AVAILABLE NITIIOGEK 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 lbs. per acre, taken to the depth uf 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 



Sulpliate of ammonia ... - 909 



Peruvian guano (14 per cent of nitrogen) 1057 

 The experience of Britisli 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 cwt. a very large, application per acre, it is plain 

 that in the surface soil of Bretschneidei-'s trials there was 

 formed during the growing season, a large manuring of 

 nitrates in addition to rohat was actually consumed by the 

 crops. 



The assimilable nitrogen increased in the beet plots iip 

 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 haa taught as to 

 the vast stores of nitrogen which may exist in the soil. 

 The amount heie is more than two 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 duo to the root fibrils that, in spite of the ut- 



