90 T. Lyttleton Lyon and James A. Bizzell 



uncropped soil; in the writers' experiments maize soil afforded a much larger 

 quantity of nitrogen in the crop and drainage. Oats also, in the writers' 

 experiments, accumulated more nitrogen in the crop and drainage water than 

 was contained in the water from the bare soil. Grass, however, gave 

 results of a nature similar to those obtained by Deherain, but in less degree. 



It is evident that in the case of grass the depressing influence on nitrate 

 formation is greater than the stimulating influence. 



The discrepancy between the writers' results and those obtained by 

 Deherain and by Leather may be accounted for in any one or more of the 

 following ways: 



1. On the soil used by the writers the plants may have absorbed a larger 

 proportion of their nitrogen in forms other than as nitrates. 



2. Possibly the very heavy clay soil used in the writers' experiments 

 retained a larger proportion of nitrates, and this would have affected 

 the bare soil more than it would the planted soil as the quantity of nitrates 

 in the former was much greater than that in the latter, 



3. The lower layers of the soil may have been the scene of a denitrify- 

 ing process, which would probably iiave decreased the nitrogen removed 

 from the bare soil'more than that from the planted soil because there were 

 more nitrates in the bare soil to be denitrified. 



4. The stimulating influence of the higher plants on nitrate formation 

 may have been greater in comparison with the depressing influence in the 

 soil used by the writers than in the soils used by Deherain and Leather. 



The evidence afforded by the experiments of Deherain and Leather indi- 

 cates that wheat, oats, potatoes, grass, and beets have a greater depressing 

 influence than they have stimulating influence on nitrate formation, and 

 that the stimulating and the depressing influence in maize practically 

 balance each other. The high nitrate content in maize soil on the writers' 

 experiment field in the spring following the growth of the maize crop, as 

 well as the results from the soil tanks, indicates that on this soil the stimu- 

 lating influence of maize is greater than its depressing influence. 



It appears from these considerations that the three kinds of plants grown 

 in the tanks at this station exerted a greater stimulating influence on 

 nitrate formation than did the same plants at Grignon, and that the extent 

 to which higher plants affect nitrate formation favorably or unfavorably 

 varies in different soils. The soil used by the writers is evidently very 

 favorable to nitrate formation. 



