United States

Department of

Aghculture

Forest Service

Southern Forest

Experiment Station

SO-278

October 1981

Biomass and Nutrient Accumulation in a Cottonwood

Plantation-The First Four Years

John K. Francis and James 6. Baker

SUMMARY METHODS

For the first 4 years, height increment of an eastern

cottonwood plantation on a clayey soil was greatest in the

first growing season; diameter growth was greatest in the

second growing season; and annual production of

biomass was greatest in the third year. Nitrogen, phosphorus, and possibly magnesium are translocated from

leaves into bark and other tissue before leaf abscission in

the fall. There is no evidence for translocation of potassium or calcium. While removal of nutrients per ton of

biomass would be greatest the first year, loss per hectare

would be as great or greater in later years, due to higher

annual yield. Whole-tree chipping would remove considerably more nutrients from the site than harvesting of

boles only. After year 2, there is little difference in nutrient

loss between summer and winter bole removal.

Additional keywords: Po~ulus deltoides Bat-k., nutrient cycling, nutrient translocation.

INTRODUCTION

Intensive plantation management, with possible future

mechanized harvesting of biomass, has made early

growth and nutrient dynamics of plantations an important

area of study. Baker and Blackman (1977) reported

trends in biomass and nutrient accumulation in an eastern cottonwood (Po~ulus deltoides Bartr.) plantation during the first growing season. Biomass and nutrient accumulation and distribution; internal cycling of nutrients;

growth, and nutrient losses which would be caused by

harvest during the first 4 years in that same plantation are

now reported.

The trees sampled in this study grew in a 2-hectare

&-acre) cottonwood plantation on the Delta Experimental

Forest near Stoneville, Mississippi. The plantation was

established on an area that recently had been cleared of

natural, mixed hardwoods and prepared for planting by

shearing, root raking, and disking. The soil is a Sharkey

clay, a member of the montmorillonitic, thermic family of

Vertic Haplaquepts. Site index for cottonwood is about 29

meters (95 feet) at 30 years.

In January 1973, 50-centimeter-long (20-inch) unrooted cottonwood cuttings (Stoneville clone 124) were

planted at a 3 x3-m (10 x 1 0-ft) spacing. The plantation

was cross-cultivated three times during the first growing

season and thinned by removing every other row of trees

at the end of the third growing season.

The plantation was divided into five .4-ha (1 -a) blocks

which were measured each year. Sampling in the first 4

years was conducted about September 1, when annual

growth was complete, and again in November after the

leaves had fallen. For each sample period, one tree per

block was selected, using the mean tree technique described by Ovington, Forrestand Armstrong (1967). Each

of the sample trees chosen had the block mean dbh and

height. Each was felled and separated into leaves

(September only), current branches, old branchwood, old

branchbark, stemwood, and stembark. In November of

years 1, 2, and 4, freshly fallen leaves from under each

November sample tree were collected.

All material was dried at 70” C (156” F), weighed,and

analyzed for total N, P, K, Ca, and Mg concentration.

Nitrogen concentration was determined by the standard

Kjeldahl procedure; P by calorimetry, using molybdenum

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

absorption spectrophotometry after the samples had

been dry-ashed and taken up in dilute HCI.

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
RESULTS AND DISCUSSION

Height growth was greatest (3.6 m or 11.8 ft) in the first

growing season and decreased annually through the

fourth season (table 1). Mean total height at the end of 4

years was 9.6 m (31.5 ft). Diameter growth was greatest

(4.1 cm or 1.6 in) in the second growing season but

dropped to 1.3 cm (5 in) in the fourth growing season

despite thinning the previous year. Four-year growth of

cottonwood on Sharkey clay is perhaps half of what might

be expected on a medium-textured soil in the area (Mohn

and Randall 1973).

