Ailanthus triphysa

at different density and fertiliser levels in Kerala,India: tree growth, light transmittance and understorey ginger yield

B. Mohan Kumar1, Joseph Thomas1 & Richard F. Fisher2

1

College of Forestry, Kerala Agricultural University, KAU P.O., Thrissur, Kerala 680 656, India, E-mail: bm.kumar@vsnl.com; 2 Temple-Inland Forest, P.O. Drawer N, 303 S. Temple Drive, Diboll,TX 75941-0814, USA, E-mail: dfisher@templeinland.com

Received 11 January 2000; accepted in revised form 28 October 2000

Key words: leaf area index, multipurpose trees, photosynthetically active radiation, soil fertility,stocking, Zingiber officinale

Abstract

Ailanthus triphysa (Family – Simaroubaceae) growth is known to vary in response to different stockingand fertiliser levels. Understorey productivity related to these differences remain elusive, yet areimportant for optimising the combined production of tree and crop components. A split plot experimentto evaluate the effect of different stocking levels and fertiliser regimes on ailanthus growth, stand leafarea index (LAI) and understorey PAR (photosynthetically active radiation) transmittance was started atVellanikkara, India in June 1991. Main plot treatments included four densities (3,333, 2,500, 1,660 and1,111 trees ha–1), replicated thrice. Four fertiliser levels (0:0:0, 50:25:25, 100:50:50 and 150:75:75 kgN:P2O5:K2O ha–1) formed the sub plot treatments. Ginger (Zingiber officinale) was planted as an under-storey crop in May 1994 with contiguous treeless control plots. Soil nutrient availability before and afterginger was assessed. Higher densities stimulated ailanthus growth modestly, while fertiliser response oftree and ginger was inconsistent. PAR transmittance below the canopy was related to tree density, LAIand time of measurement. Midday PAR flux having low standard deviations is ideal for evaluating canopyeffects on understorey light availability. Ginger in the interspaces exhibited better growth compared tosole crop. Highest rhizome yield was observed in the 2,500 trees ha–1 stocking level, which is optimumfor below five year-old ailanthus stands on good sites. It represents 52% mean daily PAR flux or 73%midday PAR flux. Ailanthus+ginger combinations improved the site nutrient capital when ginger wasadequately fertilised, despite treeless controls having relatively higher initial soil nutrient availability.

Agroforestry Systems 52: 133–144, 2001. 2001 Kluwer Academic Publishers. Printed in the Netherlands.

Introduction

A wide spectrum of trees, usually described asmultipurpose trees (MPTs), is used in tropicalplantation programmes. Important attributes ofMPTs include rapid juvenile growth, efficient drymatter production in terms of water and nutrientinputs, crown characteristics to maximise inter-ception of solar radiation and ease of regenera-tion (Kumar et al., 1998). Ailanthus (Ailanthustriphysa (Dennst.) Alston, Family: Simarou-

baceae) is a prominent MPT in the traditional landuse systems of Kerala, India (Kumar et al., 1994).It occurs in the natural evergreen forests of theWestern Ghats too (PID, 1948). The very light andsoft wood is utilised for making packing cases,catamarans, toys and drums. Most important useof ailanthus wood, however, is in the matchindustry. The tree also yields a highly viscousaromatic resin that is widely used as incense andin indigenous medicines.

Although reports on the growth and biomass

production of plantations abound, there are rela-tively few reports of experimental manipulation oftree density and/or fertiliser levels in tropicalspecies. In particular there have been very fewfertiliser and population density field experimentswith major plantation species in India. We are notaware of any studies directly relating to ailanthusgrowth and yield under varying stand density andfertiliser regimes.

Many field/tree crops are also grown in asso-ciation with ailanthus. Owing to its compactcrown, moderate root spread and deep rootingtendency, ailanthus is thought to be less competi-tive with associated crops (Mathew et al., 1992;Kumar et al., 1999). Ginger (Zingiber officinaleRoscoe, Family: Zingiberaceae), is an importantspice crop in this regard. Silvicultural manipula-tion of ailanthus stands, however, is likely tochange understorey productivity through theireffects on light regimes or belowground resourceavailability. However, individual crop responsesto ailanthus overstorey have not received muchattention. Despite the recognised importance ofstand leaf area index (LAI) as a determinant ofunderstorey productivity, information on ailanthusLAI and light transmittance is limited.

We postulated that the flux density of photo-synthetically active radiation (PAR) in the ailan-thus understorey is inversely related to LAI andstocking. Tree growth rates and stocking levelsbeing major determinants of LAI, high stockingand fertilisation may stimulate faster canopyclosure. Although this hypothesis has been testedfor temperate species (Gleeson and Tilman, 1990),it remains untested in tropical agroforestry. In thiscontext, we hypothesised that stand dynamicswould differ from other environments and thatunderstorey light conditions could also be uniquebecause of differences in tree architecture, standdensity, LAI and age structure.

