Estimates of Nutrient Drain by Dormant-Season Harvests

of Coppice American Sycamore

B. G. BLACKMON

SUMMARY

Estimates of the amount of nutrients removed by

dormant-season harvests of coppice American sycamore indicated that harvesting once (at age 4) or

twice (at ages 2 and 4) removed 20-145 kg/ha of N,

P, K, Ca, and Mg and small quantities of Mn, Zn, Fe,

and Cu. Calculations of nutrient drain indicated that

for N, gains through natural processes about equal

losses, but losses exceeded gains for P and K. However, on the fertile Mississippi River floodplain site

used in the experiment, drain does not appear to be

serious. Nutrient drain was not detectable by analysis

of soil samples taken at the beginning and end of the

study. On less fertile Coastal Plain soils, drain may be

significant, requiring fertilization to maintain site productivity.

Additional keywords: Nutrient removal, harvesting, site productivity, nutrition, fertilization,

Platanus occidentalis.

INTRODUCTION

Recent shortages of fossil fuels have underscored

the need for wood as an alternate of supplemental

source of fuel. Plantations of closely spaced American sycamore (Platanus occidentalis L.) grown on

short rotations can possibly yield the necessary large

quantities of biomass. Kormanik and others (1973)

report yields of 18 metric tons/ha per year in Georgia,

Wittwer and others (1978) report 13-ton yields in

Kentucky, and Kennedy (1975) reports 20-ton yields

in Mississippi. However, since large quantities of nutrients accumulate in tree tissues, frequent harvesting could result in a net loss of nutrients from the soil

and ultimately in significant site degradation.

In this paper, I estimate the amount of nutrient

removal by dormant-season harvests of coppice

sycamore in the Mississippi River floodplain based

on my own nutrient concentration data and the yield

data of Kennedy (1975).

METHODS

Seedlings, 1-O stock of central Mississippi origin,

were planted at 0.6 X 1 .O- and 1.2 X 1.0-m spacing.

Soil was a Commerce silt loam, a member of the

fine-silty, mixed, thermic family of Aeric Fluvaquents,

and the site is very good for sycamore (Site Index =

35 m in 50 years).

For determination of nutrient concentrations, dormant-season tree samples were taken for each

spacing by cutting two trees of mean height and

diameter from each of two plots and separating the

stems and branches. Tree tissues were combined by

component, and all material was dried at 70” C and

ground to pass through a 20-mesh screen. Trees

were harvested annually, and samples of 1 -year-old

tissue were taken in January of 1971, 1972, 1973,

and 1974 for a total of four such blocks in time.

The concentration of nitrogen in tree tissue was

determined by the semi-micro Kjeldahl method; P by

calorimetry; and K, Ca, Mg, Mn, Fe, Zn, and Cu by

atomic absorption spectrophotometry.

In a separate study, Kennedy (1975) measured the

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.
Table 1 .-Dry matter production by cutting cycle and spacing for 4 years.’

Spacing &

cutting cycle Stem

Component

Branches Total

___-_________--_________________-____ t/ha ____________________________________

0.6X1.6 meters

1 2 15.8 3.7 19.5

2 28.2 3.1 31.3

4 30.5 1.6 32.1

1.2X1.6 meters

1 12.3 2.2 14.5

2 19.9 3.2 23.1

4 27.4 1.4 28.8

‘Calculated from Kennedy (1975).

%utting cycles: 1 = 4 annual harvests, 2 = 2 biennial harvests, 4 = 1 harvest after 4 years.

dry weight of stems and branches of sycamore expected nutrient gains from precipitation, mineralplanted at two spacings - 0.6 X 1.5 and 1.2 X 1.5 m ization, and weathering with nutrient losses through

- and harvested after 1, 2, and 4 years (table 1). I tree harvesting (Boyle 1975, 1976).

estimated nutrients removed through harvesting over At the beginning of the study and after 6 years, soil

4 years by multiplying my nutrient concentrations by samples were taken at depths of O-30,30-60,60-90,

Kennedy’s dry weights (tables 2 and 3). This pro- and 90-l 20 cm from two points on each plot. These

cedure seems to be justified since concentration of samples were analyzed for extractable P by the Mismost nutrients was not related to spacing, the two sissippi soil test method (Soil Test Work Group

studies were conducted on Mississippi River floodplain soils having very similar chemical and physical1974); for exchangeable K, Ca, and Mg by atomic

absorption after extraction with 1 N NH40Ac; for orproperties, and the studies received similar man- ganic matter by chromic acid oxidation; for total N by

agement.

Drain of N, P, and K was estimated by comparing

the Kjeldahl method, and reaction with the glass

electrode pH meter.

