518 



PRINCIPLES OF SOIL MICROBIOLOGY 



tion of seedlings and the results of Barthel and Bengtsson 20 on the 

 influence of manure upon cellulose decomposition definitely indicate 

 that we are not dealing here with an injury of the process of nitrifica- 

 tion but with the actual assimilation of the nitrate by the soil fungi 

 and bacteria that use the celluloses as sources of energy. Collison 

 and Conn 21 concluded that two separate harmful factors are associated 

 with the influence of straw and other plant residues upon plant growth : 

 (1) a toxic chemical agent which acts upon the plants immediately 

 after germination, the effect not being pronounced in soils; (2) a bio- 

 logical factor as a result of the competition between soil microorganisms 

 and plants for the available nitrogen. The results of Viljoen and 

 Fred 22 on the effect of wood and wood pulp upon the growth of oats 



TABLE 51 



Influence of different kinds of wood on the growth of oats and red clover 



TREATMENT 



None 



1.5 per cent coarse wood 



3.0 per cent coarse wood 



3.0 per cent fine wood 



3.0 per cent wood burned and ash used 



YIELD OP 



OATS, 

 AVERAGE 



grams 



26.6 

 18.3 

 14.8 

 21.0 

 27.5 



YIELD OF RED 

 CLOVER, AVERAGE 



Uninocu- 

 lated 



gra ms 



27.5 

 26.5 

 21.5 

 24.5 

 60.0 



Inocu- 

 lated 



grains 



44.0 

 37.3 

 43.0 

 41.5 

 56.0 



and clover demonstrated definitely that the injurious effects are due 

 to a lack of available nitrogen (table 51). 



A study of the decomposition of two natural organic materials, 

 varying in nitrogen content, indicates that the decomposition of the 

 material of a lower nitrogen content, like timothy residues, is extended 



of soil nitrogen to nutrition of citrous plants. Jour. Agr. Res., 2: 101-113. 

 1914. 



20 Barthel, C, and Bengtsson, N. Action of stable manure in the decomposi- 

 tion of cellulose in tilled soil. Soil Sci., 18: 185-200. 1924; Idem., 1926 (p. 448); 

 also Anderson, 1926 (p. 451). 



21 Collison, R. C, and Conn, H. J. The effect of straw on plant growth. N. Y. 

 (Geneva) Agr. Exp. Sta. Tech. Bui. 114. 1925. 



22 Viljoen, J. A., and Fred, E. B. The effect of different kinds of wood and 

 wood pulp on plant growth. Soil Sci., 17: 199-208. 1924. 



