142 



On the other hand, the soil is the seat of never-ceasing oxidations, 

 caused by the free circuhition of air within it ; one of these phenomena 

 of oxidation is that which acts upon the conibustibk^ nitrog-enous 

 substances hekl in reserve by the soil; under the sinuiltaneous action 

 of a free atmospheric oxygen and of a special kind of microbe, " the 

 nitric ferment," discovered by Messrs. Schloesing and Miintz and 

 described later by Winogradski, these substances are rapidly trans- 

 formed into nitrate of calcium, or lime, which, by a happ}^ combina- 

 tion of circumstances, is the favorite nutrition of most plants; this 

 nitrate of calcium is extremely soluble and does not possess any 

 affinity for the elements of the soil, like that existing between these 

 b:ame elements and annnonia. or. again, between them and the salts 

 of potassium, Avhence it comes to pass that every infiltration of water 

 takes this nitrate along with it, even to the de]:)ths of the loAver soil, 

 and from thence into the brooks, rivers, and thence into the ocean. 

 In autumn, vdien the rains are abundant and when the denuded earth 

 evaporates only a small quantity of the water which it receives, a 

 veritable cleansing takes place systematically, and all the nitrates are 

 carried far away as fast as they are produced. 



The loss from this cause is enormous. In experiments nuide by 

 Messrs. Lawes and Gilbert, at Rothamsted, for a great many years 

 past these learned English agronomists have discovered that one 

 hectare of soil planted in wheat loses in this way 50 kilograms of 

 nitrogen — that is to say, as nnich as the wheat itself contains, or, 

 again, a quantity equal to a manuring of 300 kilograms of nitrate of 

 soda. 



These figures are far from being exaggerated, and other observers, 

 among whom I will mention Deherain, have obtained similar and 

 sometimes even higher results than those of LaAves and Gilbert. 



But this is not all. Boussingault found that rich soils continually 

 give out ammonia in the gaseous state. These are the circumstances 

 under which he discovered it : Having conceived the idea of analyz- 

 ing a sample of snow which had remained for thirty-six hours in a 

 garden bed, Boussingault found in it 10 milligrams of nitric ammonia 

 per kilogram, while the same snow taken from a terrace very near there 

 contained scarcely 2 milligrams. The difference of 8 milligrams was 

 evidently due to the emanations from the earth. If we allow that 

 this snoAV had a uniform deyith of 10 centimeters and a mean density 

 of 0.25 we shall find on a hectare a total weight of 250 tons, containing 

 2 kilograms of annnoniacal nitrogen which was given out from the 

 soil during the short time that the snow lay on the ground. 



By what coefficient must we multiply this figure in order to cal- 

 culate the amount of annual loss which takes place upon an ordinary 

 piece of arable land ? AVe do not knoAv at all, but we can affirm that 

 the result of such a calculation would give more than 10 kilograms 

 annually per hectare. 



According to Schloesing, certain soils emit nitrogen in its free, 

 uncombined state. This is particularly perceptible in soils which 

 are badly ventilated and Avhich contain a great deal of organic mat- 

 ter. The nitrogen then results from the decomposition of the nitrates 

 existing in the soil, which decomposition is attributable, as Deherain 

 and I have shown, to the development of certain anserobic micro- 

 orsranisms. 



