Impact of Different Spacings of Cooking Banana Intercropped with Rubber on Soil Fertility Attributes and Maturity Rate of the Trees in a Humid Forest Area of South Eastern Nigeria

doi:10.4236/ojf.2012.22009

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Open Journal of Forestry

2012. Vol.2, No.2, 65-70

Published Online April 2012 in SciRes (http://www.SciRP.org/journal/ojf) http://dx.doi.org/10.4236/ojf.2012.22009

Impact of Different Spacings of Cooking Banana Intercropped

with Rubber on Soil Fertility Attributes and Maturity Rate of the

Trees in a Humid Forest Area of South Eastern Nigeria

Timothy U. Esekhade, Ikokwu K. Okore*

Rubber Research Institute of Nigeria, Benin City, Nigeria

Email: *[email protected]

Received December 28th, 2011; revised February 29th, 2012; accepted March 7th, 2012

The impact of four spacing of cooking banana (CB) within the immature rubber avenues on some soil fer-

tility attributes, maturity rate of rubber trees and dry rubber content (DRC) during the initial six years af-

ter planting (YAP) were evaluated in a humid forest area of South Eastern Nigeria relative to sole rubber.

The CB spacings within immature rubber avenues were 6.7 × 3.4 m; 4.0 × 2.0 m, 3.0 × 3.0 m and 2.0 ×

2.0 m, while the sole rubber was at 6.7 × 3.4 m, all laid out in randomized complete block design with

five replications. Quantities of soil organic C, extractable P, Ca, Mg and earthworm activities were sig-

nificantly higher in the intercrops, with the highest value coming from the 4 × 2 m CB spaced plots.

However a significantly higher value of K stock was observed in the sole rubber plot and declined as the

CB spacing narrowed. While the highest proportion (>90%) of matured hevea tree at six YAP was ob-

served in the 2 × 2 m CB spaced plots; the highest DRC of 1.7 t·ha–1·yr–1 was obtained from CB 4 × 2 m

treatment. Consequently, with some of the observed soil fertility attributes and DRC recorded, 4 × 2 m

CB spacing seems to be a more suitable CB spacings within immature rubber avenues, especially in view

of the levels of K in the 2 × 2 CB plots.

Keywords: Cropping System; Nutrient Stock; Dry Rubber Content; Earth Warm

Introduction

Majority of the world natural rubber (Hevea brasiliensis

Muel. Arg) is traditionally and economically grown in the low

land humid tropics. This is principally due to its requirement

for uniform rainfall distribution, reduced temperature fluctua-

tion and relative humidity all year round (Von Uexckull &

Mutert, 1995; Rao et al., 1998). Soils of the eco-region are

known to be predominantly of low activity clay minerals char-

acterized by poor mineral nutrient fixation and/or storage ca-

pacity (Fagbani & Fapohund, 1986). Although this inherent

fertility constraint posses a lot of management problem upon

the conversion of the native forest into agriculture use (Von

Uexckull & Mutert, 1995); the soils are known for their sus-

tenance of the natural luxuriant tropical rainforest vegetation

(Novrdwijik, 2002). A number of low external input cropping

systems are traditionally used in the management of the soils

when put to agricultural use. Such management method in-

cludes diversification of crop component of the system through

inter cropping.

Intercropping of rubber with arable and quasi-peremial crops

like banana and pineapples has been found to be a sure way of

ameliorating the problem of zero income phase (immaturity

phase which often spans between 5 - 6 years) in rubber cultiva-

tion (Esekhade & Ojiekpon, 1997; Rodrigo et al., 2004) espe-

cially amongst the small holding who constitute over 75% of

rubber growers (IRSG, 2000). Reports on the effect of various

inter crop components on soil nutrient status (Zainol et al.,

1993; Esekhade et al., 2005) income enhancement; (Lydia et al.,

1999) and resource use efficiency (Rodrigo et al., 1997) and

growth performance of rubber sapling (Rodrigo et al., 2004) are

often limited to the immature period of the main crop (rubber).