Diameter and height growth culminate early in plantation-grown cottonwood (Krinard 1979). The rapid decrease in growth after culmination on the clayey soil in our

plantation is, in the authors’ opinion, a result of competition for the limited supply of available moisture in the

favorably structured and aerated upper 75 cm (30 in) of

soil. Soil nutrients are in good supply (Broadfoot, Blackmon,and Baker 1972) and competition for light seems not

to have occurred since the canopy has never approached

closure.

Dry weight of current foliage and biomass accumulated

in branches and stems is given in figure 1. The addition of

new biomass was greatest in year 3 (10.0 kg or 22.0 Ibs

per tree) and then decreased considerably in year 4 (4.3

kg or 9.4 Ibs per tree). Foliar weight culminated during

year 3 at about 6 kg (13 Ibs) per tree. However, the

proportion of foliage to total tree mass decreased from

the first through the fourth year. Percent of biomass in

branches reached a peak in year 3, then decreased.

Stem weight and percentage increased steadily throughout the 4 years.

In August of year 3, standing biomass would have been

17 metric tons per ha (7.6 tons per a), based on a known

85percent survival. Between years 3 and 4, the plantation was row-thinned. Assuming a 1 -percent mortality of

the remaining growing stock, standing biomass in August

of year 4 would have been about 10.6 metric tons per ha

(4.7 t per a).

Table 1 .-Height, diameter, and growth in years 1 through 4 of a

cottonwood plantation on Sharkey clay

Growth component 1

Total height (m) 3.6

Height growth (m) 3.6

Diameter b.h. (cm) 2.7

Diameter growth (cm) 2.7

Year

2 3 4

6.0 8.1 9.6

2.4 2.1 1.5

6.8 9.4 10.7

4.1 2.6 1.3

Table P.-Nutrient contentper tree in years 1 through 4 in a cottonwood

plantation

Component N P K C a Mg

Leaves

Branches

Stems

Total

Leaves

Branches

Stems

Total

Leaves

Branches

Stems

Total

Leaves

Branches

Stems

Total

_____________________________ g/tree _____________________________

Year 1

16.3 1.0 11.6 10.8 2.3

1.9 .3 3.4 2.7 .3

1.4 .2 1.9 1.8 .2

19.6 1.5 16.9 15.3 2.8

Year 2

42.1 3.4 22.5 61.4 10.0

12.7 3.1 14.2 21.9 2.3

9.7 2.0 9.9 13.3 1.4

64.5 8.5 46.6 96.6 13.7

Year 3

53.7 5.4 28.6 84.2 13.4

31.2 5.8 28.6 57.9 5.2

23.4 3.8 23.1 33.4 4.7

108.3 15.0 80.3 175.5 23.3

Year 4

58.0 5.8 37.0 77.6 17.3

26.7 6.5 37.3 73.7 10.6

32.7 5.4 33.0 62.1 5.9

117.4 17.7 107.3 213.4 33.8

Accumulation of nutrients in the first growing season

was small, followed by larger second- and third-year

accumulations (table 2). By the fourth year, nutrient accumulation had slowed, a reflection of smaller increases in

weight of leaves and branches (fig. 1).

Samples of freshly fallen leaves revealed changes,

usually a reduction, in leaf nutrients from earlier leaf

concentrations (table 3). The fate of the missing nutrients

is unknown; however, they could have been lost from the

leaf by leaching or translocated to other tissues. Data

from year 1 of this same plantation (Baker and Blackman

1977) indicated that N and P were translocated from

leaves into branches, stemsand roots. The bark of branches and stems are particularly important sites of redeposition. We compared nutrient concentrations in

September and November stem- and branchbark samples from years 1 through 4. Nitrogen, P and Mg were

found to have increased significantly (P = .95) in both

branch- and stembark. Potassium and Cadid not change.

The percentage of nutrients translocated was calculated on the assumption that nutrient increases in bark

and wood arise from material translocated from leaves.

