LUTHER BURBANK 



When trouble arises from this source 

 remedy is to rotate the crops or, in other words, 

 move the crop infested to another location. 



Fungous diseases are especially destructive in 

 potato fields. The potato scale, blight, and wart 

 are well-known diseases which can often be wholly 

 or partially controlled by the proper rotation and 

 the planting of uninfected seed. 



The third cause for failures is the unfavorable 

 condition of the soil produced by the toxic sub- 

 stances thrown off from the growing plants. Plants, 

 like animals, give off waste matter which is not 

 only useless but poisonous to the plant itself, and 

 often to other plants of similar nature. 



These toxic substances are often less poisonous, 

 and in some cases are beneficial, to other crops. 

 It is obvious that when waste products from a 

 certain crop have accumulated in the soil for a 

 number of years, that soil is not as well suited to 

 the crop as formerly. A change of crops prac- 

 tically always results in a more profitable yield 

 because the waste products of the first crop are 

 often not injurious to the second one. 



The fourth cause, which is far less common 

 than the others, is exhaustion from the soil of 

 certain elements necessary to plant growth. 



It is very seldom indeed that any one of the 

 elements necessary to plant growth is wholly 



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