Research NotiE1977

Fertilizer and Mulch Improves

Yellow-Poplar Growth on Exposed Hartsells Subsoils

JOHN K. FRANCIS

SUMMARY

Fertilizing and mulching of eroded Hartsells

soil increased height and diameter of yellowpoplars. To see if chemical infertility of exposed

Hartsells subsoils limits yellow-poplar growth

and to test fertilizer and mulch as remedial

agents, seedlings were planted on undisturbed

soil, soil with the topsoil removed, and soil

with the topsoil removed but mulched with leaf

litter. After one growing season, 9 of the 18

plots were fertilized.

Topsoil removal with no remedial treatment

reduced growth through four growing seasons.

Mulching did not improve growth the first year

but did in subsequent years. The first year after

application, fertilizer greatly increased growth:

thereafter growth on fertilized plots was about

the same as growth on unfertilized mulched and

undisturbed plots. Fertilizer with mulch provided no added growth. Mineral deficiencies

and rapid drying apparently limit growth on exposed subsoils, but physical structure does not.

Additional Keywords: Liriodendron tulipifera,

forest fertilization, erosion.

PLANTING ON ERODED SITES

Abundant rainfall and decay of forest vegetation have formed nutrient-rich topsoils in the

Cumberland Plateau of Tennessee, but on thousands of acres, the topsoil has eroded. When

the rich topsoil is removed - as it often is by

farming, logging, construction of forest roads

and trails, and site preparations exposing mineral soil - the loss of nutrients limits tree

growth. And once a site loses its topsoil, it

continues to erode and loses moisture rapidly,

making it suitable for only “poor site” trees

like upland oak and Virginia pine. Yellow-poplar,

which needs moist, fertile soil, grows slowly on

exposed subsoils (Loftus 1971).

The objectives of this study were to determine the extent that infertility of exposed Hartsells subsoils limits yellow-poplar growth, and

to test fertilization and mulching treatments for

trees in eroded areas.

METHODS

A typical Cumberland Plateau hollow near Sewanee, Tennessee was chosen for study. Soils

are Hartsells, an extensive Typic Hapludult. The

area was cleared of a mixed oak stand, all

other vegetation was removed, and stumps

were treated to prevent sprouting. Plots were

arranged in a randomized block design in six

blocks containing one 12 x 12 foot plot of each

of three initial treatments.

Treatments were: (1) undisturbed (2) organic

and A horizons removed (3) organic and A horizons removed and a litter layer returned. The

topsoil was removed with a shovel. The litter

layer in the third treatment was raked up and

spread again by hand after the topsoil had been

removed. In the spring of 1970, nine yellowpoplar seedlings graded 1-O with roots and tops

clipped uniformly were planted in each plot at a

4 x 4 foot spacing.

Southern Forest Experiment Station/T-l0210 U.S. Postal Services Bldg., 701 Loyola Avenue, New Orleans, La. 70113

Forest Service, U.S. Department of Agriculture.

Serving Alabama, Arkansas, Louisiana, Mississippi, Eastern Oklahoma, Tennessee, Eastern Texas.
At the end of the first growing season (fall,

1970) height and root-collar diameter of all

seedlings were measured. Four seedlings per

plot were excavated, oven dried, and weighed.

Two tons per acre of dolomitic limestone were

hoed into the surface of 9 of the 18 plots.

In the spring of 1971, fertilized plots received

150 Ibs N/acre as NH4N03 and 100 Ibs P/acre

as triple super phosphate topdressed.

Tree heights and root-collar diameters were

measured each succeeding fall for three seasons. After the last measurement, one seedling

per plot was excavated, oven dried, and

weighed. The resul’ts were evaluated by analysis of variance supplemented by Tukey’s w procedure.

RESULTS AND DlSCUSSlON

During the first growing season, growth was

significantly depressed by removal of topsoil

(table 1). Leaf mulch added to the subsoil did

not increase growth the first year. During the

second through the fourth years, however,

seedling growth on unfertilized mulched plots

Table 1. - First year response of planted yellow-poplar to

topsoil removal with and without mulching.’

