IJERD – International Journal of Environmental and Rural Development (2012) 3-1

Research article
erdUsing Soil Improvement Materials for Enhancing Drought
Tolerance of Rubber Plant
SUTTIPONG PRUANGKA*
Faculty of Technology, Udon Thani Rajabhat University, Udon Thani, Thailand
Email: dr.suttipong@yahoo.co.th

MONGKON TA-OUN
Faculty of Agriculture, Khon Kaen University, Khon Kaen, Thailand

THANAPONG TULA
Faculty of Agriculture, Khon Kaen University, Khon Kaen, Thailand

SOMPOSH KAEWRAHUN
Faculty of Agriculture, Khon Kaen University, Khon Kaen , Thailand
Received 20 December 2011

Accepted 18 April 2012(*: Corresponding Author)

Abstract A study on the effects of applying a type of clay minerals on drought toleranceof rubber plant was carried out by incorporating bentonite at 0, 2, 4, and 8 percent w/w
into loamy sand soil (Roi-et series). Factorial arrangement in CRD (complete randomizeddesign) with 3 replications was performed in this research study. It was found that mixing
bentonite 0-16 percent w/w with sugarcane bagasse, coconut fluff, peanut husk, blackburned rice husk, and fresh rice husk caused the water holding capacity to be in the rangesof 41.50-58.88, 44.3-105.0, 9.1-20.4, 128.6-154.2,   and   3.1-21.3   percent, respectively.  
After 14 days of application for rubber varieties RRIM600 and RRIT251 grown on loamy
sand, using bentonite 0, 2, 4, and 8 percent w/w caused the drought tolerance without
irrigation to be 31-35 and 29-47 days, respectively. It was also found that small andmedium sizes of rubber seedlings showed higher drought tolerance than those of big sizes
because they still survived without irrigation 40-48, and 38-43 days, respectively. All sizesof RRIM600 seedling started wilting at moisture contents 4.9-5.9 percent and then showedpermanent wilting at 3.30-3.39 percent w/w. Clay minerals used as basal application underfield experiment significantly increased drought tolerance of young RRIM600 to be 158
days after planting whereas no application on the rubber tree could stand by the age of 92135 days or averagely 111 days after planting.  Increasing 15-15-15 concentration as basal
fertilizer by the rates 100, 200, 400, and 600 g/plant significantly accelerated thetermination of rubber tree. According to this, the rubber tree died at the age of 166, 149,
107, and 102 days after planting. Chemical fertilizer associated with clay mineral as basal
application showed a trend of extending rubber age.
Key words soil improvement materials, bentonite, rubber, drought tolerance

INTRODUCTION
Since 2007 under the government policy, rubber plantation area in Northeast Thailand has been
extended to 450,000 hectares. However, large land area of the Northeast contains various andcomplicated soil types and soil properties that will directly affect the success of this policy,
particularly rubber tree younger than 5 years which should be intensively cultivated due tounsustainable root system during this growth stage (Office of Agricultural Economics, 2009).
Naturally, 85 percent of roots are in deep zone whereas effective roots for nutrients absorption, 15percent, are spreading in topsoil (Rubber Research Institute of Thailand, 2004). A preliminary datafrom survey research revealed that clay mineral used in substrate culture for seedling stage canⒸISERD181

