SOIL ORGANISMS 



423 



soil management as well as the effect of nitrijEieation on plant 

 growth. 



The inflnence of plants on nitrification is not confined to 

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

 Bizzell, in the investigation previonsly 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 





Ska SON 1910 



Nitrates in Soil Kept 

 Baee in 1911 

 Paets Per Million 



Treatment 

 IN 1910 



Nitrates in 



Soil, Parts 



per Million, 



Seasonal 



Average 



Nitrogen 



IN Crop, 



Pounds Per 



Acre 



MatI 



June 28 



Maize 



167 

 136 



104 



108 



90 

 126 



3 

 43 



29 



52 



50 



28 

 43 



22 

 36 



37 



Bare 



35 



Potatoes 



Bare 



26 

 32 



Oats 



22 



Bare 



33 



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- 



