/-Gb United States

Department of

Agriculture

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Forest Sefvice

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ResearUWte

so-349

Expwlment Statlon Auaust If488

Effects of Seedbed Density and Row Spacing on Growth and Nutrient

Concentrations of Nuttall Oak and Green Ash Seedlings

Harvey E. Kennedy, Jr.

SUMMARY

Larger size and higher percentages of plantable 1-O

and 2-O green ash (Fraxinuspennsylvanica Marsh.) and

Nuttall oak (Quercusnuttallii Palmer) seedlings were

produced in the wider spacing-lower density plots.

Greater numbers of plantable seedlings were produced in

the higher density plots. Spacing significantly affected

diameters, heights, and percentages of plantable seedlings, but with few exceptions had no effect on nutrient

concentrations of stems and roots.

Additional keywords: Fr&inuspennsy/varh, Quercus nuttaM, seedbed density, seedling, nursery.

INTRODUCTION

Oaks (Ouercus spp.) have long been the backbone of

the southern hardwoods industry. Green ash (Frsxinus

Pennsylanica Marsh.) is also a prized species because it

can be grown on wet sites where other species cannot

survive, can be utilized for lumber at smaller sizes, is

popular for specialty products, and its price is usually

stable.

Thus far, no really reliable method for assuring natural

regeneration of oaks has been developed, and many oak

stands, when cut, do not have enough oak regeneration

to satisfy landowners. Nuttafl oak (Q. nuftallii Palmer) and

green ash may also be used in species conversions, such

as replacing overcup oak (C?. lyrata Waft.)-water hickory

(Carya aquatics (Michx. f.) Nutt.) stands on sites that have

been upgraded by river overflow and thus are capable of

supporting more valuable species.

When hardwood plantations are included in management plans, foresters look for ways to reduce costs. They

may also use supplemental or enrichment planting in

natural regeneration areas to get adequate regeneration

of desirable species, either by pre- or post-harvest planting of fewer, larger seedlings per acre than the normal l0 stock used in plantations. Large seedlings could eliminate the need for expensive cultural treatments and atthe

same time assure regeneration of desired species, particularly the oaks. This paper presents data on seedbed

densities and row spacings within nursery beds that can

be used to produce larger 1-O and 2-O seedlings that may

be in better physiological condition than seedlings grown

under conventional nursery practices.

METHODS

The study was conducted in the experimental nursery

at the Southern Hardwoods Laboratory, Stoneville, Mississippi. Green ash and Nuttall oak were the species

evaluated.

Two spacings between rows were tested, either 6 or 10

inches. Three seedling densities+wo, four, or eight

seedlings per square foot-were investigated by varying

the number of plants within row spacings. Seedlings were

then grown for 1 or 2 years. Initially, five nursery beds

were used where seedlings were grown for 2 years and

another five beds the second year for the l-year-old

seedlings. Each bed was considered a replication. Beds

were divided into 12 plots, approximately 4 x 15 feet. One

seedling density x row spacing x species treatment was

randomly assigned to each plot. The central 3 x 10 feet of

each plot was planted, with the remainder left open so the

seedlings would not compete between plots. Plots with 6-

inch spacing between rows had 7 rows each, while plots

with 10 inches between rows had 5 rows each.

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In plots with 6 inches between rows, seeds were sown

every 12 inches within rows for the two-per-square-foot

density, 6 inches for the four-per-square-foot density, and

3 inches for the eight-per-square-foot density. In plots

with 10 inches between rows, seeds were sown 7.2,3.6,

and 1.6 inches apart for the two-, four-, and eight-seedling

per-square-foot densities, respectively. Two or three

acorns and several green ash seeds were sown at each

Spot t0 ensure the germination n88ded for proper density.

Seedlings were thinned, to one per spot if necessary,

when survival was assured.

STATISTICAL ANALYSES

On8 seedling at each seed spot was needed to give

proper densities. This situation was not attained in all

plots, so thinning was done with the ultimate aim of having

the required number of Seedlings per plot for th8 various

densities, even though there was not always a seedling at

each spot. Thus, plots were thinned to 60, 120, and 240

seedlings per plot for the two-, four, and eight-seedling

per-Square-foot densities, respectively.

Non-uniform germination in the nursery prevented

using all five beds or replications. Three plots from the five

beds that met the density requirements were selected for

Sampling and statistical analyses. Therefore, the effects

of blocking was lost. Individual analyses for each species

and age were don8 by using a completely randomized

design. Variables tested were root-collar diameter:

height; stem and root N, P, K, Ca, and Mg; root/shoot ratio;

p8rcentage of plantable seedlings, and number of seedlings per square foot and per acre.

There were three replications of each treatment combination. All analyses were made at the 0.05 level. Treatments (spacings) were partitioned to test for linear and

quadratic effects, and differences betW88n row spacings

that provided the same growing space per seedling.

