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EFFECT OF WATER MANAGEMENT ON FIELD PERFORMANCE OF OIL

PALMS ON ACID SULPHATE SOILS IN PENINSULAR MALAYSIA

Toh Peng Yin and Poon Yew Chin

Harrisons & Crosfield (Malaysia) Sendirian Berhad

Kuala Lumpur, Malaysia

1 Summary

The yield performance of oil palms in fields with various acid sulphate

soil conditions is examined in relation to changes in water management.

In the severely and moderately acid areas, yields improved appreciably

when after a period of deep drainage, the watertable was raised, with

increases of 36.3% and 17.6% being recorded respectively in the first

consecutive four year period after raising the watertable. These yield

improvements were maintained thereafter.

Practical recommendations are given for maintaining a high watertable

with provision for periodic flushing of the drains in oil palm planta-

tions.

2 Introduction

In Peninsular Malaysia, it has been estimated that there are about

110,000 ha of acid sulphate soils (Kanapathy 1973). These soils are

mostly interspersed amongst fertile marine alluvia along the west coast,

where oil palm is an important perennial crop.

The adverse effects of acid sulphate soils on oil palm growth were first

highlighted during the 1960 's when in a series of investigations on

amelioration of such soils, intensive drainage was carried out in an at-

tempt to remove the source of their potential acidity, viz., pyrite,

through oxidation and leaching of the resultant sulphates. This proved

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disastrous as yields in the field under investigation plunged from an

average of 15.17 tonnes fresh fruit bunches (ffb) per ha in the years preceding the intensive drainage to 6.03 tonnes ffb/ha within four

years. Subsequent examination showed that even after this period of in-

tensive leaching, reserves of unoxidized pyrite remained very large and

the soil was still very acid (Bloomfield et al. 1968) .

The next phase of investigation involved inhibition of further pyrite

oxidation by flooding the pyritic horizon. This treatment led to pro-

gressive improvements in palm condition in the following year and, three

years after this treatment, yields reached 18.80 tonnes ffb/ha and re-

mained at that level five years later (Poon and Bloomfield 1977).

Since means of resolving the acid sulphate problem were developed, cul-

tivation of oil palms on these soils has expanded considerably. It is presently estimated that the acreage of oil palms grown on acid sulphate

soils in Peninsular Malaysia amounts to about 40,000 ha (Paramananthan

1980).

Acid sulphate soils too often are being considered collectively, without

taking into account existing variations in acid severity associated with

depth of acidic layers. This may have led to misleading impressions on

the general performance of oil palms on acid sulphate soils. It is

therefore proposed to examine in greater detail, the yields of oil palms

on acid sulphate s o i l s in relation to these variations in severity.

3 Identification of acid sulphate soils and

classification of fields with acid sulphate

soil conditions

Acid sulphate soils in Peninsular Malaysia are characterized by an or-

ganic layer in the topsoil overlying a clay subsoil-in which the acidic

horizon occurs. Typically, pale yellow deposits'of jarosite occur as

large blotches on ped faces and around old root channels in this acidic

horizon.

The criteria suggested by Coulter (1967) as standards for the identifi-

cation of the acidic horizon, viz., air dried, soil pH less than 3.3 and

water soluble sulphate content more than O. 1 % ha:e been found practica- \

ble for delineation of such soi s (Hew and Toh 1973). There is however

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cons ide rab le v a r i a t i o n i n t h e depths a t which t h e a c i d i c hor izon occurs

i n . t h e s o i l , ranging from less than 30 cm t o more than 120 cm from t h e

s o i l su r f ace . The growth and y i e l d performance of o i l palms have been

observed t o be a s s o c i a t e d wi th t h i s v a r i a t i o n .

Accordingly, t h e a c i d areas have been c l a s s i f i e d a r b i t r a r i l y i n t o t h r e e

c a t e g o r i e s of a c i d i t y depending on t h e depth a t which t h e a c i d i c l a y e r

occurs:

Category of a c i d i t y Depth of a c i d i c l a y e r (cm)

Severe O - 60

Moderate 60 - 90

M i I d 90 - 120

Within i n d i v i d u a l f i e l d s , t h e r e can be a range of depths a t which t h e

a c i d i t y occurs . Therefore , f o r t h e p r e s e n t purpose, a f i e l d i s c l a s s i -

f i e d i n t o t h e r e s p e c t i v e ca tegory of a c i d i t y i f more than 70% of t h e

area f a l l s i n t o t h a t ca tegory . This d e f i n i t i o n s i m p l i f i e s i n t e r p r e t a t i o n

and p r e s e n t a t i o n of d a t a , as a v a i l a b l e y i e l d d a t a p e r t a i n only t o e n t i r e

f i e l d s .

