DECOMPOSITION OF THE PLANT AS A WHOLE 



93 



containing only small relative concentrations of nitrogen, growth 

 of higher plants may be greatly depressed. 



TABLE 22 



Influence of Nature of Organic Matter upon Nitrate Formation 

 IN Soils (from Lyon, Bizzell and Wilson) 



Associated with these changes there is an increase in the abun- 

 dance of insoluble nitrogen, organic in nature; this increase is 

 practically quantitatively equal to the decrease in the water-soluble 

 nitrogen, such as ammonia and nitrate. In the decomposition of 

 such materials as corn-stover and oat straw, increases of 200 to 300 

 per cent in the organic nitrogen are not exceptional. Under such 

 conditions there is seldom any loss of total nitrogen; as a result 

 of the creation of conditions favorable to nitrogen fixation, there 

 may even be an absolute increase in the total nitrogen. 



Somewhat similar changes occur with sulfur and phosphorus as 

 with nitrogen. There is a reduction of the amounts of these 

 elements found in inorganic forms with, however, no loss in the 

 total amounts found in the soil. 



These effects are all directly associated with the activities of the 

 microbes which are responsible for the decomposition of the organic 

 materials ; they are also concerned with the normal nutrition of the 

 microbial cells. The nitrogen, whatever its combination, is built 

 up from an inorganic into organic cell substance; there is a direct 

 proportion, in which, for a unit of organic matter decomposed or 

 per unit of energy liberated, a definite amount of nitrogen is assimi- 

 lated and a definite amount of cell substance synthesized. A great 

 abundance of soil microorganisms, including numerous bacteria, 

 actinomyces, and fungi, are able to assimilate nitrogen provided as 