Nursery beds were watered as necessary to assure

maximum survival and growth, and they received at least

1 acre-inch per W88k from rainfall and/or irrigation. Plots

were fertilized with 60 pounds per acre of nitrogen in the

form of ammonium nitrate in early June, July, and August

8aCh year. First planting in the nursery was done in early

April 1963 for the 2-O seedlings, and the second planting

was done at the same time in 1964 for the 1-O seedlings.

RESULTS AND DISCUSSION

Diameter at Root Collar

Variables measured at the 8nd of the first and Second

growing seasons were total height_ rootcollar diameter;

root/shoot dry Weight ratios: percentage of plantable

seedlings; and nitrogen (N), phosphorus (P), potassium

(K), calcium (Ca), and magnesium (Mg) concentrations in

the stems and roots. To maintain plot integrity for secondyear measurements, five seedlings per plot were selected

for sampling nutrient concentrations, starting by lifting the

first five seedlings in the southern-most row on the west

end of 8aCh plot. The five seedlings were cornposited for

one sample per plot for nutrient analysis. Variables other

than nutrient concentrations were based on averages of

all seedlings in a plot.

Means for each species at each age are shown in

tables l-4. There was a significant linear effect for 1-O.

green ash seedlings (fig. 1). Similar trends existed for 2-

0 green ash and for Nuttall oak at both ages. Linear

contrasts between means accounted for 67 to 97 percent

of the sums of squares or Variation, depending on Seedling age. S88dfing size increased significantly as spacing

increased (tables l-4). There W8r8 no differences among

treatments Of the same S88db8d density or growing

space, even though spacings b8tW88n rows and seedlings within rows varied. ~uadraticeff8ctfor 2-O green ash

seedlings was significant but accounted for only 1.6

percent of the sums of squares. This could have b88n

b8CaUS8 of more growth in the crown, which could haV8

slowed diameter growth at the widest spacing.

Helghtr

All tissue was dried at 70° C and ground before chemical analyses. Nitrogen was determined by the standard

Kjeldahl procedure: P by colotimetry with molybdenum

blue color develOpm8nt; and K, Ca, and Mg by atomic

absorption spectrophotometry after Samples had b88n

dry-ashed and taken up in dilute HCI. Root/shoot ratios

were obtained by dividing root dry weights by shoot dry

weights.

For this study, a plantable 1-O seedling was defined as

one with a minimum root-collar diameter of 0.25 inch and

15 inches in height; a plantable 2-O seedling was 0.5 inch

in root-collar diameter and 30 inches tall.

There was a significant linear effect for 1-O green ash

seedlings (fig. 2). Similar trends existed for 2-O green ash

and Nuttall seedlings. Linear contrasts b8tW8en means

accounted for 66 to 94 percent of the sums of squares or

variation in height growth. Spacing had no effect on the

heights of 1-O Nuttall oak seedlings. Seedling heights,

except for 1-O Nuttall, increased significantly as growing

space increased (tables l-4). As with roOt-cOllar diame

ters, there were no differences among treatments of the

same seedbed density or growing space, even though

spacings between rows and seedlings within rows varied.

Harvey E. Kennedy, Jr., is principal silviculturist at the Southern Hardwoods Laboratory, maMined at Stoneville, Mi88is~lppk by the Southern Forest

Experiment Station, Forest Service-MDA, in cooperation with the Mississippi Agricultural and Forestry Experiment Station and the Southern

Hardwood Forest Research &oup.

2
Table 1 .+a&bfe means, by spacing, for 1 -year-oM green ash stwlings

Variable

---

Spacing (in)

6x3 6x6 6x12 10x1.8 10x3.6 10x7.2

-----

Diameter (in) 0.25 0.35 0.44 0.25 0.33 0.46

Height (ft) 1 A9 1.81 2.07 1 Al 1.69 2.04

Stem N (%) 0.95 0.91 0.85 0.89 0.93 0.89

Stem P (%) 0.13 0.14 0.12 0.13 0.14 0.14

Stem K (%) 0.37 0.41 0.38 0.36 0.37 0.39

Stem Ca (%) 0.54 0.53 0.56 0.83 0.62 0.56

Stem Mg (%) 0.13 0.13 0.13 0.12 0.14 0.13

Root N (%) 1.40 1.21 1.32 1.33 1.38 1.30

Root P (%) 0.20 0.20 0.20 0.21 0.21 0.22

Root K (%) 0.83 0.77 0.80 0.80 0.82 0.82

Root Ca (%) 0.31 0.29 0.31 0.31 0.32 0.29

Root Mg (%) 0.15 0.14 0.15 0.14 0.18 0.15

Root/shoot ratio 0.95 1.01 1.01 1.17 1.22 1.14

Plantable seedlings (%) 44.00 75.30 94.00 39.30 70.70 92.30

Plantable seedlings/fP 3.5 3.0 1.9 3.1 2.8

Plantable seedlings (M/at) 152.4 130.7 82.7 135.1 121.0 8::;

