60 SUCCESSFUL FARMING 



of great importance in preparing plant food for our ordinary farm, garden 

 and orchard crops. They are instrumental in making nitrogen available 

 for higher plants. They also bring about availability of the mineral 

 constituents of the soil. It is essential for the farmer to understand that 

 the bacterial flora of the soil is important, and that the multiplication of 

 these bacteria is generally to be encouraged. It is also well to know 

 that there are two great classes of bacteria: first, those that thrive best 

 in the presence of plenty of air, from which they obtain oxygen; and 

 second, those that thrive best with little air and even in the total absence 

 of oxygen. These classes are spoken of as aerobic and anaerobic bacteria, 

 respectively. The first class, or those thriving best with plenty of air, 

 are made up generally of the beneficial forms, and these dominate in the 

 more productive soils. They require for their life and rapid multiplica- 

 tion food in the form of organic matter, although many forms live directly 

 on the mineral elements of the soil. They need moisture and are dormant 

 or may die when the soil remains long in a very dry condition. They 

 must have air and this is facilitated by the tillage of the soil. 



Nitrogen Increased by Bacteria. — Soil bacteria have no greater 

 function in soils than the conversion of organic nitrogen into ammonia, 

 nitrites, and finally nitrates, thus making the nitrogen available for higher 

 plants. Nitrogen is the most expensive element that farmers have to 

 purchase in a commercial form. It costs about twenty cents per pound, or 

 three times as much as granulated sugar. Nitrogen is present in the air 

 in great quantities, and it is chiefly through various forms of bacteria 

 that the higher plants are able to secure the necessary supply. Among 

 the bacteria instrumental in this process are the numerous species that 

 are found in the nodules on the roots of the various leguminous crops. 

 For ages legumes, such as clovers, have been recognized as beneficial to 

 the soil, as shown by the increased growth of the non-leguminous crops 

 that follow. Not until the discovery of these bacteria in the nodules on 

 the roots of legumes (about one-fourth century ago) was it understood 

 why legumes were beneficial. 



The species of bacteria that occur in the nodules on the roots of one 

 leguminous crop is generally different from that occurring on a different 

 leguminous crop, although there are a few exceptions to this rule. The 

 same species of bacteria occur on the roots of both alfalfa and sweet 

 clover, but a different species is characteristic of red clover, and one species 

 cannot be successfully substituted for another. It is, therefore, essential 

 to use the right species when attempting to inoculate soil artificially for 

 a particular leguminous crop. The different species of bacteria for the 

 leguminous crops will be discussed under each of those crops in chapters 

 which follow. 



There are also species of bacteria living in the soil, not dependent 

 directly upon legumes, which have the power of abstracting free nitrogen 

 from the air and converting it into forms available for general farm crops. 



