in
the germinator or soil for a month or more. The seed coats of hard
sweet-clover seeds become permeable to water very slowly, if at all, in
storage. The germination of such seeds is greatly increased, however,
when they are subjected for a time to alternating temperatures, such as
freezing and thawing. It is on this account that unhulled seed, which
germinates poorly in the laboratory, often will produce good stands
when sown during the winter. When sweet clover is to be sown in the
spring it is very important that only hulled seed which germinates
75 per cent or more be sown. As explained later under the heading
"Seeding," unhulled seed which has a low germination should be used for
seeding only during the winter months, so that there will be sufficient
time for the alternating temperatures of winter and early spring to
cause it to germinate during favorable weather.

Hulled seed usually germinates much better than unhulled seed, as is
shown in Table I.

Table I.--_Germination and hard seed content of samples of
sweet-clover seed, hulled, and unhulled, from different sources._

                                Average percentage of--
                   Number of
  Description.      samples.    Germination.   Hard Seed.
  ---------------  ----------   ------------   ----------
  Kind of seed:
    Hulled            237         53.25           18.7
    Unhulled           45         11.8            70.9

  Source of seed:
    Southern           22         14              60
    Northern           22         37              43
    Imported           28         56              12

Table I shows that northern-grown seed germinates better than
northern-grown seed and imported seed better than either. The low
germination of the southern-grown seed is probably due to the fact that
a very large percentage of it is flailed out and sown in the hull.
Northern-grown seed generally is thrashed with either a grain separator
or a clover huller. Imported seed always is hulled. In hulling seed the
rasps or concaves of the machines scratch the seed coats sufficiently
to permit water to penetrate them, so that the germination is greatly
increased. Apparently there is no reason why southern-grown seed when
it is properly hulled should not germinate as well as northern-grown
seed.

Since the Ames scarifying machine (fig. 8)[7] has been placed on the
market, it is possible to buy scarified seed. This machine is so
constructed that the seed is forced through a conveyor, part of which
is covered with sandpaper. When the seed comes in contact with the
sandpaper it is scratched, so that water will penetrate the seed coats.
When this machine is run properly the germination of seed is greatly
increased, but when carelessly operated germination may be lessened, as
many of the seeds may be broken.

[7] This machine was invented by Prof. H. D. Hughes, of the Iowa State
College at Ames. A United States patent covering this device has been
issued and dedicated to the free use of the public.

[Illustration: Fig. 8.--Ames hulling and scarifying machine.]

The retarded germination of sweet-clover seed may be overcome by
soaking it in commercial concentrated sulphuric acid for 20 minutes.
It should then be washed quickly, using running water if possible, as
sulphuric acid becomes very hot when mixed with small proportions of
water. A great deal of water therefore is necessary in order to lessen
the danger of burning. The seed should be dried quickly by spreading
it out on a floor or canvas, and it should be stirred at intervals.
Unhulled seed should never be treated with sulphuric acid. When only a
small quantity of sulphuric acid comes in contact with the hulls a very
high temperature will result and the seed will be killed. The treatment
of seed with sulphuric acid for seeding on a field scale is not to be
recommended, in view of the fact that as good or better results may be
obtained by using scarified seed.

It is very important that seed of the desired species be obtained.
Many lots of sweet-clover seed offered for sale on the market consist
of mixtures of the yellow and white species, and many samples also are
adulterated with alfalfa. Seed which is simply labeled sweet clover
should never be purchased, as seed so labeled may be any one of the
several varieties offered for sale. It is always best to state the
specific kind of seed ordered and then submit a sample to either your
State Agricultural experiment Station or one of the seed laboratories
of the United States Department of Agriculture[8] for identification
before purchasing.

[8] Samples of seed may be submitted for analysis or identification to
the Seed Laboratory of the United States Department of Agriculture at
Washington, D. C., or to any of the following laboratories maintained
through the cooperation of the Department: Branch Seed-Testing
Laboratory, Agricultural Experiment Station, Columbia, Mo.; Branch
Seed-Testing Laboratory, Agricultural Experiment Station, Baton Rouge,
la.; Branch Seed-Testing Laboratory, Oregon Agricultural College,
Corvallis, Oreg.; Branch Seed-Testing Laboratory, Purdue University, La
Fayette, Ind.; Branch Seed-Testing Laboratory, California Agricultural
Station, Berkeley, Cal.