Undisturbed Exposed B Mulched 6

Height growth (cm) 27.5 a2 18.9 b 19.2 b

Root collar

diameter (mm) 9.8 a 8.2 b 8.2 b

Top dry weight (gms) 8.4 a 4.1 b 3.9 b

Root dry

weight (gms) 9.8 a 7.4 ab 8.0 b

1 Each entry for height growth and root collar diameter is

the average of 54 seedlings and each entry for top and

root dry weight is the average of 24 seedlings.

zMeans in each line followed by the same letter are not

significantly different at the .05 level of probability.

equalled that on the undisturbed control plots

(table 2). Seedling8 on exposed subsoil that was

not mulched or fertilized grew slowly throughout the experiment (fig. I). Mulching apparently

improves the intake of water, protects the soil

from drying, and may speed mineralization of

nutrients.

In the first year after fertilization, fertilized

trees increased significantly in height and diameter (table 2). In, the following years, fertilized

seedlings grew at about the same rate as thO8e

on unfertilized mulched and undisturbed plots.

Fertilizer and mulch each helped seedlings

overcome the growth depression caused by

topsoil removal, but mulching combined with

330 -

300 -

F

y 250 -

5

P

2 200 -

4

k

h IS0 -

100 -

s o -

.U FERT.

FERT

FERT

--”

I

01 ’

I I I

2 3 4

YEARS SINCE PLAHTING

FEflT

Figure I.-Total height of yellow-poplar on fertilixed and

unfertilized plots that were undisturbed W,

had 8 horizon exposed (EBL or had 6 horizon

exposed and were mulched (MB).

fertilizer produced little additional growth. Fertilized plots quickly built up a light natural mulch

created by weed growth in the year of fertilization.

At the end of the experiment, root weight was

significantly increased by fertilization (table 2).

Root weight was depressed by removal of top

soil, but not significantly so.

The experiment indicates that the chemical

infertility of HarQells subsoil severely limits

yellow-poplar growth on exposed subsoil. Because improving the nutrient or moisture levels

of the exposed subsoil makes growth equal to

or greater than that found where the topsoil is

still present, physical properties of the subsoil

are apparently not the reason for poor growth.

Where loss of topsoil has been extensive

enough to warrant treatment, ease of application and promotion of growth and litter accumulation make fertilization a valuable aid to

establishment and early growth of yellowpoplar.

John K. Francis is research forester at the Sewanee Silviculture Laboratory, maintained at Sewanee, Tennessee, by the

Southern Forest Experiment Station, Forest Service-USDA, in cooperation with the University of the South.

2

,
LITERATURE CITED

Loftus, N. S. 1971. Yellow-poplar root develop- for. Serv. Res. Note SO-131, 5 p. South. For,

ment on Hartsells subsoils. U. S. Dep. Agric. EXP. St% New Orleans, La.

Table 2. - Yellow-poplar height growth, root-collar diameter growth, and root weight on

fertilized and unfertilized soil that was undisturbed (U), had B horizon exposed

(EB) or had B horizon exposed and was mulched (MB). Times shown indicate

time since fertilizer application.’

No Fertilizer Fertilizer

__I- U EB MB U E B M B

Height growth yr. 1 (cm) 42 a2 22 a 49 a 116b 135b 153b

Height growth yr. 2 (cm) 79 b 42 a 72 b 92 b 76 b 79 b

Height growth yr. 3 (cm) 111 b 47 a 124 b 1’18 b 92 b 90 b

Diam. growth yr. 1 (mm) 4.6 a 4.0 a 6.4 ab 13.4 bc 16.4~ 17.0 c

Diam. growth yr. 2 (mm) 11.8 bc 5.8 a 9.6 ab 15.9 c 12.2 bc 14.2 bc

Diam. growth yr. 3 (mm) 10.6 bc 5.7 a 9.5 bc 11.7c 8.6 ab 10.1 bc

Root weight yr. 3 (gms) 424 abc 125a 278 ab 986 d 608 bed 718 cd

1 Each figure is the average of 15 seedlings except for root weight which is the average of 3

seedlings.

2Means in each line followed by the same letter are not significantly different at the .05

level of probability.

3