IO8 THE SOIL SOLUTION 



In this connection it is well to consider what constitutes a 

 commercial fertilizer. It must be a substance the addition of 

 which either directly or indirectly affects the properties of the 

 soil or the growing plant ; it must be obtainable in large quantities 

 and from a source or sources of supply not readily exhausted; 

 and it must be cheap. Of the many substances filling the first 

 condition, all those which fulfill also the other conditions are 

 used as fertilizers, with the exception of common salt and human 

 excrement. In spite of the fact that it does not contain a con- 

 ventional plant-food, sodium chloride appears to produce results 

 quite similar to those produced by the usual fertilizer salts. Its 

 use has been followed generally by an increased yield of crop, 

 but occasionally by a decreased one, and it appears not improb- 

 able that further investigation would show sodium chloride to 

 have a considerable value as a fertilizer. Human excrement or 

 night soil, and the sewage and garbage refuse of our large cities 

 are not commercial fertilizers, although having undoubtedly a 

 high agricultural value. Objection has been urged to them that 

 they are "filthy" and liable to contain dangerous pathogenic 

 organisms. Both objections could be met. It seems a more 

 rational explanation that the agricultural methods of this country 

 have not yet become sufficiently intensive to necessitate the con- 

 servation of such materials or to justify their commercial 

 exploitation. 



New products will come into use from time to time, as in the 

 case of calcium cyanamid and basic calcium nitrate. But it is 

 worthy of note that these substances have become available not 

 so much because of their agricultural value, but incidentally to 

 the efforts of inventors and manufacturers to produce cheap 

 nitric acid for the preparation of high explosives. 1 There seems 



1 In this connection it may be of interest to call attention to the fact 

 that the Twelfth Census shows less than a fifth of the sodium nitrate 

 brought into the United States goes into the fertilizer trade. Moreover, 

 the production of ammonium salts by the extensive coke and gas plants 

 of the country has been practically nil not because of any inherent diffi- 

 culties in making them or because the cost of production has been high, 

 but because the market demands in this country have been too small. 



