DECOMPOSITION OF ORGANIC MATTER IN THE SOIL 33^ 



(Utions microorganisms may become serious competitors of higher 

 plants for available nitrogen food. 



Manure stored in heaps not infrequently deteriorates in quality, 

 even when losses by leaching are excluded. This deterioration is largely 

 due to the change of the water-soluble ammonia and amino-compounds 

 into insoluble protein substances. While the extent of the change into 

 protein compounds is variable it may range from less than a tenth of the 

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

 Also in the soil the same processes take place, but not so 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 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. 



22 



