E. J. Russell and E. H. Richards 541 



Comparison of laboratory experiments with the manure heap experiments. 



In comparing the results of the laboratory experiments with those 

 of the manure heap the most striking difference comes out under 

 anaerobic conditions. In the laboratory experiments ammonia accu- 

 mulates ; in the heap it does not. 



Under partial aerobic conditions there is complete similarity in the 

 products, but a difference in the extent to which the reactions proceed. 

 The maximum percentage losses have been as follows: 



Dry Total Nitrogen Nitrogen Nitrogen as 



Bullock manure matter nitrogen as NH3 as amide other compounds 



In laboratory 17 33 73 75 27 



Covered heaps ... 48 42 92 39 32 



The difference under anaerobic conditions does not seem to present 

 any great difficulties : it may be explained by supposing that the heap 

 is never wholly anaerobic, but that air always diffuses into it at some 

 period of its history. 



We may take it, therefore, that the reactions in the heap are the 

 same as those discussed in the last section. We must now proceed to 

 deal with the reactions which differentiate the decomposition of farm- 

 yard manure from that of protein under laboratory conditions, viz. 

 the formation of nitrate and the loss of nitrogen. 



The formation of the nitrate in the heap. 



Our experiments show that nitrification will take place in the heap, 

 but the accumulation of nitrate depends on two factors,— the presence 

 of air and the absence of much moisture. In the laboratory expermients 

 the manure remained uniformly moist, and nitrate was never observed, 

 in spite of the free access of air. In the heap experiments nitrate was 

 alwavs observed on the outside layers where drying had occurred, but 

 we never found it in the lower depths that had remained moist. Thus, 

 in a heap kept in the open the figures were : 



Depth below surface outer crust J-^ inch 1 inch 2 ins. 



Nitrate formed, parts of N per cent. ... 0012 0-006 Trace None 



(Bullock dung, Jan. 7, 1915, see pp. 513 and 560) 

 while in a heap of the same manure kept under cover, which became 

 drier to a much greater depth, the results were : 



Depth below surface outer crust i-| inch 2 ins. 5 ins 10 ins. 



Nitrate formed, parts of N per cent. 0-12 0-12 0-12 0-12 0-12 



(Woking heap, see pp. 516 and 562). 



