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.