382 



Niti^ate of Soda as a Manure. 



*' 1 am glad that you are advocating the use of nitrate of soda in'agriculture, 

 for I have long entertained the opinion that the functions of the nitrates, in re- 

 lation to the nutrition of plants, are of the highest importance, and that the 

 more liberal application of nitrate of soda will be a great boon to the farmer. 



" It appears to me that plants in general are more dependent on nitric acid, as 

 the source from which they derive their nitrogen, than upon ammonia. Already, 

 four years ago, I came to the conclusion that ready formed ammonia ought not 

 to be applied to calcareous soils, and have recommended accordingly to bring 

 the farmyard-manure on such land as fresh as possible ; and in artificials, to 

 supply the place of the ammonia by nitrates. 



" 1 have been led to this conclusion by the following theoretical reasonings, 

 which I had occasion likewise to observe confirmed by local practice. 



" Lime readily displaces ammonia from its salts, and being volatile, we can 

 understand that much of the most essential fertilizing constituents of well fer- 

 mented dung will be lost when it is applied to a calcareous soil. 



" If, on the contrary, organic nitrogenized matters are decomposed in contact 

 with strong bases, such as lime or potash, the nitrogen they contain is converted 

 into nitric acid, and not, as usual, into ammonia. Fresh dung, in which the 

 greater part of the nitrogen which it contains is not yet changed into ammonia, 

 as appears to me, should be employed on calcareous soils ; because it is highly 

 probable that the lime in such soils will convert the nitrogen of the nitrogenized 

 substances of the manure into nitric acid — a compound which, in combination 

 with bases, appears in many circumstances to exercise even a more powerful 

 invigorating effect than ammonia itself. In confirmation of these views I have 

 frequently observed that guano shows a much more marked effect on other 

 soils than very calcareous ones. On our own farm I have frequently observed 

 a very powerful smell of ammonia, especially in dry weather, in walking over 

 fields which had been top-dressed with guano. 



" Some years ago we used sulphate of ammonia on several thin stony calcareous 

 soils, and portions of the fields were left undressed, in order to observe any dif- 

 ference in the crop ; but not any difference could be seen in the ])ortions of 

 the fields which were not manured with sulphate of ammonia. The smell of 

 ammonia, on the land on which sulphate of ammonia was employed, was very 

 strong indeed, and I have little doubt that almost all the ammonia contained in 

 the salt has been driven off by the lime in the soil, and that for this reason no 

 effect in the appearance of the crop has been observed. 



" That guano still exercises a very powerful action on calcareous soils need not 

 astonish us, for although a portion of nitrogen, contained in it in the form of am- 

 monia, is driven off when guano is employed on such land : by far the greater 

 quantity of nitrogen in guano exists in it as uric acid and other organic compounds, 

 which, in contact w^ith lime, will give rise to the formation of nitrates on their 

 decomposition. Besides, guano contains phosphates and salts of potash." 



Our acquaintance then with the main law of manures stands 

 at present as follows : — The Nitrogen of most manures is com- 

 mitted to the soil in a neutral state, capable therefore of uniting 

 either with Oxygen to become Nitric acid, or with Hydrogen 

 to become an alkali. Ammonia. Some few manures contain 

 Ammonia ready formed, some other few Nitric acid. It seems 

 clear that the neutral nitrogenous matter is converted into Am- 

 monia or into Nitric acid before it is absorbed by the plant. So 

 that we have only two alternatives to consider, not three. But it 

 is uncertain as yet whether plants can feed indiflferently on each 

 of the two substances, or whether one of these is first transformed 



