92 



T. Lyttleton Lyon and James A. Bizzell 



The writers have already suggested that certain higher plants have a 

 distinct influence on the process of nitrification in the soil, and that this 

 influence varies in intensity with plants of different families and at different 

 stages in the growth of any one kind of plant. It was found, for instance, 

 that in a soil on which maize was growing the nitrates were sometimes 

 higher at certain periods than in a similar soil on which no plants grew. 

 Timothy (Phleum pratense), on the other hand, maintained uniformly a 

 very low nitrate content in the soil throughout the growing period. 



The question then arose whether the higher plants exert any influence 

 on the activities of the nitrifying bacteria after the plants are removed. 

 In order to test this it was decided to continue the nitrate determinations 

 for a second year, in soil that had been planted to several kinds of crops. 



Plats that had been used in 1910 for studying the effect of plants on the 

 nitrate content of soils were left bare in 1911 until July 1. In order to 

 keep down weeds the plats were disk-harrowed from time to time. Samples 

 of soil were taken from the sections of the plats that were planted and 

 those that were bare in 1910, for the purpose of ascertaining the effect on 

 the nitrate content of the soil of the different crops grown in the previous 

 year. The borings were made to a depth of eight inches below the surface, 

 and from eight to sixteen inches below the surface. In Table 35 are pre- 

 sented the results averaged for the entire season for the four plats planted 

 to the same crop, also the averages of the unplanted sections of the same 

 plats during the growing season of 1910. The table consequently shows 

 the nitrate content of the soil in the year during which the test crops were 

 grown. 



TABLE 35. Nitrates in Planted and Unplanted Sections of Plats. 



THE Growing Season, 1910 



Average for 



Plat 



Crop 



Nitrates 

 (parts per 

 million) 



On basis 



of nitrates 



in unplanted 



soil taken 



as 100 



Nitrogen 

 in crop 

 (pounds 

 per acre) 



3612, 3613, 3622, 3623 



f Maize 



\ None 



1 Potatoes 



\ None 



167 

 136 

 104 

 108 

 90 

 126 



123 

 100 



96 

 100 



71 

 100 



3 



3614, 3615, 3624, 3625. 



43 



3616, 3617, 3626, 3627 



jOats 



\ None 



29 







