(See Fig. 79.) For
dry-farm purposes the implement must be so made as to enable the
farmer to set the harrow teeth to slant backward or forward. It
frequently happens that in the spring the grain is too thick for the
moisture in the soil, and it then becomes necessary to tear out some
of the young plants. For this purpose the harrow teeth are set
straight or forward and the crop can then be thinned effectively. At
other times it may be observed in the spring that the rains and
winds have led to the formation of a crust over the soil, which must
be broken to let the plants have full freedom of growth and
development. This is accomplished by slanting the harrow teeth
backward, and the crust may then be broken without serious injury to
the plants. The smoothing harrow is a very useful implement on the
dry-farm. For following the plow, however, a more useful implement
is the disk harrow, which is a comparatively recent invention. It
consists of a series of disks which may be set at various angles
with the line of traction and thus be made to turn over the soil
while at the same time pulverizing it.
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