1908.] 



Farmyard Manure. 



i i 



perature the greater will be the amount of ammonia passing 

 off in a gaseous condition. Thus thin films of urine on the 

 floors, walls, or even on the surface of loose straw easily lose 

 nitrogen by the fermentation of the urea and subsequent 

 volatilisation of the ammonia ; the smell of a stable arises in 

 this way and is clear evidence of the escape of ammonia. As 

 will be brought out more clearly later, this volatilisation of 

 ammonia causes most of the loss of nitrogen that takes place 

 in making dung. 



The ammonium carbonate is itself subject to change and 

 even to loss by other actions than evaporation ; there are 

 always present in the manure heap various bacteria which 

 can oxidise ammonia into free nitrogen gas and water ; in 

 consequence dung which is allowed to lie about loosely grows 

 poorer in nitrogen from this cause as well as through volatilisa- 

 tion of ammonia. This process by which gaseous nitrogen is set 

 free is often called " denitrification," a term better restricted to 

 the change whereby nitrates are reduced to nitrogen gas. 

 The conditions favourable to this change have not been closely 

 investigated ; it is, however, certain that rapid oxidation, such 

 as is brought about by a loose condition of the manure or by 

 turning it, will be accompanied by some destruction of am- 

 monia. It is also favoured by the presence of soluble carbo- 

 hydrate, i.e., easily oxidisable material, and it is materially 

 reduced, if not suspended, as soon as these substances have 

 been used up. 



Another group of bacteria which are extremely abundant 

 in fresh faeces are the so-called putrefactive bacteria which 

 break down the proteids into simpler compounds, such as 

 amino-acids, amides and finally ammonia. Without discussing 

 them individually, their function is to convert the insoluble 

 nitrogeneous bodies of the straw (those of the faeces are more 

 difficult of attack because they have already resisted the 

 actions of digestion) into soluble bodies akin to ammonia 

 and therefore more nearly available by the plant. Thus, with 

 a certain amount of loss as free nitrogen, the trend of the bac- 

 terial actions taking place in the fresh farmyard manure is 

 to break down the complex insoluble compounds of nitrogen 

 to more and more simple ones, ammonia being the final term. 

 At the same time there is always a reverse change going on ; 



