U.S. Department of Agriculture

Forest Seruice Research Note S E - 289 March 1980

BURIED ORGANIC LAYER AFFECTS

THE GROWTH OF SLASH PINE IN THE FLORIDA SANDHILLS

Edwin A. Hebb’

ABSTRACT.-A technique for deep placement of organic matter within the soil, called sublayering.

was tested as a means of improving Florida sandhill sites for slash pine (Pinus elliottii var. clliortii

Engelm.). Single-tree plots were installed in four treatments: sublayering with peat moss, clearing,

clearing plus sublayering, and no treatment. Survival was poor only on the cleared plots. Heightgrowth differences between treatments were significant at the 0.0 I level but did not show sublayering

to be beneficial. Average g-year height on untreated plots was 1.26 m, 1.44 m on cleared plots, I .48 m

on sublayered plots, and 2.48 m on cleared-sublayered plots. Root excavation showed proliferation

of roots in the peat moss layer, but all roots had poor growth due to black root rot. Sublayering does

not appear to be a good substitute for mechanical site preparation, though it may have value when

applied along with it.

-Keywords: Tiefdiinpmg, soil amendments, sublayering, peat moss.

Site preparation benefits pine establishment

and growth on droughty sites by increasing available soil moisture. Competing plants are removed

or at least greatly reduced in number, so demands

on the available moisture are fewer. In Europe the

moisture regime of sandy soils has been improved

in another way-by the deep placement of organic

matter within the soil. The treatment, described

by Egerszegi (1958), is called Tiefdiingung in

German (Gyurko and others 1958),-literally,,

deep manuring,-and has been rendered “sublayering” in a translation of an article by Papp

(1958). Sublayering has been used to eliminate

irrigation and shading in forest nurseries in the dry

sandy regions of Hungary (Horvath 1960), to improve sandy forest soils in Germany (Buchholz

and Neumann 1964), and to establish pines on

sand dunes in Latvia (Bush and Kapost 1956). In

Germany, it has been credited with increasing the

yields of vegetables (Kunze 1% 1).

The experiment reported here was to test

whether sublayering by inserting peat moss in the

soil profile would improve Florida’s sandhill sites

for slash pine (Pinus elliottii var. elliottii Engelm.)

‘Hebb is Silviculturist at the Southeastern Forest Experiment Station, Marianna, Florida.

by keeping soil moisture at a higher level during

critical periods. It was also expected that treatment comparisons would clarify the role of soil

moisture in the total effect attributed to mechanical site preparation.

METHODS

The study was established on the Chipola

Experimental Forest, Calhoun County, Florida.

The soil is Lakeland sand, uniform to a depth of

3.4 m, with an A horizon of brown sand (Munsell

IOYR 5/3) about 9 cm deep. The subsoil (C horizon) is a yellowish-brown to a very pale-brown

sand (Munsell IOYR 5/6 to IOYR 8/4). Below 3.4

m, the sands are different hues of brown that

eventually blend into a layer of dark-brown sand

(Munsell7.5YR 4/2) at depths from 4 to 7 m.

1 he vegetation native to this site is primarily

turkey oak (Quercus laevis Walt.) ranging in

height from 0.9 to 3.5 m. There are a few scattered

bluejack oaks (Q. incana Bartr.) of similar

heights. Ground cover is mostly scattered clumps

of wiregrass (Aristidu strictu Michx).

The study plots are 2.4 m square; each tree

with its site constitutes a plot and a treatment.

Plot size had to be limited because of the difficulty

Southeastern Forest Experiment Station - Asheuille, North Carolina
in preparing the sublayered sites. Four treatments, replicated 16 times, were applied before

planting in February 1962:

Untreated.The scrub oak and wiregrass

vegetation was not disturbed.

Sublayered.-A layer of peat moss 3.8 cm

thick and 0.5 m in radius was placed approximately 30 cm below the planting point at the plot

center without disturbing the scrub oak and wiregrass. This was done by slanting a 3%cm metal

tube in toward the planting point from points on a

circle with a 1.2-m radius, extracting the soil, and

packing the inner 0.5 m of the hole with peat moss.

Repeating this procedure around the circle produced a buried layer of organic matter in a spokelike pattern. Some roots were severed when the

tube was introduced.

Cleared.-Sites were cleared of all vegetation with a grub hoe, and roots at the plot edges

were severed with a spadelike blade to a depth of

about 30 cm. The sites were kept bare and the

roots severed at the plot edges through 1968.