Table 2.-Variablemeans, by spacing, for 1 -year-oM Ntiall oak seedlings

Variable 6x3

Spacing (in)

6x6 6x12 10x1.8 10x3.8 10x7.2

Diameter (in) 0.25 0.30

Height (ft) 1.56 1.77

Stem N (%) 1.09 1.02

Stem P (%) 0.11 0.10

Stem K, (%) 0.29 0.29

Stem Ca (%) 0.55 0.46

Stem Mg (%) 0.10 0.11

Root N (%) 1.39 1.48

Root P (%) 0.15 0.15

Root K (%) 0.55 0.54

Root Ca (%) 0.34 0.27

Root Ma W) 0.12 0.13

Root/shoot ratio 1.53 1.48

Plantabte seedlings (%) 45.70 59.00

Plantabte seedllngsdr 3.66 2.36

Plantabte seedlings (f&kc) 159.3 102.8

0.33

1.78

I%

0.28

0.51

0.09

Ii:;“;

0.52

0.26

0.10

1.30

73.30

1.47

64.0

0.25 0.31' 0.33

1.79 1.80 1.87

0.97 1.01 1.03

0.10 0.09 0.10

0.29 0.28 0.31

0.44 0.53 0.47

0.09 0.11 0.10

1’.44 1.43 1.44

0.14 0.12 0.14

0.54 0.62 0.54

0.30 0.31 0.30

0.11 0.12 0.12

1.15 1.47 1.28

43.70 68.00 78.70

3.50 2.72 1.57

152.3 118.5 68.8

TabJe 3.-Vadabb means, by spacing, for 2-year&i green ash seedlings

Spacing (in)

VWi&l@ 8x3 8x8 8x12 10x1.8 10x3.8 10x7.2

Diameter (In) 0.37 0.52 0.63 0.37 0.50 0.83

Heiaht (tt) 3.07 3.87 4.43 3.06 3.65 4.30

Stem N (%) 0.74 0.78 0.77 0.79 0.79 0.71

Stem P (%) 0.09 0.09 0.10 0.10 0.10 0.09

Stem K (%) 0.32 0.32 0.32 0.34 0.32 0.33

Stem Ca (%) 0.69 0.84 0.66 0.87 0.66 0.81

Stem Mg (%) 0.11 0.11 0.11 0.11 0.11 0.10

Root N (%) 1.44 1.42 1.49 1.45 1.40 1.36

Root P (%) 0.16 0.14 0.16 0.17 0.15 0.15

Root K (%) 0.75 0.74 0.71 0.78 0.67 0.78

Root Ca (%) 0.34 0.33 0.38 0.38 0.37 0.36

Root Ma WI ’ 0.17 0.16 0.16 0.17 0.15 0.17

Root/shoot ratio 0.82 0.77 0.75 0.79 0.78 0.81

Plantable seedlings (%) 26.00 49.00 69.30 27.30 49.70 72.00

Plantable seedlings/w 2.08 1.96 1.39 2.16 1.99 1.44

Plantable seedlings (WC) 90.8 85.4 60.4 95.1 66.6 62.7
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Tabie 4.- Variable means, by spacing, for 2-year-oh9 Nuttall oak seedlings

Variable

Spacing (in) ,'

6x3 6x6 6x12 1.0x1.8 10x3.6 10x7.2

Diameter (in) 0.36 0.48 0.63 0.39 0.50 0.71

Height (R) 3.52 4.13 4.91 3.74 4.50 5.65

Stem N (%) 0.82 0.80 0.87 0.81 0.86 0.80

Stem P (%) 0.06 0.08 0.09 0.08 0.08 0.08

Stem K (%) 0.21 0.26 0.23 0.23 0.24 0.23

StemCa(%) 0.50 0.58 0.57 0.49 0.56 0.47

Stem Mg (%) 0.07 0.08 0.08 0.08 0.08 0.07

RootN(%) 1.54 1.48 1.59 1.53 1.56 1.59

RootP(%) 0.11 0.13 0.13 0.13 0.13 0.14

RootK(%) 0.41 0.51 0.43 0.46 0.45 0.41

RootCa(%) 0.40 0.38 0.38 0.40 0.43 0.38

Root rklg (%) 0.11 0.11 0.11 O.il 0.11 0.11

Root/shoot ratio 0.86 0.92 0.98 0.80 0.83 0.85

Plantable seedlings (%) 30.00 48.70 75.00 33.70 53.70 83.30

Plantable seedling&W 2.40 1.95 1.50 2.70 2.15 1.67

Plantable seedlings (Wac) 104.5 84.9 85.3 117.4 93.6 72.6

I I I

IO 3 6 72

SOUARE INCHES GROWING SPACE/SEEDLING

Figure 1 .-Root-cokrdiameter, byspacing, for l-Ograen Figure 2.-Total heights, by spacing, for l-0 green ash

ash seedlings in nursery. seedlings in nursery.

