DECOMPOSITION OF ORGANIC MATTER IN THE SOIL 399 



large number of species of molds and bacteria have been isolated and 

 tested as to their ability to transform ammonia, amino- and nitrate 

 nitrogen into protein compounds. Among the more recent investi- 

 gations in this field those of Lemmermann and his associates testify that 

 in three weeks 5 to 6 per cent of the nitrate added to the soil was changed 

 into protein. In the presence of barnyard manure the proportion 

 transformed was increased to 15 per cent. In the case of ammonium 

 compounds the transformation may be even more far-reaching, amount- 

 ing, at times, to more than 25 to 30 per cent of the material originally 

 present. Generally speaking, molds will assimilate ammonia nitrogen 

 more readily while bacteria and algae will assimilate nitrate nitrogen 

 by preference. However, the preference of molds for ammonia nitrogen 

 is often more apparent than real, because of the rapid formation of 

 acid residues in culture media rich in certain ammonium compounds. 

 Similarly, some species of bacteria will assimilate ammonia nitrogen 

 in preference to nitrate nitrogen. 



