SOIL ORGANISMS 



423 



soil management as well as the effect of nitrification on plant 

 growth. 



The influence of plants on nitrification is not confined to 

 the period in which they are growing on the soil. Lyon and 

 Bizzell, in the investigation previously mentioned, found that 

 certain plants grew better when preceded by one species 

 rather than by another. These authors, as already explained, 

 have suggested that certain higher plants directly influence 

 nitrification with varying intensity. The question now arises 

 as to the possibility of such plants influencing the process of 

 nitrate formation after their removal. 



The following data from Lyon and Bizzell suggest that, 

 while the effect is variable, plants seem definitely to influence 

 the production of nitrates during the season after they have 

 been removed. All of the plats were kept bare in 1911. 



Table XCII 



These results indicate that maize exerts a stimulating influ- 

 ence during the following summer. Oats and potatoes seem 

 to depress nitrate accumulation. 



232. Relation of nitrification to soil fertility. — In spite 

 of the immense amount of work that has been done on the bio- 