Estimated average translocation in years 1 through 4 of N

Francis is soil scientist at the Southern Hardwoods Laboratory at Stoneville, Mississipppi, a part of the Southern Forest Experiment Station, Forest

Servicr+USDA and cooperator with the Mississippi Agricultural and Forestry Experiment Station and the Southern Hardwood Forest Research

Group. Baker, formerly principal soil scientist at the Southern Hardwoods Laboratory, is now principal silviculturist at the Forestry Sciences Laboratory

at Monticello, Arkansas.

2
35 -

30 -

25 -

z - 2 20 -

5 _

2 15-

IO -

.EAVES

3RANCHES

TEMS

-

I 2 3 4

YEARS

Figure 1 .-Mean dry weight of leaves, branches, and stems per tree

in a cottonwood plantation in September of years 1

through 4. Brackets give 95 percent confidence interval for

total biomass.

12 rL

SUMMER

P ‘O- WHOLE TREE

s _

WINTER

WHOLE TREE

4~c SUMMER

SOLE ONLY

YEARS

Figure 2.-Nitrogen contained in tissues of a cottonwood plantation

and potentially removed by different harvesting methods

and times.

Table 3.-N&i nt levels in green leaves in September and in freshly

falle d leaves in November in years 1, 2, and 4 in a cottonwooq plantation

Year

Leaf type ~ Nutrient 1 2 4

_________ percent nutrient __-------

Green

Freshly fallen

Green

Freshly fallen ~

Green

Freshly fallen

Green

Freshly fallen

Green

Freshly fallen

N 2.40 1.76 1.23

N 1.59 1.12 1.27

P .16 .14 .17

P .12 .16 .19

K 1.25 .94 1.09

K .77 .65 1.11

C a 2.25 2.57 2.29

C a 2.82 2.30 2.21

Mg .40 .42 .51

Mg .48 .42 .47

-

and P ranged from 29 to 33 percent and 33 to 38 percent

respectively! If trends of nutrient storage of N and P in

roots reported in year 1 (Baker and Blackman 1977) hold

true for later~years, approximately half of the leaf N and P

may be conberved by translocation. Magnesium translocation estiimated by this method ranged from 3 to 48

percent. A more precise monitoring of this nutrient is

needed. Tr nslocation of nutrients from senescing

leaves to ot6er tissues has been observed by a number of

workers (D vigneaud

r

and Denaeyer-De Smet 1970,

Hopkinson 1,966, Oland 1963, Switzer and Nelson 1972).

With the advent of short rotations and complete-tree

utilization, concern has grown about nutrient depletion

from a site. Table 4 gives the quantity of nutrients which

would leaveithe site in years 1 through 4 with each ton of

dry matter removed if a harvest were conducted. Loss of

N and K by whole-tree chipping during the summer of the

first year would be larger because of high concentrations

of nutrients in the leaves and because of the larger proportion of IeaNes to total biomass. All nutrient concentrations were more stable and lower in years 3 and 4. By this

time, leaf and branch mass had nearly stabilized, while

bole volume steadily increased. As a result of these

changes, loss of nutrient per ton of material removed by

summer whole-tree chipping should be lower in later

years. Who&tree chipping in the dormant season would

produce similar results, except that nutrient levels would

not be so hibh in year 1 and would not decline as much

through ye r 3. Harvesting just the boles in either

September 1r November would remove smaller quantities of nutrients than whole-tree chipping.

If nutrient1 removal per unit area rather than per ton of

material is considered, losses due to harvest in the first

year become less important because of low first-year

biomass yields. First-year uptake and potential loss of N

would have~been less than in subsequent years (fig. 2).

3
The greatest loss of N would occur with a summer wholetree harvest. Whole-tree harvesting in winter or summer

would consistently remove more N than would bole-only

harvests. A summer bole-only harvest would remove the

smallest quantities of N from the site, followed by a winter

bole-only harvest. The advantage of summer bole-only

harvest is small in year 3 and nearly disappears by year 4.

Could short-rotation harvests deplete this site of nutrients? Given a summer whole-tree harvest every 3 years

(assuming replanting every rotation or that coppice yield

equals planted cuttings), nutrients removed per rotation

would range from ‘I kg per ha of P to 16 kg per ha of Ca.

