CROP AND FALLOW 233 



upon the nitrate content of the soil, there being a steady decrease 

 in the concentration of the nitrate content of potato and corn 

 lands as the season progressed, while that of fallow and alfalfa 

 remained practically constant, the nitrate content of the latter 

 being uniformly low through the season. According to Lyon and 

 Bizzell, soil that had produced alfalfa for five years was higher in 

 nitrates than soil that had grown timothy during the same period. 

 Furthermore, the former nitrified ammonium sulphate more readily 

 than did the latter. 



Brown found that the rotation of crops caused an increase in 

 number of organisms in a soil, also greater ammonifying, nitrifying 

 and nitrogen-fixing powers than continuous cropping to either corn 

 or clover. Furthermore, the crop on the soil at time of sampling 

 was of more importance from the bacterial viewpoint than the 

 previous crop. However, the preceding crop has a marked effect 

 upon the nitrate content of the soil, as is seen from the work of 

 Lyon and Bizzell, where plats that had been planted to certain 

 crops were kept bare of vegetation in the early part of the growing 

 season of 1911. Nitrate determinations of the soil were made and 

 the nitrate present showed a distinct and characteristic relationship 

 to the nitrate content found under the several varieties of plants 

 previously grown upon the soil. Later they showed that alfalfa 

 soil nitrified more rapidly than timothy soil, both in the soil on 

 which the crops had been grown continuously and in that from 

 which they had been removed and the soil kept bare for two seasons. 

 The author has shown that the nitrifying powers of alfalfa soil, 

 while slightly higher than that of virgin soil, is very low when 

 compared with either wheat or potato and fallow soil. Further- 

 more, the extensive work which has been conducted at the Utah 

 Experiment Station demonstrates that there is a very pronounced 

 relationship between the crop growing upon a soil and its nitrate 

 content. However, in this work the nitrate content of the alfalfa 

 and oat soil is very low, while that of potatoes and fallow is high, 

 and we find the nitrifying powers of alfalfa and potato soil high as 

 compared with fallow. 



Nitric nitrogen Nitrifying 



Crop. in soil. powers. 



Fallow 1 100 100 



Alfalfa 36 148 



.Oats 36 103 



Corn 33 77 



Potatoes 99 21 



Hence, we can conclude that alfalfa not only feeds closer upon 

 the soluble nitrates of the soil but also makes a much greater drain 



1 Fallow taken as 100. 



