196 AGRICULTURE 



operations are attended to, and the season is 

 favourable, the land at the end of the year 

 is left practically free of weeds, the sup- 

 pression of which is effected, not only by the 

 hoeing, but also by the vigorous growth of 

 the large mass of leaves which characterises 

 these particular crops. Such crops are gener- 

 ally called " cleaning crops," and their 

 presence in a rotation greatly simplifies the 

 solution of practical problems of cultivation. 

 By growing a variety of crops under a 

 system of rotation one secures a corre- 

 sponding variety of produce, which comes to 

 maturity, or which can be utilized, at different 

 seasons of the year. As a result, the main- 

 tenance of live stock of various kinds is 

 rendered economically possible ; and nothing 

 contributes more to the maintenance of the 

 fertility of a holding than the presence of 

 a large head of farm animals. On the 

 American prairies, where wheat is the only 

 crop grown over wide areas, it is practically 

 impossible to maintain any considerable 

 number of farm animals, beyond the horses 

 necessary for the work of the farm. But 

 when the point is reached where the fertility 

 of the holding has been so seriously reduced 

 that profitable crops cannot be grown, it is 

 found necessary either to abandon the 