IJERD – International Journal of Environmental and Rural Development (2012) 3-1

improve drought tolerance of rubber plant. This research aimed at applying some types of organic
material associated with bentonite clay mineral to improve drought tolerance of young rubber tree.
METHODOLOGY
There were 3 main methods used in this study as follows:
1. Effect of organic materials and clay mineral on soil water holding capacity
Five types of organic materials were used: sugarcane bagasse, coconut fluff, peanut husk, blackburned rice husk, and fresh rice husk. A 5x7 factorial arrangement in completely randomized
design (CRD) with 3 replications was performed. Factor A was the ratio of mixing between organic
materials and bentonite 0, 2, 4, 8, and 16 percent w/w, while factor B was the period of water
deficit 2, 4, 6, 8, 10, 12, and 14 days, respectively.
2. Effect of bentonite on drought tolerance
Both rubber varieties RRIM 600 and RRIT251 were used as experimental materials. A 4x3
factorial arrangement in CRD with 3 replications was performed. Factor A were bentonite 0, 2, 4,and 8 percent w/w of loamy sand. Factor B were rubber sizes, small, medium, and large. Survival
rate after water deficit was investigated.
3. Effect of mixed bentonite and basal fertilizers applied under field condition on droughttolerance
RRIM 600 was used as experimental material. A 2x5 factorial arrangement in CRD with 3
replications was performed. Factor A were bentonite mixed with organic matterials 0, and 10
percent w/w. Factor B were basal chemical fertilizer 15-15-15 at the rates of 0, 100, 200, 400, and
600 g/plant. Period of drought tolerance was collected.
RESULTS AND DISCUSSION
The research findings are as follows:
1. Water holding capacityAfter 2 days from watering at saturated moisture content, bentonite mixed with coconut fluff
showed the highest water holding capacity and then black-burned rice husk, sugarcane bagasse,
peanut husk, and fresh rice husk. The remaining moisture contents were 134-205, 130-154, 72-94,31-64, and  23-61 percent. At the day of 14th, they were 46.8-100.8, 86.0-96.3, 41.6-57.2, 10.2-20.4,
and  3.6-19.4 percent, respectively (Table 1).
Table 1  Effect of bentonite mixed with organic materials on water holding capacity(percentage of moisture contents)  Organic materials  used for mixing withbentonite 0-16  percent w/w
Sugarcane bagasse
Coconut fluff
Peanut husk
Black-burned rice husk
Fresh rice husk

Remaining moisture contents at the days
after saturation (percent)2 Days
14 Days                  72.0-98.1                                        41.5-58.8                  132.9-207.7                                         44.3-105.0                  30.4-62.9                                        9.1-20.4                  128.6-154.2                                         89.3-106.1                  20.6-65.6                                        3.1-21.3

CV  (%)
                                      3.30
4.74
10.24
4.12
2.70

2. Effect of bentonite on drought tolerance
Applying bentonite, 0, 2, 4, and  8 percent w/w on loamy sand increased drought tolerance of both
RRIM600 and RRIT251 rubbers averagely from 31 to 55 days after water deficit for RRIM600 and29 to 47 days for RRIT251. Small and medium sizes of rubber seedling showed better droughttolerance than large size. The period of surviving could last until 40-48 days for RRIM600 and 3843 days for RRIT251 (Table 2). Increasing the amount of clay mineral can increase soil microporesand then reduce bulk density. This will increase available water capacity (Russell, 1973; Brady andWell, 2002).
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IJERD – International Journal of Environmental and Rural Development (2012) 3-1

Table 2 Number of the days that rubber died after water deficit among rubber varieties andsizes, and bentonite application rates
Rubber sizes  of RRIM600
Small
MediumLarge
Average*
CV = 9.30%
Rubber sizes of RRIT251
Small
MediumLarge
Average*
CV = 7.58%

Bentonite application rates
Average*
0%
2%
4%
8%
31.67
41.67
46.67
55.00
43.75b
35.00
43.33
51.67
61.67
47.92a
28.33
38.33
45.00
48.33
40.00c31.67d41.11c47.78b55.00a43.89
LSD bentonite rates = 3.972, LSD rubber sizes  = 3.440 at 95% level
Bentonite application rates
Average*0%2%
4%8%
33.33
43.33
48.33
46.67
42.92a
28.33
43.33
48.33
48.33
42.08a
26.67
38.33
43.33
45.00
38.33b
29.44c41.67b
46.67a46.67a41.11
LSD bentonite rates = 3.033, LSD rubber sizes  = 2.627 at 95% level*Means in the same column/row followed by the same letter are not significant difference (p<0.05)  under DMRT(Duncan's New Multiple Range Test)

3. Effect of mixed bentonite and basal fertilizers applied under field condition on droughttolerance
In case of applying bentonite mixed with organic materials and basal fertilizer applied under field
condition on drought tolerance of rubber, it was found that RRIM600 significantly increased
survival period for all sizes (small, medium, and large) of young rubber tree, particularly the small
size could last until 158 days comparing with no application that could last for only 92-135 days or
averagely 111 days (Table 3).
Table  3 Number of the days that rubber (RRIM600) died after planting among rubber sizes,application rates of bentonite mixed with organic materials, and basal fertilizer
rates of 15-15-15
Small size
No application
Mixed bentonite
CV = 23.71%
Medium size
No application
Mixed bentonite
CV = 18.47%
Large size
No application
Mixed bentonite
CV = 28.61%

