LEAFLET No. 42 JNAY15
Some Effects of
SAWDUST MULCHING
of Pine Seedlings
H. G. POSEY, Assistant Forester
JACK T. MAY, Forester
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FIGURE 1. Standard manure spreader, with odded home-made metal hood, is used to
apply sawdust mulch to slash and labially pine seedbeds i'i nursery tests.
A GR ICU L TU R AL E X PER I ME NT
4 d. ALABAMA POLYTECHNIC
I=. V. Smith, Director
S T ATIO N
IN ST IT UT E
Auburn, Alabama
JANUARY 1954
upon physiological condition of the
seed and environmental factors.
When germination is completed, the
mulch may be partially or completely
removed, depending upon the nature
of the material used. Burlap, heavy
cotton fabric, sand, and pine needles
are materials that have been most com-
monly used as mulches. Burlap and cot-
ton fabric must be removed after an
appreciable number of seed have germ-
inated, but before germination is com-
pleted. Otherwise the earliest estab-
lished seedlings will be smothered, or
killed by soil fungi developing under
the cover. Pine straw may be partially
or completely removed when germina-
tion is completed. Previous study else-
where has shown no important differ-
ence in germination in the seedbed or
in the final yield of plantable trees that
can be attributed to burlap, pine straw,
or sand mulch.
Sawdust was tried at the Auburn
nursery as a seedbed mulch for long-
leaf, slash, and loblolly pine in 1951.
The sawdust was left on the beds after
germination. Observations indicated
that germination was equal to or-ex-
ceeded that obtained with pine straw.
Incidence of chlorosis seemed slightly
lower in beds mulched with sawdust.
PROCEDURE /a EXPERIMENTS
1952. Loblolly and slash pine seed-
lings were grown on plots mulched with
sawdust during the entire growing sea-
son and on plots that were mulched
with pine straw during the germination
period only. Plots covered with a
mulch during the entire growing season
are referred to as mulched plots. Plots
from which the mulch was removed af-
ter germination are referred to as un-
mulched plots.
The mulched plots received an ap-
plication of s awdu st to an average
depth of one-fourth inch immediately
after sowing, and this mulch was main-
tained during the growing season. The
unmulched plots were covered with
pine straw during a 30-day germination
period, after which the pine straw was
removed.
Soil surface temperatures were de-
termined daily at noon from June 2 to
October 19. Observations of the oc-
currence of chlorosis were made weekly
from July 7 to October 20. Seedling
mortality during the growing season
was noted. Final survival percentages,
seedling heights, and seedling diamet-
ers were determined at the end of the
growing season.
1953. Loblolly pine seed were sep-
arated by screening into three size
classes, large, medium, and small. Seed
of each size were sown and subjected
to three different mulch treatments,
namely one-fourth inch sawdust, pine
straw, and burlap. The pine straw and
burlap mulches were removed after a
28-day germination period.
Germination determinations w e r e
based on 100 per cent counts of seed-
lings obtained from known numbers of
seed sown.
RESULTS a lh MULCH
TREATMENTS
Surface soil temperature. Under
a sawdust mulch, appreciably lower
maximum surface soil temperatures oc-
curred than where no mulch was main-
tained after the germination period.
The sawdust mulch reduced fluctua-
tions in surface soil temperatures. A
decline in surface soil temperature from
June to October for both treatments,
based on 28-day averages, was regular
and in the form of a straight line.
Seedling survival. A one-fourth
inch sawdust mulch definitely reduces
mortality of established seedlings of
both species. Sawdust mulch was es-
pecially beneficial to slash pine. The
mortality of slash pine on unmulched
seedbeds in 1952 totaled 57.8 per cent.
Only 24.4 per cent died on the plots
covered with one-fourth inch of saw-
dust. For loblolly pine, the percentages
were 19.5 and 13.9, respectively (Fig-
ure 2).
Per cent
60
50
40
30
20
]0
Slash Pine Loblolly Pine
[]INo sawdust 
l1/4 inch sawdust 
mulch
FIG. 2. Seasonal mortality percentages of
slash and loblolly seedlings in unmulched
-inch sawdust mulched nursery beds.
The highest mortality rate in both
species occurred during June and July.
Since mortality was not associated with
differences in surface soil temperature,
and since the watering schedule and
other operations were similar over the
entire project, no definite reason for the
differences in survival can be assigned.
Two possible explanations may be: (1)
the longer availability of water under
a continuous mulch; and/or (2) a de-
crease in sand-splash against the stem
and needles and consequently a reduc-
tion in fungus infections.
Seedling heights and diameters.
One quarter-inch mulch sawdust did
not influence height or diameter growth
of surviving seedlings of either species.
Slash pine seedlings were taller and
markedly larger in stem diameter than
were the loblolly pine seedlings.
Chlorosis. It was strongly indicated
that one quarter-inch sawdust mulch re-
duced occurrence of chlorosis.
1 
Chlor-
osis averaged 0.02 per cent weekly in
the mulched plots as compared to 0.44
1.01 Probability level.
per cent weekly in the unmulched plots.
Chlorosis first became noticeable about
July 7. It disappeared after August 25
and did not reappear.
Chlorotic symptoms occurred in no
regular pattern on either mulched or
unmulched plots. Generally, chlorosis
was more pronounced and persisted
longer on the unmulched plots.
An association of chlorosis with
changes in surface soil temperature was
apparent.
2  
Chlorosis was most pro-
nounced when surface soil temperatures
were highest. However, the association
is not strong enough to justify using
surface soil temperatures as a predict-
ive factor for chlorosis.
3
Slash and loblolly pine seem equally
susceptible to chlorosis.
Germination. Germination percent-
ages under pine straw and burlap
mulches were, for all practical purposes,
identical.
In 1952, germination was approxi-
mately the same under the sawdust and
pine straw mulch. In 1953, germina-
tion under one-fourth inch sawdust
mulch was 8.7 per cent higher than
under burlap and 9.3 per cent higher
than under pine straw.
Seed size. As was to be expected,
germination percentage of loblolly pine
seed was directly proportional to seed
size. Large seed had the highest germ-
ination percentage and small seed the
lowest.
PRACTICAL APPLICATIONS
In the practical use of sawdust, two
difficulties may be encountered. (1) If
seedbeds are not level, it is difficult to
apply sawdust over the beds to a uni-
form depth. (2) Heavy rains or strong
winds may wash or blow some of the
sawdust from the beds, particularly
from the outside drills. These difficul-
ties can be partially eliminated by mak-
.05 Probability level.
Sr2_8.72%.
ing the beds level, keeping the sawdust
moist, and using windbreaks.
CONCLUSIONS
For many nurseries, the use of saw-
dust as a mulch on loblolly and slash
pine seedbeds appears to be highly de-
sirable. Sawdust is frequently more
readily available than pine straw and it
is cheaper than burlap. Germination
under sawdust is as good as or better
than that obtained under burlap or
pine straw.
Maximum surface soil temperatures
are materially lower under a one-fourth
inch sawdust mulch than under no
mulch.
Chlorosis seems to be less prevalent
in seedlings mulched with one-fourth
inch of sawdust than in those growing
in unmulched beds.
A materially higher percentage of
survival of loblolly and slash pine seed-
lings is obtained by maintaining a one-
fourth inch sawdust mulch on the seed-
beds throughout the growing season
than with unmulched surfaces.