86 BULLETIN 355, U. S. DEPARTMENT OF AGEICULTURE. 



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 aU 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. 



