244 SOILS AND FERTILIZERS 



sell products which remove the least fertility, or if 

 those are sold which remove large amounts, to return 

 in cheaper forms the fertility sold. In a good rotation 

 it is the plan to have at least one salable crop 

 each year. The whole farm need not undergo the 

 same rotation at the same time and the rotation may 

 be subject to minor changes as circumstances require. 

 To illustrate, wheat and flax occupy about the same 

 position in a rotation. If when the crop is to be 

 seeded the indications are that wheat will be a poor 

 paying crop and flax sell well, flax should be sown. 

 The rotation should be such that one of two or three 

 crops may be grown as circumstances require. 



318. Rotations Advantageous in Other Ways. — A 

 good rotation will be found advantageous in many 

 ways. With one line of cropping, land becomes foul 

 with special kinds of weeds which are unable to 

 thrive when crops are rotated. Frequently the rota- 

 tion must be planned so as to reclaim the land from 

 weeds. 



Relief from insect pests is often secured by a proper 

 rotation. Many insects are capable of living only on 

 a special crop and when this crop is grown continually 

 on the same land the best conditions for insect ravages 

 exist. 



319. Long- and Short-course Rotations. — Rota- 

 tions vary in length from 2 to 17 years. Long-course 



