THE FIRST BOOK OF FARMING 



These nitrifying germs attack the humus, break 

 it down, separate the nitrogen, cause it to unite with 

 the oxygen of the air and thus build it into nitric 

 acid which can be used by plant roots. This nitric 

 acid if not immediately used will unite with lime or 

 potash or soda or other similar substances and form 

 nitrates, as nitrate of lime, nitrate of potash or com- 

 mon saltpetre. These nitrates are soluble in water 

 and can be easily used by plant roots. If there are 

 no plant roots to use them they are easily lost by 

 being washed out of the soil. The work of the 

 nitrifying germs is called nitrification. 



To do their work well the nitrogen-fixing germs 

 and the nitrifying germs require certain conditions. 



The soil must be moist. 



The soil must be well ventilated to supply nitro- 

 gen for the nitrogen-fixing germs and oxygen for 

 the nitrifying germs. 



The soil must be warm. Summer temperature is 

 the most favorable. Their work begins and con- 

 tinues slowly at a temperature of about forty-five 

 degrees and increases in rapidity as the temperature 

 rises until it reaches ninety or ninety-five. 



The nitrifying germs require phosphoric acid, 

 potash and lime in the soil. 



Direct sunlight destroys these bacteria, therefore 

 they cannot work at the surface of the soil unless 

 it is shaded by a crop. 



From this we see that these bacteria or germs 

 work best in the soil that has conditions necessary 

 for the growth and development of plant roots. 



