2 9 ^ 
Journal of Agricultural Research 
Vol. IX, No. 9 
The work at the Rothamsted station (63) early demonstrated that the 
nitrates in the drainage water from the various plots varied greatly, 
depending upon the crop growing upon the soil, thus indicating a rela¬ 
tionship between the available nitrogen in a soil and the crop growing 
upon the soil; since that time many experimenters have confirmed this 
conclusion. Furthermore, King and Whitson (28) found 22 per cent 
more nitrogen developed from soil after clover than from soil after com, 
and 13 per cent more than after oats. Later work by them (29) showed 
that there are greater quantities of nitrates throughout the entire season 
in soil under com or potatoes than in soil under clover and oats. Stewart 
and Greaves (54) found that different plants show a marked difference 
in their demands upon the nitrate content of the soil, there being a 
steady decrease in the concentration of the nitrate content of potato 
and com lands as the season progressed, while that of fallow and alfalfa 
remained practically constant, the nitrate content of the latter being 
uniformly low throughout the season. According to Lyon and Bizzell 
(33), 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 (3) 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 standpoint than the previous crop. 
However, the preceding crop has a marked effect upon the nitrate con¬ 
tent of the soil, as is seen from the work of Lyon and Bizzell (35), where 
plots that had been planted to certain crops were kept bare of vegeta¬ 
tion in the early part of the growing season of 1911. Nitrate deter¬ 
minations of the soil were made and the nitrate present showed a dis¬ 
tinct and characteristic relationship to the nitrate content found under 
the several varieties of plants previously grown upon the soil. Later they 
(36) 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. However, one of us (20) 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. 
Furthermore, the extensive work which has already been published from 
the Utah Experiment Station (54) demonstrates that there is a very pro¬ 
nounced 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 com, potatoes, and fallow is higher. 
Lyon and Bizzell (37) in 1913 reviewed the work of other investigators 
and summarized their own work on the influence of higher plants on 
the formation of nitrates in the soil. From this they conclude that, 
