Above ground biomass and nutrient uptake of three tree species(Eucalyptus camaldulensis, Eucalyptus grandis and

Dalbergia sissoo) as affected by irrigation andfertiliser, at 3 years of age, in southern India

Ian HunterInternational Network for Bamboo and Rattan, Beijing, PR China

Received 15 January 1999; received in revised form 31 August 1999; accepted 21 February 2000

Abstract

Seedlings of Eucalyptus camaldulensis, Eucalyptus grandis and Dalbergia sissoo were planted in a two-replicate split-plot

factorial trial with four irrigation and three fertiliser treatments in Hosakote Forest station in southern India in September

1991. Irrigation was applied at the rate of 0, 2.5, 5 and 7.5 mm per day. Natural rainfall was approximately 800 mm per year

distributed between June and November in two monsoon seasons. NPK fertiliser was applied three times in spade-slit

dressings at 9, 18 and 27 months from planting at a zero rate, a medium rate and a rate four times that. Over the life of the trial

N was applied at the rate of 0, 80 or 320 kg/ha; P was applied at the rate of 0, 7.5 or 30 kg/ha and K at 0, 25 or 100 kg/ha.

In October 1994 when the trees were 37 months from transplanting, a biomass and nutrient content determination was

made. The two eucalyptus had a total dry weight averaging 45.3 tonnes/ha while the Dalbergia had an average dry weight of

only 7.6 tonnes. There were no interactions between species and treatments. Irrigation increased dry weight linearly across

treatments and by 74% in the highest irrigation rate. Irrigation increased stem wood weight by 90% but branch and leaf weight

by only 40%. Fertiliser increased dry weight by 23% and increased branch weight by a higher percentage than leaf weight.

The two eucalyptus had accumulated a stem volume of 60 m3/ha at a rate of 20 m3/ha per year. Nutrient content increased with

dry weight but not in proportion, so that nutrient concentrations in the higher rates of both irrigation and fertiliser treatments

were reduced, in some instances to marginal levels. Thus, the natural fertility of the site was stressed by the high growth rates.

# 2001 Elsevier Science B.V. All rights reserved.

Keywords: Irrigation; Fertiliser; Biomass; Nutrient content; Tropical plantation; Nutrient and water

1. Introduction

The 3.4 billion ha of forest in the world grow (as

well as can be estimated) at an average of 1 m3/ha per

year and thereby nicely satisfy the 3.5 billion m3 of

wood which it is estimated is consumed each year

(Solberg et al., 1996). However, deforestation is con-

tinuing; world population is still increasing and

increasing areas of natural forest are being withdrawn

from production to be placed in reserves. Everything

points to a growing imbalance between supply and

potential demand.

Fast-growing plantations will be required to ®ll in

the shortfall of supply from natural forest. The yields

that have been obtained in existing plantations (often

with species exotic to the site) have typically been

many times greater than those in natural forests. Thus,

plantations have, additionally, the possibility of satis-

Forest Ecology and Management 144 (2001) 189±199

0378-1127/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved.

PII: S 0 3 7 8 - 1 1 2 7 ( 0 0 ) 0 0 3 7 3 - X

fying the current demand for wood from a much

smaller land area than at present. Some observers

have speculated that fast-growing, tropical plantations

on easy terrain and with good infrastructure access to

industry and ports, will become the majority suppliers

of wood in the future.

Additionally, the recent Kyoto Agreement (unpub-

lished 1998) on reducing greenhouse gasses presages

the creation of `Kyoto forests' and the concept of

trading carbon sequestration by planting trees in one

country in exchange for carbon emissions in another.

The performance of fast growing plantations in the

tropics is, therefore, of increased general interest.

Eucalyptus trees are widely planted in southern

India both by industrial corporations and by farmers

of small land holdings. The trees are usually grown for

8 years, yielding approximately 80 m3/ha (Sharma,

1978). The products are widely used in the local

economy and also for industrial feed to the pulp

and paper industry. Some local workers have criticised

the use of exotic tree species and claimed that, because

they produce only limited products, they further

impoverish local people (as cited in Hunter et al.,

1998).

The establishment of fast-growing plantations in

developing tropical countries is, therefore, of increas-

ing interest but involves many choices about the

allocation of land and other scarce resources (such

as water and fertiliser) which choices may indirectly

disadvantage resource-poor local people. As part of a

larger programme of research in Karnataka, which

was funded through a development aid programme, it

was, therefore, decided to establish an experiment

with Eucalyptus trees, a local tree species and both

irrigation and fertiliser to determine

� the extent to which productivity of plantations in

southern India could be intensified by choice of

species and silvicultural inputs such as irrigation

and fertiliser;

� the extent to which exotic species were differently

responsive to and more or less productive than one

native species.

