226 FARMYARD MANURE [chap. 



as the making process proceeds it is partly broken down 

 by the hoofs of the animals and partly by bacterial 

 decay, which latter change proceeds still further during 

 the storage process until no trace of the straw structure 

 may remain, but the whole material has passed into a 

 uniform brown or black mass. The farmer is accustomed 

 to speak of the fresh straw in manure as " long," while 

 the old fermented material he calls " short." 



Before considering in detail the changes which go on 

 during the processes of making and storage, we must 

 refer back to what we have already learnt concerning 

 the fate of the valuable materials in the feeding stuffs, 

 fixing our attention for the time being upon the 

 nitrogen. It will be remembered that portions of the 

 nitrogenous compounds in the food are indigestible, and 

 are excreted by the animal in the faeces ; that part, 

 however, which is digested is excreted in the form of 

 urea in the urine, except for a small portion which the 

 animal may retain in the body. This division of the 

 nitrogen in the food represents a great difference in its 

 value as a fertiliser. The nitrogen compounds in the 

 faeces, since they have resisted the attack of the digestion 

 processes, will be very slowly attacked in the soil by 

 the bacteria which have to break down and convert 

 them into ammonia and nitrates before they can feed 

 the plant. Such materials, then, are slow in their action 

 as fertilisers, and remain for a very long time unchanged 

 in the soil. The nitrogen, however, in the liquid portion 

 of the manure in which it is present in the shape of 

 urea, will change very rapidly into ammonia, so that it 

 is an extremely active fertiliser, and far more valuable 

 than the solid parts of the manure which would contain 

 the same amount of nitrogen. The same considerations 

 apply equally to the phosphoric acid and potash ; 

 whatever part of these constituents in the food is 