Table 2.-Average nutrient concentrations in stems and branches at two spacings.

Nutrient concentration

Spacing N P K C a Mg M n Z n F e cu

meters ___________________________ percent ________________________ ______________________ ppm ______________________

Stem

0.6X1 .O ,448 ,098 * ,292 ,300 ,058 * 8.68 6.00 12.88 6.38

1.2x1 . o ,495 ,123 ,310 ,320 ,073 11.88 7.25 15.38 7.50

Branches

0.6X1 . O ,555 ,105 ,318 ,573 ,078 13.63 9.75 * 21.25 11.50

1.2x1 . o ,573 ,135 ,328 ,545 ,100 19.38 8.25 20.13 11.50

*Indicates significant difference (.05) between spacings.

B. 0. Blackman is Principal Soil Scientist at the Southern Hardwoods Laboratory, which is maintained at Stoneville, Mississippi, by the

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

Station and the Southern Hardwood Forest Research Group.

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Table 3.-Total nutrient removal (branches & stems) during a 4-year period.

Nutrient

Spacing &

cutting

cycle N P K Ca NJ Mn Z n F e cu

________________________________________---------------_________ kg/ha ________________________________________-------

0.6X1.5 meters

1 ' 91.2 19.4 57.8 68.5 12.1 ,185 ,130 ,281 ,143

2 143.8 30.9 92.4 102.6 18.8 ,289 ,199 ,431 ,216

4 146.4 31.6 94.1 100.6 la.9 ,290 ,198 ,426 ,213

1.2X1.5 meters

1 73.4 18.0 45.4 51.2 11.1 ,188 ,107 ,233 ,116

2 117.2 28.9 72.4 al.4 17.8 ,298 ,171 ,371 ,186

4 144.0 35.6 89.7 95.5 21.5 ,353 ,211 .450 ,223

'Cutting cycles: 1 = 4 annual harvests, 2 = 2 biennial harvests, 4 = 1 hatvest after 4 years.

RESULTS AND DISCUSSION

Nutrient accumulation and removal through

harvesting

For all elements studied, concentrations in

branches exceeded those in stems (table 2). With the

exception of P and Mg in stems and Zn in branches,

nutrient concentrations were not related to spacing.

I measured nutrient concentrations only for tissue

harvested on an annual cutting cycle. Since nutrient

concentration tends to be lower in older tissue

(Steinbeck and others 1974) the contents I calculated for Kennedy’s cycles of 2 and 4 years are

perhaps slightly elevated.

During the 4 years, annual dormant-season harvests of trees grown at 0.6 X 1.5-m spacing removed

91 kg/ha of N, 19 of P, 58 of K, 68 of Ca, and 12 of Mg

(table 3). Trees at the wider spacing removed 73

kg/ha of N, 18 of P, 45 of K, 51 of Ca, and 11 of Mg.

Extending the cutting cycle from 1 year to 2 and 4

years increased nutrient removal by 50-60 percent at

the closer spacing and 70-90% at the wider spacing

(table 3). As Kennedy (1975) found with yield, there

appears to be no difference in nutrient removal between the 2- and 4-year cutting cycles. Very small

quantities of Mn, Zn, Fe, and Cu were removed,

regardless of spacing or cutting cycle (table 3). Removal ranged from 0.11 kg/ha for Zn when trees

were harvested annually for 4 years and spaced at

1.2 X 1.5 m to 0.45 kg/ha for Fe when trees were

grown at the same spacing and harvested one time,

at age 4.

Nutrient drain

Sycamores obviously remove nutrients from the

soil, but the real question is whether or not this removal represents a net loss of nutrients from the site.

To answer this question, I compared the losses of N,

P, and K from harvesting with the gains that could be

expected over the 4 years from weathering, mineralization, precipitation, and other sources (table 4).

Gains in soil N sometimes exceeded losses; the

greatest net gain occurred when trees were harvested annually (table 4). Increasing the cutting cycle

to 2 and 4 years yielded an index of 0.9 at the closer

spacing, indicating a slight drain of N during the 4

years. At the wider spacing, the gain/loss index fell

below 1 .O only with the 4-year cycle.

Losses of P exceeded gains by 9 to 27 kg/ha,

depending on the cutting cycle and spacing.

Gain/loss indices ranged from 0.3 to 0.5, with a tendency toward greater drain with longer cutting cycles.

Of the three nutrients studied, P losses were

greatest. These results are similar to those of Wood

and others (1977), who found N removal to about

equal gains and P removal to exceed gain. Potassium drain was intermediate between N and P.