There are many documented reports of the growth

and biomass of tropical plantation species in relation

to adjacent native forest but there are relatively fewer

reports of biomass response to experimental manip-

ulation of silvicultural inputs. In particular, there have

been only a very few irrigation and fertiliser ®eld

experiments with major plantation species. Notable

exceptions are Stewart et al. (1990) (where seven tree

species where irrigated with ef¯uent combining nutri-

ents and water); the biology of forest growth experi-

ment in Australia where Pinus radiata was irrigated

and fertilised (McMurtrie et al., 1990); the Jadraas

experiment in Sweden and later work at Umea (Linder

et al., 1987; Nilsson, 1997) with Pinus sylvestris and a

comprehensive experiment with Eucalyptus globulus

in Portugal, (Pereira et al., 1989). All of these experi-

ments demonstrated very strong responses to irriga-

tion or fertiliser (separately or in combination) and

elevated tree growth to levels not seen before in those

environments.

Interest in southern India to the response of tree

species to irrigation is amply demonstrated by the

work of Swaminath (1988). He carried out biomass

determinations at 15, 21 and 31 months on 13 irrigated

and unirrigated exotic and indigenous species. He

found that Cassia siamea gave the greatest productiv-

ity when irrigated followed by Eucalyptus camaldu-

lensis and Eucalyptus tereticornis. Acacia

auriculiformis gave the greatest unirrigated produc-

tivity although at only 40% of the best productivity in

the irrigated plots. Dalbergia sissoo was included in

the trial but proved to be notably less productive than

the exotic species.

2. Methods

The experimental work reported here consists of

biomass determination made in a 3-year old split-plot

factorial trial with two replications, three tree species,

four rates of irrigation and three rates of fertiliser. The

main treatments were the three species and four

irrigation rates which were ascribed randomly to 24

main plots (two replications) of 10 m�30 m size.

Within each main plot, there were three sub-plots of

10 m�10 m to which one of three fertiliser treatments

was applied at random.

The site was at Hosakote Forest Station in Karna-

taka, India (148N, 788E), on a deep lateritic soil at

approximately 900 m a.s.l. and with an annual rainfall

of 800 mm. (Swaminath, 1988). The three tree species

were Eucalyptus grandis Hill ex Maiden (commonly

190 I. Hunter / Forest Ecology and Management 144 (2001) 189±199

called `¯ooded gum'); E. camaldulensis Dehnh. (com-

monly called `Red River gum') and D. sissoo Roxb. E.

grandis is a tall-growing tree of the coastal regions of

Queensland and northern New South Wales (Penfold

and Willis, 1961). It typically experiences in excess of

1000 mm rainfall per annum and cannot adjust easily

to prolonged drought. It is a widely-used plantation

species throughout the tropical world either in its pure

form or hybridised with other Eucalyptus such as

Eucalyptus urophylla. E. camaldulensis is very widely

distributed in inland Australia along river banks. It can

tolerate very low rainfall, inundation and salinity. It is

also a globally-used plantation species and probably

contributed some genetic material to the local land-

race Mysore hybrid Eucalypt (although Boland, 1981

concluded that Mysore hybrid owed most of its genetic

make-up to southern provenances of E. tereticornis).

Much is known about the climatic requirements of

both Eucalypt species (Booth and Pryor, 1991). D.

sissoo is distributed throughout the northern Indian

sub-continent as a tall forest tree (Tewari, 1994). It has

been planted throughout India. It is a nitrogen-®xing

leguminous tree used for timber, fodder and fuelwood.

It can also tolerate very low rainfall, salinity (although

not strongly) and industrially-polluted sites. It was

chosen as a suitable indigenous species which had

performed well in trials elsewhere on the Indian sub-

continent (Swaminath, 1988; Neil, 1989) and one, on

sites which suit it, as an early-successional species in

dry deciduous forest has been reported to produce

15 tonnes/ha per year of woody biomass (Rashmi-

Rajvanshi and Gupta, 1985) and a total biomass of

160 tonnes (Sharma et al., 1988).

In early September 1991, 1-year old seedlings of E.

grandis, E. camaldulensis and D. sissoo which had

been raised in large polythene bags in the local forest

nursery, were planted at 2 m�2 m spacing in a split

plot design experiment on a lateritic soil in Hosakote

forest by the Karnataka Forest Department. The whole

forest station is fenced to exclude grazing animals.

