204 



FARMYARD MANURE 



[chap. 



total nitrogen, but also that present as salts of ammonia, 

 and as amido-compounds easily changing into ammonia 

 It will be seen that the cake-fed dung is always 

 considerably richer in nitrogen, the average percentage 

 being 073 as against 0-523, a superiority of nearly 40 

 per cent. Moreover, the extra nitrogen in the cake- 

 fed dung is mostly in the highly available forms, the 

 ammonia, urea, and amido-compounds which represent 

 the digestible nitrogen of the cake; the insoluble nitro- 

 Table LX.— Crop Returns from the above Manures. 



gen in the cake-fed dung is only 0-488, as against 0-415 

 in the dung made from roots and hay, a superiority of 

 less than iS per cent. That the superiority of the 

 cake-fed dung as regards the soluble nitrogen com- 

 pounds is not even more pronounced, is due to the 

 change back from ammonia into proteins effected by 

 bacteria during storage; in 1907, when the dung was 

 sampled as it left the yard, both lots contained practically 

 the same proportion of insoluble nitrogen, and both pos- 

 sessed an exceptional amount of ammonia, which, how- 

 ever, was three times as much in the cake-fed as in the 

 other manure. These differences in composition are 

 clearly reflected in the crops grown with equal quan- 

 tities of the two manures, the weights of which are 

 summarised and reduced to a common standard (the 

 yield of the unmanured plots being taken as 100) in 

 Table LX. The crops grown in these trials were 



