NITROGEN, NITRIFICATION, NITROGENOUS MANURES 133 



Dyer has calculated the income and outgo of ni- 

 trogen from manured and unmanured plots at the 

 Rothamsted Station for a period of fifty years. " Of 

 the total 10,000 pounds of nitrogen estimated to have 

 been supplied, then, we find (in round numbers) that 

 1600 pounds have been recovered in the increased 

 crops and that about 2500 pounds are found in the 

 surface soil, leaving 5900 (or, in round numbers, 

 6000) pounds to be accounted for otherwise. It is 

 clear, therefore, in spite of the notable surface ac- 

 cumulation, but little of the large quantities of nitrogen 

 supplied in the dung and not returned in crops is to 

 be found in the subsoil. The greater part of it has 

 disappeared either as nitrates in the drainage or per- 

 haps, and probably largely, by fermentative processes 

 yielding free nitrogen." 68 



145. Gain of Nitrogen in Soils. Lawes and Gilbert 

 found a gain of nitrogen when land was permanently 

 covered with vegetation. 44 Pastures and meadows 

 contain more than cultivated land of similar character. 