Ginger is a shade-loving plant (KAU, 1991),however, both excessive and sub-optimal shadelevels are considered harmful to its growth.Nonetheless, only limited efforts were made toevaluate the effects of varying shade levels onginger productivity and/or optimise shade treedensity in integrated ginger-multipurpose treeproduction systems (Jaswal et al., 1993). There-fore, in the present study we evaluated the influ-ence of different stand density and fertiliser

regimes on ailanthus growth, LAI and understoreyPAR transmittance. We also compared growth,yield and quality of ginger grown with ailanthusat varying density and fertiliser levels.

In addition, fast growing trees may activelywithdraw soil nutrient reserves, especially duringthe early phase of growth (Kumar et al., 1998).After canopy closure, however, forest plantationsmay act as self-nourishing systems throughnutrient cycling. Associated crops, therefore, arelikely to suffer nutrient competition early. Data oninterspecific competition between ginger andailanthus based on the present experimental set upare presented elsewhere (Thomas et al., 1998).Fertilisers supplement the nutrient requirements ofactively growing trees and associated crops.However, site fertility is a major determinant offertiliser response. We, therefore, investigated soilnutrient availability at varying ailanthus stockinglevels and the impact of ginger cultivation on soilnutrient reserves in ailanthus+ginger systems.

Materials and methods

Study site and treatments

The study was conducted at Vellanikkara, Thrissurdistrict, Kerala (10°13

′ N latitude and 76°13′ Elongitude and at an elevation of 40.29 m above sealevel). Vellanikkara has a mean annual rainfall of2,670 mm, most of which is received during thesouth-west monsoon (June to August). The meanmaximum temperature ranges from 29.1 °C (July)to 36 °C (May) and the mean minimum tempera-ture varies from 21.9 °C (January) to 25 °C (May).Soil of the experimental site is an Ultisol (TypicPlinthustult – Vellanikkara series midland laterite– Ustic moisture regimes (dry period – Februaryto May) and Isohyperthermic temperatureregimes). The soil physico-chemical properties atthe beginning of the experiment were as follows:pH: 5.74, total N: 0.13%, available P (Bray):14.10 mg g–1, exchangeable K: 44.17 mg g–1 andorganic C: 1.28%.

A split plot experiment on ailanthus wasinitiated in June 1991, with the following treat-ments. Main plot (95 m × 10 m) treatmentsincluded four population densities (D1 – 3,333trees ha–1: 3 × 1 m spacing; D2 – 2,500 trees ha–1:

134

2 × 2 m spacing; D3 – 1,660 trees ha–1: 3 × 2 mspacing; and D4 – 1,111 trees ha–1: 3 × 3 mspacing), replicated thrice. Four fertiliser levels(F1 – 0:0:0; F2 – 50:25:25; F3 – 100:50:50 and F4

– 150:75:75 kg N, P2O5 and K2O ha–1) formed thesub plot treatments. Each subplot was 20 × 10 m.Five-meter wide unplanted buffer strips separatedthe plots. About three-month old containerisedplanting stock was used for establishing the trial.The plots were manually weeded twice a year andwatered once a week during the dry season fol-lowing planting. Survival was uniformly good(over 95% in 1994).

Fertilisers in the form of Urea (46% N),Mussorie rock phosphate (23–24% P2O5) andMuriate of potash (58% K2O) were applied inbasins (50 cm radius and 10–12 cm deep) dugaround each tree in August 1992 and September1993, immediately after the heavy monsoonseason. The fertilisers were mixed with soil in thebasin and covered with a thin layer of earth.

Ginger experiment

The experimental work reported here relates to thethird year of the trial when ginger was raised asan understorey crop. Ginger was planted in May1994, following a package of recommendedpractices (KAU, 1993), on 9 × 1 m beds betweenrows of ailanthus. There were six beds each in allplots. Cultivar used was Kuruppampady, a dryginger type known for its tolerance to shade,disease and pest incidence. Details of culturalaspects are summarised in Thomas et al. (1998).Three monospecific ginger plots having six bedseach were established in the contiguous area forcomparative purposes. It, however, did not formpart of the replicated trial, as the plots were notrandomised along with the remaining plots.

Sampling ginger plants

To evaluate ginger growth, the crop was harvestedat 55, 116 and 211 days after planting. At everysampling, an area of 1 m2 each was selected fromthree random beds per plot. All ginger clumps inthe selected quadrats were uprooted and observa-tions on tiller height, number of tillers per plantand number of leaves per plant recorded. Leavesof all uprooted clumps were separated, and their

area measured using an automatic Leaf Area Meter(LI 3100, LI COR Inc, Lincoln, Nebraska) at 55and 116 days after planting, for calculating gingerLAI. The leaves, culms, roots, residual rhizomes(planted) and new rhizomes were cleaned and theirfresh weights determined, bed-wise. They wereoven-dried at 70 °C till constant weights andexpressed as dry weights on a per hectare basis.However, on the 55th day, the below groundportions were not fractionated into roots andresidual rhizomes and on the 211th day of obser-vations, no residual rhizomes were detected. Alsono leaf area measurements were taken on the 211thday, as most of the leaves were dried up at thisstage either partly or fully. The final ginger cropwas harvested 234 days after planting. Threereplicates of 1 m2 area each was selected from thethree remaining undisturbed beds per plot. Freshand dry weights of mature rhizomes were recordedafter cleaning.

