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.