498 The Storage of Farmyard Manure 



by beasts, is exposed to air. It appears, therefore, to be a complex 

 process, requiring both aerobic and anaerobic conditions. It is shown 

 that the loss can be explained on the following general hypothesis. 



Some of the molecular groupings which arise under anaerobic 

 conditions are known to be unstable under aerobic conditions, and 

 vice versa. Thus, one of the derivatives of propionic acid formed under 

 anaerobic bacterial decomposition of protein shortens itself and becomes 

 a derivative of acetic acid as soon as air is admitted. 



Most of the cases on record are eliminations affecting the number 

 of carbon atoms, but it seems quite conceivable that nitrogen should 

 be eliminated in similar manner. 



On this view we suppose air to diffuse into the heap and to give 

 rise to COg, so that the atmosphere in the heap is a constantly varying 

 mixture of oxygen, carbon dioxide, and nitrogen. When the oxygen 

 happens to be in sufficient excess the aerobic processes go on ; when, 

 on the other hand, the oxygen falls too low the anaerobic changes 

 set in, and some of the compounds formed under the aerobic conditions 

 become unstable, and lose their nitrogen. Conversely, products 

 formed under anaerobic conditions may lose nitrogen as soon as more 

 air diffuses in. 



Alternate nitrification and denitrification is a special case of this 

 hypothesis : nitrate may be supposed to form during the aerobic 

 conditions, and then become denitrified under the anaerobic conditions. 

 We have shown that this actually takes place to some extent : nitrates 

 are formed on the outside of the heap wherever there is sufficient 

 dryness and sufficient air, but they decompose directly they are 

 washed into the interior. We do not suppose that this particular 

 process accounts for the whole of the loss: there are mechanical diffi- 

 culties in the transfer of sufficient quantities of nitrate from the Outside 

 to the inside of the heap ; it is possible of course that nitrates are formed 

 in the interior also but that they decompose at once so that they cannot 

 be detected. We have not in the present paper attempted to pursue 

 this matter more closely. 



We now come to the application of our results to the storage of the 

 manure heaps. 



Field experiments show that the best results are obtained when 

 the manure loses as little dry matter as possible, and when it contains 

 the maximum of total nitrogen and ammonia. 



Laboratory experiments show that these conditions are attained 

 when the manure is stored under anaerobic conditions at about 26° C. 