The irrigation treatment was applied at the rate of 0,

2.5, 5 and 7.5 mm per day. Irrigation was achieved by

®lling tower-mounted tanks of 750 l capacity each day

and allowing them to drain into the main plots through

drip-nozzles adjacent to the trees. The varying rates of

irrigation were achieved by placing 0, 1, 2 or 3 tower-

mounted tanks adjacent to each plot. A vertical-walled

trench 1.5 m deep and approximately 1 m wide was

dug around each main plot ensuring that sideways

surface movement of water between irrigation treat-

ments could not occur. The material from the ditches

was used to construct a low berm around each main

plot to prevent surface run-off (see Fig. 1).

Irrigation was applied daily regardless of rainfall.

Natural rainfall was not monitored directly at the site

but is known (from adjacent weather stations) to be

approximately 800 mm per year distributed between

June and November in two monsoon seasons (Swa-

minath, 1988). Thus, the irrigation rates were approxi-

mately equivalent to 800 mm (the zero rate of

irrigation), 1700, 2600 and 3500 mm (the highest rate

of irrigation plus natural rainfall) of rainfall per year.

The irrigation additions were chosen to cover a range

of irrigation intensities up to supra-optimal levels.

It was known from many studies (Prasad et al.,

1985; Krishnamurthy and Vijayan Clement, 1986;

Karnataka Forest Department, unpublished data) that

eucalyptus in Karnataka responded to fertiliser at time

of planting and that nutrient concentrations in euca-

lyptus for many nutrients tended to be low or marginal

(Kushalappa, 1986). Nitrogen (N), phosphorus (P) and

potassium (K) fertiliser was, therefore, applied three

times in spade-slit dressings beside each tree at 9, 18

and 27 months from planting at a zero rate, a medium

rate and a rate four times that. Over the life of the trial

N was applied at the rate of either 80 or 320 kg/ha; P

was applied at the rate of either 7.5 or 30 kg/ha and K

at 25 or 100 kg/ha. The rates were chosen, based on

prior knowledge about the soils, on fertiliser responses

in other studies (e.g. Prasad et al., 1985) and on

general principles of fertilising forest trees (e.g. Hun-

ter and Smith, 1996), to supply an adequate and a high

rate of nutrients. The fertiliser applications were dis-

tributed in time to avoid the risk of loss of fertiliser

nutrients and root burn that might have occurred if the

whole amount had been applied to small seedlings

(Hunter and Smith, 1996). Small amounts of magne-

sium (Mg) at 20 kg/ha, zinc (Zn), boron (B) and

copper (Cu), at 5 kg/ha each, were applied at 9

months. This precautionary application, to ensure that

unexpected nutrient de®ciencies did not occur, was

based on a comparison of the values published in

Drechsel and Zech (1991) with those experienced in

several hundred foliar analyses of a wide range of

species collected from a wide range of sites in Kar-

nataka (Kushalappa, 1986, Karnataka Forest Depart-

I. Hunter / Forest Ecology and Management 144 (2001) 189±199 191

ment, unpublished data). Fertiliser applications were

timed to coincide with the onset of rains so as to give

an even opportunity for uptake in both irrigated and

unirrigated plots. The fertiliser was applied in spade

slits to avoid the risk of loss over the surface.

During the life of the trial, water use measurements,

leaf physiology measurements and soil water status

were taken regularly and either have been (e.g. Calder,

1992; Gurumurthy, 1994) or are to be reported sepa-

rately by other workers. Early results from the trial

have been documented by Gurumurthy (1994). His

thesis showed that from the earliest months of the trial,

there has been a very strong difference in growth

between the species with D. sissoo growing much

the slowest and E. grandis growing slightly slower

than E. camaldulensis. A strong irrigation response

emerged early with all species showing a response to

some irrigation but proportionately smaller increases

to high rates of irrigation. In the ®rst 15 months of the

trial, there was a strong and signi®cant fertiliser

response in all species in interaction with irrigation

but in the latter phase of the trial differences due to the

fertiliser treatment began to fade. Gurumurthy (1994)

also analysed foliage samples and found strongly

signi®cant differences between the species but few

differences to other treatments. E. grandis had an

average N content of 25 mg/g, while E. camaldulensis

had 15.6 mg/g. All species were low in phosphorus-

averaging 0.8 mg/g only. E. grandis had only 2.6 mg/g

potassium while other species had double that. Foliar

Ca averaged 22 mg/g; foliar Mg 4 mg/g. Levels of Zn,

manganese (Mn) and iron (Fe) were very adequate

while levels of only 3 mg/kg Cu were found in some

treatments.