There is paucity of information on the effect of the intercrop

components on the subsequent growth and yield and the soil

fertility attributes at the maturity of the main crop.

Consequently, it is the objective of this study to evaluate the

effect of different spacing of a Musa spp in an inter crop with

rubber on some soil fertility indicators such as nutrient stock

and earthworm activities at the maturity and maturity rate

(attainment of tappable girth size) of the main crop under such

cropping system in high rainforest area of south eastern Nige-

ria.

Materials and Methods

Site Description

The study herein reported is the extension of an experiment

established in 1993 (Esekhade & Ojiekpon, 1997) on the inter-

cropping of Para rubber (Hevea brasiliensis Mull. Arg) and

Musa Spp (cooking banana) in an acid sand soil of Akwete,

South eastern Nigeria. Akwete lies at Lat. 4.8998˚N and Long.

7.3359˚E. The rainfall pattern is bimodal with peaks in the

months of June, July and September and a mean minimum and

maximum temperature of 23.7˚C and 32˚C, respectively.

The landscape is nearly plain with a maximum elevation of

2% and the soil being classified as Arenic plaudit (USDA) or

Dystric Nitroso (FAO) and sandy alluvium parent material

*Corresponding author.

T. U. ESEKHADE ET AL.

(Fabgbami & Fapohunda, 1986). At 0 to 30 cm depth the soil

had 84% sand, 8% silt and 8% silt with CEC of 6.40

Cmol·Kg–1, Organic matter of 1.8% and a pH of 4.4.

Experimental Layout

The experiment was laid out in Randomized Complete Block

Design (RCBD). The treatment consist of sole rubber at the

spacing of 6.7 × 3.4 m and four intercrop spacing (6.7 × 3.4 m,

4.0 × 2.0 m, 3.0 × 3.0 m and 2.0 × 2.0 m) of cooking Banana

within immature rubber avenue of 6.7 × 3.4 m. Each of this

treatment was replicated five times. The rubber clones and

cooking banana cultivar used are RRIM 501 and Cadaba, re-

spectively. Details of the field arrangement and management

practices are contained in Esekhade and Ojiekpon (1997).

Maturity Rate Determination

The effect of Banana spacing on maturity period (rate) of

rubber trees was assessed by measuring the girth of 15 trees at

the height of 1.5 m above the bud grafted union at six months

intervals in each treatment from the third year after planting.

However, for ease of handling, data are presented on yearly

basis.

Dry Rubber Yield (DRC) Determination

For DRC determination, latex exploitation of the trees be-

tween 1999 and 2001 was used. The S2D2 (half-Spiral, every

third day) tapping method was deployed to obtain the latex. The

dry rubber content (DRC) of the latex was determined by air

drying at room temperature until a constant weight was ob-

tained.

Soil Analysis Procedure and Nutrient Stock

Determination

Composite soil samples were taken at the depths of 0 - 15

and 15 - 30 cm at the onset of the experiment. At the beginning

of latex exploitation, composite samples were equally taken

across the treatments at similar depth like those of the pretreat-

ment samples. The composite samples consisted of four random

sub samples from each treatment. All the samples were air

dried and sieved through a 2 mm mesh sieve. The sample were

analyzed for organic C, total N, available P and exchangeable

bases (Ca2+, Mg2+ and k+) following Page et al. (1982) procedure.

Stored nutrients (extractable P, K, Ca and Mg and total N and

organic C) in each of the treatment were calculated by multi-

plying the soil concentration by the bulk-destiny and thickness

of the soil horizon considering the soil mass of each of the

treatment (Ellert & Bettary, 1995).

