MIXED FERTILIZERS 51 



increases the speed of oxidation, raises the temperature, 

 increases the general rate of decomposition, and sometimes 

 assists in nitrogen fixation. All the fertilizing elements, 

 that is, nitrogen, phosphorus, and potassium, increase the 

 rate of decomposition, because they facilitate the multi- 

 plication of the bacteria. As the bacterial food is used up 

 the rate of decomposition slackens. 



Decomposition in the manure heap may proceed in 

 undesirable directions. When nitrogen is made to change 

 into compounds unsuited to the growth of crops the word 

 " denitrification " is commonly applied to this state of 

 affairs. " Denitrification " is often applied in two different 

 senses. Firstly the sense of the actual evolution of nitrogen ; 

 this may occur chemically by the interaction of nitrous acid 

 upon ammonia, or by bacterial evolution of nitrogen from 

 proteins. The latter is probably only a special case of the 

 former, since the action of nitrous acid upon ammo-acids 

 is directly comparable to its action upon ammonia, and such 

 changes are probably brought about by bacterial agencies. 

 Once nitrogen is given off from the manure heap as elementary 

 nitrogen it becomes mixed with the nitrogen of the atmosphere 

 and may be regarded from a practical point of view as finally 

 lost. The above is the reversal of the process of nitrogen 

 fixation. The other meaning of " denitrification " is the 

 reversal of the process of nitrification. In the process of 

 nitrification the protein is broken down to simpler organic 

 nitrogen bodies, then to ammonia, then to nitrites, and lastly 

 to nitrates. When this process is reversed the proportion 

 of nitrates diminishes. The reversion of nitrogen can be 

 imitated in the laboratory by heating sugar, a nitrate, and 

 potash in a tube, when organic nitrogen compounds are 

 formed. In the manure heap these changes are chiefly 

 controlled by the bacteria. Attempts to prevent the loss 

 of ammonia from the manure heap by the addition of sub- 

 stances of an acid nature have done little good, although for 

 town stables a sprinkling of gypsum is useful for sanitary 

 purposes. 



The main object of storage should be to promote 



