May 28,1917 
Influence of Crop , Season , Heater on S<n 7 Bacteria 
321 
the concentration of the surface foot in favor of the potato soil. But 
these results show conclusively that the soil solution is influenced to a 
depth of at least 6 feet by the crop grown upon it. 
Table XXI.— Concentration of the soil solution where various quantities 0* water have 
been applied 
[Results reported as nitric nitrogen parts per million of soil solution] 
Water applied (inches). 
First 
foot. 
Second 
foot. 
Third 
foot. 
Fourth 
foot. 
Fifth 
foot. 
Sixth 
foot. 
Average. 
37*5 . 
14. 2 
9.9 
10. 0 
8. 2 
8. 1 
6.7 
9*5 
25. 
I ? .7 
10. 2 
xo. 4 
10, 4 
10. 5 
11. 6 
12.1 
15 . 
16. 8 
13*4 
ii, 2 
8. 1 
8.6 
7.2 
10. 0 
None. 
35-6 
27-5 
28. 0 
25. 2 
3 °. o 
24. 8 
28.5 
The concentration of the soil solution varies with the quantity of 
water applied to the soil during the season. It is three times as con¬ 
centrated in the soil which received no irrigation water as in the soil 
which received 37.5 inches; but the difference is not great between the 
concentration of the heaviest irrigated soil and those which received 
much smaller quantities of water. 
INFLUENCE OF WATER ON THE NUMBER OF ORGANISMS AND ON THE 
AMMONIFYING AND NITRIFYING POWERS OF THE SOIL 
All of the plots which have been considered in the previous discussion 
were sampled, and bacteriological analyses made of the soils. The sam¬ 
ples for this work were taken on the same day in the spring, midsummer, 
and fall as were the samples for the direct chemical analyses. These, 
however, were taken to a depth of only 12 inches. Three individual 
determinations were made at each sampling during each season for the 
three years, so each result as reported, unless stated to the contrary, 
represents the average of nine or more analyses. Determinations were 
made of the number of organisms developing upon synthetic agar, the 
ammonifying powers, and the nitrifying powers of the soil. The results 
have been so arranged that we can compare the soil from each of the 
plots receiving the various quantities of water with each other and 
these in turn with the unirrigated. Furthermore, it is possible to com¬ 
pare directly the number of organisms, ammonia, and nitric nitrogen 
produced, as all are reported in the same table (Table XXII). 
ALFALFA 
There were four plots in the alfalfa series. These received varying 
quantities of water; otherwise, they were all treated alike. To one plot 
were applied 37.5 inches of water; to another, 25 inches; to a third, 15 
inches, while one was unirrigated. The average results for the three 
years are given in Table XXII. 
82983°—17 - 1 
