ining for the soil a supply of nitrogen from the
air by introducing a legume at regular intervals, and (2) the
prevention of injury to the crops from fungous diseases, insect
enemies, weeds or other causes. Other reasons are often advanced, some
of which are entirely erroneous, while others are of quite secondary
importance.

The rotation should be carefully studied with reference to the farm
scheme as previously outlined. Reasons for modifying the rotations are:
(1) To change the kind or proportion of crops grown, (2) to change the
amount of labor required, or (3) to increase the crop-producing power
of the soil.

During 25 years the four crops of maize, oats, wheat, timothy and
clover hay have been taken in rotation from the four tiers of plats at
the Pennsylvania State College, so that the influence of the soil has
been entirely eliminated. At the December farm prices for the decade
ending December 1, 1906, the value of these four crops per acre have
been: Maize, $29.67; oats, $14.49; wheat, $18.49; and hay, $18.05. It
will be noted that during 25 years the average income from an acre of
maize has been almost exactly twice that from an acre of oats. The
region where these results were obtained is relatively unfavorable to a
large yield of maize. It is obvious, therefore, that a modification in
the rotation may modify the average income from the farm materially,
provided such modification does not reduce the fertility of the soil.
Thus, while the average income per acre during 25 years for the
four-course rotation above mentioned was $20.17, if the rotation were
increased to a five-course rotation by the addition of another year of
maize, the average income would be $22.45 an acre.

It may be desirable to modify the rotation in order to increase or
decrease a certain crop usually fed upon the farm. Thus, with a
four-course rotation of maize, oats, wheat, clover and timothy,
one-fourth the area would produce hay; while with a six-course
rotation, composed of maize, oats, wheat, each one year, and hay three
years, one-half the area would produce hay. If it is desired to still
further reduce the area in oats and wheat, a seven-course rotation
could be arranged with maize, two years in succession. This is the
rotation that would be desirable for a dairy farm where it is planned
to keep as many cows as practicable and to buy the concentrates
largely. Either the wheat or the oats could be taken out of this
rotation if e