821 
May j, 1925 Soil Mulch in Absorption and Retention of Moisture 
Fig. 1.—Mean daily temperature, based on an 11-year average, at Lind, Wash. During the period from 
November 15 to March 15 . when mean temperatures are comparatively low, evaporation is less active than 
at any other time, and the opportunity for precipitation to be absorbed by the soil is correspondingly 
greater. The general frelationship between mean temperature and rate of evaporation is shown in 
Figure 2 
Fig. 2—Relation between mean temperature, mean relative humidity, and total evaporation from a free 
water surface, by weeks, at Lind, Wash., May 9 to October 30, 1924. The dates given represent 
weekly centers 
high, relative humidity is low, and 
little or no rainfall occurs. Retention 
then becomes paramount. The fal¬ 
low period, from a moisture stand¬ 
point, extends from the removal of one 
crop to the beginning of the growing 
season of the next. Practically, on 
the Adams Station, it therefore con¬ 
sists of a first period of absorption, 
extending through the first fall, winter, 
and spring, followed during the sum¬ 
mer by a period in which retention is 
important, and this, in turn, followed 
by a second period of absorption. The 
soil moisture content at the beginning 
and end of either of these periods 
should, therefore, give a basis for 
reliably measuring the effect of the 
mulch in whichever function is most 
important for that period. 
The soil of the Adams Station is a 
very fine sandy loam of the Ritz- 
ville series. It is a typical semiarid 
soil, deep and uniform. The me¬ 
chanical analysis of the soil by feet 
to a depth of 4 feet is given in Table I. 
Table I.— Mechanical analysis, hy feet, to a depth of 4 feet of the soil on the 
Adams Branch Station, Lind, Wash. (19). 
Soil section 
First foot,-. 
Second foot. 
Third foot.. 
Fourth foot 
Fine 
gravel 
Coarse 
sand 
Per cent 
Per cent 
0.00 
0.08 
.00 
.08 
.00 
.11 
.00 
.06 
Medium 
sand 
Fine 
sand 
Per cent 
Per cent 
0.13 
9.82 
.08 
8.68 
. 14 
8.04 
.05 
6.10 
Very 
fine sand 
Silt 
and clay 
Total 
Per cent 
Per cent 
Per rent 
45.88 
45.05 
100.96 
46. 75 
44.40 
99.99 
52.01 
39.70 
100.00 
50.24 
43. 45 
99.90 