Gain/loss indices ranged from 0.5 to 1.0.

Besides gain/loss indices, nutrient reserves of a

site must be considered. Although gain/loss indices

indicate a drain of P and K, the study site has a

reserve of 464 kg of P/ha and 1 ,148 kg of K. Assuming a maximum drain of 27 kg/ha of P over a 4-year

rotation, about 17 rotations of 4 years each would be

required to deplete the site of available P. Since the

maximum drain of K is 49 kg and the soil has a

reserve of 1,148 kg, it would take 23 rotations of 4

years each to deplete the available K. Yet, drain

probably should not be considered in terms of time

required to exhaust nutrient supplies. The soil would

not supply adequate nutrition for tree growth long

before total depletion. Also, if harvests were conducted during the growing season, removing foliage

3
Table 4.-Sail nutrient reserves, expected gains, losses, and gainlloss indices for coppice sycamore

harvested over a 4-year period.

Nutrient

N P K

0.6X1.5-m spacing _____________ kg/ha ______________

Available soil reserve (O-30 cm)’ 6 3 464 1146

Gains expected in 4 years2 134 9 4 5

Loss in harvest (by cutting cycle):

l3 9 1 1 9 5 8

2 144 3 1 9 2

4 146 3 2 9 4

_____________ Index _______------

Gain/loss index (by cutting cycle):

1 1.47 .47 .78

2 .93 .29 .49

4 .92 .29 .48

1.2X1.5-m spacing _____________ kg/ha ______________

Available soil reserve (O-30 cm) 6 3 464 1148

Gains expected in 4 years 134 9 4 5

Loss in harvest (by cutting cycle):

1 7 3 1 8 4 5

2 117 2 9 7 2

4 144 3 6 9 0

_____________ Index ______________

Gain/loss index (by cutting cycle):

1 1.84 .50 1.0

2 1.14 .31 .82

4 .93 .25 .50

1 Nutrient reserves were determined by analysis of soil from the study site. Available N was estimated from

total N, assuming 2% availability.

*Expected gains are those estimated by White (1974) for soils in south Alabama. Gains include inputs

from mineralization, weathering, and precipitation.

3Cutting cycles: 1 = 4 annual harvests, 2 = 2 biennial harvests, 4 = 1 harvest after 4 years.

from the site, nutrient drain would occur at a more LITERATURE CITED

rapid rate.

Soil analyses did not reveal significant losses in Boyle, J. R.

nutrients, perhaps because of the inability to meas- 1975. Nutrients in relation to intensive culture of

ure small changes in available forms of nutrients. forest crops. Iowa State J. Res. 49: 297-303.

This study was conducted on a highly fertile soil. If Boyle, J. Ft.

the reserve of soil P were only 40 to 50 kg/ha, as in 1976. A system for evaluating potential impacts of

many soils of the southern Coastal Plain, two rota- whole-tree harvesting on site quality. Tappi

tions could deplete the extractable P, assuming 59(7): 79-81.

biomass production comparable to that observed in Kennedy, H. E., Jr.

this study. Since the rate of biomass production and 1975. Influence of cutting cycle and spacing on

nutrient accumulation is usually lower on Coastal coppice sycamore yield. U.S. Dep. Agric. For.

Plain soils, three or four rotations, or 12 to 16 years, Serv. Res. Note SO-193, 3 p. South. For. Exp.

might be required to deplete soil P. But sub-optimum Stn., New Orleans, La.

nutrition would occur in a much shorter period. On Kormanik, P. P., G. L. Tyre, and R. P. Belanger.

such sites, fertilization would probably be necessary. 1973. A case history of two short rotation coppice

4
plantations of sycamore on southern Piedmont

soils. In IUFRO biomass studies. [Nancy, France

June 1973, and Vancouver, B.C. August 1973.1

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Soil Test Work Group.

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United States. South. Coop. Ser. Bull. 190,23 p.

Steinbeck, K., R. G. Miller, and J. C. Fortson.

1974. Nutrient levels in American sycamore coppice during the dormant season. Ga. For. Res.

Pap. 79, 5 p.

White, E. H.

1974. Whole-tree harvesting depletes soil nutrients. Can. J. For. Res. 4: 530535.

Wittwer, R. F., R. H. King, J. M. Clayton, and 0. W.

Hinton.

1978. Biomass yield of short rotation American

sycamore as influenced by site, fertilizers, spacing, and rotation age. South. J. Applied For. 2:

15-19.

Wood, B. W., R. F. Wittwer, and S. B. Carpenter.

1977. Nutrient element accumulation and distribution in an intensively cultured American sycamore plantation. Plant and Soil 48: 417-433.

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