The Seed Laboratory of the United States Department of Agriculture
during the winter of 1915-16 obtained 172 trade samples of sweet-clover
seed and, as may be seen from Table II, many of the samples were not
true to name.

Table II.--_Trade samples received in response to requests for
white sweet clover seed._

  Key to Columns
    [A] White sweet clover.
    [B] Biennial yellow sweet clover.
    [C] White and biennial yellow sweet clover.
    [D] Annual yellow sweet clover.

                           Number of    Seed when tested
  Seed labeled--            samples.      found to be--    Alfalfa and--
                                       [A]  [B]  [C]  [D]  [A]  [B]  [C]
  White flowering sweet
    clover, white sweet
    clover, or Holhara
    clover, or _Melilotus
    alba_.                     147     91   10   28   --    13    1    4
  Sweet clover                  22      6    4    2    5     5   --   --
    Not labeled                  3      1   --   --    2    --   --   --
                              ----   ---- ---- ---- ----  ---- ---- ----
      Total                    172     98   14   30    7    18    1    4


PREPARATION OF THE SEED BED.

Sweet clover requires a well-settled and firm seed bed, with just
sufficient loose soil on the surface to permit the seed to be well
covered. When the seed is sown in the spring on winter grain the
seed bed usually is in good condition. At this season of the year the
seed may be sown, so that it will be covered by freezing and thawing
weather. It may be sown also when the ground is in condition to
cultivate and then may be harrowed or drilled in. When the seed is sown
with spring grain the seed bed is not as firm as it should be for the
prompt germination and establishment of the young clover plants. If
sown in this manner the soil should be worked into a fine condition and
firmed as much as possible. It is good practice to roll the ground with
a corrugated roller after seeding. Better stands are usually obtained
by seeding on fields that have been disked and harrowed than on those
that have been plowed.

When sweet clover is seeded without a nurse crop it should not be sown
on freshly plowed land which has had no opportunity to settle. The land
preferably should be plowed several months before the seed is to be
sown, and then worked at intervals with soil packers or harrows. Double
disking and harrowing just previous to seeding are to be strongly
recommended in preference to plowing at this time.

When sweet clover is to be seeded in the fall on grain stubble, the
ground should be disked and worked into good condition as soon as the
grain can be removed. If the seed is sown immediately the field should
be rolled after seeding.

Fall-plowed ground ordinarily makes an ideal seed bed for spring
seeding. Soil which has been previously planted to a cultivated crop,
such as corn, is usually put in sufficiently good condition for
sweet clover by disking. Good success has been attained by merely
broadcasting the seed on sandy soil and scratching it in with a harrow.
Such a seed bed appears to be ideal when the seed can be covered
sufficiently to insure plenty of moisture. It must be remembered that
young sweet-clover plants are not drought resistant and that every
precaution should be taken in seasons of drought or on laud which
drought affects badly to so prepare the seed bed that the largest
quantity of moisture will be conserved.

Excellent stands have been obtained at times by double-disking native
prairie sod and either covering the seed with a harrow or sowing it
with a drill.




SEEDING.


The proper time to seed sweet clover should be determined by the
germination of the seed, the climatic conditions of the region, and
the condition of the seed bed at the time of sowing. When growing
under natural conditions, seed which has lain in the ground over
winter germinates in sufficient quantity during the following spring
to produce a stand. It is therefore assumed that since this seed has
passed the winter on or in the ground and has produced a good stand
the following spring, sweet clover may be sown at any time of the year
and a satisfactory stand obtained. Little is thought of the enormous
number of seeds which shatter from a single plant and fall on an area
not exceeding 5 or 6 feet in diameter. Single plants have produced as
many as 350,000 seeds (the approximate number in 1½ pounds), or about
10,000 seeds for each square foot of ground covered. It matters little
how many of these seeds germinate in the fall they mature or during the
following winter, when the seedlings will be killed by freezing, for
there will be enough viable seeds left in the ground to germinate when
conditions are favorable in the spring. Conditions are very different
when sweet clover is sown on cultivated soil at the rate of 5 to 20
pounds of seed to the acre--25 to 100 seeds to the square foot. When
this quantity is sown, it is necessary that it be planted at such a
time that the greatest number of seeds will germinate and produce
plants.


