344 COMPARATIVE EFFECTS OF THESE TWC NITRATES. 



were already present in abundance, — while, on the other hand, a field 

 that is defective in both constituents of the salt (nitric acid and potash 

 or soda), will be more grateful for the same addition of it than one in 

 which either of them already abounds. In this way, it is not unlikely 

 that the discordant results of experiments, even on the same farm, and 

 especially when the soils are different, may occasionally be explained. 



i. Special ejects of the nitrates of potash and soda. — On this alka- 

 line constituent of the two nitrates will depend the special action of each 

 when applied to the same soil under the same circumstances. It has 

 rot yet been clearly made out that any definite special action can be 

 ascribed to them, yet some experiments bearing upon this point liave 

 already been published, to which it will be proper to advert. From 

 the study of the special action of given manures upon given crops, 

 practical agriculture has much good to expect. 



1°. At Rozelle, near Ayr (1840), nitrate of potash caused oats to 

 coine away darker and stronger, and give a heavy crop, w^hile in the 

 same field nitrate of soda produced no benefit. The soil was inferior, 

 light, and sandy, with a red irony subsoil (Capt. Hamilton). It is add- 

 ed that the crop was injured by the early drought, from which it never 

 recovered. This fact renders the special effect of the nitrate of potash 

 in this case doubtful. 



2°. In the experiments upon wheat, made by the same gentleman 

 on the same farm, — it is to be presumed upon a similar soil, — 



Nitrate of soda gave . . 46 bush, grain, and 52 cwt. straw ; 



Nitrate of potash gave . . 42 bush, grain, and 76 cwt. straw ; 



the produce of straw being here also greatly in favour of the potash salt. 



3°. Dr. Daubeny also, in the experiment upon wheat above detailed, 

 found the nitrate of potash to increase the produce considerably, while 

 the nitrate of soda caused no increase whatever. The soil was stiff" clay 

 upon the corn-brash. 



These superior effects of the potash salt may certainly be ascribed to 

 the greater deficiency of the several soils in potash than in soda, a sup- 

 position which in the case of the Rozelle experiment is consistent with 

 the fact, that common salt, when tried upon the same land, produced 

 no good effect. If however, as some suppose, (p. 328), potash and soda 

 are capable of re-placing each other in the living vegetable without ma- 

 terially affecting its growth, this explanation cannot be the true one. 

 Further experiments, however, if carefully conducted, will not fail to 

 clear up this question. 



4°. On a gravelly soil Mr. Dugdale obtained an increase of 12 bush- 

 els of wheat by the use of nitrate of soda, while nitrate of potash in- 

 creased the crop by only half a bushel. 



This result may be explained after the same manner as the preceding 

 — the soil may have already abounded in potash. 



5°. In Perthshire, upon a moist loam, Mr. Bishop obtained an equal 

 increase of hay from the use of both nitrates; each having caused the 

 production of a double crop. 



The equality in this case may have risen from the effects being 

 wholly due to the nitric acid, both potash and soda being already abun- 

 dant in the soil. This is consistent with the situation of the locality in 