Fig. 1. The trial site in 1993. A ditch separating main plots can be clearly seen. Another crosses at right angles just in front of the standing

figures. The triple irrigation towers of a high irrigation rate plot can be seen on the right behind the standing figures. The towers are irrigating a

plot of E. camaldulensis. Opposite, and behind the standing figures on the left is a plot of D. sissoo.

192 I. Hunter / Forest Ecology and Management 144 (2001) 189±199

Tree height and diameter were measured annually

on an inner measurement plot of 3�3trees. The trial

was maintained according to protocols laid out in

Adlard (1990). Fig. 1 shows the site as it appeared

in 1993.

In October 1994, when biomass determination com-

menced, it was found that in 53 of the 72 plots all nine

trees had survived. Twelve plots had eight surviving

trees; three had seven and a further four had between

three and six surviving trees.

Calculation of biomass per unit area was done using

the proportional basal area method described by

Madgwick (1981). In this method, the ratio of the

summed basal areas of sample trees to that of the

whole plot basal area, is used to scale up the biomass

of the sampled trees to an area estimate. It has the

advantage over other techniques and an advantage that

is important where analysis of variance will subse-

quently be used to test plot means, that none of the

experimental error variance attributable to between

plot differences is lost in calculating plot values.

Alternative methods of calculating biomass, such as

across-treatment regressions, subsume between plot

variance in the regression and thereby reduce esti-

mates of experimental error. The author has used the

technique several times to estimate the signi®cance of

biomass changes in designed trials (e.g. Hunter et al.,

1986; Hunter and Hunter, 1991). In order to utilise the

method, it is necessary to have a current determination

of plot basal area. Accordingly, in October 1994, when

the trees was 37 months from transplanting and

immediately before the biomass determination, tree

diameters in the trial were remeasured. The purpose of

remeasuring the trees was simply and only to provide a

basis for the use of the proportional basal area method

of scaling up from sample trees to area estimates and

not for direct comparison of volume between species.

The Eucalyptus were measured at breast height

(1.3 m) but the D. sissoo was measured at the root

collar because many plants were less than 1.3 m tall

and tended to be very branchy and bushy. The parti-

cular scaling up method from sample trees to plot

aggregates is more reliable when it estimates the full

amount of conducting tissue above the point of mea-

surement. Three sample trees were selected strictly at

random (using a random number table of Nos. 1±9,

generated by the random function in Microsoft Excel)

from amongst the nine inner plot trees and felled. The

sample trees were divided into stem, branches and

leaves. Wet weights of each component were taken.

Stem subsamples of approximately 5 cm length were

taken at 1 m intervals up the stem and divided into

wood and bark. Subsamples of other components were

taken by mixing and quartering. Samples were stored

in a refrigerator for less than 1 week before being

¯own back to the UK for analysis. Dry weights of each

sample were calculated. Dried samples were analysed

by a commercial laboratory. N was determined by the

Kjeldahl process as described in Ministry of Agricul-

ture, Fisheries and Food (1981). For P, K, Ca, Mg and

Cu, the plant samples were dry ashed, dissolved in

hydrochloric acid, as described in Ministry of Agri-

culture, Fisheries and Food (1981) and the concentra-

tions were determined by Inductively Coupled Plasma

Spectrophotometer. Both biomass and nutrient content

per plot were calculated using the proportional basal

area method. The signi®cance of the differences

between species, irrigation rates and fertiliser treat-

ments was tested using GENSTATanalysis of variance

on the split plot design. Linear and quadri-linear

effects were extracted. The following conventions

were used in reporting statistical signi®cance: NS:

not signi®cant; 0.0n: signi®cant at the level shown;

(*): signi®cant at the 0.05 level; (***): signi®cant at

the 0.01 level.

Soil samples were taken from 0 to 25 and 25 to

75 cm and analysed by a commercial laboratory for

pH, total N (by Kjeldahl), total P (by perchloric acid

digestion), total K (by nitric and perchloric acid) and

available P (Olsen), available K and available Mg

(ammonium nitrate extraction). Methods used were

as described in Ministry of Agriculture, Fisheries and

Food (1981) and Page et al. (1982).

Published volume tables (e.g. Sharma, 1978) were

used to turn the Eucalyptus tree diameter and height

into an approximate estimate of volume.

3. Results

Results of soil analysis (Table 1) indicate that the

soil had a low but deeply distributed N and P content

and an apparently adequate K, Ca and Mg content.

Analysis of variance indicated strongly signi®cant

dry weight differences between species and between

irrigation and fertiliser treatments. Since, interactions

I. Hunter / Forest Ecology and Management 144 (2001) 189±199 193

between species, irrigation and fertiliser were never

signi®cant for dry weight, the main effects will be

discussed separately.

