i84 FARMYARD MANURE [chap. 



always short, and is less easy to handle in consequence, 

 but it requires no making and can be applied straight 

 from the yards even to the lightest of soils. 



However the farmyard manure has been made, it 

 thus starts with a mixture of excrement, urine, and 

 litter, which become more or less consolidated and 

 mixed together by the trampling of the animals. Other 

 changes, however, intervene very rapidly, and these in 

 the main are brought about by bacteria, which for 

 convenience may be divided into two groups, one acting 

 on the cellulose and other carbon compounds of the 

 straw that make up the bulk of the manure, and the 

 other acting on the nitrogenous compounds that do not 

 weigh so much but supply the main fertilising properties 

 of the dung. 



Among the more important of the organisms dealing 

 with nitrogenous material are those which attack the 

 urea in the urine and by adding to it the elements of 

 water give rise to a carbonate of ammonia, which very 

 readily dissociates into free ammonia and carbonic acid 

 — both gases, and therefore capable of escaping into 

 the atmosphere. 



CO(NH2)2 + 2H20 = (NHJ2CO3 = 2NH3 + CO2 + H2O 



There exists more than one organism bringing 

 about this change, but the best knowp is a small coccus 

 known as Micrococcus urecB, which is widely disseminated 

 in the air and dust, and is naturally extremely abundant 

 in such places as stables and cattle stalls, where it is 

 always giving rise to ammonia. This change into 

 ammonium carbonate is an extremely rapid one; in 

 the liquid draining from a yard or a manure heap, or 

 even in the liquid manure tank, little or no urea can be 

 detected, so complete has been the change to ammonia. 

 As long as the liquid containing the ammonium car- 