Nutrbnt Concentrations

Individual analyses by species and age showed that

spacing treatments had no effect on the nutrient concentrations of stems and roots (tables l-4). One-year-old

seedlings, with only a few exceptions, had higher nutrient

concentrations in the stem and roots than P-year-old

seedlings. Although concentrations were ’ generally

higher in 1-O seedlings, total amounts of a given nutrient

would have been larger in the 2-O seedlings because of

their larger sizes.

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2.1

2

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5

4

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O.!

6

4

s

316~ I2

4 * IO I 1.6

5 t IO Y 3.6

6 s IO I 7.2

I6 3 6 72

SOUARE INCHES GROWING SPACE/SEEDLING

Root/Shoot Dry Weight Ratlos

Root/shoot ratios for a given species and age were not

affected by spacing (tables l-4). Although they were not

statistically compared, 1-O green ash seedlings apparently had a larger root/shoot ratio than. 1-O Nuttall. These

differences had disappeared in 2-O seedlings, and root/

shoot ratios were about the same in both species.

4
I

Percentage and Numbsr of Plantable Seedlings

The number of seedlings per square foot and per acre

were calculated by using the percentage of plantable

seedlings and inital density (tables l-4). For 1-O green

ash, analyses of variance showed a significant negative

linear effect for number of seedlings per acre (fig. 3).

Because this was a calculated value, percentage of

plantable seedlings and number of seedlings per square

foot would follow- the same trend. Similar trends also

existed for 2-O green ash and Nuttall oak at both ages.

Linear contrasts between means accounted for 91 to 97

percent of the sums of squares or variation, depending on

seedling age. The number of plantable seedlings per acre

decreased significantly as spacing increased (tables l-4).

There were no differences among treatments of the same

seedbed density or growing space, even though spacings

between rows and seedlings within rows varied.

Although lower percentages of plantable seedlings

were produced in the higher density-closer spacing treatments, the largest number of plantable seedlings per

square foot and per acre were produced at the higher

densities, simply because there were more seedlings per

plot.

SUMMARY AND CONCLUSIONS

In this study, larger seedlings and higher percentages

of plantable seedlings were produced in the wider spacing, lower density plots. The greater numbers of plantable

seedlings were grown at the higher densities because

there were more seedlings per plot from the beginning.

Spacing affected root-collar diameters, heights, and percentages of plantable seedlings. Results of this study

indicate that nurserymen could use densities of 8-10

seedlings per square foot and produce good 1-O hardwood seedlings. Densities apparently have more effedt

)n growth during the second year. When growing larger

seedlings for supplemental or enrichment planting, four

slants per square foot would produce a high number of

)lantable seedlings per acre of more desirable size.

Spacing generally did not affect the m&lentconcentraions of roots or stems. If nutrients were available, seedngs were able to take up enough to meet their demands

3r satisfactory growth.

For good survival and early growth, the root system of

eedlings should be in balance with the top, otheNvise the

eedlings will not grow much until the root systembecomes

stablished. About a 1 :l root/shoot. ratio is generally

ccepted as standard. Apparently, 1 -year-old green ash

ad a larger root/shoot ratio than 1-O Nuttall oak; however,

-

236.6

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 6

3r6ml2

4 = IO I 1.6

S m IO I 3.6

6 * IO I 7.2

01 I I I

I6 3 6 72

SOuARE INCHES GROWING SPACE/SEEDLING

Figure 3.--Number of plantable seedings per acre for 7 -

0 green ash seecflings in nursery.

the differences were not apparent in the 2-O seedlings of

either species. Therefore, any of the spacings used

should not adversely affect root/shoot ratios.

The larger 2-O seedlings would have to be planted in

holes made with a gasoline-powered or tractor-mounted

auger. These augers produce a 8- to O-inch-diameter

hole, which would mean some root pruning would be

necessary for the root system to fit the hole. Our experience at the Southern Hardwoods Laboratory indicates

that pruning can be done without harming the seedlings.

This planting method would be expensive on a per-tree

basis. However, when one considers planting fewer (80-

75) trees per acre in supplemental planting, without

expensive site preparation and cultural treatments, costs

should be comparable to conventional planting of 1-O

seedlings along with cultivation. Potential benefits of the

large seedlings are rapid early growth and reduction in

wildlife damage (Johnson 1988).

LITERATURE CITED

Johnson, Robert L. 1988. Studies show steps to more

success planting oak forests. Forest Farmer 48( 1): 20-

21.

' U. S. GOVERNMENT PRINTING OFFICE: 1988 - 566019 / 85012