MANURES. 59 



one bushel to the acre makes land always more productive, but 

 that a larger quantity would for two or three years afterward 

 render it actually sterile." See Appendix C. 



We cannot, however, recommend salt, as a general manure, 

 to any extent, as the application of it is attended with consider- 

 able hazard. If too heavily applied, it will not only diminish, 

 but completely check vegetation. Experience is entirely op- 

 posed to the indiscriminate application of common salt in any 

 considerable quantity to land. 



Potassa, (potash,) acid, and forming the well known sub- 

 stance saltpetre, has been employed as a manure, and appa- 

 rently with very good effect. It is found in greater or less 

 quantities in all vegetables; soda, generally in plants growing 

 near the sea, (sea-weeds, as we have seen, form a good but not 

 a lasting manure,) or in soils impregnated with marine salt. 

 The saline combinations of potash are expensive, and this is 

 probably one great objection to their general use; for, there is 

 reason to believe that potassa, like lime, exercises a certain in- 

 fluence on the soil, by rendering soluble, certain substances 

 which were insoluble. 



Some persons are of opinion that the astonishing effect pro- 

 duced on vegetation by the application of the green-sand or 

 marl of New Jersey, and other localities, is in due proportion 

 to the predominance of potash in its composition, without re- 

 ference to the other ingredients which are in combination with 

 it. Sure it is, that marl, in which neither lime nor potash is 

 present, is considered valueless. 



Potash was known to the ancient Gauls and Germans, and 

 soda was familiar to the Greeks and Hebrews. This latter 

 substance, which is found native in Egypt, and is there called 

 natron, was known to the ancients by the name of nitrum. 



The whole subject or range of saline manures, it is to be 

 observed, deserves more extended investigation than it has yet 

 obtained. That all saline bodies which exist habitually in 

 plants are beneficial to vegetation, we may almost, from analo- 

 gy, infer. We see this in the case of the carbonate of lime, 

 the sulphate of lime, and the phosphate of lime, and it is not 

 unreasonable to infer that all saline bodies which exist in plants 

 in their common state, may be employed as manures. 



The knowledge in which we are now deficient, regards the 

 quantity in which these substances should be applied. The 

 carbonate of lime is that in which it appears the greatest lati- 

 tude may be given. The sulphate of lime acts in smaller 

 quantity, and so likewise does the phosphate. 



Common salt, supplied in small quantities in manures, pro- 

 motes vegetation, while a larger quantity is injurious; and the 