HULLED SWEET-CLOVER SEED.

Hulled seed makes up a large percentage of the sweet-clover seed sown.
The germination of hulled seed varies considerably, although ordinarily
it is higher than that of unhulled seed. Seeding experiments conducted
at Arlington, Va., with seed which germinated 80 per cent show clearly
that seed which germinates well should not be sown during the winter
months in those sections of the country where midwinter thaws are
likely to occur, and especially in sections south of the latitude of
southern Ohio. In these experiments seed was sown during each month
of the winter. Good stands were obtained only on those plats which
were sown in the latter part of February and during March and April.
At least 75 per cent of the seed sown during November, December, and
January germinated on warm days during winter thaws and was killed
by later cold weather. Notwithstanding the fact that sweet-clover
seedlings will endure fairly low temperatures, seed germinating more
than 50 per cent should not be sown during the winter months, and
preferably not more than a week previous to the average date for the
last severe freeze.

No data have been secured on winter seeding in those portions of the
United States where open winters do not occur. It is probable that in
those sections the winters are sufficiently cold to prevent germination
before spring. Good results may be obtained by winter seeding, but as
usually no trouble is experienced in those sections in obtaining a
stand by seeding as soon as the soil can be worked in the spring, it
is strongly recommended that seeding be done with hulled seed, which
germinates well at this time of the year.

Many excellent stands have been obtained by seeding late in the spring,
but in most sections seeding at this time is not as certain to produce
a good stand as earlier seeding. Late spring seeding may be preferable
when the ground is weedy and the clover is to be seeded without nurse
crop. Under these circumstances a crop of weeds may be destroyed before
seeding.

Very good success has been obtained in the Southern and Central States,
and in some of the Northern States, by seeding sweet clover in the
late summer or early autumn. When there is sufficient moisture in the
soil for germination and when good seed is used, better stands have
been obtained by seeding about eight weeks before severe frosts are
to be expected than from spring sowing. This is particularly true in
regions where late spring droughts or severe summer droughts are likely
to occur. Seeding at this time may be done after an early crop has
been harvested and when weeds are not likely to be troublesome. Plants
from fall seeding mature from 10 days to two weeks later the following
season than plants from spring sowing of the same year. The later time
of maturing is an advantage, in that the plants will be ready to cut
during better haying weather. The root growth is not as large from fall
seeding as from spring seeding, and therefore not quite as much humus
is added to the soil. Late fall seedings are very likely to be injured
from heaving on wet clay soils.


UNHULLED SWEET-CLOVER SEED.

Unhulled sweet-clover seed is sown principally in Kentucky, Alabama,
and Mississippi. On the limestone soils of regions, which appear to be
naturally adapted to sweet clover, very good results are obtained by
using unhulled seed. It is not because southern-grown unhulled seed
germinates better than northern-grown unhulled seed that better stands
are obtained in the South from it, but it is mainly because southern
farmers better understand the somewhat exacting conditions necessary
for obtaining a stand with this kind of seed. Unhulled sweet clover
contains a large percentage of hard seeds which will not germinate
until they have been in the soil for some time and have been subjected
to varying temperatures.

Seeding experiments have been conducted at Arlington, Va., where
unhulled seed which contained 90 per cent of hard seed was sown during
each month of the winter. Good stands were obtained on those plats
seeded at the rate of 24 pounds (3 pecks) of seed to the acre during
December and January, and fair stands on the plats seeded at this rate
in February. Later seedings failed to produce a stand.

A large percentage of the unhulled seed sown in the South is seeded
during January and the first part of February. Good stands are seldom
obtained from unhulled seed south of the latitude of Washington, D. C.,
when the seed is sown later than the middle of February.

