356 MAIZE 



chap, the following crop. For example, a crop of wheat withdraws 

 VIIL large amounts of phosphoric acid from the soil, but takes re- 

 latively small quantities of lime and potash, while a crop of 

 beans requires a great deal of potash and relatively less 

 phosphoric acid. 



(2) Some crops are surface feeders while others root more 

 deeply, drawing their food from the lower layers of the soil. 

 By alternation of deeper with shallower rooted crops the avail- 

 able food supply is utilized to better advantage and made to 

 last longer. 



(3) Certain crops replace in the soil certain ingredients 

 which have been removed by other crops, for instance such 

 crops as lucerne and peanuts give back nitrogen. 



(4) Rotation of crops helps to clean the ground of "vol- 

 unteer" plants from the preceding crop, which, in the case of 

 wheat, oats, and especially of maize, cause so much mixing 

 or crossing of seed, with resulting loss to the farmer. 



(5) As different crops require different treatment of the 

 soil, a change enables the farmer more easily to clean the 

 land of such weeds as are particularly injurious to a given 

 crop, tn the rotation the farmer can use crops which are 

 known as " cleaning " crops. 



The general results of rotation may be summarized as : — 



(a) The production of crops of greater vigour and better 

 yield. When crops of the same kind are grown continuously 

 on the same land the crop becomes less vigorous and, con- 

 sequently, more susceptible to attack by insect and fungous 

 pests. Rotation disturbs the " balance of nature " in such a 

 way that the pest dies from lack of its normal food or goes 

 away to search for it elsewhere. 



(b) The reduction of the manure bill. 



(Y) A principle of rotation is the division of the land into 

 two to four portions, no two of which bear the same crop in 

 the same season. A well-arranged rotation reduces the labour 

 required at any one time, inasmuch as not all crops require to 

 be planted, cultivated, or harvested at once. 



The principal points to observe in planning a rotation are : — 



(1) Have at least one leguminose crop in the rotation. 



(2) Have at least one cultivated or " cleaning crop," or, in 



its place, a "smother crop" for weeds. 



