182 FOOD FOR PLANTS 



pletes the account of the loss. This loss, they claim, 

 does not go on under wholly anaerobic or wholly 

 aerobic conditions but under mixed anaerobic and 

 aerobic conditions which arise when manure is being 

 produced. They explain further that in the natural 

 manure heap nitrogen is also lost as gaseous am- 

 monia as well as in the form of nitrogen gas. 



It is very probable that in a more limited way, 

 similar changes take place when organic compounds 

 are placed in the soil and that a part of the loss of 

 nitrogen noted in our experiments must be thus ac- 

 counted for. It is a well-known fact that when an 

 organic substance like cottonseed meal or dried blood 

 is mixed with soil and incubated in the laboratory for 

 a few days, escaping ammonia may be detected, and 

 from this it is a natural conclusion that when large 

 quantities of organic matter are placed in the soil 

 under natural conditions, some ammonia will be lost 

 by volatilization, especially when the temperature 

 and moisture conditions are favorable. This then, 

 together with the evolution of gaseous nitrogen, 

 would in part at least explain the heavy loss of nitro- 

 gen where manure was used at the rate of 16 tons per 

 acre. 



A discussion of this subject would not be completed 

 without a brief reference to the effect of cultivation 

 on nitrogen losses. 



Shutt ^ for example has shown that when the 

 prairie soils of Saskatchewan were left undisturbed 

 the loss of nitrogen was slight, but as soon as cultiva- 

 tion was commenced losses set in. 



Cited by RusseU (4). 



