246 IMPORTANCE OF MICROBES IN SOIL FERTILITY 



substance, with the result that certain of the simple products 

 formed in the reaction are once more built up into complex sub- 

 stances. The microbe may be likened in this respect to any other 

 living organism which is large enough to be seen with the naked 

 eye. Food is consumed by an animal in the form of organic 

 compounds which furnish energy for it« development. Some of 

 the organic materials are broken down with the liberation of 

 energy which is utiUzed for synthesizing cell substance and con- 

 ducting other vital processes. During active growth, an appre- 

 ciable part of the consumed elements remains in the body as tis- 

 sues of the animal. The remainder is eliminated as waste products 

 such as carbon dioxide, water, urea, and a variety of organic sub- 

 stances. Similarly, in the development of the microbe, the trans- 

 formations are associated with cell growth and Uberation of waste 

 products. 



Although the results of this synthesis may or may not 

 be desirable from the point of view of soil fertihty, this is 

 merely a result of the nutritional development of microorganisms 

 under the environmental conditions existing in the specific habitat. 

 The organism develops in competition with its associates to make 

 the best growth possible under the circumstances. In the absence 

 of growing plants for a period of time, there is a continuous deple- 

 tion of sources of energy for cell development, and the waste 

 products of the cells become the simple inorganic substances from 

 which further plant growth develops. The renewal of growth of 

 higher plants again starts the supply of food for the microbe. 



Each reaction brought about by microbes is accompanied by a 

 definite amount of growth as indicated by the amount of cell 

 substance synthesized, depending upon the nature of the organism, 

 amount of energy and nutrients available, and environmental con- 

 ditions. The larger organisms of the soil, namely, those of an 

 animal nature, feed on the smaller microbes. These numerous 

 changes thus result in the manufacture of a considerable amount 

 of organic matter of microbial origin in the soil. Frequently 

 large quantities of nitrate nitrogen, phosphates, and other nutrient 

 elements which are so essential to the growth of higher plants are 

 temporarily stored away in the bodies of the microbes. In carry- 

 ing out these processes, the microbes compete with the green 

 plants for the available soil nutrients. Fortunately, even the 

 microbes are not invulnerable against the attack of their own kind, 