Quality attributes of ginger

Ground samples of dried mature rhizomes wereanalysed for essential oil and oleoresin contents.Twenty gram samples were mixed with equalamount of (NH4)2SO4 (non-frothing agent) and 200mL distilled water in a round bottom flask and theessential oil extracted using Clavenger’s distilla-tion still (AOAC, 1975). Ginger oleoresin wasestimated by solvent extraction (5 g groundsamples) in a Soxhlet extractor using petroleumether (b.p. 40°–60°).

Observations on ailanthus

Height and diameter at breast height (DBH) of alltrees (excluding those on the border) wererecorded on May 28, 1994 and April 19, 1995.These observations roughly correspond to threeand four years of ailanthus age (before and afterginger experimentation respectively). We deter-mined crown widths of trees (April 1995) byprojecting the crown on the ground, in two per-pendicular directions (NS and EW) and computingtheir means.

135

Stand Leaf Area Index

We estimated overstorey stand leaf area indexfrom a height of about 1.5 m using a Plant CanopyAnalyser (LAI 2000, LI-COR Inc, Lincoln,Nebraska) in all plots (48). This instruments isdesigned to estimate LAI of plant canopies indi-rectly from measurements of radiation above andbelow the canopy, based on a theoretical relation-ship between leaf area and canopy transmittance(Stenberg et al., 1994). Strachan and McCaughey(1996) adjudged this method appropriate forcharacterising the spatial and vertical canopystructure of forest stands, as it spatially integratesthe overstorey and gives an approximation ofsingle-sided LAI. A single measurement of LAIwas accomplished by taking the LAI 2000 unitoutside the plot (in the open) to record an ‘abovecanopy reading’ of sky brightness and thensampling ten random locations in the centralca. 15 × 6 m region of each plot (beneath canopyreadings). Care was taken to ensure that the unitwas facing the same direction both outside andinside the stand. A sunlit canopy was avoided bytaking measurements just after sunrise and justbefore sunset when the solar elevation is low (on16th and 18th of March 1995). A view restrictorof 90° was used in all measurements to preventdirect sunlight from reaching the sensor and at thesame time to occlude the measuring person fromthe area of view.

PAR measurements

We made continuous understorey measurements(6 a.m. to 6 p.m.) of PAR in all treatment combi-nations in the first replication (16 plots) fromMarch 17 to April 27, 1995 using a Line QuantumSensor (LI 191SA, LI-COR Inc, Lincoln,Nebraska). Other replications were excluded, asthe time required to complete this measurementwas enormous. Within each plot, the line quantumsensor was installed on small wooden platforms ina random tree alley at 50 cm or 150 cm above theground on two consecutive days. Plot borders andlocations where ailanthus suffered an infrequentmortality were explicitly avoided while selectingtree alleys for PAR measurements. The line of thesensor was oriented toward magnetic south as treerows were oriented east-west. A battery powered

data logger (LI 1000, LI-COR Inc) integrated themean flux of PAR at hourly intervals. PARincident above the canopy of each plot wassimultaneously recorded by the data logger witha Point Quantum Sensor (LI 190SA, LI-COR Inc)mounted on a 10 m pole rising above the canopy.PAR above canopy ranged from 18 µ moles s–1 m–2

(6–7 a.m.) to 2,054 µ moles s–1 m–2 (12 noon to1 p.m.). Corresponding understorey PAR levelswere 9 µ moles s–1 m–2 and 1,981 µ moles s–1 m–2.The understorey PAR flux was converted to PARtransmittance – the ratio of PAR below the canopyto PAR incident on the top of the canopy. Theplant canopy analyser also uses a similar approach,but its optical sensors comprising five detectorsare arranged in concentric rings that measureradiation from selected sections of the sky(Stenberg et al., 1994). Moreover, for continuousmeasurement of PAR flux, to characterisetemporal variations, the canopy analyser isprobably ill suited.

Soil chemical analyses

Soil samples were collected (before and after theginger crop) from the 0–15 cm layer at threerandom points between tree rows in differenttreatments. The samples were air-dried and groundto pass through a 2 mm sieve. Triplicate sampleswere analysed for soil pH using an aqueoussuspension of soil (1:2 ratio), organic C byWalkley and Black method and total N by micro-Kjeldahl method. Available P was extracted usingBray–1 extractant and determined colorimetrically(chloromolybdic acid blue colour method) withstannous chloride as the reducing agent.Exchangeable K was estimated flame-photomet-rically using 1N neutral CH3COONH4 as theextractant.

Statistical analyses

The data on growth of ailanthus and ginger wereanalysed following the analysis of variance tech-nique (ANOVA) for split plot experiments inMSTAT. Differences between monospecific andmixed ginger situations were evaluated usingpaired ‘t’ test. PAR transmittance was regressedon ailanthus LAI and ginger yield on understoreyPAR transmittance.

