CH. x] Storage of Farmyard Mmmve 171 



Changes on storing. Dung cannot generally be used 

 directly it is made but often has to be kept for a period 

 and applied to the land when convenient. Bacteria, 

 moulds, etc. cause considerable decomposition during 

 storage and much heat is evolved. Relatively dry 

 manure, e.g., horse dung, rises considerably in tempera- 

 ture; wetter manure like cow dung does not because of 

 the great amount of heat needed to warm up all the 

 water present and because much water means little air. 

 This production of heat involves the combustion of 

 material in the heap so that there is a corresponding 

 loss of dry matter. The loss of nitrogen may be con- 

 siderable and is of course additional to the loss of 15 per 

 cent. incmTed during the making of the manure. 



The changes that take place are very complex : they 

 are under investigation at Rothamsted by the bacteri- 

 ologist and the Rupert Guinness chemist. Two groups 

 of constituents are known to break down; the cellulose 

 and other carbohydrates in the straw, and the nitrogen 

 compounds in the straw, urine and faeces. The decom- 

 position of some of the carbohydrates of the straw is 

 desirable because they encourage the removal of nitrates 

 from the soil by micro-organisms, an action which would 

 be distinctly harmful if it went on to any extent, and 

 which in fact has caused bad effects when straw has been 

 applied to soil in sprmg. The necessary decomposition 

 is brought about in the soil if sufficient time elapses 

 between the addition of the straw and the sowing of the 

 seed. This effect of undecomposed straw may be one 

 reason for the advantage of autumn application of farm- 

 yard manure over spring application (p. 185). 



The breaking down of the complex nitrogen com- 

 pounds is necessary to provide ammonia and nitrates 



