144 



ammonia, we know that the average air contains extremely few 

 nitric compounds. According to the analyses made first by G. Ville 

 and later by Schloesing, the atmosphere contains at most from 25 to 80 

 grams of ammonia per cubic kilometer. It would, therefore, be 

 necessary, in order to provide for the loss which we have just spoken 

 of. that the soil and its plants should absorb in the space of a year all 

 the ammonia contained in a column of air having the surface of the 

 field for its base and a height of 400 kilometers under a constant pres- 

 sure equal to the barometric height at sea level. Thi*s is about 50 

 times the quantity required for the carbonaceous nutrition of a crop 

 weighing when dry 5.000 kilograms. 



Such an hypothesis is inadmissible; besides, if it were correct we 

 should not be able to understand why a crop of graminea? cultivated 

 in a sterile soil, aided only by a small quantity of fertilizer, never 

 contains more nitrogen than was contained in the seed and in the 

 manure given to it. 



The above-mentioned deficiency, then, always remains, whichever 

 way we look at it. Let us see if it is real or if the soil receives any 

 compensation. 



Since the application of chemical analysis to agricultural re- 

 searches no decrease in the average fertility of our arable lands has 

 been discovered: on the contrary, many have become richer in con- 

 sequence in the improvements in the methods of cultivation and, 

 above all, in the regidar use of fertilizers. They have therefore 

 become more productive, and the average yield of wheat in France, 

 which, at the beginning of this century, was only at the rate of 11 

 hectoliters to the hectare, has gradually risen to 15 and 10 hectoliters. 



This fact alone is in direct opposition to the hypothesis of a 

 gradual impoverishment of the soil. Here are other objections more 

 striking still : 



The forests, the meadows high up on the mountains, which are 

 never manured, have from the remotest ages furnished, in the form 

 of wood. milk, cheese, wool, or viands, quantities of nitrogen inferior, 

 no doubt, to what it would be under a more intense cultivation, but 

 constant and without the soil which produces them showing the least 

 sign of exhaustion. 



This virgin soil is even more fertile than our best arable lands. 

 In Auvergne Truchot saw meadow lands containing !) grams of 

 combined nitrogen per kilogram: Joulie mentions some which 

 contain 1.5 grams, and 1.8 grams per 100 of nitrogen, while land of 

 good quality on which cereals were cultivated 3'ielded ordinarily 

 ten times less. Finally, and it is with this that we terminate this 

 part of our subject, certain plants, among which we must place in 

 the first rank grasses of natural or artificial meadoAvs. cause a 

 progressive enriching of the soil even in the absence of every species 

 of fertilizer, and notwithstanding that they contain more nitrogen 

 than other crops, said to be exhausting, such as the root plants and 

 cereals. 



Practical agriculture has long since demonstrated this fact in 

 regard to leguminous plants: all farmers know that wheat planted 

 after a crop of clover or of lucerne grass yields a much better harvest 

 than it would have done under the most copious fertilizing, and it 

 is for this reason they speak of the leguminous plants as ameliorators 

 or natural fertilizers of the soil. 



