70 CHAPTER V 



(b) The range of roots of crops varies, so that shallow- 

 rooted crops benefit by the decaying residues of deep-rooted 

 plants which have accumulated plant food in the upper stra- 

 tum from lower strata of the soil. 



(c) The humus supply is maintained. 



(d) As a result of rotative cropping the soil is kept in a 

 better physical condition, the soil micro-organisms conse- 

 quently thrive better, and the decay and disintegration of the 

 soil forming materials are more continuous than where the 

 same crop is grown year after year. The annual natural 

 accumulation of available plant food is greater, and conse- 

 quently smaller dressings of manures are necessary than would 

 otherwise be the case. 



(8) Volunteer crops are more easily controlled, and there- 

 fore varieties are more easily kept pure. Where maize is 

 grown continuously an undesirable cross-polination — e.g., 

 yellow on white varieties — may occur from plants grown from 

 the seed left in the soil from the previous crop. 



(9) Some crops are supposed to accumulate compounds in 

 the soil, toxic to themselves, w'hich are rendered harmless by 

 the growth of other crops. 



(10) The land is more fully occupied with crops than 

 where a single cropping system is followed. 



(11) Lastly, rotative cropping necessitates organisation 

 and good management, which in turn stimulate business 

 development. A farmer following good rotative farming knows 

 that each year he can expect approximately the same propor- 

 tion of each crop, a fact important not only because of its bear- 

 ing upon the profitable use of his labour, but valuable in its 

 relation to his whole business as a farmer. He knows how 

 much he is likely to have to handle of each crop, how much 

 stock he can keep, the variety of food he can feed them, and 

 the amount of money he is likely to receive from the sale of 

 certain of his crops. To be wejghed against the advantages 

 of practising rotations are the smaller considerations ; firstly, 

 that it requires greater skill to handle a variety of crops well ; 

 and, secondly, more machinery is required. 



The factors to be considered in planning a rotation are 

 many and varied, and in South Africa, where cultivation in 

 most parts is of a.n extensive rather than an intensive nature, 

 certain difficulties, due largely to the small variety of crops 

 grown and the very uncertain climatic conditions in many 

 areas, are encountered. On some rich soils, and where land is 