Earthworm Activities Determination

For earth worm activities determination, surface casts were

sampled from five randomly placed 1 × 1 m wooden quadrant

in each experimental unit at the end of rains at the third and

sixth year after planting. The cast were dried at 105˚C for

weight determination. From similar quadrants soil monoliths

(50 × 50 × 20 cm) were obtained using the Tropical soil Biol-

ogy and Fertility (TSBF) approach (Anderson and Ingram,

1993). Earth worm in each monolith were hand sorted and put

into 10% ethanol and later transferred to 40% formaldehyde

before being counted and weight for abundance and biomass

evaluation respectively.

Data generated were subjected to analysis of variance using

RCBD procedure. Where significance differences occurred for

a given variable across the treatment means were separated by

the use of Least Significant Difference (LSD) approach.

Results

Soil Nutrient Stock

As shown in Table 1, the effect of the inter crops (irrespec-

tive of the spacing of the cooking banana) on the stocks of nu-

trients measured except N and K, were significant (higher)

compared to the sole rubber at 0 - 15 and 15 - 30 cm soil depths.

Organic C accumulation across the treatments followed similar

trend. The stock of organic C (30.87 and 28.36 Mg·ha–1) ob-

tained at the inception of tapping from plots where cooking

banana were intercropped at the spacing of 6.7 × 3.4 and 4 × 2

m, respectively within the rubber avenue, differed significantly

from the 24.53 Mg·ha–1 obtained from the sole rubber at 0 - 15

cm. The result at the lower depth 15 - 30 cm followed the same

trend. The effect of the cooking banana spacing within the rub-

ber avenues on total N stock did not differ significantly from

that of the sole plot at 0 - 15 cm, but did at the 15 - 30 cm depth.

The highest value (112 kgN·ha–1) at 15 - 30 cm depth was re-

corded from plots with 4 × 2 m spacing of cooking banana. The

stock of available P and exchangeable bases (Ca and Mg) dif-

fered significantly between the intercrop plots and the sole with

higher values being recorded from the intercrops with exception

of K. The effect of the component crop spacing within the rub-

ber avenue showed that as the spacing narrowed, the soil P

stock decreased with a significantly higher values being ob-

tained from 6.7 × 3.4 and 4 × 2 m compared to 3 × 3 and 2 × 2

m cooking banana spaced plots at the two depths.However, the

values from the intercrop were significantly higher than those

recorded from the sole plots.The stocks of exchangeable Ca and

Mg across the treatments followed similar trend, while the

stock of K+ in the soil under sole rubber was significantly

higher than those of the inter crops with values amongst the

intercrops following the P distribution tend (Table 1) irrespec-

tive of the soil depth.

Earth Worm Activities

Earth worm activities measured as surface cast, biomass and

abundance (Table 2) differed significantly across the treat-

ments irrespective of the sampling period (three or six YAP).

The quantities of the surface cast deposited across the inter

crops at any of the sampling period, were significantly higher

than those of the sole cropping irrespective of the component

crop spacing within the rubber avenue. Amongst the intercrops,

as the spacing of the CB within the main crop narrowed, the

quantity of earth worm cast deposit increased at the third year

after planting. However, this differed at the sixth year after

planting with highest cast deposit (442.06 g·m–2) being obtained

from plots with CB spaced at 4 × 2 m within the rubber avenue.

The effect on earth worm biomass and abundance followed simi-

lar trend with the intercrop system having higher values.

Rubber Tree Maturity Rate

On rates of the attainment of taable girth size amongst rubber pp

T. U. ESEKHADE ET AL.

Table 1.

Effect of cooking banana spacing in an intercrop with rubber on the quantities of nutrient (kg·ha–1) and

organic C (Mg·ha–1) stored in the soil (0 - 30 cm) at 6 years after planting (maturity period).

