28 



INVESTIGATIONS ON FARMYARD MANURE. 



XIV. " The Changes taking place during the Storage of Farmyard 

 Manured E. J. Russell and E. H. Ricpl\rds. Journal 

 of Agricultural Science^ 1917- 8, 495-563. 



The changes in a manure heap are at a minimum under anaerobic 

 conditions, and they are as follows : — 



In the laboratory experiments as much as 17 per cent, of the dry 

 matter may be converted into gas, in the heap the proportion is less. 



The non-nitrogenous constituents are particularly affected, one 

 quarter of the pentosans may disappear during the process and other 

 constituents break down in like proportion. The gas evolved contains 

 carbon dioxide, marsh gas and hydrogen. 



The nitrogenous compounds also break down, part of the complex 

 compounds giving rise to ammonia. In the laboratory experiments 

 more ammonia is found at 26° C. than at 15° C ; in the only heap where 

 we were satisfied that the conditions were anaerobic there was no 

 accumulation of ammonia. 



No nitrates are formed. 



There is no loss of nitrogen during the process ; the whole of the 

 initial nitrogen being recovered within the error of the experiment. 



The aerobic changes are as follows : — 



The loss of dry matter is greater and the temperature rises higher 

 than under anaerobic conditions. The gases evolved contain no hydro- 

 gen or marsh gas. The loss of dry matter shows some relationship to 

 the aggregate rise of temperature. 



There is almost always a larger decomposition of complex nitrogen 

 compounds than under anaerobic conditions. Usually no ammonia 

 accumulates in the laboratory experiments, and in the heap there is 

 invariably a loss. Nitrate is found in the dry outer portion of the 

 heap, but not in the moister interior, nor was it found in the laboratory 

 experiments where the manure remained moist ; the necessary con- 

 ditions appear to be dryness and sufficient air. 



Under conditions of perfect aeration no loss of nitrogen occurs. 

 Under ordinary conditions of incomplete aeration, however, there is 

 an evolution of gaseous nitrogen. 



The loss of ammonia shows some relationship to the maximum 

 temperature attained. 



Exposed heaps lose more dr}- matter than sheltered heaps and also- 

 more ammonia, if any appreciable quantity is present ; but the loss 

 of total nitrogen is not always greater. Field experiments show that 

 the loss of crop producing power caused by exposure is greater than the 

 analytical figures indicate. 



The loss of nitrogen is not a necessary accompaniment of the loss 

 of dry matter, since, as already stated, it does not occur under purely 

 aerobic or purely anaerobic conditions, although other constituents are 

 lost. But the loss of nitrogen that takes place in the mixed aerobic 

 and anaerobic conditions occurring in practice varies under comparable 

 conditions with the loss of dry matter, all constituents of the heap 

 apparently breaking down simultaneously. An exception occurs when 

 the temperature has risen high, e.g., to 70° C, after which decomposition 

 of dry matter and loss of nitrogen proceed more slowly than loss of dry 

 matter, so that there is an actual ronrontration of nitrogen in the heap. 



