CHAPTER VI 



THE RELATION OF MICROORGANISMS TO 

 SOIL FERTILITY 



The basic work of the farmer is the growing of plants of 

 economic value. All other work is incidental and insig- 

 nificant in comparison with the growing of the green plant 

 that is to supply food for man and for the animals he has 

 brought to his service. The farmer's primary interest is 

 then-fore in the soil, as the place in which the plants he 

 desires to cultivate will grow. 



There are many factors that determine whether the soil 

 is a place in which the plant can grow well and yield to the 

 farmer a large return for his labor. The texture of the 

 soil must be such that the roots of the plant can penetrate 

 it freely, in order that they may draw food and water from 

 a large volume of the soil. The water content of the soil 

 must vary within certain limits. If it is too low, the 

 growth of the plant will be checked; if it is too high, the 

 factors preparing the food for the plant will be interfered 

 with, and again growth will be retarded. The temperature 

 must be favorable for the plant, and also for the agents that 

 are active in making the food ready for it. Lastly, there 

 must be a supply of food in fitting form for the crop. If 

 the farmer is to be successful in the highest sense, he must 

 control these various factors. 



The control can not be absolute, but it may be exercised to 

 a high degree. The farmer must have before his eyes not 

 only the crop of the year, but of the next year, of the next 