The use of unhulled seed has usually been attended with failure in
the northern portion of the United States, although occasionally good
stands have been obtained the following spring from late fall seeding.
This failure is in part due to the fact that the seed has been sown
in the spring and at a tine when only seed germinating well should
be used. When unhulled seed is to be sown north of the latitude of
Washington, D. C., it should be sown not later than February 15, and
preferably earlier. Observations show that fairly good stands may be
obtained by seeding during the winter, but care should be taken not to
sow seed earlier than necessary on land which is subject to washing.
Farmers should have no trouble in purchasing hulled seed, and therefore
it is recommended that only hulled seed which germinates well be sown.


RATE OF SEEDING.

The rate at which sweet clover should be seeded varies with the
germination of the seed, the condition of the seed bed, the climatic
conditions of the region, and the method of seeding. Throughout the
humid sections of the eastern United States sweet clover ordinarily is
seeded at the rate of 15 to 20 pounds of hulled seed to the acre. From
12 to 15 pounds should be ample where the seed bed is in good condition
and the seed germinates 75 per cent or more. In Illinois, the western
North-Central States, the Mountain States, and the Pacific Coast States
good stands are generally obtained by sowing 10 to 12 pounds of hulled
seed to the acre. In eastern Washington it is claimed that from 5 to 8
pounds to the acre are sufficient for good stands.

When sweet clover is grown under irrigation, 8 to 10 pounds of hulled
seed usually are sufficient, and from 2 to 4 pounds per acre are enough
when seeded in rows from 2 to 4 feet apart. Of unhulled seed 3 to 6
pecks (24 to 48 pounds) or 20 pounds of hulled seed are usually sown in
the South for pasturage or hay. In any region at least 10 pounds more
of the unhulled than of hulled seed should be sown to an acre. Unless
annual yellow sweet-clover seed is thoroughly cleaned it should be sown
at the rate of 25 to 30 pounds to the acre.


METHODS OF SEEDING.

The methods used for seeding red clover or alfalfa in any particular
region will be suitable for seeding sweet clover. Good results have
been obtained by broadcasting the seed on winter grain in the spring
when the ground is in a honeycombed condition. Perhaps a better method
is to wait until the ground can be worked and then to broadcast and
cover the seed with a harrow or to sow it with a drill. Unhulled seed
is usually broadcasted, since it is necessary to sow it before the
ground is in condition to be worked. Unless the hulls have been rubbed
smooth, some difficulty may be experienced in seeding it evenly with a
drill.

When sweet clover is to be sown with spring-seeded grain or when it is
to lie sown without a nurse crop it may be drilled in or sown broadcast
and covered with a harrow. Better stands are generally obtained with a
smaller quantity of seed when it is sown with the drill than when it is
broadcasted on honeycombed ground. When the seed is sown at the time
the grain is planted, the grass-seeder attachment of the drill commonly
is used. In some sections the end-gate seeder is used almost entirely.
When the seed is sown by either of these methods it may be seeded alone
or mixed with the grain. When only the clover seed is sown with a
drill, the alfalfa and clover seed drills are to be preferred.

Sweet-clover seed may be mixed with some inert substance of
approximately the same size and weight and sown with an ordinary grain
drill. Finely cracked corn, cracked wheat, or coarse bran often are
used for this purpose. When one portion of sweet clover is mixed with
two portions of a filler find the drill is set to sow one-half bushel
of wheat, it will usually sow from 15 to 20 pounds of sweet clover
to the acre. As this quantity will vary with the different types of
drills, it is necessary to test each drill, so that the seed may be
mixed with the filler in such proportions that the desired quantity
will be sown. The drill may be tested by blocking it up, so that
the geared wheel is off the ground, and this wheel may be turned a
sufficient number of times to establish a definite portion of an acre.
The seed that runs through can then be weighed and the rate per acre
determined. The rate may be determined more accurately by plugging up
the grain tubes or by tying a small sack on each tube and pulling the
drill for a specific distance over the field to be sown. The jar of the
drill will cause it to drop more seed than when it is blocked up and
run by hand.

