236 SOILS AND FERTILIZERS 



324. Rotation Advantageous in Other Ways. 

 A good rotation will be found advantageous in other 

 ways. With one line of cropping, land becomes 

 foul with weeds and insects which are unable to 

 thrive when crops are rotated. Frequently the rota- 

 tion must be planned so as to reclaim the land from 

 weeds, and ravages caused by insect pests. Many in- 

 sects are capable of living only on a special crop ; 

 w.hen this crop is grown continually on the same land 

 the best conditions for insect ravages exist, and relief 

 is only secured by rotation of crops. Fungus diseases 

 also are most liable to occur on soils which produce 

 annually the same crop, as the conditions are favorable 

 for the propagation and hybernating of disease pro- 

 ducing spores. 



325. Long- and Short- Course Rotations. Rota- 

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

 rotations are more generally followed in European 

 and other of the older countries. The length of the 

 rotation can only be determined by the conditions ex- 

 cisting in different localities. As a general rule long- 

 course rotations should be attempted only after a 

 careful study of all of the conditions relating to the 

 system of farming that it is desired to follow. For 

 northern latitudes a rotation of four or five years 

 gives excellent results. In some localities three- 

 course rotations are the most desirable. 



A rotation that is suitable for one locality or kind 

 of farming may be unsuitable for other localities or 

 conditions. Because of variations in soil, climate, 



