Change from Soluble to Insoluble 335 



of Wagner's statement that freshly voided manure 

 should contain equal portions of available and unavail- 

 able nitrogen. However, samples a few days old actually 

 contain 25 to 35 parts of available nitrogen to 100 parts 

 of unavailable nitrogen. It was similarly observed by 

 Maerker that fresh manure which contained 40 parts of 

 available in 100 parts of total nitrogen was sufficiently 

 changed in 2 J months to contain only 11 parts of avail- 

 able nitrogen. 



The change of available into unavailable nitrogen.— 

 The decreased proportion of available nitrogen is un- 

 questionably due in part to the volatilization of ammonia. 

 It is Ukewise due to the actual increase in the quantity 

 of insoluble nitrogen compounds. It has been demon- 

 strated that the bacteria and molds that develop in 

 the manure appropriate the soluble nitrogen compounds 

 for their growth and convert them into comparatively 

 inert protein substances. These protein substances, 

 like those in the green- manures, must again undergo 

 decay before they may become available as a source of 

 nitrogen to higher plants. 



Conditions affecting the change. — Under favorable 

 conditions, the conversion of the soluble nitrogenous 

 substances in manure into insoluble compounds . may 

 proceed very rapidly, as may be demonstrated by simple 

 laboratory experiments. The insoluble nitrogen com- 

 pounds thus formed consist, for the most part, of the 

 bodies of the microorganisms. Because of their small 

 size, these undergo decay rather rapidly when incor- 

 porated into the soil. None the less, an appreciable 

 amount of time is required for the decomposition and, 



