sept. 9,1918 Variations in Moisture Content of a Loess Soil 
473 
Table XIV .—Depth of penetration and addition of moisture to the surface foot of soil 
Date of sampling. 
* 
Rain¬ 
fall. 
Inter¬ 
val be¬ 
tween 
cessa¬ 
tion of 
rain 
and 
samp¬ 
ling. 
Maximum penetration. 
Water added 
to surface foot 
by the rain. 
Approximate 
ratio in fallow 
before rain. 
Fallow. 
Grass 
field. 
Ex¬ 
posed 
sub¬ 
soil. 
Fallow. 
Grass 
field. 
1 to 3 
inches. 
4 to 6 
inches. 
Inches. 
Hours. 
Inches. 
Inches. 
Inches. 
Inches. 
Inches. 
July xo . 
O. 24 
24 
I 
I. r 
2. 6 
June 1. 
* 50 
IO 
2 
2 or 3 
2 
o *3 
o- 5 
I. 2 | 
2. 6 
Tulv 11. 
.81 
A 
6 or 7 
2 
I. 
2. 6 
j j x . .. . 
• § 
j 
Aug. s. 
I. 30 
6 
6 
7 
3 
.4 
I. I 
2. 5 
3*1 
Aug. 16. 
2 . II 
6 
11 or 12 
10 
3 
•9 
1.8 
2. 6 
3*1 
June 14. 
2. 71 
24 
a 12 
°I2 
°I2 
1.4 
2. 5 
i *5 
2.4 
a Rain on this occasion penetrated beyond the maximum depth of sampling: 12 inches. 
The effect of a rain in increasing the moisture content of a fallowed 
field depends not only upon the amount of rain and the rapidity of its 
fall but also upon the moistness of the surface soil. Thus, an inch of rain 
that has fallen just slowly enough to avoid all run-off may have pene¬ 
trated during the first 24 hours only 4 or 5 inches into a silt-loam soil 
when the initial ratio was only 0.5, whereas it would have penetrated 
twice as far had the initial ratio been 1.5 (j, p. 402-403). The half¬ 
inch rain of June 1 was held within the surface 2 inches, a comparatively 
dry layer in the third inch separating this upper partly moistened sec¬ 
tion from the already moist soil below (fig. 5). 
LOSSES THROUGH EVAPORATION 
It is evident that in the grass fields, and during August in the cornfield, 
the losses of water from the levels below the surface 3-inch section took 
place almost entirely through transpiration. In the fallow, when the 
ratios were as high as 2.8 to 3.3, there would be a slow downward move¬ 
ment of moisture into the subsoil if this were less moist until the ratio 
had fallen to some point between 1.9 and 2.4 (2, p. 50), while at the same 
time there would be a slow upward movement until the ratios in the sec¬ 
tions at some little distance from the surface had fallen to about the same 
point. In cylinder experiments with surface soil from the fallow field 
it was found with two sets of 3-foot cylinders which had been filled with 
soil having initial ratios of 2.4 and 3.0, respectively, that at the end of 
78 days the lower half of the surface foot showed ratios of 1.9 and 2.1, 
respectively. From other laboratory experiments it is evident that 
losses through evaporation from the portions of the soil 6 inches or more 
below the surface take place very slowly after the ratio has once been 
reduced to 2.0. From both laboratory experiments (2, p. 50) and field 
observation (2, p. 63), it is evident that the downward movement of 
