THE SOIL MULCH IN THE ABSORPTION AND RETENTION 
OF MOISTURE 1 
By M. A. McCall 2 
Dry Land Specialist, Washington Agricultural Experiment Station 
INTRODUCTION 
Without irrigation successful crop 
production over a large part of the 
western United States is dependent on 
moisture stored in the soil. In part, 
this is due to limitations in total pre¬ 
cipitation, to its seasonal distribution, 
or to a combination of the two; but, 
in any case, the factors affecting the 
control of soil moisture are of the 
greatest practical importance. 
At one time the soil mulch was as¬ 
sumed to be the basis of all moisture 
control. It was regarded as essential, 
both in effective absorption and in 
retention. More recently, however, 
the mulch and its necessity seem mat¬ 
ters of doubt, and while no one advo¬ 
cates the discontinuance of mulch¬ 
forming tillage, former ideas at least 
seem to be considered untenable. In 
discarding former theory, however, no 
general principle has been developed 
in its stead, and so far as more than 
local application is concerned, the 
situation is somewhat hazy. As in¬ 
dicative of the present somewhat con¬ 
tradictory state of affairs, the follow¬ 
ing may be noted: 
REVIEW OF LITERATURE 
Barker (4) 3 found that at Lincoln, 
Nebr., the loss of water due to direct 
evaporation from the soil was a small 
factor after the water became thor¬ 
oughly distributed in the soil. Young 
(26), for the same conditions, con¬ 
cluded that a loose soil mulch was not 
much more effective than an un¬ 
mulched soil in retarding the evapora¬ 
tion of moisture already established in 
the soil. Burr ( 8 ), working at North 
Platte, Nebr., when starting with a 
soil almost filled with water, and dur¬ 
ing a season of heavy rainfall, arrived 
at a conclusion similar to that of Young. 
For a less favorable season, and with a 
soil comparatively dry below the 
second foot, Burr states that “from 
the viewpoint of storing water a culti¬ 
vated surface is essential.” 
Atkinson, Buckman, and Gieseker 
(3) show that summer tillage saved 
moisture in excess of that retained in a 
soil not tilled, but no direct statement 
is made that the benefit of the tillage 
was due either to the mulch effect or 
to killing weeds. 
Call and Sewell (.9), after a careful 
study of the moisture content of a 
mulched and an unmulched soil, con¬ 
clude that under Kansas conditions a 
cultivated soil is no more effective than 
a bare uncultivated one in preventing 
evaporation; and in addition conclude 
(10) that “in the past too much em¬ 
phasis may have been placed on tillage 
as a direct means of conserving mois¬ 
ture and liberating plant food and too 
little on it for the purpose of destroying 
weeds.” After a rather extensive re¬ 
view of literature from a variety of 
sources, Sewell (22) emphasizes this 
latter conclusion. 
Merrill (21) quotes Farrell as report¬ 
ing certain experiments at Nephi, 
Utah, in which fall plowing did not 
give beneficial results in moisture con¬ 
servation; but further quotes Widtsoe 
as concluding from other data that 
“fall plowing undoubtedly conserves 
the winter precipitation.” 
Cardon (11) shows that at Nephi, 
Utah, during each of the four years 
1909 to 1912, inclusive, fall-plowed soil 
contained less moisture than that not 
plowed until spring. 
Harris and Jones (16), reporting on 
the same and additional data as that 
of Cardon, show graphically a similar 
result. In addition, they show that in 
the fall an unmulched soil contained 
practically as much moisture as did 
a mulched one. They conclude that 
weed removal is the most marked 
benefit of tillage. 
1 Received for publication July 3, 1924; issued June, 1925. Published with the approval of the Director 
of the Washington Agricultural Experiment Station as Scientific Paper No. 117, College of Agriculture 
and Experiment Station, State College of Washington. 
2 The author is now Agronomist in Charge of Cereal Agronomy, Office of Cereal Investigations, Bureau 
of Plant Industry, U. S. Department of Agriculture. 
3 Reference is made by number (italic) to “Literature cited,” p. 831. 
Journal of Agricultural Research, 
Washington, D. C. 
(819) 
Vol. XXX, No. C 
May 1, 1925 
Key No. Wash.-5 