It is often desired to seed sweet clover on land which can not be
cultivated. When sown on such land it is recommended that unhulled
seed or seed that contains a large percentage of hard seed be used and
that it be broadcasted during the winter. The subsequent freezing and
thawing will cover many of the seeds and cause them to germinate. It
is a good plan to scatter in deep gulleys mature plants that have not
shattered all their seed. The branches of these plants will help to
hold the seed in place until it germinates and the young plants become
established.

Seed may be scattered on native prairie ground in the late winter, but
unless it is trampled into the ground by live stock disappointing
results are likely to be obtained at first. Fair results have been
secured by planting seed with disk drills on prairie sod after it had
been double-disked in the early spring. This method should be used in
preference to broadcasting the seed and depending on cattle to trample
it in. Mr. George Hummer, of Prairie Point, Miss., reports good success
in his locality by simply broadcasting 1 peck of unhulled seed on
Bermuda-grass sod not later than January 1.




INOCULATION.


Excepting soil acidity, lack of inoculation probably is responsible
for more failures with sweet clover than any other one cause. When
sweet-clover plants are not inoculated they must depend upon the
available nitrogen in the soil for their supply, and as the crop is
grown for the most part on soils low in nitrogen the plants can not be
expected to make more than a small growth. (Fig. 9.)

[Illustration: Fig. 9.--White sweet clover at Arlington, Va., showing
the effect of inoculation upon their growth. The plants at the left
represent the average growth on the inoculated plats; those at the
right the average growth on the plats not inoculated. The plats had
been previously limed and were seeded on the same date.]

Arny and Thatcher, at the Minnesota Agricultural Experiment Station,
obtained 10 times as much dry matter in the tops and seven times as
much in the roots of sweet-clover plants which had been grown on
thoroughly inoculated soil as from plants Which had been grown on soil
not inoculated. Moreover, the plants grown on the inoculated soil
contained 117 pounds more nitrogen to the acre than those grown on the
uninoculated soil.

Experiments in many other sections of the country, and especially in
the northeastern quarter of the United States, where but little sweet
clover or alfalfa has thus far been grown, show that inoculation
is very essential to success. Ordinarily it is not necessary to
inoculate sweet clover when it is to be planted on land where alfalfa,
bur-clover, or black medic thrives, because the same strain of
inoculating germs inoculates all of these plants. However, when this
closer is to be planted on land where none of the plants inoculated
by this strain of the organism have been grown, inoculation should be
provided. In localities where sweet clover or other plants inoculated
by the same strain of bacteria thrive, the early growth has at times
been made much more vigorous by inoculating the soil or seed thoroughly.

It is not safe to assume that a certain piece of soil is inoculated
because any one of the plants inoculated by the same strain of the
organism is growing or has been grown on other fields in the same
vicinity. Many fields have come under observation where sweet clover
was a failure because the plants were not inoculated, when plats or
fields of alfalfa growing near by were abundantly inoculated.

There are several methods of inoculating sweet clover, any one of which
when properly applied should give good results.


THE SOIL-TRANSFER METHOD.

The soil-transfer method of inoculation consists in scattering over the
field to be seeded 200 to 400 pounds to the acre of soil collected from
sweet-clover, alfalfa, or bur-clover fields where the healthy plants
show an abundance of tubercles on the roots. It is strongly recommended
that this soil be scattered on a cloudy day or in the early morning or
in the evening and immediately harrowed or disked into the ground, as
the sun's rays are very injurious to the inoculating germs. It is a
good plan for the person scattering the soil to walk directly in front
of the harrow. When this practice is followed little harm can be done
by the light. To facilitate even scattering, the soil may be mixed
thoroughly with two or three times its weight of other soil, preferably
from the field where the sweet clover is to be sown. Soil used for
inoculating sweet clover does not necessarily have to be scattered
on the land just previous to sowing the seed. It may be scattered a
few months or a year in advance of the time the sweet clover is to be
seeded and be just as effective as if it were scattered at a later
time. In general, where sweet clover is to be seeded in the spring on
winter grain, the inoculation should be applied before the grain is
sown.

Good success has been obtained by drying in a dark place soil
containing the inoculating germs, sifting it, and running it through
the fertilizer compartment of a grain drill. When this method is
employed it is not necessary to use as much soil as when it is
scattered broadcast.

