86 BULLETIN 355, U. S. DEPARTMENT OF AGRICULTURE. 
Probably the most important object of the rotation of crops on 
a large part of the best agricultural land of this country is concerned 
with the maintenance and increase of humus and vegetable matter 
in the soil. (Ref . No. 4, p. 275.) Increase of humus in the soil takes 
place when crops are grown which are not intertilled and have fine 
root systems permeating even compact soils. The use of land 
as meadow and pasture is, therefore, one of the most effective ways 
for adding to the humus content of the soil. If the meadow or pasture 
contains legumes, the nitrogen as well as the humus content is in- 
creased. 
Planning the cropping system. — To gain the advantages mentioned 
above, a rotation of crops must be very carefully planned. The es- 
sential parts of the rotation consist in (1) intertilled crops, (2) grain 
crops, and (3) grass and legume crops to be used either as hay or 
pasture. But in working out the plan for rotation the farmer must 
consider not only the crops to be grown, but the relative yield of 
each, since it is necessary that the farm be laid out in fields of essen- 
tially uniform size. On an 80-acre dairy farm, for instance, the 
farmer might wish to grow corn, oats, or other grain, clover, and have 
some pasture. While the best division of the farm among these 
crops might be an even one, it is necessary to adjust the total yields 
of the several crops grown until the division of the farm into fields 
of equal size is practicable. It is possible, however, to grow any of 
these crops more than one year on the same piece of land in a single 
rotation, so that if it is desired to have more than one-fourth of the 
land in corn, that can be arranged by growing this crop two years in 
succession, or if more grain is desired the same method may be used. 
Again, a large number of farms include unimproved land, which can 
be used as permanent pasture but can not readily be brought into 
the rotation with other crops. 
Relation of rotation to type of soil. — Each type of soil must be con- 
sidered separately with reference to the rotations for which it is best 
adapted. (Ref. No. 7, p. 506.) On sandy soils short rotations give 
better results than long rotations. As far as practical, at least one- 
third or one-fourth of the soil of a sandy farm should be in a legume 
or other crop, part or all of which is to be turned under for green- 
manuring purposes. On one of the best potato farms in Wisconsin 
the following rotation is practiced: First, potatoes in which rye is 
sown ahead of the potato digging, so that it makes a good start in 
the fall, and then timothy. Clover is sown and dragged in the fol- 
lowing spring. This gives a 3-year rotation of potatoes, rye, and 
clover. Practically all of the clover is plowed under as a green- 
manure crop. In this way the soil is kept well supplied with active 
organic matter, and the sand is protected from blowing by the rye 
in the fall and spring. 