136

Results and discussion

Ailanthus growth as influenced by tree population density and fertiliser regimes

A comparison of the tree growth data shows thatmean annual increment for tree height ranged from0.72 to 0.85 m yr–1 and for DBH from 1.28 to 1.60cm yr–1 at four years of age. Although populationdensity and nutrient availability are recognised askey factors that influence tree growth, we did notobserve the expected impact of this on ailanthusgrowth till four years of age, except on stand LAI(Table 1). Mean crown width was below 1.70 mat four years of age indicating that the stands areprobably below full site occupancy/crown closure(sensu Long and Smith, 1984). Such non-signifi-cant differences in tree growth as a function of treespacing/density has been reported previously also(Karim and Savill, 1991). However, LAI estimateincreased (P > 0.01) as tree population densityincreased implying the potential of high densitystands for early canopy closure.

Although stand leaf area index increased

modestly at the highest level of NPK (Table 1),the differences were not statistically significant.Response to fertiliser application is likely whenthe soil is deficient in nutrients. As discussed inthe ensuing section, soil nutrient availability wasmoderate to high at our experimental site. Highleaching losses of applied fertilisers are probablein the wet tropics. In addition, weeds in theinterspaces may compete for nutrients, as the treesdid not reach canopy closure. Hence fertilisingjuvenile ailanthus stands on good sites in the wettropics probably makes little sense.

Understorey PAR transmittance

The sequence of graphs in Figure 1 illustratesdiurnal variations in under canopy PAR transmit-tance of four ailanthus densities at 150 cm abovethe ground. PAR flux ranged from 26 to 96% offull light depending on the stocking level and timeof measurement. Temporal variations make itdifficult to characterise understorey light regimesin MPT stands, which is required for explainingvariations in growth and yield of associated crops.

137

Table 1. Effect of population density and fertiliser levels on growth of four year-old ailanthus and the relative proportion ofphotosynthetically active radiation (PAR) available below ailanthus canopy saplings in Kerala, India.

Treatments Mean ht. DBH Crown width Leaf area index PAR transmittance (m) (cm) (cm)

� (%)

Density (trees ha–1)3333 3.41 5.92 1.55 < 3.93 a 40 a2500 3.41 6.23 1.61 < 3.17 b 52 b1660 3.19 6.42 1.69 < 2.71 b 54 b1111 2.87 5.14 1.58 < 1.96 c 75 c

F test NS NS NS < 0.01 < 0.01

Fertiliser levels (N : P2O5 : K2O kg ha–1 yr–1)

0:0:0 3.03 5.50 1.59 < 2.94 5050:25:25 3.43 6.30 1.58 < 2.89 61100:50:50 3.36 6.24 1.72 < 2.88 56150:75:75 3.04 5.66 1.55 < 3.07 54

F test NS NS NS < NS iNS

Density × fertiliser interaction

F test NS NS NS < NS iNS

DBH = diameter at breast height (1.37 m); NS = not significant.� estimated using LI-COR Plant Canopy Analyser.PAR represents daily means over the period from 6 a.m. to 6 p.m. measured during the period from 17 March 1995 to 27 April1995 at 150 cm above the ground.Means followed by different superscripts are significantly different in the ANOVA.

Brown and Parker (1994) also reported similarconcerns. Having lower standard deviations(Figure 1), midday PAR flux is probably the leastvariable within a density level. Hence PARtransmittance between 1,200–1,300 h provides abetter approximation of mean daily PAR flux, andmust be used in preference to instantaneous PARmeasurements in light interception studies. Ourdata also show that midday (1,200–1,300 h) PARflux into the understorey was consistently thehighest (range: 73–96% at 150 cm and 67–91%at 50 cm above ground). It is expected thatcanopies would block progressively less radiationas the sun moves higher in the sky where pathlength through the canopy is shorter.

As expected, our structural measurements,specifically stand LAI estimated using the plantcanopy analyser (Table 1) were consistent with thePAR transmittance data presented in Figure 1.Mean LAI ranged from 1.96 to 3.93 and peakedin the high-density stand (3,333 trees per ha–1).Midday PAR flux followed a negative exponentialrelationship with increasing LAI (Figure 2).Higher light interception by leaves may explainthis exponential decrease in light intensity withincreasing canopy depth/LAI. Canopy architectureand dimensions are also cardinal determinants ofunderstorey light regimes. Kumar et al. (2000)

138

Figure 1. Diurnal patterns of PAR transmittance in fouryear-old ailanthus stands of different densities at 150 cmabove ground in Kerala, India (A – 3333 trees ha–1 B – 2500trees ha–1 C – 1660 trees ha–1 D – 1111 trees ha–1). Each barrepresents an hourly mean pooled over four fertiliser levels,and the corresponding standard error. Values on X-axisrepresent the upper end of the I h time interval.