A comparatively new method which has given successful results calls
for dampening each bushel of seed and spreading it on a cloth, paper,
or cement floor, where half a gallon of throughly inoculated soil from
sweet-clover or alfalfa plants may be sifted over it. Some people
prefer to add a trace of glue or sugar to water, so that more of the
soil will adhere to the seed, although some soil will remain on the
seed if the glue or sugar is not used. When only this quantity of soil
is used it should be collected from around the roots of sweet-clover
plants which are abundantly inoculated. Such soil may be collected
in the fall and kept until spring in a cool, dry, dark place with
no injury to the inoculating organisms. Seed treated in this manner
should be kept in the dark and should be sown as soon as possible after
treating.


THE PURE-CULTURE METHOD.

The pure-culture method has the advantage of greater case of
transportation and freedom from danger of introducing harmful pests
upon the farm. Inoculation by pure cultures may be carried out in
either of two ways:

(1) A bottle of pure culture of the proper kind of bacteria is opened
and the culture mixed with a convenient quantity of water; this diluted
culture now is mixed thoroughly with a considerable quantity of soil,
preferably from the field where the legume is to be sown; the treated
soil is then distributed in the same manner as when inoculation is made
by the soil-transfer method.

(2) A pure culture of the proper kind of bacteria should be applied
to the seeds in such a way that they will all be moistened. The seed
should then be permitted to dry in a shady or dark place and should be
planted as soon as possible after it is dry. Drying may be facilitated
by adding dry, sifted soil, preferably from the field where the seed is
to be sown. Inoculating organisms very often die within a week after
the seed is inoculated. It is highly desirable, therefore that the
inoculation be made the day the seed is sown. Inoculated seed never
should be dried in the sun.

The question is often asked whether it is advisable to inoculate seed
with pure-culture method and sow it on honeycombed ground in the
spring. No experiments have thus far been completed to determine the
advisability of this procedure. Some inoculation would probably result
from this practice, because the bacteria on that portion of the seed
next to the ground would be protected from the sunlight and would in
a short time under ordinary conditions be covered by the freezing and
thawing of the soil. While it is hardly possible to obtain as complete
inoculation by this practice as by other methods, it is to be preferred
to no inoculation.




TREATMENT OF THE STAND.


The manner in which a stand of sweet clover is handled should depend
somewhat upon the method and date of seeding and the purpose for which
it is sown. Climatic conditions should also be taken into consideration
and the handling of the crop governed accordingly.


TREATMENT THE FIRST SEASON.

The most serious objection to seeding sweet clover in the spring
without a nurse crop is weeds. In many sections of the country seeds
will take as much water from the soil and make as much or more shade
than a crop of grain. In spite of the fact that sweet clover will
withstand more adverse conditions than red clover or alfalfa, a heavy
growth of weeds will greatly <DW44> the growth of the plants and in
some cases kill most of them. (Fig. 10.) On plats sown in April without
a nurse crop at Arlington, Va., it was necessary to mow weeds five
times during the summer of 1915 in order to keep them partly checked.
Where it is necessary to mow a field so many times the plants are not
only checked or killed, but as much time is required for this work as
would be necessary to harvest a crop of grain. This trouble may be
overcome in part by pasturing the sweet clover the first season, but
even then during wet weather it may be necessary to cut the weeds at
least once before the plants become well enough established to turn
live stock on the field. The plants should at no time be clipped closer
than 5 inches from the ground.

After a field of sweet clover has become well established, it may
be pastured throughout the summer and fall. Close grazing should be
avoided during the summer, or the plants may be killed, but they may
be pastured fairly close to the ground in the autumn, as it does not
appear as necessary to provide a winter covering as is the case with
red clover. Close pasturing or clipping late in the fall has had a
marked effect on the growth of the plants the following spring on some
fields and no apparent effect on the stand and growth of the plants
on other fields. A portion of a field in Livingston County, Ill., was
clipped close to the ground in the late fall of 1915. On June 1, 1916,
the stand was somewhat heavier on the unclipped part of the field.
More noticeable than the thickness of the stand was the fact that the
plants on the unclipped portion were 8 to 10 inches higher than those
on the clipped area. It is reasonable to believe that plants going into
the winter with no protection are more likely to be injured than those
having some protection.