3.1. Dry weight

The productivity of D. sissoo was very much less

than either of the two Eucalyptus, however, interac-

tions between species and other treatments were not

signi®cant (Table 2). D. sissoo is a deciduous tree. It

had a low total leaf weight in this study because it was

in its `spring ¯ush' and had not fully extended its

leaves. The eucalyptus by comparison had different

proportions of old and new leaves than would have

been the case at another time. A study conducted at

another time would have yielded different results for

foliar mass. Nevertheless, it is unlikely that D. sissoo

leaf weight even in full ¯ush, would have equalled that

of the Eucalyptus since the branch mass to support the

foliage is smaller and biomass studies generally tend

to show a broad correlation between branch mass and

foliage mass. The D. sissoo trees in this trial were very

branchy and bushy with branch dry weight per tree

nearly the same as stem wood weight. This branchi-

ness may be a juvenile trait since adjacent, older D.

sissoo outside the trial had formed small upright trees.

On the other hand, it may have been a genetic char-

acteristic of the particular seed source used since

Jitender-Singh and Bangarwa (1995) report high

variability in these characteristics between seed

sources.

Both Eucalyptus had very similar total dry weight

but E. camaldulensis had more wood and fewer

branches and leaves than E. grandis.

Irrigation strongly and signi®cantly increased both

wood weight and bark weight while leaving bark

percentage largely unchanged (Table 3). The linear

effect of increasing irrigation was highly signi®cant

for wood and branch weight. Leaf and branch weight

were increased slightly but not signi®cantly. The total

dry weight of D. sissoo was increased from 3.6 to

9.7 tonnes by 5.0 mm per day of irrigation. Within the

restrictions imposed by the normal site variability of a

large two-replicate trial, it was not possible to dis-

criminate statistically between the response of the two

Eucalyptus to irrigation. Both increased total dry

weight by between 42 and 47% in response to the

two higher rates of irrigation.

Fertiliser signi®cantly increased total dry weight of

all three species (Table 4). Fertiliser signi®cantly

increased the stem wood and bark component of all

three species but had no signi®cant effect on branch

and leaf weight. D. sissoo showed the same additive

total dry weight response to fertiliser (at approxi-

Table 1

Results of soil analyses

Element Soil depth

0±25 cm 25±75 cm

Total N (%) 0.080 0.084

Total P (ppm) 139 116

Total K (ppm) 1560 2255

Available P (ppm) 7.1 6.5

Available K (ppm) 42 27

Available Mg (ppm) 135 166

pH 5.9 5.8

Table 2

Dry weight of biomass components by species (tonnes/ha),

averaged over irrigation and fertiliser treatments

Species Biomass component

Wood Bark Branches Leaves Total

D. sissoo 3.3 0.7 3.2 0.4 7.6

E. camaldulensis 29.4 6.6 4.1 5.0 45.1

E. grandis 26.3 5.8 6.7 6.7 45.4

Significance of

species differences

*** *** *** *** ***

Table 3

Dry weight response to irrigation, averaged over fertiliser

treatment, by species and biomass component but combining

woody materiala (wood, bark and branches) (tonnes/ha)

Irrigation

rate (mm)

Species

D. sissoo E. camaldulensis E. grandis

Wood Leaf Wood Leaf Wood Leaf

0 3.4 0.2 31.3 4.6 25.6 5.3

2.5 7.7 0.4 34.1 4.3 39.3 7.5

5.0 9.3 0.4 40.2 4.8 44.6 6.8

7.5 8.5 0.5 54.6 6.5 45.6 7.1

a Significance of irrigation effect: stemwood (*), stembark (*),

branches (NS), leaf (NS); there was a significant linear effect in

stemwood, bark and in total biomass; wood is composed of

stemwood, stembark and branches.

194 I. Hunter / Forest Ecology and Management 144 (2001) 189±199

mately 6 tonnes/ha) as the two Eucalyptus. However,

D. sissoo was much more responsive, since this addi-

tive amount represented an addition to a smaller initial

state, increasing dry weight overall by 140% as opposed

to between 15 and 20% for the two Eucalyptus.

Since the linear effect of both irrigation and ferti-

liser treatments was usually signi®cant but the quad-

ratic effect (either as a positive or negative coef®cient)

never was, it seems probable that still higher produc-

tivity could have been achieved with greater irrigation

and more fertiliser.

3.2. Nutrient concentrations

Changes in nutrient concentration across treatments

can provide an indication of how greatly the treat-

ments have stressed the inherent nutrient supplying

ability of the site.

