Sept. 9,19*8 Variations in Moisture Content of a Loess Soil 
475 
tory experiments already reported (No. 2, 3), but which were carried out 
after this field study had been concluded. The difference is shown in 
Table XV, compiled from the data in Tables X and XII. 
Table XV .—Difference in ratios shown hy uncropped surface soil and exposed subsoil , 
from data for the ?-i 2 ~inch section 
Date. 
Ratio. 
Date. 
Ratio. 
Surface 
soil. 
Subsoil. 
Differ¬ 
ence. 
Surface 
soil. 
Subsoil. 
Differ¬ 
ence. 
May 25, 27. 
July 11. 
30. 
2. 6 
2.8 
2. 7 
2. 0 
2. 2 
2. I 
O. 6 
.6 
.6 
August 3. 
9 . 
16. 
26. 
2. 8 
2.7 
2.9 
2.7 
2. 2 
2. I 
2. I 
2. O 
0. 6 
.6 
.8 
•7 
PROPORTION OF RAINFALL ACCUMULATED IN THE FALLOW 
With the fallow field it is of interest to know how large a proportion 
of the total precipitation, 13.78 inches, which fell between the first and 
last samplings was accumulated in the surface soil and subsoil together. 
From the data in Table IX it is evident that after only three rains, 
those of April 20-21 (1.71 inches), June 12-14 (2.81 inches), and August 
15-16 (2.11 inches), could any appreciable amount of water have pene¬ 
trated beyond the twelfth inch. In the case of the last two rains the 
minimum amounts of water required to raise the ratios from those 
existing before the rain to those found immediately after must have been 
approximately 1.4 and 0.8 inch, respectively, thus leaving a maximum 
of only 4.4 inches which could have passed into the second foot. More¬ 
over, this amount would be possible only on the assumption that there 
was.no run-off, while the data in Table XIV indicate that with the heavy 
rains the loss by run-off amounted to nearly half of what fell. On all 
three occasions at the time of the sampling there doubtless was some 
water in the surface foot which would later have passed into the second 
foot if evaporation had been prevented, but under the conditions which 
prevailed it is probable that only a negligible quantity actually did so. 
On August 30 the first foot of soil contained the equivalent of about 
0.8 inch of rain less than it did on April 5. Thus, it appears probable 
that out of the 13.78 inches of rain which fell during the five months 
less than 2 inches were accumulated in the fallow. 
More frequent cultivation of the surface, with the object of maintain¬ 
ing a dry mulch, would probably have only reduced the amount of water 
accumulated, as, on one hand, moist soil would have been brought to 
the surface to lose its water by evaporation, and, on the other, very dry 
soil, with a ratio below 1.0, would have been brought next the moist 
layer in the fourth or fifth inch to absorb part of the free water contained 
in this and retain it as hygroscopic water. 