Org. Total Avail. Exchangeable

Treatment

(Cooking banana Spacing) C N P Ca Mg K

0 - 15 cm depth

Rubber sole 6.7 × 3.4 m 24.53 125.52 24.62 109.1 107.3 83.01

Rubber + CB (6.7 × 3.4 m) 28.36 128.3 44.66 121.22 113.41 63.42

Rubber + CB (4.0 × 2.0 m) 30.87 128.13 43.68 121.1 113.21 65.66

Rubber + CB (3.0 × 3.0 m) 26.88 128.1 36.95 119.32 117.72 61.62

Rubber + CB (2.0 × 2.0 m) 26.88 126.3 34.12 134.12 118.1 55.32

LSD (0.05) 3.36 NS 6.35 10.15 4.62 15.32

15 - 30 cm depth

Rubber sole 6.7 × 3.4 m 16.42 98.21 30.34 30.24 25.72 19.09

Rubber + CB (6.7 × 3.4 m) 20.92 111.05 36.45 36.45 13.79 22.11

Rubber + CB (4.0 × 2.0 m) 25.35 112.68 34.92 34.92 11.88 16.92

Rubber + CB (3.0 × 3.0 m) 21.36 11.38 22.61 27.61 13.58 18.68

Rubber + CB (2.0 × 2.0 m) 19.67 10.98 25.66 25.66 6.95 37.01

LSD (0.05) 4.13 2.68 3.36 5.51 6.1 2.31

Values in parenthesis are spacing of cooking banana within the main crop (rubber) avenues.

Table 2.

Earth worm cast, biomass (fresh weight) and abundance as affected by cooking banana inter crop at dif-

ferent spacing within rubber avenues at the third and sixth years after plantation establishment.

3rd Year Earth Worm 6th Year Earth Worm

Cast Biomass Abundance Cast Biomass Abundance

Treatment

(g·m–2) (No·m–2) (g·m–2) (No·m–2)

Rubber sole 6.7 × 3.4 m 195.04 46.57 127.09 350.92 49.34 138.32

Rubber + CB (6.7 ×3.4 m) 262.87 50.13 151.79 430.14 53.52 145.44

Rubber + CB (4.0 × 2.0 m) 269.17 54.64 136.05 442.06 64.08 155.55

Rubber + CB (3.0 × 3.0 m) 270.57 58.56 138.96 414.16 64.64 150.52

Rubber + CB (2.0 × 2.0 m) 275.19 60.50 143.96 410.43 73.62 53.20

LSD (0.05) 8.35 5.12 10.33 21.11 4.92 11.31

Values in parenthesis are spacing of cooking banana within the main crop (rubber) avenues.

trees as shown by girth sizes or range across the treatments

(Table 3); trees in the intercrops showed faster rate as measuerd

in per centages over time with most of the sampled trees attain-

ing ≥ 50 cm girth at end of the 5th year compared to the sole.

The attainment of tappability amongst the rubber trees in the

intercrop increased as the spacing of CB within the avenues

narrowed, with approximately 85% of the sampled trees in the

plot with CB at 2 × 2 m spacing attaining > 50 cm girth at the

fifth year after planting. Across the treatments, plots where CB

was spaced 2 × 2 m and 3 × 3 m within the tree avenue, the

proportion of trees attaining the tappable girth size exceeded

the standard 60% often recommended for economic tapping and

this occured at the fifth year after planting.

Dry Rubber Yield

The mean annual yield of rubber (DRC) within the inter

crops were significantly higher than those of the sole plot (Ta-

ble 4). At the onset of tapping (1999), the highest yield of 1.3

t·ha–1 DRC was obtained from plots where CB was inter cropped

at 4 × 2 m spacing. This trend continued all through the data

period. However, the yield from plots with CB being spaced at

3 × 3 m and 2 × 2 m were higher than those from plots where

CB was intercropped at 6.7 × 3.4 m spacing within the rubber

avenues.

Discussion

Soil Nutrient and Earthworm Activities

The result of this study showed the potentials of rubber plan-

tation in improving nutrient status of soil as well as organic

matter build up as the years of establishment progress (Table 1);

irrespective of the cropping system. This observation buttressed

the widely reported potentials o rubber plantation is building f

T. U. ESEKHADE ET AL.

Table 3.