These small amounts removed about equal the quantity

of nutrients added by rainfall (Wells, Nicholasand Buol

1975). If there is no net loss of nutrients by other means,

this site could be cropped for cottonwood continuously

without depleting the site of nutrients.

Table 4.--Quantities of nutrients which would be removed per ton of

dry material harvested in years 1 through 4 of a cottonwood

plantation

Time and type

of harvest N P K C a f%

_____________________ grams per dry ton _____________________

Year 1

Sept.’ whole tree 13,400 105 1,040

Sept. bole only 420 6 0 490

Nov.’ whole tree 994 104 453

Nov. bole only 790 9 0 370

Year 2

Sept. whole tree 766 100 554

Sept. bole only 290 6 0 300

Nov. whole tree 640 9 1 316

Nov. bole only 480 7 1 221

Year 3

Sept. whole tree 589 8 0 434

Sept. bole only 260 4 0 250

Nov. whole tree 409 8 0 392

Nov. bole only 296 5 7 300

Year 4

Sept. whole tree 513 7 6 473

Sept. bole only 250 4 0 260

Nov. whole tree 369 6 5 327

Nov. bole only 258 4 4 247

‘Represents late growing season harvest.

%epresents dormant season harvest.

1,086 211

470 6 0

672 119

510 100

1,150 162

400 4 0

570 8 9

364 6 3

954 125

370 5 0

833 107

581 9 4

936 151

480 5 0

736 8 5

526 5 0

LITERATURE CITED

Baker, James B., and B. G. Blackman.

1977. Biomass and nutrient accumulation in a cottonwood plantation-The first growing season. Soil Sci.

Sot. Am. J. 41:632-636.

Broadfoot, W. M., B. G. Blackman, and J. B. Baker.

1972. Soil management for hardwood production.

Proc., Southeast. Hardwoods Symp. 1971:17-29.

U.S. Dep. Agric. For. Serv. Southeast. Area, State

and Priv. For., Atlanta, Ga.

Duvigneaud, P., and S. Denaeyer-De Smet.

1970. Biological cycling of minerals. Pages 199-255 In

D. E. Reichle, ed. Analysis of Temperate Forest

Ecosystems. Springer-Verlag, New York. 304 p.

Hopkinson, J. M.

1966. Studies on the expansion of the leaf surface. VI.

Senescence and the usefulness of old leaves. J.

Exp. Bot. 17:762-770.

Krinard, R. M.

1979. Five years’ growth of pruned and unpruned cottonwood planted at 40- by40-foot spacing. U.S. Dep.

Agric. For. Serv. Res. Note SO-252,5 p. South. For.

Exp. Stn., New Orleans, La.

Mohn, C. A., and W. K. Randall.

1973. Interaction of cottonwood clones with site and

planting year. Can. J. For. Res. 3:329-332.

Oland, K.

1963. Changes in the content of dry matter and nutrient

elements of apple foliage during senescence and

abscission. Phys. Plant. 16:682-694.

Ovington, J. D., W. G. Forrest, and J. S. Armstrong.

1967. Tree biomass estimation. Pages 4-31 In H.

Young, ed. Symp. on Primary Productivity and

Mineral Cycling in Natural Ecosystems. Univ. of

Maine Press, Orono. 245 p.

Switzer, G. L., and L. E. Nelson.

1972. Nutrient accumulation and cycling in loblolly pine

(Pinus taeda L.) plantation ecosystems: The first

twenty years. Soil Sci. Sot. Am. Proc. 36:143-147.

Wells, C. G., A. K. Nicholas, and S. W. Buol.

1975. Some effects of fertilization on mineral cycling in

loblolly pine. Pages 754-764 In Mineral Cycling in

Southeastern Ecosystems. U.S. Energy Res. Dev.

Adm.

*U.S. GOVERNMENT PRINTING OFFICE: 1981-569-082/8