P:XPERIMENT station bulletins. 147 



SOME ESSENTIAL SOIL CHANGES PRODUCED BY MICRO- 

 ORGANISMS. 



S. FRED EDWARDS. 



Bulletin No. 218. 

 INTRODUCTION. 



The object of this bulletin is to review simply and briefly the present knowl- 

 edge ot soil bacteriology in its relation to agriculture with a view to em- 

 phasizing the close relationship between bacteriologic principles and the com- 

 mon operations of tilling the soil. 



The problem of rendering his poor soil more productive, and his good soil still 

 better, is one in which every farmer of today is interested. We venture the 

 statement that of all the "run down" or abandoned farms in the United States 

 there is not one which cou^d not be made productive again if proper methods of 

 handling the soil were employed. 



The failure of land to yield a crop is not due in most cases to a lack of plant 

 food in the soil. Results of chemical analyses show that in average soils through- 

 out the country there is in the first eight inches, enough nitrogen to last 90 years, 

 enough phosphoric acid to last 500 years, and enough potash to last 1,000 years. 

 Why, then, if the soil contains such stores of plant food, does it fail to support 

 crops? Simply because these elements are locked up in such chemical combina- 

 tions that the plants are unable to utilize them. 



The great problem, then, of modern agriculture, is not entirely the conservation 

 of plant food in the soil, but rather the unlocking of the rich stores already in 

 the soil, and placing them in a condition to be assimilated by plants. This un- 

 locking process is carried on naturally by the soil micro-organisms. 



Plants, from the mightest forest tree to the tiniest blade of grass, consist of a 

 complex combination of microscopic cells, each cell containing protoplasm. This 

 protoplasm is continually changing, taking up food which is brought to it in the 

 sap, and casting off its waste products in much the same manner as the protoplasm 

 in the animal body. 



Bacteria are also plants, consisting, however, of but a single cell filled with 

 protoplasm, which, like that of the higher plants, is continually active in assimi- 

 lating from the surrounding medium the food elements necessary for its main- 

 tenance. These myriads of little plants, invisible to the naked eye, in taking their 

 food from the chemical compounds of the soil, produce in those compounds just 

 the changes necessary to render them useful to the higher plants in making their 

 growth. 



CONDITIONS OF GROWTH. 



In. ord^r that bacterial activity may go on with undiminished vigor, there are 

 certain conditions of the soil which must be provided, certain requirements of 

 the bacteria which must be complied with, namely: temperature, moisture, re- 

 action, respiration, and food supply. 



TEMPERATURE. 



Soil bacteria are most active at a temperature of 60° to S0° Fah., although 

 some will grow at temperatures as low as 35° and as high as 98° Fah. Hence 

 the different soil processes induced by bacterial action are carried on most 

 rapidly during the summer months, and cease with the setting in of cold weather, 

 proceeding again with the opening of spring. 



