DECOMPOSITION OF ORGANIC MATTER IN THE SOIL. 267 



water soluble material to more than three-quarters or four-fifths of it. 

 Also in the soil the same processes take place, but not as intensively. A 

 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 report the 

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

 into protein. In the presence of barnyard manure the proportion trans- 

 formed was increased to 15 per cent. In the case of ammonium com- 

 pounds the transformation may be even more far-reaching, amounting, 

 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. 