The degree of a c i d i t y i n t h e v a r i o u s f i e l d s t h a t have been s e l e c t e d f o r

t h e p r e s e n t s tudy , has been determined from s o i l ana lyses performed on

s o i l samples c o l l e c t e d a t an i n t e n s i t y of one p o i n t pe r 10 acres. A t

each sampling p o i n t , s o i l samples were c o l l e c t e d a t 15 cm i n t e r v a l s up

t o a depth of 120 cm. Analyses d a t a accumulated over s e v e r a l yea r s have

been used.

4 Yield of o i l palms on a c i d su lpha te s o i l s

The y i e l d performance of o i l palms i n a c i d su lpha te areas, c l a s s i f i e d

i n t o va r ious c a t e g o r i e s of a c i d i t y , i s examined i n r e l a t i o n t o changes

i n water management. Various pe r iods have been cons idered , w i th t h e per-

i od 1964-1967 r ep resen t ing t h e pe r iod p r i o r t o t h e wide-scale in t roduc-

t i o n of t h e p o l i c y of main ta in ing a h i g h w a t e r t a b l e . Yie ld performance

of palms a f t e r thk r a i s i n g of w a t e r t a b l e s i s examined i n consecut ive

pe r iods of f o u r yea r s from 1968 t o 1979.

The average y i e l d s pe r annum f o r f o u r consecut ive pe r iods of f o u r yea r s

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each , commencing from 1964, f o r palms under t h e va r ious c a t e g o r i e s of

a c i d i t y are summarized i n Table 1. Only t h e pre-I960 p l a n t i n g s have been

inc luded i n t h i s compi la t ion so t h a t areas s e l e c t e d have experienced a

s u f f i c i e n t l y long pe r iod of adverse growing cond i t ions p r i o r t o t h e in-

t roduc t ion of appropr i a t e ame l io ra t ive measures. I n a d d i t i o n , y i e l d d a t a

have a l s o been provided f o r comparable age palms growing on non-acid

su lpha te s o i l .

Table I . Yields of pre-I960 o i l palm p l a n t i n g s under va r ious c a t e g o r i e s

of a c i d i t y

Yie ld (tonnes f fb /ha /yea r )

Category of a c i d i t y Area (ha) 1964-67 1968-71 1972-75 1976-79 Severe 273 11.44 15.59 17.52 18.06 Moderate 366 16.38 19.27 19.08 18.98 M i Id 12 22.81 23.43 22.14 17.32

Non-acid su lpha te 888 23.89 24.14 22.44 20.41

The p o l i c y t o ra ise w a t e r t a b l e s w a s a f f e c t e d i n t h e ma jo r i ty of t h e a c i d

s u l p h a t e areas dur ing 1967. It w i l l be noted (Table 1 ) t h a t t h i s ameli-

o r a t i v e measure r e s u l t e d i n s u b s t a n t i a l improvements i n palm product iv-

i t y i n t h e seve re and moderately seve re a c i d areas.

There are i n s u f f i c i e n t areas of mild a c i d i t y i n t h e same age group f o r a

proper comparison. However, t h e y i e l d t r end i n one f i e l d i n d i c a t e s t h a t

o i l palm y i e l d s are n o t adve r se ly a f f e c t e d when t h e a c i d i t y occurs a t

90-120 cm. Rais ing t h e w a t e r t a b l e i n t h a t area d i d n o t r e s u l t i n dra-

matic improvement i n y i e l d performance. The very s a t i s f a c t o r y y i e l d s re-

corded dur ing 1964-1967 i n t h i s mi ld ly a c i d f i e l d may a l s o be a t t r i b u t e d

t o t h e f a c t t h a t , i n normal p r a c t i c e , t h e depth of i n t e r n a l f i e l d d r a i n s

r a r e l y exceeded 90 cm and t h e a c i d i c l a y e r w a s never sub jec t ed t o very

i n t e n s e drainage.'

The growth and p r o d u c t i v i t y of t h e o i l palm i s g r e a t l y in f luenced by t h e

s o i l mois ture s t a t u s and prolonged pe r iods of dry weather can p r e c i p i -

t a t e seve re y i e l d d e c l i n e s . Thus, i r r e s p e c t i v e of t h e s o i l a c i d i t y

l e v e l , o i l palms w i l l respond t o water management p r a c t i c e s aimed a t

avoidance of mois ture stress development.