D. sissoo had signi®cantly higher N concentrations

in all components than the two Eucalyptus. D. sissoo

foliar N averaged 35 mg/g, while E. camaldulensis

averaged 14 mg/g and E. grandis 16 mg/g. In the

unfertilised irrigation treatments, leaf nitrogen in

the two Eucalyptus tended to increase slightly at

the lowest rate of irrigation relative to the control,

before declining to be lower in the highest rate of

irrigation than in the control. Thus, indicating that the

irrigation treatment had slightly stressed the site's

ability to supply adequate nitrogen. Fertiliser had a

signi®cant interactive effect with species on foliar N.

D. sissoo foliar N increased while the Eucalyptus

foliar N decreased across fertiliser rates.

P concentrations were generally low, averaging

0.1 mg/g in wood, 0.4 mg/g in bark and 0.3 mg/g in

branches. The species differed only in P in the foliage

where D. sissoo had a higher concentration (2.1 mg/g)

than the Eucalyptus (0.8 mg/g). There were signi®cant

fertiliser effects on P concentration usually in inter-

action with species. Increased fertiliser application

caused an increase in P concentration in D. sissoo,

but a decrease in Eucalypt. A similar, but non-sig-

ni®cant effect was detectable with irrigation. Thus, the

increase in growth brought about by irrigation and

fertiliser, produced a demand for P which exceeded

the site's ability to supply it (with or without addi-

tional fertiliser P) and led to a reduction in foliar P to

levels judged to be marginal or de®cient (Drechsel and

Zech, 1991).

By analogy with other species and with published

references (Drechsel and Zech, 1991), K concentra-

tions in leaves were generally adequate for satisfactory

growth averaging 11.4 mg/g in D. sissoo, 7.9 mg/g in

E. camaldulensis but only 4.7 mg/g in E. grandis. In

wood and bark components, E. camaldulensis had

slightly the highest concentration of the three species.

The pattern of K variation with irrigation and fertiliser

was similar to that observed for P. K concentrations in

D. sissoo generally increased with increased inputs

while those of the Eucalyptus decreased.

D. sissoo had Mg and Ca concentrations higher than

the Eucalyptus in all components by at least 50%.

Fertiliser decreased Mg concentrations in wood and

irrigation decreased Mg in the leaves of Eucalyptus

but not D. sissoo. The highest rate of fertiliser

decreased foliar Ca concentrations. Copper concen-

tration in leaves of E. grandis was reduced to a

marginal 3.8 mg/kg by the highest rate of fertiliser.

One can conclude from the macro-nutrient concen-

trations that the very high levels of productivity

brought about by irrigation and fertiliser in the two

Eucalypt species had slightly stressed the site nutri-

tionally. Foliar concentrations in the more productive

treatments were low for N and P but still adequate for

most other nutrients. Thus, although higher produc-

tivity could possibly have been achieved through

fertiliser, much higher rates would have to be used

and more elements (particularly Mg and Cu) would

have to be included in order to balance the nutrition.

For most nutrients, the two Eucalyptus tended to

have similar concentrations while the D. sissoo had

Table 4

Dry weight response to fertiliser by species and biomass

component but combining woody materiala (wood, bark and

branches) (tonnes/ha)

Fertiliser

rate

Species

D. sissoo E. camaldulensis E. grandis

Wood Leaf Wood Leaf Wood Leaf

0 4.2 0.2 37.1 5.1 35.1 5.9

1 7.3 0.4 40.1 4.9 39.4 7.0

4 10.1 0.5 43.0 5.2 41.8 7.2

a Significance of fertiliser effect: stemwood (NS), stembark (*),

branches (***), leaf (NS); there was a significant linear effect

across rates in stembark, branches and in total biomass; wood is

composed of stemwood, stembark and branches.

I. Hunter / Forest Ecology and Management 144 (2001) 189±199 195

higher concentrations. However, D. sissoo was a

markedly lower manganese accumulator than the

Eucalyptus. It is also reasonable to conclude, from

the very strong percentage fertiliser response of D.

sissoo, that it is a much more demanding species than

the two Eucalyptus, particularly for P, and that had it

been possible, by irrigation, to increase productivity to

that of the two Eucalyptus the site would have been

unable to supply nutrients at the level apparently

required.

3.3. Nutrient content

The results for nutrient content re¯ect the contrast-

ing trends seen for weight and concentration. Nutrient

content differed markedly between species (Table 5).

Given that dry weight productivity differed by a factor

of 6:1 between D. sissoo and the two Eucalyptus

(which had similar dry weight productivity) the results

given in Table 5 imply a marked difference in nutrient

productivity between the three species. D. sissoo

produced much less dry weight per unit of N than

the other species, although it ®xed that nitrogen itself.

