rious
probably than those that are in motion, owing, it may be, to the less
supply of dissolved oxygen in the former.

Soils suitable in themselves, but lying on stiff clay bottoms or
underlaid with hard pan within two or three feet of the surface, will
not maintain a good stand of alfalfa. The plants in these may grow well
for a time, probably a year or two, after which they will fail. The
roots are not able to go down to gather food. When the subsoils are
simply stiff clays, deep subsoiling, as already intimated, may render
much service, but when composed of hard pan this may not be practicable.
In moist climates, however, reasonably good crops have been obtained
from soils with underlying rock not more than four feet below the
surface.

The fact should not be overlooked that soils may have the requisite
physical conditions for growing alfalfa, and they may possess in fair
supply the essential elements of plant food, and yet alfalfa will not
succeed at the first when sown on these, because of the absence of the
soil bacteria, the presence of which is essential to the vigorous growth
of the plants. Because of this, growers should be slow to conclude that
alfalfa will not flourish on the soils on which they sow it until they
have first tried to grow it on those soils that have been inoculated
with the requisite alfalfa bacteria. For the methods of procedure in
such cases see page 53. Some persons claim that soils which will grow
medium red clover in good form will also grow alfalfa in good form.
This does not necessarily follow. While there is much of similarity in
the soils suitable for the growth of both, alfalfa may fail on lands
that grow red clover luxuriantly until the bacteria proper to alfalfa
have been introduced. Soils may be tested for bacteria, and even in
winter, by sowing some seed in pots and treating them like
well-cared-for house plants. When the plants are 2 to 3 months old, if
tubercles are found on the roots, the conclusion would seem safe that
such soil does not require inoculation.

=Place in the Rotation.=--In a certain sense it can scarcely be said of
alfalfa that it is a rotation plant, because of the long term of years
for which it is grown in an unbroken succession. Nevertheless, in all
places it cannot always be maintained for a long term of successive
years without renewal. In the Eastern States it is frequently, though
not always so crowded by various grasses, that the fields in which it