Part 1

Transcribers Note

Text emphasis denoted as _Italics._

SWEET CLOVER: GROWING THE CROP

H. S. COE

Assistant, Office of Forage Crop Investigations

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.

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.

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.

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.

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.

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.

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.