May 1,1925 Soil Mulch in Absorption and Retention of Moisture 825 
soil was actually the absorption shown 
by the data, plus the undetermined 
loss. On the basis of the data, the 
unmulched soil absorbed 53 per cent 
and the mulched soil absorbed 31 per 
cent of the total intervening precipita¬ 
tion. The unmulched soil was 69 per 
cent superior in total absorption and 
slightly over 200 per cent superior in 
the amount of moisture below the 
first foot. 
In every instance the unmulched 
soil was superior as an absorbing 
agent. The comparative efficiency of 
the mulched and unmulched soils in 
absorption is shown graphically in 
Figure 4. 
In 1922 the loss from the mulched 
soil amounted to 0.71 inch, and, con¬ 
sidering the gain in the lower 2 feet, 
this loss came entirely from the first 
foot. The unmulched soil sustained a 
loss of 1.61 inches, and of this loss 0.21 
inch came from below the first foot. 
Neither the mulched nor the unmulched 
soil lost moisture from the third foot 
in 1922. 
In 1923 the mulched soil showed a 
total loss from July 6 to September 20 
of 0.49 inch. Of the total loss, but 
0.04 inch came from below the first 
foot, and none was lost from the third 
foot by evaporation. The unmulched 
soil in the same period lost 0.95 inch 
Fig. 4.—Average moisture content in acre-inches of mulched and unmulched soils at the end of the first 
period of moisture absorption during the fallow year, Adams Branch Station, Lind, Wash., 1920 to 1923, 
inclusive 
RETENTION 
Data showing the relation of the 
mulch to retention are given in Table 
IV. These data show that during the 
summer of 1921 the soil covered by 
a 6-inch soil mulch lost 1.02 inches of 
moisture. Of this total loss by evapo¬ 
ration, 0.12 inch came from below 
the first foot. In the lower 2 feet 
of this soil there was a gain by down¬ 
ward movement of 0.27 inch. The 
soil covered by a 4-inch mulch lost a 
total of 1.59 inches of moisture, or 
56 per cent more than the 6-inch 
mulched soil. Of this amount 0.55 
inch came from below the first foot, 
and 0.10 inch came from the third 
foot. The unmulched soil lost 2.02 
inches of moisture. This was 198 per 
cent of that lost from the 6-inch mulch. 
Of the total lost from the unmulched 
soil, 0.85 inch came from below the 
first foot, and 0.32 inch came from the 
third foot. 
19976—25f 
of moisture, with 0.32 inch coming 
from below the first foot. A very small 
loss by evaporation was indicated from 
the third foot of the unmulched soil. 
The data for retention show the 
mulch to have a positive effect in con¬ 
serving moisture, when considered 
only from that standpoint, and that 
efficiency in retention is increased by 
depth in the mulch. The comparative 
efficiency of the mulch in retention is 
shown in Figure 5. 
CONCURRENT ABSORPTION AND RETEN¬ 
TION 
Ordinarily, on the Adams Station, 
the mulch need be considered only as 
a retentive agent during the summer 
season, but in June, 1923, a rainfall of 
3.69 inches gave an opportunity to 
observe it as an absorbing agent under 
such conditions also. In effect, the 
mulch was functioning in absorption 
and retention at one and the same time 
(Table V). 
3 