Effects of cooking banana (CB) spacing in an intercrop with rubber on the maturity rate of rubber based

on girth ranges between the 3rd and 6th year after plantation establishment.

Years After Planting

Treatment Girth Range (cm)

3 4 5 6

(%)

<30 67 53 0 0

31 - 35 30 42 0 0

36 - 40 3 5 25.5 6

41 - 45 0 0 15.5 7

46 - 50 0 0 28.5 22

Rubber sole 6.7 × 3.4 m

>50 0 0 30.5 65

<30 58 33 0 0

31 - 35 25 38 0 0

36 - 40 17 29 10.5 3.5

41 - 45 0 0 16 4.5

46 - 50 0 0 25 7

Rubber + CB (6.7 × 3.4 m)

>50 0 0 48.5 85

<30 50 28 0 0

31 - 35 36 52 0 0

36 - 40 14 20 0 0

41 - 45 0 0 20.5 0

46 - 50 0 0 30 10

Rubber + CB (4.0 × 2.0 m)

>50 0 0 49.5 90

<30 45 20 0 0

31 - 35 32 50 0 0

36 - 40 23 23.5 0 0

41 - 45 0 6.5 15 0

46 - 50 0 0 23.5 8

Rubber + CB (3.0 × 3.0 m)

>50 0 0 61.5 92

<30 42 13 0 0

31 - 35 27 9.5 0 0

36 - 40 16 30 0 0

41 - 45 14 37 10.5 3

46 - 50 1 10.5 5 3.5

Rubber + CB (2.0 × 2.0 m)

>50 0 0 84.5 93.5

Value in parenthesis are spacing of cooking banana (CB) within the main crop (rubber) avenues.

up soil nutrient and organic C through efficient nutrient cycling

mechanism (Delabarre & Serier, 2001) and enhanced envi-

ronmental conservation facilitated by biodiversity maintenance

and conservation similar to natural forest ecosystem (Beukema

et al., 1997).

On annual basis, the mean (6 years) values of the soil organic

C stock and stocks of N, P, K, Mg and Ca observed across the

treatments in this study are within the range reported by Dela-

barre and Serier (2001) as a mean annual value of 25 year rub-

ber plantation, but above the organic C stock recorded (Nolte et

al., 2001) from a natural fallow land of similar age in Camer-

oon, under a similar soil. The intercropping of cooking banana

within the rubber avenue resulting to a significantly (P > 0.05)

higher organic C stock and stocks of P and exchangeable base

cations except K, relative to the sole rubber (Table 1) could be

due to higher biomass generation and retention from the banana

residue.

Similar higher nutrient levels have been reported in banana

T. U. ESEKHADE ET AL.

Table 4.

Mean yield performance of rubber between 1990 and 2001 as influ-

enced by cooking banana spacing within rubber avenues in an intercrop

system.

Mean annual yield rubber

(kg DRC ha–1·yr–1)

Treatment

1999 2000 2001 Mean

Rubber sole 6.7 × 3.4 m 920.7 1636.9 1736.6 1431.4

Rubber + CB (6.7 × 3.4 m) 1024 1644.6 1745.8 1471.5

Rubber + CB (4.0 × 2.0 m) 1264.8 1835.8 1937.6 1679.4

Rubber + CB (3.0 × 3.0 m) 1049.8 1782.3 1884.6 1572.2

Rubber + CB (2.0 × 2.0 m) 1015.4 1705.8 1810.8 1510.7

LSD (0.05) 20.8 60.3 43.6

Values in parenthesis are the spacings of cooking banana (CB) within the imma-

ture rubber avenues.

associated cropping system (Bekundal et al., 2000) compared to

other cropping systems. This is attributed among other things to

the reduced rate of nutrient loss ( leaching) resulting from early

shading of the surface soil by the banana plant, applied mulch-

ing materials and retention of a large quantity of the plant resi-

due after harvest. However, a lower level of K Stock was re-

corded from the intercropped plots compared to the sole. This

could be ascribed to higher uptake of K and buttressed by the

observed decline in the nutrient as the spacings of the intercrop

component narrowed. Similar observation was made (Wilson,

1985) who reported the storage of a greater proportion of K at

the fruit portion of the plant compared to the other parts. The

implication is that as the fruit are being harvested and taken

away from the farm for consumption, a large amount of K is

being exported from the field and could have some adverse

effect on the development of the rubber.

