May 28,1917 Influence of Crop , Season , Water on Soil Bacteria 
3<>9 
The nitric nitrogen in the surface foot of all these plots is very 
high during the spring and fall. In the summer they are high only 
in the plots which received 15 inches and no irrigation water, thus showing 
the effect of the water upon the soluble nitrates of the soil. In all of 
the irrigated plots the total nitric nitrogen found in the soil at the end 
of the season is practically the same as in the spring. But the unirrigated 
plot, between the fall and spring sampling, gains 94 pounds of nitric 
nitrogen. Now, if this be a correct measure of the nitric nitrogen pro¬ 
duced by the various plots during the winter and spring months, there 
must have been large quantities of the nitric nitrogen which was produced 
in the irrigated soil carried below 6 feet. It is not likely that the water 
content of the irrigated plots would have become sufficient to retard 
nitrification to this extent, although it may have been retarded to a 
degree by the lower temperature which would prevail in the heavily 
irrigated plots. But this would be far from sufficient to account for 
the excess quantity of nitrates found in the unirrigated soil. Much of 
this, therefore, must have disappeared in the drain waters. 
The influence of the irrigation water upon the nitric-nitrogen content 
of the soil is noticeable throughout the year, and the quantity present 
at any time decreases as the proportion of water applied to the soil 
increases. It is interesting to compare the total nitric nitrogen of the 
various plots in spring and fall with that removed by the crop under the 
various treatments (Table VIII). 
Table VIII .—Summary of nitrogen transformations in potato land 
[Results expressed in pounds] 
Water applied. 
Character of nitrogen. 
.,37.5 
inches. 
inches. 
• l 5 
inches. 
None. 
Nitrogen removed in crop. 
Nitric nitrogen in soil in spring. 
Nitric nitrogen in soil in fall. 
Original nitric nitrogen removed from soil. 
Nitric nitrogen formed during season. 
Excess of nitric nitrogen formed during season 
in irrigated soil. 
20. 4 
33*7 
3 i *5 
2. 2 
18. 2 
93*2 
2-5 
24. 8 
49*9 
47*9 
2.0 
22. 8 
97.8 
3-9 
33*2 
443 
35*3 
9.0 
24. 2 
99.2 
6.6 
19.x 
196.3 
102. 2 
94.I 
- 75*0 
Excess per acre-inch of water applied. 
This gives the best results both for total quantity of water applied 
and quantity per inch of water where an application of 15 inches of 
water is used. Furthermore, these results indicate that one of two 
things must have occurred in these plots: Either the formation of nitric 
nitrogen has been increased to a greater extent than shown by these 
results by the irrigation water, or else the water has carried none to a 
greater depth than 6 feet. And all of our results have pointed strongly 
