Research Note RN-272

1981

Response of Newly Established Slash Pine to Cultivation and Fertilization

A. E. Tiarks and J. D. Haywood

SUMMARY

Response of newly established slash pine to fertilization is increased if herbaceous plants are controlled. To find the amount of cultivation required in

Louisiana, fertilized and unfertilized rows of planted

pines were hand-hoed in a wedge-shaped pattern.

By using this technique, the amount of cultivation

was varied from none to complete.

Slash pine growth was linearly related to amount of

cultivation for both fertilized and unfertilized trees.

Pine response to cultivation or fertilization was much

greater when both cultural practices were applied.

Addltlonal keywords: Weed control, tree form,

herbaceous competition.

INTRODUCTION

Fertilizer applications to newly planted slash pine

can increase early growth. However, field observations indicate the effect of fertilizer is often negated

by herbaceous plant competition because the herbaceous plants respond better than pine to added

nutrients. Smith and Schmidtling (1970) reported

that disking alone increased the height of slash pine

by 2 feet at age 5 and that fertilization of cultivated

plots increased growth by another 5 feet. Combined

cultivation and fertilization on an old field site increased the height of 4-year-old slash pine by 2.1

feet (Westberg 1951). We established an experiment

to find the response of slash pine to varying degrees

of cultivation by hoeing and to fertilization with

nitrogen, phosphorus, and potassium.

METHODS

The study was established on a site in Central

Louisiana that had been clearcut, chopped, and

burned. Vegetation, mainly grasses and forbs, had

completely occupied the site. The soil was a Beauregard silt loam (Plinthaquic Paleudult, fine-silty, siliceous, thermic), was low in fertility, and had slow

internal drainage. Analysis of soil samples, taken

from 0 to 6 inches, showed 2.1 percent organic

matter (wet oxidation without external heat, Jackson

1958) 0.04 meq/lOO g of potassium (1 N NH40Ac

extraction, Chapman 1965b), and 1 .l mg/kg of available phosphorus (Bray #l with a 15-minute shaking

time, Jackson 1958).

Slash pine seedlings 1-O bare rooted nursery

stock were graded for uniformity and hand-planted

in February 1974 at 1.5 foot intervals in eight rows

150 feet long and 10 feet apart. In April 1974, four

of the rows were selected at random and fertilized

with 200 pounds N, 200 pounds P205, and 70 pounds

of K20 per acre.

The amount of cultivation was varied from none

to complete by hand-hoeing a wedge-shaped pattern

along each row. Thus, the amount of cultivation

applied to each row increased from none at one end

to a lo-foot wide strip at the other end. The rows

were hand hoed four times the first year. In the

following 3years, hoeing was repeated as necessary

to keep the competition from reoccupying the site.

Care was taken to avoid injury to the pine roots.

Heights of all trees were measured at the end of

the first and fourth growing seasons. At the end

of the first season, every other tree was cut off

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.

1
O- I I I I

0 2 4 6 6 I

WIDTH OF CULTIVATED STRIP (FEET)

Figure 1 .--Effect of fertilization and varying amounts of culfivation on the above ground biomass of l-year-old slash

pine (*P<O.O5).

at the root collar and ovendried and weighed. At

the end of the second growing season, every other

tree was removed, leaving the effective spacing

for the third and fourth growing season at 6X10

feet. All of the remaining trees were cut off at the

root collar at the end of the fourth growing season.

Needles and branches were removed, shredded with

a leaf mulcher, and the wet weight was recorded.

A subsample was taken and dried to determine

moisture content for calculation of dry weight of

needles and branches. The entire main stems were

immersed in water for volume measurements, then

dried and weighed.

To determine the relationship between cultivation and tree growth, linear, quadradic, and cubic

regression equations were calculated using width of

the cultivated strip and ovendry top weights for the

first year’s growth. The level of significance was

preset to 0.05. As only the linear model was significant, linear regression equations between the

width of the cultivated strip and the fourth year

measurements of height, root collar diameter, main

stem volume, ovendry weight, and weight of the

needles and branches were calculated.

01 I I I I

0 2 4 6 8

WIDTH OF CULTIVATED STRIP (FEET)

1

Figure 2.-Effect of fertilization and varying amounts of cultivation on the above ground biomass of slash pine 4 years

after establishment (*pCO.O5).

Separate regressions were calculated for fertilized

and unfertilized trees to find if the cultural treatments had affected tree form. Height was used to

predict root collar diameter while log of height-bydiameter-squared (HO*) was used to predict log of

volume of the main stem, log of the weight of needles

and branches, and log of the total biomass. The

residuals from these equations were then regressed

against the width of the cultivated strip to see if

competition control affected the relationships.

The top, dry weight had increased proportionately

to the area hoed after the first growing season (fig.

1). The top weight of unfertilized trees increased

from 0.05 to 0.12 pounds/tree as the width of the

cultivated strip increased from 0 to 10 feet (fig. 1).

Cultivation increased dry weight of the tops from

0.04 to 0.26 pounds/tree in fertilized rows.

After 4 years, hoeing increased top dry weight

production from 5.3 to 9.0 pounds/tree on the unfertilized rows, and from 9.0 to 23.7 pounds/tree

A. E. Tiarks is Research Soil Scientist, J. D. Haywood is Assistant Silviculturist, Southern Forest Experiment Station, Forest ServiceUSDA, Pineville, La. The authors wish to acknowledge former colleague W. H. McKee, Jr., now with the Southeastern Forest Experiment

Station, Charleston, SC., who developed the experimental design used in this experiment.

