Change of Rotation. yi 



nary perennials, and in yet others, creeping 

 perennials. 



2. Modify the rotation. In the conflict 

 with weeds, it is greatly advantageous to 

 drop out of the rotation for a time such 

 crops as allow the weeds which infest the 

 soil where they grow to ripen their seeds. 

 Some weeds, as, for example, those which 

 grow as winter annuals, ripen their seeds 

 early in the season. The seeds of these 

 weeds mature in crops of winter wheat, rye, 

 and hay, but ordinarily they do not mature 

 in spring cereal crops, for the reason that 

 these weeds begin their growth in the pre- 

 vious autumn. If, therefore, in the infested 

 fields winter wheat, rye, and hay are 

 dropped out of the rotation for a short 

 time, and spring crops grown in their stead, 

 the destruction of the weeds mentioned and 

 of those of kindred habits will be greatly 

 facilitated. Other weeds ripen their seeds 

 late. Ragweed, for example, more com- 

 monly grows up after the early cereal crops 

 and meadows have been cut, and, if undis- 

 turbed, it matures its seeds before frost. 

 Grass seed, therefore, in fields infested with 

 this sort of weed, should not be sown for 

 the purpose of producing meadow until the 



