46 THE CHEMISTRY OP THE PAEM. 



heavy land at Kothamsted to wheat and barley, only about 

 10 to 15 per cent, of the nitrogen has been recovered in 

 the increase ; but the effect on the barley has continued 

 for many years after the application of the manure ceased. 

 It is evident that a small quantity of an active manure 

 will accomplish the same work as a large quantity of one 

 less active. 



The residues of phosphatic and potassic manures are 

 available for subsequent crops, but are distinctly less 

 effective than fresh applications of the same manures. 



