EDITORS PKKFACK. Vll 



boiiic acid, there is also a provision for tlie fonnatiou of 

 nitrogenous compounds. Wlien Nature thus provides 

 for a supply of nitrogen without the aid of man, it is 

 likely that exhaustion of all other elements of food in 

 the soil will take place by cultivation before this occurs 

 with nitrogen. The inefficacy of the mass of nitrogen 

 in the soil cannot be attributed to its existing in two 

 forms, in one only of which it is assimilable. This is 

 proved by experiments with soils and with farm-yard 

 manure. When the nitrogen of the soil is not available, 

 some other cause must be sought for than its existence 

 in a state in which it is sparingly assimilable. This 

 cause will be found to be the absence of some other 

 elements of food, which, upon being supplied, will at 

 once render the seemingly inoperative nitrogen at once 

 energetic. 



The diminution of the amount of available food 

 elements in the arable surface soil, by the cultivation 

 and sale of corn, necessitates the restoration of the 

 removed mineral matters. This is effected to a limited 

 extent by foreign manuring agents, but chiefly by the 

 formation of manure by means of fodder plants. By 

 the system of rotation, green crops whicli draw their 

 mitriment from the subsoil are introduced between the 

 cereals. By the deep penetrating roots of the former, 

 the mineral matters of the subsoil are absorbed, and 

 in the form of manure are transferred to the arable 

 surface'soil. But if this process continues, and the corn 

 and cattle are still sold, and no rejilacement from without 

 is made of the lost mineral matters, the time will arrive 