On the other hand, many fields in different parts of the country have
been closely clipped or pastured in the late fall with no noticeable
injury. Because of the value of the hay or pasturage in the late summer
and autumn of the year of seeding, it is strongly recommended that the
first year's growth be utilized. If the field be cut for hay it is
well to leave a 4-inch or 5-inch stubble, as this will serve to catch
drifting snow during the winter, thereby adding to the protection
against winterkilling. If the field is not pastured the first season
and weeds are not troublesome, a cutting of hay may be made when growth
ceases in the fall.

[Illustration: Fig. 10.--White sweet-clover plant (at the left),
showing the effect of a heavy growth of weeds. Had the weeds not been
present the plant at the left should have been larger than the one
at the right, as the seed was sown two weeks earlier and the other
conditions for growth were ideal. Four-fifths of the plants on the plat
which had a heavy growth of weeds were entirely killed.]

When sweet clover is seeded with grain, moisture conditions should
serve to determine whether the grain should be permitted to ripen or
be cut for hay. When untimely droughts appear the plants may be killed
if the grain is not cut as early as possible.

In the South and in some sections of the Eastern and North-Central
States where the soil contains an abundance of limestone and is well
inoculated, a cutting of hay may usually be obtained after a grain
crop has been harvested. In other sections of the North in only
exceptionally favorable weather will more than pasturage be obtained
after the grain is cut.


TREATMENT THE SECOND SEASON.

One of the special advantages of sweet clover is that it produces good
pasturage somewhat earlier in the spring than most forage crops. In
the North, with the exception of the extreme northern portion of the
United States, it will furnish a cutting of hay in June or excellent
pasturage until that time and a crop of hay or seed in late summer. In
the South two cuttings of hay and a seed crop may be harvested. After
maturing seed the plants die. It is a common practice in many sections
to pasture the crop until about June 10, when the stock is removed and
the plants are permitted to mature seed. If the plants have not been
grazed closely they should be clipped at this time, so that the seed
crop will ripen more evenly. Sweet clover may be pastured during the
entire second season's growth, provided sufficient stock is kept on the
field to prevent the growth from becoming woody. If the plants become
coarse the pasture may be clipped, leaving an 8-inch stubble, so as to
induce a new growth which will be more palatable. If it is desired to
have the pasture reseed itself stock should be removed at least eight
weeks before heavy frosts are expected, or only sufficient stock should
be permitted to remain on the pasture to keep some of the plants in
check.




SWEET CLOVER IN MIXTURES.


Very little sweet clover thus far has been grown in mixtures with other
crops. A few farmers have sown red clover and sweet clover together,
but such a mixture has no advantage over sweet clover seeded alone
for hay, as sweet clover should be cut at least two Weeks before the
red clover is ready to harvest. Sweet clover is being seeded to some
extent on native prairie sod in the Northwest, where it is claimed it
adds greatly to the value of the native grasses for pasturage. A thin
seeding of sweet clover is often desired in bluegrass pastures on this
account. One of the best pastures in eastern Iowa consists of a mixture
of bluegrass, timothy, and sweet clover. The Mississippi Agricultural
Experiment Station recommends a mixture of Johnson grass and sweet
clover. In this mixture the first cutting will consist of almost pure
sweet clover, while the second and third cutting's will be a mixture
of those plants. A number of southern farmer have had good success in
seeding sweet clover on Bermuda-grass sod.

The New Jersey Agricultural Experiment Station has obtained excellent
results from a mixture of Dwarf Essex rape and sweet clover, and also
by the addition of soy beans to this mixture. It was found that by
seeding 6 pounds of rape and 10 pounds of sweet clover per acre an
abundance of nutritious pasturage was produced and that pigs preferred
this mixture to alfalfa. When soy beans were added it was seeded at
the rate of 1 bushel of soy beans, 6 pounds of Dwarf Essex rape, and
18 pounds of sweet clover. The soy beans were drilled by themselves,
and the rape and sweet clover were mixed and seeded with a press drill.
Brood sows made a gain of from three-fourths to 1 pound a day during
July on this mixture without additional feed and gave unusual evidence
of thrift and vigor.