D. sissoo also produced less dry weight per unit of P,

Ca and Mg than the Eucalyptus and less than E.

grandis for K. E. grandis was slightly less ef®cient

than E. camaldulensis for N, P and Mg.

The apparent uptake of the three species differed.

The calculation of apparent uptake rests on the

assumption that the differences in nutrient content

between fertilised and unfertilised plots (Table 5)

are directly attributable to the fertiliser applied and

not to some indirect effect on soil chemistry. This

assumption must be incorrect to some degree since

increased nutrient uptake also occurred in simply

irrigated plots. However, fertiliser appeared to

increase N content by between 23 and 29 kg out of

the 80 applied at the lower rate and 48 to 53 out of 320

applied at the higher rate in D. sissoo and E. grandis.

E. camaldulensis appeared to take up less N Ð only

18 kg/ha at the highest fertiliser rate. Apparent ferti-

liser uptake, therefore, varied from 20 to 12%. P

content increased only slightly re¯ecting the decrease

in concentration observed as growth accelerated

(Table 6).

There was a curvilinear trend in nutrient content

across irrigation rates for most nutrients since the

increase in nutrient content across rates of irrigation

(Table 7) was less than the corresponding increase in

dry weight. The interaction between species and irri-

gation was rarely signi®cant (only for potassium in

bark and calcium in leaves).

4. Discussion

The results of this study are of great potential

interest to the discussions about future ®bre supply

and carbon sequestration for a number of reasons.

In the ®rst place, it is clear that with appropriate

inputs, such plantations of exotic species can greatly

exceed the productivity generally reported for native

tropical forest (Solberg et al., 1996). The two Euca-

lyptus had accumulated an estimated stem volume of

60 m3/ha at a rate of 20 m3/ha per year. Thus, less than

10% of the land would be impacted by the use of such

plantations than would be necessary if the same

requirements were to be satis®ed by native forest.

Gupta (1979), moreover, concluded that the economic

rate of return on irrigated plantations of eucalypt in

India was attractive by comparison with other invest-

ment opportunities. Hence, wood supplies could

potentially be satis®ed from a very reduced land area.

It should be noted, however, that in the farmland

surrounding this trial area, there is a variety of farm

sizes and economies. The richer farmers are already

utilising irrigation to produce crops. There is anecdo-

tal evidence that depth to water in village wells used by

poorer farmers has increased. If the technology dis-

cussed in this paper were to be adopted, it is likely, that

for capital availability reasons, the land utilised for

such plantations might tend to be the higher quality

land of the richer farmers for which there is currently

great resource competition and perhaps not the lower

Table 5

Nutrient content by species (kg/ha), averaged over fertiliser and

irrigation treatments

Species N

content

P

content

K

content

Ca

content

Mg

content

D. sissoo 72.4 2.5 18.0 56.4 14.2

E. camaldulensis 148.6 10.5 124.3 287.8 47.7

E. grandis 185.4 12.2 84.5 223.6 57.3

Significance of

difference

between species

*** *** *** *** ***

196 I. Hunter / Forest Ecology and Management 144 (2001) 189±199

quality more isolated land which tends to remain

covered in relict forest or be used for subsustence

farming. Additionally, as was pointed out in Hunter

et al. (1998), the use of fertiliser to increase produc-

tivity competes for economically scarce resources but

the use of irrigation competes for absolutely scarce

resources, by depleting groundwater, and may end up

seriously disadvantaging resource-poor farmers.

Table 6

Effect of fertiliser application, averaged across irrigation treatments, on N, P and K nutrient content (kg/ha) by biomass componenta (but

combining stemwood, stembark and branches)

Nutrient Fertiliser rate Species

D. sissoo E. camaldulensis E. grandis

Wood Leaf Wood Leaf Wood Leaf

N contentb 0 38.7 8.0 76.4 67.7 66.3 93.0

1 56.3 13.9 76.6 62.7 77.8 110.6

4 80.6 19.7 85.8 76.5 92.5 115.6

P contentc 0 0.9 0.4 6.6 3.6 7.0 5.49

1 1.7 0.8 6.5 3.2 6.3 6.09

4 2.3 1.3 6.4 4.6 6.2 5.75

K contentd 0 10.3 2.4 80.6 40.7 47.3 27.9

1 14.0 4.8 86.9 40.9 52.3 38.0

4 15.8 6.7 86.6 37.3 56.1 31.9

a Wood is composed of stemwood, stembark and branches.b Significance of fertiliser effect: stemwood (NS), stembark (***), branches (***), leaf (*).c Significance of fertiliser effect: stemwood (NS), stembark (NS), branches (NS), leaf (*).d Significance of fertiliser effect: stemwood (NS), stembark (NS), branches (NS), leaf (NS).

