298 AGRICULTURAL ANALYSIS 



plants a supply of nitrogen in the most highly available state. 

 There is perhaps no other kind of plant food which is offered to 

 the living vegetable in a more completely predigested state, and 

 none to which a quicker response will be given. By reason of 

 its high availability, however, it must be used with care. A too 

 free use of such a stimulating food may have, in the end, an 

 injurious effect upon the crop, and is quite certain to lead to the 

 waste of a considerable portion of expensive material. For this 

 reason sodium nitrate should be applied with extreme care, in 

 small quantities at a time, and only when it is needed by the 

 growing crop. It would be useless, for instance, to apply this 

 fertilizer in the autumn with the expectation of its benefiting 

 the crop to a maximum degree the following spring. Again, if 

 the application of this salt should be made just previous to a 

 heavy rain, almost or quite the whole of it would be removed 

 beyond the reach of the absorbing organs of the plant. 



When once the nitric acid has been absorbed by the living 

 rootlet it is held with great tenacity. Living plants macerated 

 in water give up only a trace of nitric acid, but if they be pre- 

 viously killed with chloroform, the nitric acid they contain is 

 easily leached out. 



The molecule of sodium nitrate is decomposed by dissociation 

 or otherwise in the process of the absorption of the nitric acid. 

 The acid enters the plant organism and the soda is left to combine 

 with the soil acids. The nascent soda may thus play a role of 

 some importance in decomposing particles of minerals contain- 

 ing potash or phosphoric acid. Some authorities say the decom- 

 position of the sodium nitrate takes place in the cells of the ab- 

 sorbing plant organs, for it is difficult to understand how it 

 could be accomplished externally. While the soda, therefore, is 

 of no importance as a direct plant food, it can hardly be dis- 

 missed as of no value whatever in the process of fertilization. 

 Many of the salts of soda, as, for instance, common salt, are quite 

 hygroscopic and serve to attract moisture from the air and thus 

 become carriers of water between the plant and the air in sea- 

 sons of drought; and sodium nitrate itself is so hygroscopic as 

 not to be suited to the manufacture of gunpowder. 



