Mar 3,1923 
Effectiveness of Mulches upon Soil Moisture 
729 
MOVEMENT OF SOU# MOISTURE 
Soils have a great attractive and adhesive force for water (2). The 
retention of water on the surface of soil particles, despite gravitation, 
is due to surface tension (3). The surface of the film of water encircling 
a soil particle is in an elastic condition exerting a considerable pressure. 
If the films of water became thicker and heavier, a part of the water would 
gradually pass out, and if the films became thinner they would acquire the 
power of absorbing and retaining fresh supplies of neighboring water. 
Briggs and Lapham (4) have attributed the cause of the movement of 
soil moisture to viscosity, concentration of solution, surface tension, and 
moisture film curvature. Lynde and Dupre (28) believe that osmosis 
may cause a considerable movement. King (23) and Alway and Clark 
(j) have demonstrated the movement of moisture in the soil. Water 
always tends to move from the wet to the dry soils (14). Briggs (3), 
Briggs and Lapham (4), Widtsoe and McLaughlin (45), and Loughridge 
(27) have shown that the final distribution leaves the most moisture 
nearest the source of supply and the least farthest away. 
EFFECT OF CULTIVATION ON THE TRANSPIRATION OF PLANTS 
Sleskin (40) and Schroeder (37) have determined the water require¬ 
ment of plants under cultivation by growing beets in cultivated and 
cement-covered plots. They found the proportion of beet crop grown 
under cultivation to that which received the cement-covered treatment to 
be 26.9 to 16.1. At the end of the experiment, the soil under the cement- 
covered plot contained more moisture than that under the cultivated plot. 
Experiments by Widtsoe (43 p. 14-23) led to the opposite conclusion. 
The transpiration ratio was invariably smaller on the cultivated than on 
the uncultivated soils. On the college loam, the ratios on the cultivated 
and uncultivated plots were 252 and 603; on the sandy clay, 428 and 
535; and on the infertile clay, 582 and 750. The favorable effect of 
cultivation was shown in the great reduction in the water cost of dry 
matter resulting from simple tillage. 
As a general rule, the more water offered the plant the larger the total 
yield of dry matter {38, 44). Mayer (29) found that the yield increases 
with the increase in soil saturation up to a certain point, after which 
there is a strong diminution in the yield of dry matter. Harris (u) 
and Morgan (31) have proved that the transpiration ratio increases as 
quantity of water added to the soil increases—that is, the water cost of 
crops becomes larger as more water is used. 
TIME OF tillage 
Harris and Jones (13, p. 24-26) collected moisture samples from the 
Nephi substation showing that the moisture content of the fall-plowed 
and spring-plowed plots receiving like treatments was practically same in 
all cases. The percentage moisture of the spring-plowed plots increased 
slightly with depth of cultivation, while the fall-plowed plots slightly 
decreased inversely with depth of cultivation. Straw mulch on the fall- 
plowed land is the most effective. In comparing fall plowing with spring 
plowing, Harris, Bracken,|and|Jensen ( 12 , p. 30-37) did not find any 
material difference in the yield of Turkey wheat. Cardon (6) has shown 
