104 Decomposition of Plant and Animal Residues 



Table 18. 



IXFLUEXCE OF NiTROGEN CoNTENT OF PlANT RESIDUES ON THE LIBERATION 



OF Nitrogen as Nitrate (from Lyon, Bizzell, and Wilson) 



To hasten the decomposition of straw and of similar plant ma- 

 terials, some available nitrogen and phosphorus may have to be 

 added in the form of inorganic salts. The microorganisms bringing 

 about decomposition of the plant and animal residues are living sys- 

 tems. They grow and multiply; they require considerable amounts 

 of energy and nutrients. In the straw and in the stubble of cereals 

 and other plants, they find sufficient energy but not enough essential 

 nutrient elements, especially nitrogen and phosphorus. Hence, these 

 must be added to favor the activities of the organisms which thus 

 bring about the rapid destruction of the plant materials. When 

 green plants, however, such as young rye and clover, or plant and 

 animal residues high in nitrogen and in phosphorus are added to the 

 soil, the microorganisms are able to decompose them rapidly, without 

 the addition of inorganic salts; the plant nutrients are liberated. 



The results presented in Table 19 fully confirm those given in 

 Table 18, even though totally difi^erent types of material are used. 

 Plant substances high in nitrogen decompose rapidly; a large part 

 of the nitrogen is liberated as ammonia, and comparatively little 



Table 19. Products of Decomposition of Rye Plants Harvested at Different 

 Stages of Growth (from W'aksman and Tenney) 



Stage of 

 Growth 



of Plant 



I 



II 



III 



TV 



CO2 

 Given Off 

 mg C 

 286.8 

 280.4 

 199.5 

 187.9 



Nitrogen 



Liberated 



as Ammonia 



7ng N 



22.2 



3.0 











Nitrogen Consumed 



from Ammonium 



Salt Added to Soil 



vig X 









 7.5 

 8.9 



*See Taljle Hi 