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on the fertilized rows (table 1 ).‘The intercept values

were significantly different (fig. 2) so 4 years after

planting, fertilizing uncultivated trees had increased

biomass production by 70 percent. Fertilization

alone was equal to cultivation alone. The two combined produced a 347 percent increase in total biomass or 207 percentage points more than expected

if the two treatments had been additive.

The response to increasing width of cultivation

was linear for both periods reported (figs. 1 and 2)

and for both fertilized and unfertilized trees. Thus,

the amount of cultivation required to maximize slash

pine growth planted at a lo-foot spacing or less

was 100 percent of the plantation, even during the

establishment year. Because of large tree to tree

variation, the regression equations accounted for only

a small part of the variability. Graphs and statistical

analysis of residuals from the regression equations

indicated the remaining variation to be random.

Root collar diameters, volume of the main stem,

and weight of needles and branches also increased

linearly as cultivation increased from none to complete. The linear regression equations, calculated

from data representing the continuously varying

amounts of cultivation were used to predict the

parameters of tree growth at no cultivation, and at

complete cultivation (at 10 feet). The accumulative

growth of the trees representing the combinations

of no cultivation and cultivation, and fertilizer and no

fertilizer are shown in table 1.

On the fertilized trees, cultivation increased both

the height and root collar diameter. However, on the

unfertilized rows of trees, cultivation increased the

root collar diameter but not the height. To establish

if this difference was real, we regressed root collar

diameters against heights of fertilized and unfertilized

trees separately (table 2). We then fitted the residuals from these equations against width of the

cultivated strip. Residuals of unfertilized, but not

of fertilized trees were significantly related to width

of cultivation (r2=0.29 and 0.03, respectively).

To find if other changes in tree form might have

occured, height-times-diameter-squared relationship was used to predict volume of the main stem,

total ovendry weight, and the weight of the needles

and branches (table 2). All of the equations were

significant. When the residuals from these prediction equations were plotted against the width of

the cultivated strip, no trend was discernible. Also,

equations fitted for the relationships using fertilized

or unfertilized trees were not significantly different.

Thus, the cultivation or fertilizer treatments did

not affect the relationship between height-timesdiameter-squared and any other measured parameter.

DISCUSSION AND CONCLUSIONS

After 4 years, fertilization alone and complete competition control alone were about equally effective

Table 1 .-Four-year growth of slash pine as affected by cultivation and fertilization. Values for cultivation are

estimated by regression and represent no weed control and complete control

-

Cumulative growth Unfertilized Fertilized

after 4 years Uncultivated Cultivated Uncultivated Cultivated

Red, in 2.7 a1 3.6 b 3.6 b 5.1 c

Ht, ft 6.5 a 9.2 ab 10.5 b 14.4 c

Volume of main stem, cu. in. 214a 330 b 354 b 921 c

Total biomass, Ibs/tree 5.3 a 9.0 b 9.0 b 23.7 c

Weight of needlesand branches, Ibs/tree 2.6 a 4.6 b 4.2 b 11.3 c

lVaIues in the same row followed by the same letter are not significantly different (P=O.O5).

Table P.-Equations used to model relationships among tree variables

Treatment Equation

____.-

r*

Fertilized

Unfertilized

All

All

All

I Red = 0.461 + 0.026 height

Red = 0.370 + 0.026 height

Volume = 0 516(Rcd*xheight)0.ss6

needle + branch wt = 010137 (Red* x heig ht)“.7ss

Total biomass = 0.0142 (Red* X height)0.s5’

0.72*

0.74

0.94

0.88

0.95

‘RCD = root collar diameter. Biomass in pounds, Red and height in inches, volume in cubic inches.

*All equations are significant (P = 0.05).
in improving biomass production. When both treatments were applied, they interacted to increase biomass by 347 percent. Baker (1973) in a study on

the Florida sandhills, found the response to cultivation and fertilization was additive rather than

synergistic as reported here.

Complete cultivation is necessary for maximum

early growth of the pines. However, in practice,

complete control is not advisable on slopes where

erosion would be a problem. The minimum amount

of ground cover that would control erosion should

be left between trees.

With maximum cultivation, fertilized trees were

about a foot taller after 3 years than unfertilized

uncultivated trees were after 4 years. Therefore,

cultivated and fertilized trees had gained more than

one year’s growth over untreated pines. We speculate

that removal of herbaceous competitors and fertilization will not affect growth rates after crown closure.

Crowns of fertilized-cultivated pines were closing

after four growing seasons while those of untreated

pines were not. As crown closure had not occurred

in untreated rows, the difference in accumulated

dry weight.should continue to increase between the

cultivated-fertilized trees and untreated trees, thus

shortening the rotation interval by more than the

1 year measured so far for treated pines.

Baker, J. B.

1973. Intensive cultural practices increase growth

of juvenile slash pine in Florida sandhills. For.

Sci. 19:197-202.

Bey, C. F., and R. D. Williams.

1976. Weed control in black walnut plantations.

U.S. Dep. Agric. For. Ser. Res. Note NC-203.4 p.

North Central For. Exp. Stn., St. Paul, Minn.

Chapman, H. D.

1965. Total exchangeable bases. IN C. A. Black,

ed., Methods of Soil Analysis. Part 2. Chemical

and microbiological properties, Am. Sot. Agron.,

Inc., p. 902-904.

Jackson, M. L.

1958. Soil chemical analysis. p. 159-l 60. PrenticeHall Inc., New Jersey.

Smith, L. F., and R. C. Schmidtling.

1970. Cultivation and fertilization speed early

growth of planted southern pines. Tree Planters’

Notes 21(1):1-3.

Westberg, D. L.

1951. Cultivating boosts fusiform rust infection.

J. For. 49:253.

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