MANURES. 249 



potash in considerable quantity, the result will be the production 

 of as large a crop as, in view of the composition and circumstances 

 of the soil, it is possible for potash to produce, and the crops may 

 be doubled or quadrupled, as the result of the application of the 

 potash alone. But they, at the same time, remove from the soil 

 double or quadruple the quantity of phosphoric acid that was 

 required by the smaller crop ; and the result is, that while the 

 manure has by no means had the effect of exhausting the soil, 

 but has rather added to its valuable ingredients, the crops produced 

 in consequence of the use of that manure have exhausted the soil 

 of some ingredient which the manure did not supply, namely, 

 phosphoric acid. 



In the case cited above — that of the production of large crops 

 of wheat by the aid of Peruvian guano in Maryland — it is prob- 

 able that the ammonia of the guano increased so largely the pro- 

 duction of wheat, that the soil was robbed, in the course of a few 

 years, of elements which the guano did not supply in sufficient 

 quantity ; and, these elements being once removed, no amount of 

 any other constituent would suffice for the growth of plants to 

 which they are absolutely requisite. 



Therefore, in the use of either superphosphate of lime, or of 

 bones or bone-dust, the principal available ingredient supplied being 

 phosphoric acid (and perhaps ammonia), the soil may, as a con- 

 sequence of the greater production, be robbed of potash, or some 

 other element, to such an extent as to be permanently injured. 

 It is wrong, however, in this case to blame the manure for the 

 result. We should rather blame ourselves for having pursued such 

 a system of cultivation as has taken away elements of the soil's 

 fertility, trusting to some other element to supply its place. 



To use a homely illustration of our meaning, we will take the 

 case of a merchant tailor who receives a large accession to his stock 

 in the form of woolen cloth, and has not the means of increasing, 

 materially, the quantity of his other supplies. If stimulated by 

 this addition to his stock, he takes an army contract for overcoats, 

 and employs a sufficient number of hands, under contract for the 

 season, to make them, the result will probably be that he will run 