Figure 2. Relationship between PAR transmittance at noon(1,200–1,300 h) and stand leaf area index measured usingplant canopy analyser (see methods section) in four year-oldailanthus stands in Kerala, India

reported that Acacia auriculiformis characterisedby a dense/deep crown intercepted more lightwhile Casuarina equisetifolia with its needle-likecladophylls and ailanthus owing to its small crownfacilitated greater light penetration into the under-storey.

Fertiliser levels exerted only a modest influenceon understorey PAR flux. Although we expecteda progressive reduction in understorey availabilitywith increasing fertiliser levels such a trend wasnot evident. Studies with other trees show a pro-nounced effect of nitrogen in increasing the areaand/or mass of foliage (Heilman and Fu-Guang,1994). These workers found that N-fertilisedcanopies captured more light. Effects of othernutrient elements on leaf area expansion or foliarbiomass are, perhaps less clearly understood.

Ginger growth attributes

We observed a favourable effect of higher treedensities on shoot growth and leaf number ofginger at 211 days after sowing (Table 2). Similartrends were discernible at other observation datestoo (data not shown). Since ginger is a shade

loving plant, such a consistently favourableeffect of higher densities on vegetative growth isexpected and corroboratory results were obtainedby Jaswal et al. (1993).

Ginger LAI showed statistically significantvariations at 116 days after planting (Table 2) andat 55 days. Among the ailanthus stocking levels,highest ginger LAI was either in 3,333 trees ha–1

(55 days) or in 2,500 trees ha–1 stands (116 days).High LAI mirrors an increase in tiller number orleaf size or both. Overall ginger leaf production,leaf retention and leaf size was greater undershaded conditions. Ginger grown in associationwith higher tree densities thus remained greenerfor a longer period, implying higher leaf areaduration and greater potential productivity.

Chemical fertilisers applied to the tree compo-nent (during two previous years) did not show anyconsistent influence on vegetative growth of theassociated ginger crop. Fertilised ailanthus stands(150:75:75 N:P2O5:K2O kg ha–1 yr–1) seemed tofavour ginger leaf development and retention(Table 2). But data on tiller number and leaves pertiller, showed no consistent pattern.

139

Table 2. Biometric observations on ginger intercropped in a three year-old ailanthus plantation (211 days), ginger leaf area index(116 days) and rhizome yield (dry) at final harvest (234 days) in Kerala, India.

Treatment Mean tiller Number of Number of Leaf area Rhizome yieldheight (cm) tillers/clump leaves/clump index (Mg ha–1)

Density (trees ha–1)3333 52.9 a** < 4.7 47.6 a** < 1.96 a < 3.7 a2500 47.3 b** < 3.7 35.6 b** < 2.73 b** < 5.0 b*1660 46.6 b** < 4.2 38.1 b** < 2.53 ab** < 3.6 a1111 44.0 b** < 4.4 34.4 b* < 1.38 c < 4.0 a

F test < 0.05 < NS < 0.05 < 0.01 < 0.01

Sole ginger 28.1 < 4.6 20.0 < 1.38 < 3.5

Fertiliser levels (N:P2O5:K2O kg ha–1 yr–1)

0:0:0 49.0 < 4.6 a 45.2 a** < 1.69 a < 3.950:25:25 49.2 < 3.7 b 34.6 b* < 2.17 b* < 4.4100:50:50 45.5 < 4.7 a 40.9 ab** < 2.12 b* < 4.1150:75:75 47.0 < 4.0 b 35.0 b** < 2.61 c** < 3.9

F test NS < 0.01 < 0.05 < 0.01 < NS

Density × fertiliser interactionF test < 0.05 < 0.01 < 0.05 < 0.05 < NS

* Paired ‘t’ values comparing treatment with sole ginger, significant at 5% level and ** significant at 1% level. Means followed by different superscripts are significantly different in the ANOVA.

Ginger dry matter production

Above ground dry matter accumulation followeda curvilinear pattern with time. Maximum shootdry weight was observed at four months afterplanting (data not shown). Senescence of olderleaves may probably account for the reduction inshoot dry weight at the final stage of observation.As for below ground biomass yield, it essentiallyfollowed an exponential trend with time.

Monospecific ginger plots had significantlylower above and below ground biomass yieldsthan ailanthus+ginger combinations (Figure 3).With increasing ailanthus density, above groundginger biomass increased modestly. Rhizomeyields were significantly greater at 1,111 and 2,500trees ha–1 than at other density levels. The precisedensity at which such favourable effects can beobserved is also a function of tree age. The presentresults, nevertheless, suggest that at three to fouryears of age, 2,500 ailanthus trees ha–1 is appro-priate. Being a substantially lower stocking level,low-density stand (1,111 trees ha–1) is unlikely tobe acceptable, if optimisation of the combinedproduction of tree and field crop is of utmostimportance.

Overall, fertiliser application to the tree cropcomponent did not exert any pronounced effect onbiomass yield of ginger at 211 days (Figure 3).

