SUCCESSION OF CROPS IN ROTATIOX. 



235 



necessary consequence from cultivation by the system of 

 farm-yard manuring, and which can only be met, as he 

 thinks, by a rotation of crops. 



It is generally supposed that the best remedy is the 

 hoe ; but though mechanical application may retard the 

 developement of weeds for a time, it cannot effectually 

 prevent them. The hoe has some share in removing 

 them, but not all. 



The succession of crops in rotation is always made 

 dependent upon the cereals ; the preceding crops are 

 selected of such a kind that their cultivation will not 

 injure, but rather improve, the succeeding corn-crop. 

 The selection of the particular kind, however, is always 

 governed by the condition of the soil. 



In a field abounding in stalk and leaf constituents, it is 

 often found useful to have wheat preceded by tobacco or 

 rape, lye by turnips or potatoes, since these plants by 

 di'awing from the soil a large amount of leaf and stalk 



chamomilla), and the corn camomile (Anthemis arvensis). All these 

 plants contain, in their ash, as much potash as is found in clover, and 

 7 to 18 per cent, of chloride of potassium, a salt which forms one of 

 the principal constituents of the urine of animals, and which is brought 

 to the field in the fami-yard manure. 



(KiJLiNG, 'Annal. d. Chem. und Pharm.' vol. Ivi. p. 122.) 



