It is not necessary to leave more than an ordinary stubble when cutting
the sweet-clover hay crop in the fall of the year of seeding. A stubble
4 or 6 inches in height, however, will serve to hold drifting snow and
undoubtedly will be of some help in protecting the plants from winter
injury. While sweet clover without question is more hardy than red
clover, usually more or less winterkilling occurs, and any protection
which may be afforded during cold weather will be of considerable
benefit.
While the first crop in the second year comes from the crown buds, the
new branches which produce the second crop of the second year come from
the buds formed in the axils of the leaves on the lower portions of the
stalks which constitute the first crop, as shown in figure 4. These
branches usually commence growth when the plants are about 24 inches
high. In fields where the stand is heavy and where the lower portions
of the plants are densely shaded, these shoots are soon killed from
lack of necessary light. (Figs. 4 and 5.) The branches which are
first to appear and which are first to be killed are those closest to
the ground. It is therefore very important when cutting this crop to
cut the plants high enough from the ground to leave on the stubble a
sufficient number of buds and young branches to produce a second crop.
[Illustration: Fig. 4.--Sweet-clover plants, showing the direct
relation that exists between the thickness of stand, the time of
cutting, and the height at which the stubble must be cut if a second
crop is to be expected. The plant at the left was cut 10 day later than
the plant at the right. Note the height at which it was necessary to
cut this plant so that a second crop would develop and also the scars
on the stubble where young shoots had started earlier and were killed
from lack of sunlight. When the stand is thin the young shoots will
survive, as they did on the plant at the right, even though the field
is cut at a later date.]
Examination of hundreds of acres of sweet clover in different sections
of the United States during the summers of 1915 and 1916 showed that
the stand on at least 50 per cent of the fields was partly or entirely
killed by cutting the first crop the second season too close to the
ground. A direct relation exists between the thickness of the stand,
the height of the plants, and the height at which the stubble should
be cut if a second crop is to be harvested. It is very essential to
examine the fields carefully before mowing, so as to determine the
height at which the plants should be cut in order to leave at least one
healthy bud or young branch on each stub. In fact, the stand should
be cut several inches above the young shoots or buds, the stubble may
die back from 1 to 3 inches if the plants are cut during damp or rainy
weather.
[Illustration: Fig. 5.--Stubble of sweet clover collected in fields
where 90 per cent of the plants had been killed by cutting too closely
to the ground. The heavy stands in these fields were not cut until the
plants had made a growth of 36 to 40 inches. Note the scars on the
stubble where young shoots started, but died from lack of light.]
When fields of sweet clover contain only a medium-heavy stand and when
the plants have made no more than a 30-inch growth, a 5 to 6 inch
stubble usually will be sufficient to insure a second crop, but where
fields contain heavy stands--15 to 25 plants to the square foot--it
may be necessary to leave an 8-inch stubble. In many fields examined
in northern Illinois in June, 1916, heavy stands had been permitted to
make a growth of 36 to 40 inches before cutting. In a number of these
fields a very large percentage of the plants were killed when an 8
to 12 inch stubble was left. (See fig. 5.) A careful examination of
such fields showed that the young branches had started on the lower
portions of the stalks and had died from lack of light before cutting.
In semiarid regions, where the plants do not make as rapid growth as in
humid sections, they may, as a rule, be clipped somewhat closer to the
ground without injury.
On account of the difference in the growth that sweet clover makes
on different types of soil and on account of the difference in the
thickness of the stand obtained in different fields, it is impossible
to give any definite rule as to the proper height to cut the first crop.
[Illustration: Fig. 6.--Shoe sole to be placed on the inner shoe of the
mower, so that a high stubble may be left when mowing sweet clover:
_A_, End view of the back part of the sole; _B_, side view of the sole,
showing general shape; _C_, shape of the front end of the pole when
it is to be used on mowers having shoes of the type used on Deering
machines; _D_, forward end of the sole represented in _B_. The toward
end of the sole shown in _B_ and _D_ should be made for machines having
shoes of the type used on McCormick mowers.]