Although density × fertiliser interaction onrhizome yield was significant no clear trend wasdiscernible. Our data suggest that fertilisersapplied to the tree crop component (three to fouryears of age) of an agrisilviculture system, maynot directly benefit the associated ginger crop,owing to its ‘restricted root system’ (Thomas etal., 1998).

Final yield of ginger

Rhizome yield in ailanthus+ginger combinationwas consistently higher than the sole crop, despitemodest differences with 3,333 and 1,660 treesha–1. Highest fresh and dry rhizome yields,significantly superior to other density levels, wasobtained in the 2,500 trees ha–1 treatment. It wasapproximately 40 per cent higher than the solecrop (Table 2). Dry weight differences at 211 daysafter sowing (Figure 3) followed a similar trendalbeit the 2,500 and 1,111 trees ha–1 treatmentswere statistically at par.

Higher rhizome yield in ailanthus+gingercombinations can be explained based on theshade-loving nature of the crop. When grown inassociation with a tree crop component, especiallyat higher levels of tree stocking, ginger vegeta-tive growth, leaf area development (Table 2) andfoliar nutrient levels, particularly N (data not

140

Figure 3. Above and below ground biomass production of ginger intercropped in a three year-old ailanthus plantation in Kerala,India as influenced by tree density (trees ha–1) and fertiliser doses (N:P2O5:K2O kg ha–1 yr–1 applied to ailanthus, see methodssection for details) at 211 days after planting (Paired ‘t’ values comparing treatment with sole ginger (treeless control) signifi-cant at 5% level (*) and 1% level (**); Bars with different letters are significantly different at 5% level in ANOVA).

given) were favoured. Higher photosyntheticefficiency at higher tissue nutrient levels mayexplain the observed yield increase.

Ginger yields topped when midday (peak) PARflux was 73% of full light at 150 cm above theground. The corresponding figures for mean dailyunderstorey PAR flux was 52%. Linear modelslinking midday PAR availability and rhizomeyield, however, produced weak relationships(Figure 4). Earlier workers, using either inanimateshade materials or field crops such maize, peas orokra as shade providers have reported widelyvarying shade requirements for ginger rangingfrom 25% (Jayachandran et al., 1991) to 66% offull sunlight (Wilson and Ovid, 1993). Presumablythere are variety differences in the shade require-ment of ginger. Alternately, the instantaneousmeasurements used to characterise light intensityin these studies may be inadequate in view of thetemporal and spatial variations in below canopylight environments. We, therefore, confirm that amean daily PAR transmittance of 50–55% fulllight (Table 2) or a peak (midday) transmittanceof 67–73% (Figure 4), corresponding to a treedensity of 2500 trees ha–1, may be optimal for theginger cultivar ‘Kuruppampady’.

Present investigations have been conductedbetween three and four years of ailanthus age. Atree density of 2500 trees ha–1, though consideredadequate at this stage, may cause more intenseshading in older stands. Nonetheless, it probablyrepresents the best trade-off for ailanthus standsbelow five years, as it ensures a reasonable treepopulation/wood yield and understorey crop yield.

Quality attributes

Essential oil and oleoresin contents of ginger aretwo quality parameters for which the ginger cropis valued. Ailanthus densities and fertiliserregimes did not seem to influence these parame-ters. Essential oil contents ranged from 0.91 to0.98% and oleoresin from 2.5 to 3.98% of dryrhizome. Sole crop of ginger, however, representedthe highest essential oil and oleoresin concentra-tions, despite having the lowest rhizome yields.Contrary to expectations, 2,500 trees ha–1 had thelowest values in this respect, albeit having toppedin rhizome yield. Although ANOVA showed non-significant variations in this respect, paired ‘t’tests comparing monospecific ginger plots withdensity and fertiliser treatments were significant.

141

Figure 4. Ginger yield as influenced by under canopy midday (1200–1300h) PAR transmittance at 150 cm above the ground ina four year-old ailanthus plantation in Kerala, India.

Perhaps there is an inverse relationship betweenbiomass production and the chemical quality para-meters. Varughese (1989) reported corroboratoryresults, although some workers (Babu andJayachandran, 1994) observed that ginger grownunder shade may have higher essential oil andoleoresin concentrations.

Changes in soil fertility

An appraisal of the pre-ginger soil data suggeststhat three years of ailanthus growth resulted in anoticeable reduction in site nutrient capital(Table 3). In general treeless plots had highervalues for mineral elements and organic C thanailanthus plots. Furthermore, soil N, available Kand organic C concentrations were significantlylower in the high density stand (3,333 trees ha–1)than other stocking levels and/or treeless control.Reduction in soil nutrient levels particularly atpeak densities can be explained based on acceler-ated nutrient removal by trees. Ailanthus being afast growing tree may absorb nutrients rapidly,

especially during the initial years. The magnitudeof nutrient extraction is presumably a function oftree density. However, 2,500 trees ha–1 treatmentrevealed high values for soil N, available K andorganic C. Implicit in this is perhaps a morecomplex relationship between stand density andthe magnitude of nutrient removal. Reduction insoil pH can be rationalised based on litter decom-position and the consequent release of organicacids (Jamaludheen and Kumar, 1999). Denserstands probably produce more litter and areexpected to have relatively lower pH values.Fertiliser application to ailanthus apparentlymodified the soil P, K and organic C levels, butno consistent pattern appeared. High doses ofchemical fertilisers (150:75:75 N:P2O5:K2O kgha–1 yr–1) also increased the soil organic C levels,which is intriguing.

