118 FIRST PRINCIPLES OF AGRICULTURE. 



Rotation Courses. The number of years intervening 

 between the growth of crops in regular order is termed 

 a "course." A rotation course may range from the sim- 

 ple two-year to the more complex six or eight year 

 course, though the four-year course is generally adopted. 

 The poorer the land the shorter the course; and the 

 reverse, the better the land the longer the course, are 

 principles now well established. 



Taking the number of crops and periods of rotation 

 possible, it is evident that the number of possible courses 

 is too large to admit of definite description or comment. 

 A few examples only are given and discussed, in order to 

 more clearly illustrate the principles already pointed out. 



Examples of Rotation Courses. These are adapted 

 to what is termed " arable farming," where the live stock 

 is only sufficient to provide labor and the necessities of 

 the family. 



No. 1 is defective for two reasons : first, because uncul- 

 tivated crops similar in character and capacity of obtain- 

 ing plant-food succeed each other; and second, because 

 the oats preceding the wheat prevents a proper cultivation 

 of the soil and preparation of the seed-bed for wheat. 

 This rotation is widely used, mainly because it is eco- 

 nomical of labor. Until very recently the custom was 

 to plant the corn on clover-sod, follow with oats without 

 manure, and then lime and manure for wheat. 