At the end of the first three years of the intercrops, the ob-

served significantly higher earthworm activities (surface cast,

biomass and abundance) in plots with cooking banana at closer

spacing (Table 2) could be as a result of shade provided by the

banana plant. Since the banana plant were at closer spacing (2 ×

2 m) within the rubber avenue, their leaves could have been

closely interlocked than those at the wider spacing (6.7 × 3.4 m

or 4 × 2 m); thus providing better shade and moisture conserva-

tion—a mechanism known to affect earthworm activities. The

higher earthworm activities observed in the plots with cooking

banana at 4 × 2 m at the sixth year sampling (maturity of plan-

tation) could be ascribed to higher organic matter content in

that plot (Table 1) resulting from the presence of banana plants

and its residue. Thus the observed higher earthworm activities

in the intercrop compared to the sole rubber is in order and its

implications on nutrient cycling and other ecosystem services

are paramount.

Rubber Tree Maturity Period

As shown in Table 3, inter-cropping shortened the maturity

(tappability) period of the rubber tree with higher percentages

of trees attaining maturity in plots with cooking banana at

closer spacings 2 × 2 m and 3 × 3 m compared to others, at five

years after planting. Theis observation could partly be attrib-

uted to improved management methods resulting from inte-

gration of banana (Esekhade et al., 2005) and the early shading

effect of the banana which may have alleviated the commonly

observed radiation induced photosynthic reduction in young

Hevea plants due to easy penetration of sun rays during the

early growth stage under sole rubber cropping system (Senevi-

rathna et al., 2003). Such shading effect is known to promote

leave production, with an associated leave area increase per

plant. Similarly, increased growth rate and dry matter accumu-

lation have been observed among rubber plants intercropped

with cassava (Esekhade, 2004).

The observed non-impairment of rubber tree growth and

maturity by cooking banana, even at closer spacings is in line

with the work of Rodrigo et al. (1997). Also the higher values

of soil nutrient stocks and biological activities in the intercrop

plots (Tables 1 and 2) may have had some positive effect on

the growth of the tree and consequently its maturity. Hauser et

al. (1997) observed a positive relation between earth worm

activeties and crop performance (growth and yield).

Dry Rubber Yield

The positive effect of the intercrops on rubber did not only

enhance the maturity (tappability) period of rubber, but also

affected the latex yield measured as dry rubber content (DRC),

compared to the sole. However, the pattern of DRC values

across the treatments did not follow the trend observed for the

maturity rate (%) of the plants, rather the highest DRC values

were consistently obtained from plots where the trees were

intercropped with cooking banana at 4 × 2 m (Table 4). This

could be due to high soil nutrient concentration under the

treatment (Table 2) aswell as soil biological activities (earth

worm) which may have influence yield. The effect of soil nu-

trient status on dry rubber content is reported by Delabarre and

serier (2002) and Esekhade et al. (2005).

Conclusion

The problem of overcoming the zero income phrase associ-

ated with rubber cultivation has necessitated the research into

the environmental and economic implication of intercropping

of rubber with other early maturing high value crops. This

study revealed that not only did intercropping of rubber with

cooking banana resulted to improve soil fertility in terms of soil

nutrient and biological activities (earth worm) but it also short-

ened the maturity period of the tree compared to the sole.

However, intercropping banana at closer spacings within the

avenue needs further investigation because of the reduction in

soil K stock. From the information gathered from the study,

intercropping with cooking banana at 4 × 2 m within the rubber

avenue ensures better rubber performance in terms of yield and

soil resources conservation.

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