AVAILABLE NITROGEN OF THE SOIL. 287 
a form available to crops. Assuming that ammonia and 
nitric acid chiefly, if not exclusively, supply vegetation 
with nitrogen, it is seen that the greatest quantity of 
available nitrogen ascertained to be present at any time in 
the soil was 148 Ibs. per acre, taken to the depth of one 
foot. This, as regards nitrogen, corresponds to the follow- 
ing dressings :— 
lbs. per acre. 
Saltpeter (nitrate of potash) -  - 1068 
Chili saltpeter (nitrate of soda) : 898 
Sulphate of ammonia - - - 909 
Peruvian guano (14 per cent of nitrogen) 1057 
The experience of British farmers, among whom all 
the substances above mentioned have been employed, 
being that 2 to 3 cwt. of any one of them make a large, 
and 5 ewt. avery large, application per acre, it is plain 
that in the surface soil of Bretschneider’s trials there was 
Sormed during the growing season a large manuring of 
nitrates in addition to what was actually consumed by the 
crops. 
The assimilable nitrogen increased in the beet plots up 
to the 30th of June, thence rapidly diminished as it did 
in the soil of the paths. In the oat and vetch plots the 
soil contained, at none of the times of analysis, so much 
assimilable nitrogen as at the beginning of the experi- 
ments. In September, all the plots were much poorer in 
available nitrogen than in the spring. 
Table IV confirms what Boussingault has taught as to 
the vast stores of nitrogen which may exist in the soil. 
The amount here is more than fwo tons per acre. We ob- 
serve further that in none of the cultivated plots did this 
amount at any time fall below this figure; on the other 
hand, in most cases it was considerably increased during the 
period of experiment. In the uncultivated plot, perhaps, 
the total nitrogen fell off somewhat. This difference may 
have been due to the root fibrils that, in spite of the ut- 
