673 



I have been treating only of the mineral constituents of the soil r 

 but no less necessary is the organic matter of the soil to its fertility. 

 If the organic nitrogen was not in the soil in sufficient quantity and 

 readily available, although the potash and phosphoric acid were 

 there in the best proportions, the soil would be either barren or 

 produce but very small crops. The nitrogen, before it can be 

 absorbed by the plant, must be converted into nitric acid or a 

 nitrate. This is accomplished through the agency of micro-organ- 

 isms in the soil. This brings us now to the consideration of the 

 biological properties of soils. 



Every cultivated or fertile soil has within it an enormous 

 number of bacteria ; in fact, the soil is generally said to be teeming 

 with them. The number that is estimated to be contained in 15 

 grains of soil is variously stated to be from one half to a million. 

 These micro-organisms are the silent workers in the soil that pre- 

 pare the necessary food for the plants, as the plants themselves 

 are not capable of absorbing nitrogen in the state in which it is 

 found in organic matter. The importance of these micro-organ- 

 isms to the agriculturist is very great. The soils should be kept in 

 a condition most suitable for these micro-organisms to fully carry 

 out their proper functions. If the soil is not kept in a condition 

 suitable for the nitrification of the organic nitrogen, the very 

 opposite effect may be produced, and loss may take place in the 

 soil by another class of bacteria, which causes the dentritication of 

 the nitrates in the soil with liberations of free nitrogen. 



Our knowledge of the nitrification of the organic nitrogen in 

 the soil is of recent date. The first to discover that it w is caused 

 by the action of bacteria in the soil were the two French chemists, 

 Schloesing and Munt/, who announced their discovery in 1877. 

 It was not till 1890 that we knew the true action of the bacteria on 

 nitrogen in the process of nitrification, when R. Warington and 

 Professor P. Frankland discovered and isolated two different 

 bacteria or micro-organisms that take part in the process of nitrifi- 

 cation. One of these bacteria acts by converting the nitrogen into 

 nitrites, and the other converts the nitrites into nitrates, in which 

 state the plants can absorb it. 



They appear to be able to obtain their carbon from a purely 

 mineral source when no organic matter is present a fact that is 

 opposed to our previous ideas of those micro-organisms, as it has 

 always been held that micro-organisms must obtain their carbon 

 from a vegetable source. The conditions necessary, or favorable, to 

 nitrification arc that phosphoric acid must be present for nitrifica- 

 tion to take place ; it requires the presence of an alkaline base such 

 as carbonate of lime for the nitric acid to combine with as it is 

 formed. The presence of carbonate of soda, except in minute 

 quantities, has a prejudicialxjlYect, or may stop the process entirely. 

 Gypsum has been found to have a good effect. It probably acts 

 by neutralizing the excess of alkalinity, which stops the process. 



