THE FARMER'S MAGAZINE. 



229 



soil in large dressings. The shell-marl formed, as we 

 are aware, of the debris of cockles, had become incor- 

 porated with the earth we are about to speak of, in 

 consequence of an application of 70 cubic metres per 

 hectare. In 1 kilogramme of this shell-marl, recently 

 taken from the pit, I was not able to detect the least 

 trace of nitrate. 



A very white marl, from La Chaise, near Louzouer 

 (Loiret), examined immediately after its extraction, 

 contained the proportion of 7.2 grs. of nitrate of pot- 

 ash per cubic metre. In the marl of the same deposit, 

 extracted in 1853, and which, since that time, had re- 

 mained in a lump on the edge of the marl-pit, we ob- 

 tained from the same volume 19 grammes of nitrate. A 

 very argillaceous marl, from the hills of Chaumont, 

 contained 25 grammes. 



The chalk at Meudon is extracted from three overlying 

 workings. The limestone taken from the upper stratum, 

 in a cutting actively worked at a point where the quar- 

 riers were engaged, contained per cubic metre the 

 equivalent of 16 grammes of nitrate. A fact worthy of 

 observation is, that we have found no nitre in the infe- 

 rior (lower) beds of chalk. When we know what is the 

 mass of calcareous matter we incorporate with the soil 

 in a dressing of marl, we can understand that, in spite 

 of the weak proportion of nitrates they contain, they 

 must be sought for, since they may form part of the 

 substances which are held enclosed in ihe marls in only 

 very minute quantities, but which at the same time are 

 not less efficacious, such as phosphates of lime and al- 

 kaline carbonates. 



With some exceptions, we have met with saltpetre in 

 the earths examined in suflSciently weak proportions. 

 But we ought not to forget that the experiments have 

 been executed during a rainy autumn, and that the 

 rain tends to take away, or at least to displace the ni- 

 trates. We have ascertained, in fact, that the nitre of 

 a cubic metre of earth from a kitchen-garden has varied 

 from 316 to 13 grammes, according as they were ex- 

 tracted before or after the occurrence of the rainy days. 

 What is, above all, n§cesssary to observe in the results 

 obtained, is the fact of the frequency of saltpetre in 

 vegetable earth, whether it belongs to the forest-soil, 

 situated at such a height above valleys, that it receives 

 as manure nothing else than the rain, or makes part of 

 a tilled soil to which the most intense manuring is ap- 

 plied. 



As water tends to dissolve the nitrates, we should 

 expect to find a stronger proportion of these salts in a 

 soil moderately manured, kept sheltered from the rain. 

 I have, in point of fact, met with very remarkable quan- 

 tities of saltpetre in the soil of hothouses, which has 

 more than one analogy with artificial nitre-beds. 



In one kilogramme of earth of a hotbed in the Jardin 

 des Plantes, 1 found the proportion of 6 centigrammes 

 of nitrate of potash, or 89 grammes per cubic metre, A 

 kilogramme of earth, taken from another hotbed in 

 the same establishment, has yielded the equivalent of 6 

 decigrammes of nitrate of potash, or 804 grammes per 

 cubic metre.* 



Our learned contemporary, M. Moquin Tandon, hav- 

 ing readily authorized me to take from the hothouse of 

 the botanic garden of the College of Medicine the sam- 

 ples which I required, 1 have been enabled to detect, in 

 1 kilogramme of the light black mould from the surface 

 of the frame, the equivalent of 0.121 grammes of nitrate 

 of potash, or 161 grammes per cubic metre. 



In one kilogramme of strong earth, taken at the depth 

 of 30 centimetres below the light mould, we obtained 

 the equivalent of 0.107 grammes of nitrate of potash, or 

 185 grammes per cubic metre. It will not, perhaps, be 



* These earths had not the same density ; but I report from 

 memory the weight of the litre of each earth examined. 



useless to observe here, that it is precisely in this same 

 hothouse of the College of Medicine that M. de Luca 

 has made his interesting experiments upon the nitrifica- 

 tion of potash by the elements of the atmosphere. 



Whether the nitrates, of which I have given the large 

 dose in the soil of hothouses, have their origin in 

 the atmosphere, or that they may be formed as the re- 

 sult of modifications which the organic matters in ma- 

 nure gradually undergo, in presence of alkaline or 

 earthy bases ; or, still further, that they result simply 

 from the successive accumulations of nitrates brought 

 by the water employed in watering it; or, lastly, 

 from these various causes united ; it is still clear 

 that their continuance in the earth depends essentially 

 on this circumstance, that the pluvial waters do not 

 carry them away. Setting aside also the favourable in- 

 fluence of the temperature of humidity, everything leads 

 us to believe, that it is in a hothouse that a manure pro- 

 duces its maximum of beneficial effect. On this subject 

 I may be permitted to offer some reflections. 



In the actual state of our knowledge it is natural to 

 attribute the azoteous principles of vegetables whether 

 in the form of ammonia or of nitric acids, regard being 

 had to the question of ascertaining if the azote of the 

 acid does not pass into the state of ammoniac under the 

 influence of vegetable organism. The azote of albumen, 

 of casein, and of fibrine of plants, has very probably 

 formed part of a sal ammoniac or a nitrate. Perhaps 

 we might add to these two salts a brown matter which 

 we obtain from manure. But even with the adjunction 

 of this matter, still so imperfectly known, it remains an 

 established fact that every immediately active element of a 

 manure is soluble, and, consequently, that a manured soil, 

 when exposed to continued rain, loses a portion more or 

 less strong, of the fertilizing agents which have been given 

 to it ; besides, we constantly find in drainage waters the 

 true lixiviate of the land — nitrates and sal-ammoniacs. 

 And if it be true that the summits of mountams and 

 elevated table-lands have no other manure than the 

 mineral substances derived from the rocks from which 

 they are found, and the meteoric waters, it is not less 

 so that in the most ordinary conditions of cultivation, a 

 soil strongly ameliorated yields to the pluvial waters 

 which pass through it more fertilizing principles than it 

 receives from it. In giving to the soil a coat of manure 

 in a slightly advanced stage of decomposition, containing 

 by that means, rather the elements of ammoniacal pro- 

 ducts and nitrates, than of those salts themselves, the 

 inconvenience resulting from the action of protracted 

 rains, is less than if they gave it rotten dung, in which 

 the soluble salts already predominate. Besides, amongst 

 the incontestable advantages arising from the application 

 of liquid manures, I think we ought to place in the first 

 rank, that of bringing to the plants cultivated, only 

 matters properly modified to be absorbable, offering 

 them to the plants only in proportion to their wants ; 

 the true dressing bearing a certain resemblance to the 

 most delicate proceedings of experimental physiology, 

 and which preserves the manure from the dissolvent ac- 

 tion of the rain waters. 



If the meteoric- waters over which the agriculturist has 

 no command, produce often an effect unfavourable to his 

 cultivation, by their abundance and, above all, their un- 

 seasonable intervention, it is not thus with spring and 

 river waters, brought by irrigation ; or those which are 

 held by absorption in a valley in a suitable state of 

 moisture. These waters, when we measure them to the 

 soil, yield to it the entire of the useful substances they 

 hold in solution or in suspension ; calcareous and alka- 

 line salts, carbonic acid, organic matters, &c., and la 

 order to show in what large proportion these dissolved 

 or attracted substances are introduced, I shall recapitu- 

 late that in a series of experiments which I had under- 



