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BENEFICIAL ACTIVITIES OF BACTERIA 



tato blight will not affect wheat. Rotation of crops also kills 

 insect pests that live only on a certain plant. (3) The un- 

 gathered roots and stalks of crops remain in the ground, 

 decay, and produce organic acids. These acids are sometimes 

 injurious to the plant producing them, but not to other plants. 

 Hence, the crops should be changed. Bone meal or lime is added 

 to neutralize these acids. Each commercial fertilizer used, how- 

 ever, adds that much to the farmer's expense. (4) Almost all 

 crops remove great quantities of nitrates from the soil. These may 



A number of different bacteria aid in transforming nitrogen into a form which plants can 

 use. There is a constant renewal of nitrogen in the soil. 



be restored in a variety of ways. Animal waste, manure, may be 

 spread over soil and allowed to decay. This increases the nitrogen 



