Aerobic and Anaerobic Loss 313 



abundance of oxygen to combine with and give rise to 

 the . formation of carbon dioxid and of . water. The 

 nitrogen thus detached from its combinations may be 

 evolved as a free gas, or may still remain united to 

 hydrogen as ammonia. In either case, the losses are 

 considerable. 



When anaerobic processes prevail, as in compacted 

 manure, the oxygen needed by the bacteria is withdrawn 

 from the organic matter itself. It thus happens that 

 the gases evolved in anaerobic fermentation also con- 

 tain carbon dioxid. However, the limited supply of 

 oxygen greatly retards decomposition. Some of the hy- 

 drogen passes off in an uncombined state, or unites 

 with carbon to form marsh-gas. The nitrogen is changed 

 into more simple organic substances or into ammonia. 

 The remaining mass becomes poorer in oxygen and 

 proportionately richer in carbon; also in nitrogen, when 

 the decomposition is properly controlled. The darker 

 color of old manure, like the dark color of fertile soils, 

 is due, therefore, to humus substances comparatively 

 rich in carbon, and more resistant to decay than the 

 substances from which they were derived. 



The differences in aerobic and anaerobic decomposi- 

 tion of manure from the standpoint of losses involved, 

 is well illustrated by an experiment of Hansen's as cited 

 by Stutzer. The manure from ten cows, fed and*bedded 

 alike, was removed twice a week and placed in two 

 cemented pits. In one of these it was stored loosely, and 

 the excess of liquid excreta allowed to drain away into 

 a smaller pit. In the other, it was carefully trampled 

 down and the liquid excreta retained- 