Cleared and sublayered.-Sites were cleared

as in the preceding treatment and, at the planting

point, soil and roots were excavated to an 0.9 l-m

diameter x 32-cm depth. The bottom of the hole

was covered with enough peat moss to make a

3.8-cm layer when packed. The roots and part of

the subsoil were discarded, the remainder of the

subsoil returned to the hole, and the topsoil replaced. As in the previous treatment, the plots

were kept bare and roots severed at the plot edges

through 1968.

In March 1962, after treatment of the sites,

two 1-O slash pine seedlings were planted about 10

cm apart at the center of each plot. After establishment seemed assured (in June 1962), the extra

seedling was clipped off. Height measurements

were taken through 1969, the eighth year in the life

of the seedlings on the plots. Determinations of

soil moisture were made in 1965 and of root distribution in 1965 and 1968.

An unquantified influence on the study trees

was black root rot caused by Sclerotium

bataticola Taub, and Fusarium oxysporum

Schlecht. var. auriantiacum (Lk.) Wr., which

was found to be “almost universally present” on

slash pine in the area (Smalley and Scheer 1963) at

the time the study was installed and was evident

when roots were examined at the conclusion of

the study.

RESULTS

Data on height of slash pine 8 years after

2

planting were analyzed by analysis of variance,

and differences by site treatment tested using the

Duncan multiple range test (Duncan 1955;

Kramer 1956). The cleared-sublayered treatment

was significantly better than other treatments at

the 0.0 1 level.

Seedlings on the cleared-sublayered plots

grew faster than those on other plots during the

first year after planting and increased their height

advantage each year thereafter (fig. I). Eight

years after planting, heights averaged 2.48 m on

cleared-sublayered plots, 1.48 m on sublayered

plots, 1.44 m on cleared plots, and 1.26 m on

untreated plots.

Figure I.-Height growth of slash pine by treatment.

Since the death of one seedling would have

meant the loss of an entire plot, seedlings from the

same planting stock, which had been held in the

nursery bed, were planted in December to replace

first-year losses. Two of the seedlings in the

cleared plots died; one in the untreated. After

replanting, survival of slash pine again was

poorest among the cleared plots, where eight

seedlings ultimately died. One tree of each of the

other treatments died.

When excavated 8 years after being laid

down, the layer of peat moss appeared to be

altered very little. Soil moisture sampled gravimetrically after 17 days without rain was found to

be higher at the layer of peat moss than above or

below it, and higher in the peat moss layer than in

the soil horizon from the same depth in plots that

did not receive the sublayering treatments (table
I). Gyurko and others (1958) also found moisture

to be higher in the organic layer. (Furthermore,

they found that where two layers had been installed, they were more moist than the sand between them.) Disregarding the layers of peat

moss, soil moisture was slightly higher on the two

types of cleared plots than on the plots with undisturbed vegetation.

Table I.---Soil moisture on plots. by treatment. Average of

plots of three Mocks

Depth

Treatment

I I

sampled

I

Untreated Suhlayered Cleared

I I

Cleared-

(cm) sublayered

I I I

Prrwtrt O~‘L’O/IIIHP

7.5 3.0 2.x 4.7 4.0

15.0 2.9 3.6 5.0 5.2

22.5 4.2 4.0 5.6 5.4

30.0 3.0 ‘24.3 5.3 ‘21.1

37.5 4. I 4.0 5.6 5.x

’ Peat moss layer.

Bush and Kapost ( 1956) and Papp ( 1958) have

reported enhanced root growth in the layer of

organic_ matter, but root sampling of the study

trees revealed no special concentrations of small

roots (1.5 mm in diameter). Excavated plots

showed a concentration of the larger roots in the

layer of peat moss (fig. 2). The lack of small roots

may have been the result of black root rot, which

would tend to leave the stubs of roots while

destroying the finer parts (fig. 3).

SUBSTITUTION OF SAND PINE

After the slash pines had grown on the plots 8

years, they were chopped out and sand pines (P.

clausa var. immuginata Ward) were planted in

their places. (Sand pine had been found to be

much better suited to sandhill soils than was

slash.) At that time the peat moss layers appeared

to be nearly intact, so it was hoped that planting

sand pine would allow at least partial comparison

of the effect of sublayering on the two pines.

Growth of sand pine in the first few years

after they were planted showed little effect from

the layer of peat moss. At that time some of the

peat moss was left. The pines were measured at 2

years and at 6 years, but only at the latter age was

there a significant difference in heights among

treatments (table 2). Unlike slash pine, sand pine

Table Z.-Height growth of sand pine planted after the slash

pine

I

Planted

Treatment’

age

(years)

Clearedsublayered

rt1rtrr.s

2 0.34 0.37 0.27 0.34

6 2. Zha 2.32a I.71 2.3%

‘Treatment means not followed by the same letter differ

significantly at the 0.05 level.

had good survival under all treatments but did not

excel in height under any one of them.

