SECTION IV. 

 RELATION OF BACTERIA TO SOIL. 



CHAPTER XIX. 

 RELATION OF BACTERIA TO FERTILITY. 



The farmer is interested in the soil as the home of the 

 plant. Unless its home is one favorable in every way to 

 the kind of plants the farmer is attempting to grow but 

 meager yields will reward his efforts. In order that the 

 soil shall be a favorable place for such growth, a num- 

 ber of conditions must be present. Its physical proper- 

 ties are important. It must not be hard and dense so 

 that the delicate roots of the young plant in search of 

 food cannot make their way through it. It must be in 

 good tilth. Moisture, not too abundant or too small in 

 amount, must be available. The temperature of the soil 

 must be conducive to rapid plant growth. These things 

 are all important and are to a great extent at least under 

 the control of the farmer. 



Plant food. Another important condition required 

 is the presence of a sufficient supply of plant food in an 

 available form f or 4ise by the plant. Certain chemical 

 elements as potassium, calcium, magnesium, phosphorus, 

 nitrogen, sulphur, and iron are essential in order that 

 normal development may occur. These substances the 

 plant obtains from the soil. The carbon, oxygen, and 



