No. 6. DEPARTMENT OF AOniCULTURE. 439 



verts into such a coiulition that the plaut can use i(. The nitrogen 

 accumulated in (his wa}- and distributed Ihrough the roots and 

 branelies of the plants remains in the soil and forms a humus rich in 

 nitrogen, and adds the most valuable fertilizer without any expense 

 to the farmer. Through the agency of these and similar organisms 

 and plants, the properties of which we have not yet discovered, the 

 nitrogen of the soil has been accumulated. We have not only these 

 nitrogen accumulating organisms in the soil, but a large number of 

 others, among which are the nitrifying bacteria which convert the 

 nitrogen of the organic matter into nitrites and nitrates which seems 

 to be the most available condition of plants to use it. This process 

 is called nitrification and the following conditions have been found 

 to be essential for the development and operations of the bacterium 

 which produces it. 



1. A supply of fod for the bacterium, consisting of the humates of 

 phosphoric acid and potash. 



2. A sufficient supply of oxygen, because the bacterium belongs to 

 aerobic class. 



3. An amount of moisture to enable the bacterium to produce the 

 chemical changes required. 



4. A temperature ranging between 54 and 77 degrees F. 



5. The absence of strong sunlight , because like most of these 

 plants it can no't thrive in strong sunlight, but immediately beneath 

 the surface of the soil in the presence of air seems to be the most 

 prolific field for its development and operations. 



6. The presence of some alkali element, such as lime, to combine 

 with the nitric acid formed by the organism for the absence of an 

 alkali is the most potent factor for non-nitrification. 



There seems to be two stages of nitrification and two bacteria, one 

 for each stage, nitrous and nitric bacteria, both of which make ni- 

 trogen available for plant food. We have not only these beneficial 

 bacteria in the soil, but some which produce exactly the opposite 

 results; instead of preparing available nitrogen in the soil, they set 

 it free. The bacterium which produces these results belongs to the 

 anaerobic class, which thrives only in the absence of air, and the 

 conditions most favorable for its operations is a soil so saturated with 

 water or so compacted as to exclude all air; when these conditions 

 prevail, the nitrogen of the organic matter in the soil is set free. 

 Kitrogen can not be fixed in the soil like the rest of the fertilizing 

 elements, such as potash and phosphorus, because all the salts of 

 nitric acid are soluble in water. There is a general tendency for the 

 soluble phosphates and potash fertilizer to become fixed or to change 

 into the insoluble state. When a solution of potassium nitrate is 

 added to a column of clay soil it will be found that the filtrate run- 

 ning through contains barely a trace of potassium nitrate, but in- 



