Relations of Higher Plants to the Formation of Nitrates 93 



The nitrates were highest under the maize, next highest under the 

 potatoes, and lowest under the oats. Similar results had been obtained in 

 previous years. 



The last column of Table 35 shows the quantity of nitrogen removed per 

 acre by each crop. The maize crop was a very poor one, which accounts 

 for the small quantity of nitrogen contained in that crop. It is doubtless 

 true that the small maize crop is partially responsible for the high nitrate 

 content of the maize soil ; however, this high nitrate content has been found 

 in maize soil in previous years when the crop was good. Again, the per- 

 sistently higher nitrate content of the maize soil as compared with the 

 unplanted soil can be explained only on the assumption that nitrate for- 

 mation is much more active where the maize is growing, for certainly more 

 nitrates are being removed from the planted soiL 



Nitrates are higher in the potato soil than in the oat soil, although the 

 former crop removed nearly fifty per cent more nitrogen than did the 

 latter. The nitrate content of a planted soil is not determined by the 

 total quantity of nitrogen removed by the crop, but by a number of factors, 

 of which one appears to be a direct influence which each species of plant 

 exerts on the activity of the nitrifying organisms. 



In the year following that in which the results given above were obtained, 

 these plats were kept free from vegetation until July 1 and nitrates were 

 determined from time to time. In Table 36 is given a statement of the 

 nitrates in the previously planted and in the unplanted sections of these 

 plats, on each of the dates when the soils were analyzed: 



TABLE 36. 



Nitrates in Soil Planted in the Previous Year and Unplanted 

 IN 1911 





Crop 



May 1 



June 5 



June 28 



Plat 



Surface 

 eight 

 inches 



Second 

 eight 

 inches 



Surface 

 eight 

 inches 



Second 

 eight 

 inches 



Surface 

 eight 

 inches 



Second 

 eight 

 inches 



3612, 3613, 3622, 3623 

 3614, 3615, 3624, 3625 

 3616, 3617, 3626, 3627 



f Maize 



1 None .... 

 / Potatoes. . 

 \ None .... 



1 Oats 



\ None .... 



51 

 48 

 31 

 43 

 23 

 32 



53 

 52 

 26 

 43 

 21 

 40 



78 

 68 

 50 

 80 

 41 

 68 



45 

 44 

 26 

 43 

 33 

 35 



40 

 40 

 29 

 35 

 22 

 34 



34 

 30 

 24 

 29 

 22 

 32 



