230 THE LIVING ORGANISMS OF THE SOIL [chap. 



crop was sown, the temperature of the pots, or of the 

 ground in the field experiment quoted, was very high, 

 so that it is easy to see that an abnormal condition, 

 both as regards nitrification and the supply of oxygen 

 and water, must have been developed. 



There are not lacking both long-continued experi- 

 ments and ordinary farming experience to show that 

 nitrates and other artificial manures can be used in 

 conjunction with dung with the best effects. 



For example, the mangold crop at Rothamsted 

 shows the following average results for the recovery of 

 nitrogen from various nitrogenous manures used first 

 with ^ mineral manures alone and then with annual 

 dressings of 14 tons per acre of farmyard manure, a 

 quantity that never would be employed so frequently 

 in practice : 



Percentage of Nitrogen in dung recovered. 



