302 Soda-Salts in Aginculture. 



all very soluble salts that are not positively poisonous, but none 

 is so cheap and so innoccuous as this, and therefore so well cal- 

 culated to discharge this important function. 



', It will be seen that the value of a fertilizing agent does not 

 always depend upon the fact that it is an essential element of 

 nutrition ; the substance which we apply to the land with a view 

 of increasing our crops may have no value whatever as a direct 

 fertilizer, and may, as is the case with chloride of sodium, not 

 even make its appearance in our grain-crops, and yet it may be 

 instrumental in materially raising the produce of wheat. 



Again, such non-essential salts in general may nevertheless 

 play an important part in tlie nutrition of plants l)y assisting the 

 solution and uniform distribution of fertilizing constituents which 

 occur in the soil in a sparingly soluble or insoluble condition. 

 It is well known to chemists that chloride of sodium exercises 

 such a dissolving action upon several bodies, and thus it is not 

 too great a stretch of fancv to assume that it will act beneficially 

 in the field by dissolving and rendering available earthy fer- 

 tilizing constituents Avhicli without its aid will remain in an 

 inert condition for a long time. 



The remarkable changes Avhich solutions of salts of j^otash 

 undergo in passing through different soils naturally leads us to 

 suspect that similar changes take place when dilute solutions of 

 soda-salts are filtered through a soil. 



We know, indeed, that soda to some extent, though, in com- 

 parison with potash, only to a small extent, is absorbed by most 

 soils, and that its absorption, like that of ammonia, potash, phos- 

 phoric acid, &c,, is mainly due to chemical action, and not merely 

 to physical attraction. 



All soils possess a wonderful capacity of adapting or convert- 

 ing crude fertilizing substances into combinations fitted to support 

 the process of nutrition of plants. The changes which soluble 

 fertilizers undergo in contact with soils of various characters are 

 frequently quite unexpected. Tlie results of titration experiments 

 are very much influenced by the comj)osition of each individual 

 soil operated upon, and by the strength and even the quantity 

 of the saline solution brought into contact with it. We must, 

 therefore, be careful how we attempt to deduce from the results 

 of special experiments an universal or natural law of husbandry. 

 The results of such experiments are not without value ; they hold 

 good, however, only under the particular conditions under which 

 they were performed in the laboratory, and probably many more 

 years of hard study and conscientious self-denying work on 

 many intelligent practical observers will still be required, before 

 our knowledge of the mysterious process of vegetable nutrition 

 will be much advanced. 



