CHAPTER V. 

 THE ROTATION OF CROPS. 



The term " crop rotation " is used to define the successive 

 growing of different crops upon the same fields in order to assist 

 in maintaining soil productivity. It is used to differentiate 

 between the system defined and that of " continuous cropping." 

 In the latter practice the same class of crop is grown continu- 

 ously. 



According to the similarity in their effect on the soil, of 

 the methods employed in their production, and the purposes for 

 which they are grown, crops are classified into groups having 

 common characteristics. 



The following is a rough classification of the more common 

 groups : — 



(1) Cultivated, Hoed or Cleaning Crops. — These are 

 crops planted so as to facilitate inter-tillage during growth, e.g., 

 maize, potatoes, kaffir corn and mangels. Cultivation between 

 the rows destroys weeds, and by improving aeration assists in 

 making plant food available. While the immediate effect of the 

 cultivation is beneficial when a delicate feeding crop is to follow, 

 the effect of continuously growing crops of this group is to im- 

 poverish the soil. Little organic matter is added to the soil, 

 and cultivation accelerates the rate of oxidation of soil humus ; 

 consequently the tilth of the soil is impaired unless the system 

 of farming practised provides measures for restoring the humus 

 content. In general, cultivated crops must be regarded as 

 humus destroyers. 



(2) The Small Grain Crops. — These crops, e.g., winter 

 cereals, millets, and flax, are seeded in rows close together by 

 means of grain drills, or are broadcasted very thickly. No 

 ordinary inter-tillage is possible, although they are usually har- 

 rowed shortly after germination ; but from this time on no cul- 

 tivation of the land is possible until after the crop has been 

 harvested. A cereal is any graminaceous crop grown for its 

 edible grain, e.g., wheat, rye, maize, rice, etc. 



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