Power of Soils to absorb Manure. 



143 



for the present. AVe have seen that whenever a salt of ammonia 

 or of potash reaches the soil, and gets distributed through it, a 

 change occurs — a double silicate of alumina and ammonia or 

 potash is formed, and the salt which was added no longer exists 

 there. The ammonia or potash henceforth exists in the soil only 

 in the form of silicate, and is presented to the roots of a plant 

 only in that form, or in the form of carbonate, derived from it by 

 the action of carbonic acid in the soil. And inasmuch as all 

 average soils possess this property of conversion in more than the 

 degree necessary for the quantity of manure which reaches them, 

 the inference is obvious and incontestable, that nature has given 

 to the soil this power for the specific purpose of preparing the 

 food of plants, and we then have the soil occupying a place inter- 

 mediate between that of mere dead matter and the living organism 

 of plants. Further, if the combinations of these two, so to speak, 

 innocent and mild acids, the carbonic and silicic, are the only ones 

 appointed by nature, it follow^s that the salts of mineral acids, the 

 sulphates and muriates, are not suited, indeed positively in- 

 jurious, to vegetation. This may account for the unhealthy 

 grossness of wheat fed with crude ammoniacal salts, which have 

 reached its roots without sufficient incorporation with the soil, 

 whilst wheat grown after the Tullian system seems never to 

 become over luxuriant, for in the latter case, as the ammonia is 

 only obtained by virtue of the power of the soil to abstract it 

 from the air, so it can never exist in it in any other than the form 

 in which it is best suited for the wants of the crop. And this 

 leads me, in conclusion, to remark that it is quite possible that 

 light soils, w^hich, from their w^ant of power of preparing the 

 manure, cannot be safely manured with guano or ammoniacal 

 salts for the wheat crop, might perhaps benefit largely by the use 

 of these double silicates — that an ammoniacal double silicate being 

 the ready formed food of the cereals, might be an admissible 

 source of ammonia when neither guano nor any other source of 

 ammonia could be used. Whether the compounds now described 

 could be produced at a sufficiently cheap rate for any practical 

 application, I cannot at present state ; but if so, I think it very 

 probable that they might be of great service in practical agri- 

 culture : and owing to the property of solidifying ammonia pos- 

 sessed by some of them, they might be , made the means of 

 obtaining this valuable alkali from sources which are not at 

 present available. 



I am still engaged in follovv' ing up the bearings of this highly 

 interesting subject, and shall hope at a future time to have further 

 important results to bring before the attention of the members of 

 this Society. 



