828 
Journal of Agricultural Research 
Vol. XXX, No. 9 
plowed land, and that the loose surface 
of the fall-plowed land retains more 
of the precipitation of winter than 
the compact surface of the stubble 
land.” 
Cardon recognized that fall plowing 
hindered moisture absorption, although 
he did not directly attribute the effect 
to the mulch as an inhibiting agent. 
The various data presented having 
shown the mulch to be an inhibitory 
agent in absorption and a positive 
agent in retention, the fundamental 
reasons for these reactions merit atten¬ 
tion. 
On the Adams Station the prevail¬ 
ing type of rainfall is characteristically 
in the form of light, intermittent 
showers. Very rarely does a single 
winds or other factors favoring evapo¬ 
ration immediately following a rain 
will more quickly remove moisture 
from the loose soil of a mulched sur¬ 
face than from the more firm soil in 
an undisturbed condition. After an 
intervening period of evaporation, a 
second shower falling on the two soils, 
because of the larger amount of mois¬ 
ture remaining in the unstirred soil, 
is absorbed and conducted more deeply 
into the unstirred soil than where the 
mulch is present. Alway and McDole 
(2) have shown that depth of penetra¬ 
tion increases in direct proportion to 
initial moisture content, as has also 
been noted by Burr ( 8 ) and by Buck¬ 
ingham (7). Such deeper penetration, 
following a series of showers with inter- 
Fig. 6 —Average moisture content in per cent of moisture-free soil of fall-plowed and spring-plowed soils 
at the end of the first winter of the fallow, Nephi, Utah, 1909 to 1912, inclusive 
rain total 0.50 inch, and the majority 
of individual showers amount to 0.30 
inch or less. Cardon (11) says: 
“Most of the rainstorms at Nephi 
have been small and generally almost 
negligible.” This type of rainfall un¬ 
doubtedly is a factor in the inhibitory 
reaction of the mulch. 
When sampling, the surface 6 inches of 
a mulched and an unmulched soil im¬ 
mediately after a rain, the moisture 
content of the mulched soil on a per¬ 
centage basis is always greater, the 
loose soil having more moisture in pro¬ 
portion to soil in the surface area. 
This fact was noted by Cardon (11) 
and by Harris and Jones (16). 
Widtsoe and McLaughlin (24) and 
Fortier (13) have called attention 
to the fact that evaporation is always 
greater from a soil the greater the per¬ 
centage of moisture present, or, as 
stated by the former, “the rate of loss 
of water from a soil increases as the 
initial per cent of water in the soil 
increases.” This means that drying 
vening periods of evaporation, gives 
the unstirred soil its final moisture ad¬ 
vantage, the result being due to the 
cumulative effect of intermittent rain¬ 
fall and intervening evaporation, rather 
than to original superior penetration in 
the more firm soil. A light, intermit¬ 
tent rainfall contributes to the result, 
since heavy showers, by wetting en¬ 
tirely through the mulch, destroy the 
mulch effect, the mulch in such cases 
being an actual benefit in so far as it 
prevents surface run-off. 
Bouyoucos (6) has shown that when 
freezing occurs in soils not saturated, 
there is a withdrawal of soil water from 
the finer capillaries into the larger pore 
spaces. Dry-farm soils are seldom so 
saturated that the familiar heaving ef¬ 
fect of more humid regions occurs, but 
it is possible that there might occur in 
freezing a certain withdrawal of mois¬ 
ture from the more firm soil below into 
the larger interspaces of a loose mulch. 
With subsequent thawing, a larger pro¬ 
portion of moisture would thus be left 
