526 MISCELLANEOUS FARM SUBJECTS 



under the action of nitrifying bacteria is every year carried off in 

 various waterways and ultimately reaches the ocean, where, of 

 course, it is of no benefit to man. 



A third great source of nitrogen loss is through the action of a 

 group of bacteria which have the power of breaking down nitrates, 

 depriving them of oxygen, and reducing them to ammonia or nitro- 

 gen gas, when they are, of course, unavailable for plant food. This 

 process of denitrification, while very useful in the septic tank, 

 which is the most sanitary method of sewage disposal, is the source 

 of considerable loss to the farmer, and manures may often be ren- 

 dered practically worthless by the action of these bacteria. 



Other means by which nitrogen is lost so far as plant foods 

 are concerned, are the washing out of nitrogen salts from the soil 

 and the burning of explosives which are largely composed of some 

 nitric salt that would be directly valuable to the vegetable kingdom. 

 Of the three important elements nitrogen is the most easily lost to 

 the farmer by washing of the soil. (Ont. Agr. Dept. B. 148; 

 Y. B. 1902.) 



Nitrogen Must Be Supplied. No soil where plants of any kind 

 will grow is wholly devoid of nitrogen, but some soils are much 

 more abundantly supplied w r ith this valuable element than others. 

 The quantity of nitrogen present in soils in the form of organic mat- 

 ter (humus) may vary from one-tenth to two-tenths of one per 

 cent in the surface layers, or 7,000 to 28,000 pounds per acre in the 

 first three feet. Since from each acre of such land fifteen bushels of 

 wheat would remove about twenty-five pounds, and one ton of 

 clover hay about fifty pounds of nitrogen, it is easy to understand 

 that the majority of agricultural soils contain within themselves 

 a store of nitrogen sufficient for many years to come. But before 

 the nitrogen thus locked up in soils in the form of organic matter 

 can be made available to plants it must undergo a series of complex 

 chemical changes, through the agency of bacterial life, by which 

 the nitrogen of said organic matter is converted into ammonia and 

 finally into nitric acid. 



Some plants take much more nitrogen from the soil than do 

 others, and when grown continuously they exhaust the available 

 supply. The sources of nitrogen supply are: (1) The nitrogen 

 already contained in the soils; (2) that supplied to the soil by the 

 decay of organic matter; (3) the fixation of atmospheric nitrogen. 

 The air is a mechanical mixture of oxygen and nitrogen about 4 

 parts of the latter to one of the former. 



The nitrogen in soils is of two types: (1) The ammonia, 

 nitrites, and nitrates, in which forms it is available to crops; and 

 (2) the nitrogen locked up in organic matter and not directly 

 available. The nitrate nitrogen (nitrogen in the form of nitrates) 

 is in most soils present only in small quantity. This supply is 

 quickly taken out by crops or washed out by rams, and if it is not 

 renewed by the action of certain bacteria on the nitrogenous or- 

 ganic matter in the soil or from the atmosphere by other bacteria 

 it must be added directly as nitrate of soda or nitrate of potash, or 