A comparison of the pre- and post-ginger (standage: three and four years) soil data indicate thatraising ginger in the interspaces of ailanthus mayenrich soil fertility (Table 3). This, however, con-flicts with the trend from treeless control plots

142

Table 3. Effect of tree population density and fertiliser levels on soil chemical properties before and after the ginger experimentin Kerala, India.

Treatments Pre-ginger (ca 3 years of age) Post ginger (ca 4 years of age)

Total Available Exch. OC Soil Total Available Exch. OC Soil N P K pH N P K pH(%) (mg g–1) (mg g–1) (%) (%) (mg g–1) (mg g–1) (%)

Density (trees ha–1)3333 < 0.11 a 10.4 61.3 a** < 1.52 ab** < 5.77 a** 0.14 11.13 a 108.75 a < 1.86 a < 6.03 a2500 < 0.15 b 10.4 85.4 b** < 1.71 b** < 5.76 a** 0.15 8.42 b 095.21 b** < 2.05 b < 6.00 b1660 < 0.13 c 12.0 76.5 c* < 1.48 a** < 5.87 b* 0.14 10.21 a 088.96 b** < 1.74 a < 6.00 b1111 < 0.15 b 11.4 70.8 d** < 2.14 c** < 5.84 c** 0.15 11.22 a 092.92 b** < 2.35 c < 5.97 c

F test < 0.01 NS < 0.01 < 0.01 < 0.01 NS < 0.05 i< 0.01 < 0.01 < 0.01

Sole ginger < 0.15 13.43 79.17 < 2.82 < 5.90 0.15 10.53 110.0 < 2.61 < 6.04

Fertiliser levels (N:P2O5:K2O kg ha–1 yr–1)0:0:0 < 0.13 14.1 a 44.2 a** < 1.28 a** < 5.74 a** 0.15 10.45 078.75 a** < 1.67 a** < 6.00 a50:25:25 < 0.13 10.4 bc* 93.30 b** < 1.84 b** < 5.86 b** 0.15 9.91 107.71 b < 2.27 b < 6.05 b100:50:50 < 0.13 8.8 b** 79.0 c < 1.85 b** < 5.84 c** 0.14 9.62 097.08 c** < 1.92 c* < 5.95 c150:75:75 < 0.14 10.8 c* 77.5 c < 1.88 b** < 5.80 d** 0.14 11.02 102.29 d** < 2.13 a* < 6.00 a

F test < NS < 0.01 < 0.01 < 0.01 < 0.01 NS NS i< 0.01 < 0.01 < 0.01

Density × fertiliser interaction

F test < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 NS < 0.01 i< 0.01 < 0.01 < 0.01

Means followed by different superscripts are significantly different in the ANOVA.* Paired ’t’ values comparing treatment with sole ginger, significant at 5% level and ** significant at 1% level.exch = exchangeable; OC = organic carbon; NS = not significant.

where no such enrichment was discernible. Greenmanure and/or fertiliser additions associated withginger cultivation can potentially improve sitefertility. However, presence or absence of theailanthus canopy may decide how long such aresidual effect may persist. Exposure may hastensoil organic matter decomposition and hence undera tree canopy the elevated nutrient and organicmatter status lasts longer.

Conclusions

Tree density exerted only a modest influence onailanthus growth during the 36–48 months of age.Owing to higher LAI, high-density stands had sub-stantially lower understorey PAR flux than lowdensity stands. Other determinants of understoreyPAR flux include time of measurement and canopyarchitecture. Our data suggest that midday PARflux being less variable is convenient for evalu-ating canopy effects on understorey light avail-ability. Ginger performed better when middayPAR flux was between 67–73% of full sunlight.This in turn corresponds to a population densityof approximately 2,500 trees ha–1 at four years ofage on good sites. Optimal shade tree densitybeing a function of age and site quality, may belower in older stands and/or higher on poor sites.Stand density management in ailanthus+gingercombinations should, therefore, attempt main-taining a peak midday PAR flux of 67–73% or amean daily PAR flux of 52–54% in the under-storey for optimising ginger productivity. Shade-grown ginger remained greener and therefore,physiologically active for a longer time, despitehaving relatively lower essential oil and oleoresinconcentrations compared to monospecific ginger.

Leaching losses and weed competition probablyreduced fertiliser use efficiency. Hence fertilisingjuvenile ailanthus stands may be restricted to poorsites. Agronomic management to enhance fertiliseruse efficiency including weed control is, therefore,critical. Fertilisers applied to ailanthus stands areunlikely to benefit ginger grown in association.Three years of ailanthus growth resulted in anoticeable reduction in soil nutrient and organiccarbon contents. Raising ginger in the interspacesof ailanthus following recommended practices (seeThomas et al., 1998), however, brought about a

slight improvement in the nutrient capital of thesite, perhaps due to fertiliser and green manureapplication to the ginger crop.

