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 8 
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 ail 
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. This is about 59 
times We 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 gramine 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 regular 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 16 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 9 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 yielded 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 meadows, 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 
Tha 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. 
