222 THE CHEMISTRY OF THE FARM 



ammonium by the action of certain bacteria present 

 in the atmosphere and the soil. The nitrogen of urea 

 may apparently be reckoned as of equal value to that 

 in ammonium salts. The nitrogenous matter of the 

 solid excrements is certainly of far less value, con- 

 sisting chiefly of vegetable matter which has already 

 resisted the prolonged attacks of the digestive fluids 

 and of the bacteria of the intestines ; it will become 

 available as plant food only by slow decomposition in 

 the soil. 



The constituents of animal excrements are in the 

 condition of greatest value as manure at the time 

 when they leave the animal ; after mixing with litter 

 and storage in heaps their manure value considerably 

 diminishes. The manure from food thus yields its 

 best return when the food is consumed upon the land, 

 and the manure at once ploughed in ; this happens 

 when sheep receive oilcake while feeding off a crop 

 of swedes. During the fermentation of the manure 

 with litter the constituents enter into new com- 

 binations; the ammonia produced from the urine 

 combines with the humic acids formed from the 

 decomposing litter, insoluble amide compounds being 

 produced. The potash also eilters into combination 

 with the humic matter. The constituents of farm- 

 yard manure are thus not so immediately available for 

 plant food as the original animal excrements. The 

 nitrogen of farmyard manure has been valued by 

 Wagner, from its effect in producing crops, at 45 per 

 cent, of the value of nitrogen in nitrate of sodium. 



Besides the change in condition, we have further 

 to take into account the serious losses in quantity, 

 which the constituents of animal manure may suffer 