0
134.7
162.7
148.7a0131.0
214.0
172.5a0135.0
168.7
151.8ab15-15-15  (g/plant)
100
200
400
128.7
115.0
84.7
202.3
182.3
129.0
165.5a148.7a106.8b15-15-15  (g/plant)
100
200
400
140.0
119.3
96.7
208.7
169.7
112.0
174.3a144.5a104.3b15-15-15  (g/plant)
100200
400
144.0
132.0
89.0
202.7
167.7
101.0
173.3a149.8a95.0bcAverage*
600
91.7
113.0
102.3b
600
72.0
112.0
92.0b
600
72.0
94.0
83.0c

110.9b157.9a134.4
Average*111.8b163.3a137.5
Average*
114.4b146.8a130.6*Means in the same column/row followed by the same letter are not significant difference (p<0.05)  under DMRT(Duncan's New Multiple Range Test)

Because of high specific surface areas, clay mineral as inorganic colloid generally increases
cation exchange capacity (CEC); therefore, it induces the sustainability of soil fertility. Plant
nutrient retention and availability are increased (Brady and Well, 2002). When organic materials
are decayed, cementing agent will increase soil aggregation process and then increase soil water
holding capacity (Tester, 1990; Asher et al., 2002). Applying 15-15-15 as basal fertilizer at the rateof over 200 g/plant increased the termination of RRIM600 at 92-102 days after planting. MediumⒸISERD183

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size seedling could stand for drought tolerance better than the other small and large sizes.
Averagely, rubber died within 138, 134, and  131 days for medium, small, and large sizes,respectively.
CONCLUSION
Bentonite 0-16 percent w/w mixed with coconut fluff showed the highest water holding capacity
and then black-burned rice husk, sugarcane bagasse, peanut husk, and fresh rice husk. The
remaining moisture contents were 46.8-100.8, 86.0-96.3, 41.6-57.2, 10.2-20.4, and 3.6-19.4 percent,respectively. Bentonite 2-8 percent w/w increased drought tolerance 29.81-50.86 percent for  RRIM600 and 41.54-58.52 percent   for RRIT251. Small and medium sizes of rubber seedlingshowed better drought tolerance than large size. They were 42.9-43.3, 42.1-45.0, and   38.3-39.1
days, respectively. RRIM600 was better than RRIT251 in terms of drought tolerance. They were31.6 days, and 29.4 days, respectively. Applying bentonite mixed with organic materials and basal
fertilizers under field condition increased survival period for all sizes (small, medium, and large) ofyoung rubber tree. Applying over 200 g/plant of 15-15-15 as basal fertilizer increased thetermination of seedlings. Averagely 88-100 days or 3 months after planting with no rainfall, rubberdied.
ACKNOWLEDGMENTS
This research project was funded by The National Research Council of Thailand (NRCT) under2008-2010. Thanks are extended to the Division of Land Resource and Environment, Faculty ofAgriculture, Khon Kaen University for the conveniences and equipments in laboratory test.
REFERENCES
Asher, C., Greendon, N. and Menzies, N. 2002. How to unravel and sole fertility problems. ACIAR(Australian Centre for International Agricultural Research) Monograph No. 83, Canberra, Australia.
Brady, N.C. and Well, R.R. 2002. The nature and properties of soils. Macmillan Publishing Company, NewYork.
Office of Agricultural Economics 2009. Agricultural data of Thailand. Ministry of Agriculture andCooperatives. Bangkok, Thailand.
Rubber Research Institute of Thailand 2004. Guideline for rubber plantation in Northeast Thailand.
Department of Agriculture. Ministry of Agriculture and Cooperatives. Bangkok, Thailand. 37.
Rusell, E.W. 1973. Soil condition and plant growth. 10th ed. Longman. London.
Tester, C.F. 1990. Organic amendment effects on physical and chemical properties of sandy soil. Soil Sci.
Soc. Am. J. 54, 827-831.

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