[Illustration: Fig. 11.--A cornfield, showing the effect of fall and
spring plowing in killing sweet clover that had made but one year's
growth. The portion of the field at the left was plowed in the autumn,
while that at the right was plowed the following spring, after the
plants had started growth. The corn is 4 inches high.]




ERADICATION OF SWEET CLOVER.


Some farmers hesitate to plant sweet clover on their farms for fear
they will have difficulty in eradicating it when the fields are planted
to other crops. The results obtained annually by hundreds of farmers
are sufficient proof that there is no foundation for such fear; in
fact, farmers are experiencing much difficulty in cutting the first
crop the second season so high that the plants will not be killed. The
new crop of sweet clover, unlike that of red clover and alfalfa, must
come from the buds left on the stubble, so when the plants are cut
below these buds they will be killed. As sweet clover is a biennial,
the plants die as soon as the seed crop is produced.

When the first year's growth of sweet clover is to be turned under
for green-manure it is recommended that the field be plowed after the
plants have made some growth the following spring rather than in the
fall of the year of seeding. When the first year's growth is plowed
under the same fall many of the plants will not be entirely covered,
and these will made a vigorous growth the following spring. When the
plowing is delayed until the plants have made some growth the following
spring no trouble will be experienced in eradicating them. (Fig. 11.)


       *       *       *       *       *


PUBLICATIONS OF THE U. S. DEPARTMENT OF AGRICULTURE RELATING TO FORAGE
CROPS.


AVAILABLE FOR FREE DISTRIBUTION BY THE DEPARTMENT.

  Cowpeas. (Farmers' Bulletin 318.)
  Alfalfa. (Farmers' Bulletin 339.)
  Soy Beans. (Farmers' Bulletin 372.)
  Red Clover. (Farmers' Bulletin 455.)
  Alfalfa Seed Production. (Farmers' Bulletin 495.)
  Forage Crops for the Cotton Region. (Farmers' Bulletin 509. )
  Vetches. (Farmers' Bulletin 515.)
  Vetch Growing In the South Atlantic States. (Farmers' Bulletin 529.)
  Crimson Clover: Growing the Crop. (Farmers' Bulletin 550.)
  Crimson Clover: Seed Production. (Farmers' Bulletin 646.)
  The Field Pen as a Forage Crop. (Farmers' Bulletin 690.)
  Bur Clover. (Farmers' Bulletin 693.)
  Button Clover. (Farmers' Bulletin 730.)
  The Clover leafhopper and Its Control in the Central States.
    (Farmers' Bulletin 737.)

FOR SALE BY THE SUPERINTENDENT OF DOCUMENTS, GOVERNMENT PRINTING
OFFICE, WASHINGTON, D. C.

  Leguminous Crops for Green Manuring. (Farmers' Bulletin 278.) Price,
    5 cents.
  Lespedeza, or Japan clover. (Farmers' Bulletin 441.) Price, 5 cents.
  Crimson Clover: Utilization. (Farmers' Bulletin 579.) Price, 5 cents.
  Alfalfa Production: Pollination Studies. (Department Bulletin 75.)
    Price, 5 cents.
  Red-Clover Seed Production: Pollination Studies. (Department Bulletin
    289.) Price, 5 cents.
  Variegated Alfalfa. (Bureau of Plant Industry Bulletin 169.) Price,
    10 cents.
  Leguminous Crops for Hawaii. (Hawaii Agricultural Experiment Station
    Bulletin 23.) Price, 10 cents.



WASHINGTON : GOVERNMENT PRINTING OFFICE : 1917


       *       *       *       *       *


Transcribers Note


All illustrations moved to avoid splitting paragraphs. Sweet clover and
sweet-clover variants retained.







End of the Project Gutenberg EBook of USDA Farmers' Bulletin No. 797: Sweet
Clover: Growing the Crop, by H. S. Coe

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