May 1,1925 Soil Mulch in Absorption and Retention of Moisture 823 
Table II.— A comparison of total and conserved soil moisture in the soil to a depth 
of 4 feet after the year of fallow, for six variations in fallow preparation 
[The essential difference between these variations lies in the presence or absence of a soil mulch during all 
or a part of the first major period of moisture absorption. Adams Branch Station, Lind, Wash., 1918 
to 1923, inclusive] 
Soil moisture in acre-inches to a depth of 4 feet after the year of fallow 
Tillage variations 
i 
1918 
1 
1919 
1920 
1921 
1922 
1923 
Aver¬ 
age 
Con¬ 
served 
mois¬ 
ture a 
Compar¬ 
ative 
amount 
of con¬ 
served 
moisture 
Dry fall-plowed_ _ _ 
3. 35 
4.97 
4.89 
5. 07 
4. 67 
5.00 
4. 66 
2. 58 
100 
Harvest-disked, dry fall-plowed. 
4. 34 
5.34 
4.76 
4. 82 
5. 48 
5.03 
4. 96 
2 . 88 
111 
Harvest-disked, wet fall-plowed. 
Harvest-disked, early spring- 
3. 94 
5.54 
4. 58 
5.05 
5. 24 
4. 76 
4. 85 
2. 77 
107 
plowed_ . . _ ... 
4. 61 
5.63 
4. 87 
5. 52 
6.18 
5. 52 
5. 39 
3.31 
128 
Wet fall-plowed_ _ 
3. 75 
5.49 
4. 80 
5.04 
5.18 
5. 57 
4. 97 
2. 89 
112 
Early spring-plowed_ .. 
4.70 | 
I 
5.98 
5. 32 
5.76 
6 . 47 
5. 60 
5. 64 
3. 56 
138 
° Residual moisture, 2.08 acre-inches to a depth of 4 feet, average of four seasons. 
data indicate that on the average there 
was some saving of moisture through 
weed removal by harvest-disking. 
Despite this saving, however, the 
effect on absorption more than counter¬ 
balanced the gain from killing weeds, 
as shown by the slightly lower average 
moisture content of the harvest disking 
and early spring plowing, when com¬ 
pared with spring plowing with no pre¬ 
vious treatment. A comparison of 
harvest-disking and wet fall-plowing 
with wet fall-plowing alone shows the 
same effect, due to the same cause. 
It might be suggested that the 
moisture advantage of the spring- 
plowed soil was due entirely to the 
holding of snow by stubble. This 
factor undoubtedly is of some import¬ 
ance under certain conditions, but, so 
far as this experiment was concerned, 
it was relatively unimportant in de¬ 
termining total moisture. The effect 
of the mulch on absorption played a 
much larger part in the final result. 
This is indicated by comparing the 
moisture content of the harvest-disking 
and spring-plowing with that of the 
harvest-disking and dry fall-plowing. 
Stubble was not extensive on any of 
the plats, and as a result of the tillage, 
neither of these variations carried a 
stubble cover during the period of snow¬ 
fall. The lower average moisture con¬ 
tent of the second must be attributed, 
therefore, to a more pronounced in¬ 
hibitory effect due to the deeper mulch 
of the dry plowing as compared with 
that of the disking. This indicates 
that, within certain limits, the inhibi¬ 
tory effect is proportional to depth in 
the mulch. That the effect of the mulch 
on absorption is not due to the physical 
condition resulting from tilling this 
particular soil when dry is shown by 
the fact that the mulch created by the 
wet fall-plowing also reacted in in¬ 
hibiting absorption. 
It is apparent, therefore, that during 
each of the six fallow periods covered 
by these data, soil covered by a mulch 
during all Or a part of the first period 
of absorption contained less moisture 
at the end of the fallow than where no 
mulch existed during the same period 
of absorption. This indicates that the 
lower moisture content was due to an 
inhibiting effect of the mulch on ab¬ 
sorption. 
absorption 
Detailed data on absorption are 
available for the seasons of 1920 to 
1923, inclusive, and on retention for 
the seasons of 1921 to 1923, inclusive. 
In the study of absorption certain plats 
of the experiments, mulched and un¬ 
mulched, were sampled at the beginning 
and at the end of each major absorp¬ 
tion period. In the study of retention 
two plats were given no surface tillage 
whatever, but were kept free of growth 
by shaving with a sharp hoe. Any 
loose soil was removed by winds, and 
the surface of these plats was as free 
from both weeds and mulch as could be 
desired. The moisture content of these 
plats at the beginning and the end of 
the retention period was compared 
with that of other plats mulched during 
the same period. The data on ab¬ 
sorption (Table III) will now be con¬ 
sidered, followed by the results on re¬ 
tention (Table IV). 
In the spring of 1921 the unmulched 
soil had absorbed 3.53 inches of water 
per acre. This was approximately 
67 per cent of the total precipitation 
