THE YEAST OF THE SOIL. 

 By William H. Bowker, Boston. 



Read before the Society, January 9, 1909. 



In the discussion of this subject I shall not contribute anything 

 new to science, but I shall try to apply some of the scientific j^rinci- 

 ples and teachings which have been worked out during the past 

 decade. 



"The yeast of the soil," as we shall consider it, is not plant food, 

 but low organisms of life which exist in the soil and but for which 

 agricultural soils would be practically barren. "The yeast of the 

 soil" is what is scientifically known as bacteria, — organisms 

 which thrive in the soil and by means of which unavailable plant 

 food, especially nitrogen in the form of organic matter, such as 

 stable manure (leaves, stalks, etc.), is rendered available. The 

 great discoveries of Hellreigel, the leading investigator along this 

 line, demonstrate that higher orders of plant life are dependent upon 

 lower oixiers of life. We could not profitably grow a corn or potato 

 crop unless these organisms were growing at the same time in the 

 soil, or had previously existed there and done their work. 



We speak of a soil as being cold and non-])roductive. It may be 

 cold from an excess of water, or because it is too compact and 

 heavy, but the moment we drain it or lighten it by cultivation, it 

 becomes productive. The real reason it becomes productive is 

 that we admit air and warmth, which are necessary to develop the 

 growth of the little "yeast plants" (bacteria) which, in turn, attack 

 the stable manure or other organic matter (humus), and l^reak it 

 down, rendering it available to plants. Farmers say that they can 

 hear corn grow on warm days and hot nights, which is almost liter- 

 ally true. It is because the weather is favorable to the growth of 

 the nitrifying plants (bacteria of the soil) which convert the 

 unavailable nitrogen into available and soluble forms. 



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