Table 7

Effect of irrigation on N, P and K content averaged across fertiliser treatments (kg/ha) by biomass componenta (but combining stemwood,

stembark and branches)

Nutrient Irrigation rate Species

D. sissoo E. camaldulensis E. grandis

Wood Leaf Wood Leaf Wood Leaf

N contentb 1 32.4 8.3 59.4 63.1 53.6 89.7

2 68.8 15.6 70.5 63.6 90.6 124.9

3 69.3 15.0 86.6 64.1 83.8 99.3

4 63.9 16.6 101.8 85.6 87.6 111.7

P contentc 1 1.1 0.6 4.4 3.6 4.5 5.1

2 1.8 0.9 6.0 3.7 6.4 6.5

3 2.1 0.9 8.8 3.7 7.0 4.9

4 1.6 1.0 6.8 4.3 8.0 6.6

K contentd 1 6.5 2.8 65.8 32.1 27.9 19.7

2 10.3 4.7 73.9 37.8 56.0 39.8

3 20.7 5.2 82.1 34.1 59.0 34.8

4 15.91 5.8 117.1 54.6 64.7 36.3

a Wood is composed of stemwood, stembark and branches.b Significance of irrigation effect: stemwood (NS), stembark (*), branches (NS), leaf (*).c Significance of irrigation effect: stemwood (NS), stembark (*), branches (NS), leaf (NS).d Significance of irrigation effect: stemwood (***), stembark (***), branches (*), leaf (*).

I. Hunter / Forest Ecology and Management 144 (2001) 189±199 197

It is clear also that in this study, the two exotic

species greatly out-produced the only native tree

species tried. Such a result may not hold for all native

species and all circumstances, although many trials in

India or lowland Nepal with D. sissoo have yielded

similar results (e.g. Nath et al., 1990; Neil, 1990). This

currently reported result might, however, produce an

impetus for activity which runs counter to most cur-

rent thinking in development assistance (Neil, 1989)

and amongst environmental groups Ð amongst whom

native species are greatly to be preferred (see, for

example, the Forest Stewardship Council's Principles,

unpublished 1994). The recently negotiated (in the

Helsinki Process) Criteria and Indicators for Sustain-

able Forest Management at the Forest Management

Unit level also contain a slight prejudice against the

use of exotic species for afforestation.

It is interesting that the productivity of E. camal-

dulensis and E. grandis, coming as they do from very

different environments and with different ecological

conditions, should be similar when fertilised and

irrigated. The use of ¯ooded gum as a main plantation

species in these conditions would, however, be the

riskier since the variability of survival both between

and within unirrigated plots was much greater for this

species than for Red River gum. Hence, if for any

reason, irrigation failed, the performance of ¯ooded

gum would probably suffer much more and in unpre-

dictable ways.

The rapid growth, strong nutrient uptake and fre-

quent harvesting pose potential problems for contin-

ued and sustainable productivity.

The Eucalypt trees had grown in 3 years, with

irrigation and fertiliser to a size similar to that which

Mysore hybrid (the locally used Eucalypt hybrid)

attains in 8 years (see, for example, Sharma, 1978)

and were judged to be of harvestable size by local

foresters. It is current silvicultural practice to harvest

only the log after debarking. However, local people

sometimes remove the other components from the site

subsequently. Table 8 shows how marked the effect on

nutrient cycling of different residue handling techni-

ques can be. The very high proportion of the total

nutrient content in bark, branches and leaves, could, if

allowed to return to the site assist in maintaining site

productivity in the longer term.

Acknowledgements

The trial was meticulously maintained by Karna-

taka Forest Department Staff and achieved its objec-

tives. The author is grateful to the Karnataka Forest

Department for allowing him to carry out this work on

a trial which they maintained. The author is also

grateful to Mr. P. Adlard and Dr. I. Calder for allowing

this activity in a trial which they had been instrumental

in establishing.

The author gratefully acknowledges the contribu-

tion of Mr. Andrew Smith, Dr. Prasanna and Mr. Javed

Mumtaz to the ®eldwork and Mr. John Sherrington

University of Greenwich for advise on statistical

procedures. Chemical analysis of plant material was

carried out by NRM Laboratories, Bracknell. The

author gratefully acknowledges the funding provided

by the UK ODA Forestry Research Programme admi-

nistered by the Oxford Forestry Institute.

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N, P, K content in the two Eucalyptus by biomass component (kg/ha). Averaged across fertiliser and irrigation treatments

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