Nine years after the sand pine were planted,

one sublayered plot and four cleared-sublayered

plots were dug into. By that time the peat moss

layers were found to be faint and thin, and the

material powdery.

DISCUSSION

Sublayering by itself has not proved to be a

good substitute for mechanical site preparation

for planting slash pine. It did improve growth in

this experiment only where combined with clearing. Growth was best on the cleared-sublayered

plots, possibly because of the complementary

effect of the treatments, but more probably the

result of eliminating all roots when installing the

treatment.

Sublayering did increase soil moisture in the

region at the peat moss layer during a dry period.

However, slash pine growth was not improved, so

competition for moisture cannot be the only limiting effect on unprepared native sites.

Growth on cleared-sublayered plots, though

the best of any of the four treatments, is still less

than that noted on chopped sites in other studies.

On a site preparation study installed nearby, the

average height of &year-old slash pine on the

chopped plots was 5.52 m. In the present study,

the poorer growth may result from the repeated

severing of pine roots at the edges of the plots.

Root excavation showed that black root rot is

abundantly present-probably in most of the

plots-so the effects of sublayering are weakened

by the abnormal root growth of the trees; however, the effect of the rot may have been general

because the disease was found under all treatments. The disease organisms are common to the

area and slash pine is especially susceptible, so it

3
is doubtful that the study could have been conducted with slash pine free of the disease.

Even in the first few years after planting,

when the layer of peat moss appeared to be suffrciently intact to have some effect, sand pine did

not follow the nattem of slash nine. Most references to the period that the layer is useful concern

short-term crops. Although Papp (1958) and

Mar-ton (1970) did not study its persistence specifically, they believed the layer would be effective for at least 3 years.

Figure 2.-Excavated roots of representative saplings, showing treatment effects on (A) an untreated

plot, (E) a sublayered plot showing the layer, (C) a cleared plot, and (D) a cleared-sublayered plot

showing the layer. The roots are infected with black root rot, and most taproots terminate abruptly

0.5 to 0.6 m below the surface.

4
Figure 3.-The roots (fig. 2) removed from the soil show the pattern of growth on (A) an untreated plot.

(B) a sublayered.plot showing growth along the slanting organic layer, (C)a cleared plot, and (D) a

cleared-sublayered plot showing the proliferation of roots at the organic layer. The black tape line is

0.6 m long and 0.3 m from the top of the board.

LITERATURE CITED

Buchholz. F., and E. Neumann.

1964. [The effect of cultivation and fertilizing on the

moisture economy of, and rooting in. sandy

forest soils in Brandenburg.] (Abstr.) AlbrechtThaer Arch. 8525-536.

Bush, M.K., and V. Ya. Kapost.

1956. [Possibility of afforesting the sand dunes in the

vicinity of Riga.] (Abstr.) Tr. Inst. Lesokhoz,

S. Problem Akad. Nauk LatvSSR (II):

l63- 197.

Duncan, D. B.

1955. Multiple range and multiple F tests. Biometrics

il(l):l-42.

Egerszegi, S.

1958. [Creation and permanent maintenance ofa deep

fertile layer in loose sandy soil.] (Abstr.) Acta

Agron. (Budapest) 7(4):333-364.

Gyurko. P.. L. Varga, and E. Szabo.

1958. [Recent investigations of the microbiological

effect of deep manuring sand soils.] Acta

Agron. (Budapest)8(3/4):313-341.

Horvath. L.

1960. [Raising Scats pine seedlings on sands by deep

manuring.] (Abstr.) Erdd 8( 12):469-472.

Kramer, C. Y.

1956. Extension of multiple range tests to group

means with unequal numbers of replications.

Biometrics 12:307-3 IO.

Kunze. A.

1961. [Increasing the fertility of light sandy soil by

deep placement of organic fertilizers.] Dtsch.

Landw. 12:436-440.

Marton, A.

1970. [Investigations on the role of subsoiling and

various inactive layers on sand on the Nyirseg. I

Novenytermeles. l9( l):89-96.

Papp. L.

1958. [Improving the production of pine seedling

stock in the sandy area of the great plain (of

Hungary).] Erdo 7: I I I- 118. (Trans. by John

Stransky 1961.)

Smalley, G. W.. and R. L. Scheer.

1963. Black root rot in Florida sandhills. Plant Dis.

Rep. 47(7):669-67 I.

5 *U.S. GOVERNMENT PRINTING OFFICE: 1980 - 640-190/4533


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