320 SOILS AND MANUBES 



covered with cement or clay. When the manure is 

 to be stored for a considerable time it is often built up 

 in the form of a mound with sloping sides, like the roof 

 of a house, and thatched over to protect it from rain. 

 This can be done as the manure accumulates, and is not 

 only cheaper but is considered better than a built roof, 

 which in summer at least tends to promote loss by 

 evaporation. As a special precaution, a layer of peat is 

 sometimes placed under the manure to absorb the liquid, 

 which instead of being lost thus forms an additional 

 quantity of valuable manure. It is to be noticed that the 

 loss by drainage affects not only the nitrogen but all 

 the soluble constituents more or less alike. 



Loss by Evaporation. A certain loss of nitrogen by 

 evaporation of ammonia and the liberation of the free 

 element is practically unavoidable. In both cases it is 

 due mainly to the access of air, and is therefore greatest 

 when the manure is in a loose state. The liberation of 

 free nitrogen gas, it has been shown, results directly or 

 indirectly from the oxidation of ammonia. The two 

 factors which chiefly govern the loss by evaporation of 

 ammonia are the temperature and the extent of surface 

 exposed. The high temperature produced by the more rapid 

 fermentation which takes place in the presence of air, 

 causes the ammonium carbonate to dissociate into am- 

 monia and carbonic acid, and a loose condition of the 

 manure also facilitates the escape of the gases. 



It has been shown that fermentation is most rapid 

 and the temperature highest during the initial stages, 

 and it is probably during this stage that the greatest 

 loss occurs. As the manure becomes more compact the 

 rate of fermentation falls off, owing to the exclusion of 

 air, and the temperature is gradually reduced. Under 

 these conditions the loss of nitrogen both in the free 

 state and in the form of ammonia is greatly diminished. 



