26 



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 rains, and if it is not re- 

 newed by the action of certain bacteria on the nitrogenous 

 organic 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 some other manure must be used containing directly 

 available nitrogen, Manures containing directly available nitro- 

 gen are very expensive. The best of these is nitrate of soda, and 

 at the present rate of use the known supply will be exhausted 

 in less than fifty years. More than 1,543,120 tons were used in 

 1905. Prof. Sylvanus P. Thompson has reiterated in a recent 

 address* the prophecy of Prof. William Crookes, that we shall 

 have a wheat famine unless the yield per acre, averaging for the 

 whole world 12 7-10 bushels, can be increased. He believes 

 with Crookes and many others who have studied the question 

 carefully that the supply of nitrates is the most important factor 

 in the situation, and it is important not only for wheat but for all 

 other crops. We are not, however, as Professor Thompson seems 

 to believe, dependent on the electrical method, briefly discussed 

 later in this paper, for obtaining this supply. The larger part of 

 the nitrogen required in agriculture is now and will always be 

 obtained from the atmosphere through the agency of certain soil 

 bacteria. By careful study of these organisms and their require- 

 ments we can greatly increase their activity. The electrical 

 method, however, will be useful in supplying a part of the imme- 

 diately available nitrate needed in intensive agricultural opera- 

 tions. 



THE DECAY OF ORGANIC MATTER. 



The organic matters which are added to the soils in manures 

 and in vegetables and animal remains must go through certain 

 processes of decay before the plant foods they contain become 

 available to crops. Bacteria and fungi of various kinds are the 

 active agents which bring about these changes. Decay is not a 

 simple process, the same in all places and under all conditions. 

 The process varies when the same materials under the same 

 conditions are acted upon by different organisms or groups of 

 bacteria which produce it. 



In general, organic materials contain two classes of com- 

 pounds ; (1) The nitrogenous or albuminoid compounds, like flesh 

 and blood of animals and the protoplasm of plant cells ; and (2) 

 the non-nitrogenous compounds, the carbohydrates (such as sugars, 

 starches and cellulose) and the hydrocarbons, as fats. The first 

 class contains the nitrogen formerly taken from the soil as nitrate 

 by some plant, but which in its highly organized form is unavail- 

 able to crops until converted into ammonia or nitrate again 

 by certain bacteria. The compounds of the second class 

 serve as food for certain bacteria which are able to obtain their 

 nitrogen from the air and will be discussed later. 



*See Nature, vol., 73, p. 355, 1906. 



