822 
Journal of Agricultural Research 
Vol. XXX, No. 9 
The study of the mulch was made on 
the plats of the summer-fallow experi¬ 
ments. There are two series of these 
plats, one series being in crop and one 
in fallow each year. The plats are 
one-twentieth of an acre in area, 1 rod 
wide by 8 rods long. 
Samples for moisture determinations 
were taken by foot sections to a depth 
of 4 feet, this depth being sufficient dur¬ 
ing the period of somewhat deficient 
moisture covered by the study. 
Methods of sampling and of deter¬ 
mining soil moisture are given in 
Bulletin 164 of the Washington Agri¬ 
cultural Experiment Station (19). 
Moisture data are given in acre- 
inches, rather than in per cent of mois¬ 
ture-free soil. The volume weight of 
the surface 6 inches of a plowed soil is 
materially different from that of the 
same soil in an undisturbed condition, 
and the same per cent moisture content 
does not signify the same amount of 
moisture present in the same effective 
depth in the two cases. In the soil on 
which this study was made the volume 
weight of the plowed layer is approxi¬ 
mately 60 per cent of that before stir¬ 
ring. The volume weight of the sur¬ 
face foot of such a plowed soil is 80 
per cent that of the unstirred. Mois¬ 
ture content of the surface foot, where 
necessary, was calculated on this basis. 
In Table II are given total soil 
moisture data for certain tillage varia¬ 
tions in preparing the fallow, which 
indicate the reaction of the mulch in 
absorption each year during 
the period 1918 to 1923, in¬ 
clusive. 
All of the tillage variations 
as given in Table II were 
maintained in a well-mulched 
condition during the summer- 
period of retention. So far 
as this period and the suc¬ 
ceeding period are concerned, 
the result for all should have 
been similar. The essential 
difference between the varia¬ 
tions was in the presence or 
absence of a soil mulch dur¬ 
ing all or a part of the first 
period of absorption. The 
only plats on which no mulch 
existed at any time during 
this first period were those 
of the early spring plowing 
with no previous treatment. 
All of the others were 
mulched for varying periods, 
either with a light mulch 
created by disking in August 
immediately after harvesting 
the preceding crop, or with 
a heavier mulch created by 
plowing at some later date. 
Not once during the 6-year 
period did any of the mulched 
plats equal the unmulched 
plats in final moisture con¬ 
tent. In several instances 
the shallow mulch of the 
harvest-disked and spring- 
plowed plats was almost as 
efficient in saving moisture, 
but this efficiency was not 
due to equality in moisture 
absorption. This is shown 
by comparing the dry fall-plowing 
alone and the dry fall-plowing with 
previous harvest-disking. As far as 
absorption was concerned, these two 
treatments should have given an 
identical effect, the difference between 
the two being in the presence or 
absence of weed growth in the stubble 
in the interim between harvest and 
the date of dry fall plowing. The 
comparative result between these two 
treatments is not always the same, 
due to the fact that weeds were not 
always present in the stubble, but the 
Fig. 3.—Precipitation by months, at Lind, Wash., September 1, 
1916, to August 31, 1923. The tendency for greater precipitation 
during the winter months is apparent, as well as the unusual 
rainfall of June, 1923 
