216 ANNUAL REPORT OF THE Off. Doc. 



into the atmosphere, and there is no doubt, but that a very con- 

 siderable amount of nitrogen is thus dissipated. The soluble ni- 

 trites and nitrates may be removed from the surface layers of the 

 soil by drainage into the subsoil, where they usually find their way 

 by the percolation of rain water from above. This loss by drain- 

 age is greatest during the late summer and autumn, when the pro- 

 cess of nitrification is excessive, and hence, it is important to grow 

 some crop which will catch this nitrogen. Here, we have the ex- 

 planation why Indian corn does not exhaust the soil, as rapidly, 

 as some other crops. The growth of corn extending much further 

 into the late summer and autumn, the plant is adapted to utilize 

 the nitrates formed by the active processes of nitrification. In 

 the third place, under certain conditions of soil, the nitrogen may 

 be united chemically so as to form insoluble compounds, and thus, 

 the available nitrogen is locked up in some unavailable form, or by 

 the process of denitriflcation, the nitrogen may be set free upon 

 the decay of dead plants and animals that are found in any given 

 soil, and thus lost to the growing crop. Perhaps, the largest amount 

 of nitrogen is removed from the soil in the harvesting and disposal 

 of growing crops. These crops are in general sold at our large 

 centers of population, or are exported to foreign countries, where, 

 they are lost, in the form of manurial wealth to the country in which 

 they are produced. In the husbanding of our natural resources, 

 the sewage from our large cities, which is poured into the rivers and 

 ultimately finds its way to the sea should be pumped into reservoirs 

 where, by a proper system of distribution, it can be delivered to the 

 fields, where it is most needed. Connected with this sewage dis- 

 posal is the encouragement of home industries and local markets, 

 where the produce of our farms might be utilized directly without 

 the expensive outlay necessary to export such products to foreign 

 lands. 



Having briefly outlined the ways in which the soil becomes im- 

 poverished, it is important clearly to state how the nitrogen of the 

 soil may be accumulated. One of the most important sources of 

 supply is barnyard manure, which contains large quantities of am- 

 monia, but that ammonia cannot be absorbed directly by the root 

 hairs of the plant. We have abundant experimental proof that 

 green plants, except the leguminosae, can utilize the nitrogen only 

 in the form of nitrates, or only to a very slight extent, as am- 

 moniates. The ammonia in the manure must be converted into the 

 higher form. It has been found that there are two steps in this 

 conversion through the activity of soil bacteria. One kind of bac- 

 terium converts the ammonia into nitrous acid, or nitrites, the other 

 organism transforms the nitrous acid (nitrites) into nitric acid, or 

 the salts of nitric acid, the nitrates. The growth of these organ- 

 isms in the soil is stimulated by aeration, by the requisite moisture 

 and by a feebly alkaline condition of the soil. Too much organic 

 mateiial, too much water and too acid a condition of the soil, in- 

 hibits the growth of the micro-organisms concerned in nitrification. 

 Once the ammonia is converted into nitrates, the supplies of nitrogen 

 in the soil become available to green plants. The root hairs of all 

 our crops take up the nitrates in the soluble form, and in the green 

 parts, they are converted into protojilasm, or by protoplasmic ac- 

 tivity stored as nitrogenous reserve food. Many plants are inde- 