Acknowledgements

This research has been financed in part by a grantmade by the United State Department ofAgriculture under Co-operative AgriculturalResearch Program US-India Fund. Field andlaboratory facilities provided by the AssociateDean, College of Forestry, Kerala AgriculturalUniversity, Vellanikkara, are gratefully acknowl-edged.

References

AOAC (1975) Official Methods of Analysis of the Associationof Official Analytical Chemists, Washington, pp 554–555

Babu P and Jayachandran BK (1994) The quality of ginger(Zingiber officinale R.) as influenced by shade and mulch.South Ind Hort 42(3): 215–218

Brown MJ and Parker GG (1994) Canopy light transmittancein a chronosequence of mixed-species deciduous forests.Can J For Res 24: 1694–1703

Gleeson SK and Tilman D (1990) Allocation and the tran-sient dynamics of succession on poor soils. Ecology 71:144–1155

Heilman PE and Fu-Guang X (1994) Effects of nitrogenfertilisation on leaf area, light interception and productivityof short rotation Populus trichocarpa × Populus deltoideshybrids. Can J For Res 24: 166–173

Jaswal SC, Mishra VK and Verma KS (1993) Intercroppingginger and turmeric with poplar (Populus deltoides G-3Marsh). Agrofor Syst 22: 111–117

Jayachandran BK, Meerabai M, Salam MA, Mammen MK andMathew PK (1991) Performance of ginger under shade andopen conditions. Indian Cocoa, Arecanut and Spices J XV(2): 40–41

Jamaludheen V and Kumar BM (1999) Litter of nine multi-purpose trees in Kerala, India-variations in the amount,quality, decay rates and release of nutrients. For EcolManage 115: 1–11

KAU (1991) Final Research Report. ICAR Adhoc Scheme onShade Studies in Coconut based Intercropping Situations,Kerala Agricultural University, Vellanikkara (unpublished)

KAU (1993) Package of practices recommendations – Crops93. Directorate of Extension, Kerala AgriculturalUniversity, Vellanikkara, India, 237 pp

Karim AB and Savill PS (1991) Effect of spacing on growthand biomass production of Gliricidia sepium (Jacq.) Walp.in an alley cropping system in Sierra Leone. Agrofor Syst16: 213–222

Kumar BM, George SJ and Chinnamani S (1994) Diversity,

143

Structure and standing stock of trees in the homegardensof Kerala in peninsular India, Agrofor Syst 25: 243–262

Kumar BM, George SJ, Jamaludheen V and Suresh TK (1998)Comparison of biomass production, tree allometry andnutrient use efficiency of multipurpose trees grown inwood lot and silvopastoral experiments in Kerala, India.For Ecol Manage 112: 145–163

Kumar BM, George SJ and Suresh TK (2000) Productivity offorage grasses grown in association with fast growingmultipurpose trees and assessment of post-rotation soilfertility in the humid tropics of peninsular India. AgroforSyst (in press)

Kumar SS, Kumar BM, Wahid PA, Kamalam NV and FisherRF (1999) Root competition for phosphorus betweencoconut, multipurpose trees and kacholam (Kaempferiagalanga). Agrofor Syst 46: 131–146

Long JN and Smith FW (1984) Relation between size anddensity in developing stands: a description and possiblemechanisms. For Ecol Manage 7: 191–206

Mathew T, Kumar BM, Suresh Babu KV, UmamaheswaranK (1992) Comparative performance of some multi-purposetrees and forage species in Silvo-pastoral systems in thehumid regions of southern India. Agrofor Syst 17: 205–218

PID (1948) The Wealth of India. Vol I A-B. Raw Materials.Publication and Information Directorate, Hillside Road,New Delhi 110012, India, p 42

Stenberg P, Linder S, Smolander H and Flower-Ellis J (1994)Performance of the LAI-2000 plant canopy analyser in esti-mating leaf area index of some Scots pine stands. TreePhysiol 14: 981–995

Strachan IB and McCaughey JH (1996) Spatial and verticalleaf area index of a deciduous forest resolved using theLAI-2000 Plant Canopy Analyser. For Sci 42: 176–181

Thomas J, Kumar BM, Wahid PA, Kamalam NV and FisherRF (1998) Root competition for phosphorus betweenginger and Ailanthus triphysa in Kerala, India. AgroforSyst 41: 293–305

Varughese S (1989) Screening of varieties of ginger andturmeric for shade tolerance. MSc Thesis (unpublished).Kerala Agricultural University, Vellanikkara, Thrissur,India, 81 pp

Wilson H and Ovid A (1993) Growth and yield responses ofginger (Zingiber officinale Roscoe) as affected by shadeand fertiliser applications. J Pl Nutr 16: 1539–1545

144