The f u l l impact of a l t e r i n g t h e w a t e r t a b l e by dra inage i n a c i d su lpha te

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s o i l s becomes apparent from the y i e l d t rends i n an a r e a over which s o i l s

were completely ac id su lpha te (severe) . Figure 1 i l l u s t r a t e s the y i e l d

t rends i n such a 1952 p lan t ing (121 ha) during the per iod 1960-1979.

Drains i n the a rea under considerat ion w e r e deepened i n 1961/1962 t o 120

c m and t h e i r frequency increased t o one per 4 palm rows i n an e f f o r t t o

leach out the oxidized sulphates .

Drainage intensi ty and depth increased to drain per 4 palm rows

\and 120 an depth.

Figure 1. E f f e c t of increased drainage and subsequent r a i s i n g of water-

t a b l e on y i e l d of o i l palms on severe ac id su lpha te s o i l s

This i n t e n s i f i e d drainage caused a s t eep y i e l d dec l ine from 14.31 tonnes

f f b / h a t o 6.03 tonnes €fb/ha t h r e e years la ter (Poon and Bloomfield

1977). Raising of the wa te r t ab le by s t r a t e g i c placement of water re ten-

t i o n blocks along the d r a i n s produced highly economic y i e l d responses.

Though s i g n i f i c a n t y i e l d improvements were recorded i n the a reas where

wa te r t ab le s w e r e r a i sed a f t e r a per iod of f r e e drainage cond i t ions , t he

y i e l d l e v e l s i n these a reas d id n o t reach those ob ta inab le on non-acid

su lpha te s o i l s .

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Table 2 summarizes the yield performance of 1966-1973 oil palm plantings

on moderately acid soils which have not been subjected to intensive free

drainage since commencement of planting. Yields of similar age palms on

non-acid sulphate soils are included for comparison.

Table 2. Yield comparison of 1966-1973 oil palm plantings on acid sul-

phate and non-acid sulphate soils

Mean yield (tonnes ffb/ha)

Category of acidity Area (ha) 3-5 yr. 6-8 yr. 9-11 yr.

Moderate 1319 19.94 25.85 26.07

Non-acid sulphate 1051 21.45 28.19 25.75

It is apparent from Table 2 that yields of subsequent oil palm plantings

established on acid sulphate soils with appropriate raised watertable

policy from commencement of planting have been similar to those of

plantings on non-acid sulphate soils. There are no comparative data for

plantings on severely acid soils.

5 Current recommendations for water management of

acid sulphate soils

The proper management of drainage and irrigation is crucial in relation

to oil palm performance in hyperacidic subsoil conditions. The problem

of drainage is two-fold. Free drainage conditions will result in the in-

tensification of acidity while inadequate drainage will give rise to

flooded conditions, both of which will adversely affect palm perform-

ance.

The appropriate drainage intensity within fields depends largely on soil

characteristics' such as permeability and water retention, which are de-

pendent on soil texture and structure. Acid sulphate soils in Peninsular

Malaysia are generally heavy textured and occur in low-lying situations.

A s such, they require the installation of an extensive drainage system

prior to oil palm cultivation.

The drainage system on acid sulphate soils involves a network of field

drains running parallel to palm rows which drain into collection drains.

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The collection drains are in turn connected to the main drains which - lead directly to the tide gate and the outlet drain beyond. This pattern

of drainage i s illustrated in Figure 2.

1 I I

Water retention I

I

I block

- - - --- ---------

L

Water retention 1 1 , . block I I

I L -

I r-7

v

I

I c -4

a c

E

-4

1

- Collection drain

Field

I kain:

1

- Collection drain

Figure 2. Schematic diagram of drainage system

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Typical dimensions f o r t h e f i e l d , c o l l e c t i o n and main d r a i n s are given

below:

Width (m)

Type of d r a i n A t top A t bottom Depth (m)

F i e l d 1 .o0 0.45 0 .75

co 1 lec t ion 2.00 0.60 1.50

Main 3.30 1.20 1.80-2.40

The f i e l d d r a i n s are spaced between 6 rows of palms o r 47 m a p a r t while

t h e c o l l e c t i o n d r a i n s are loca ted 396 m a p a r t . The main d r a i n s are lo-

cated 738 m apa r t . To obv ia t e f looding, t h e d r a i n dimensions must be

va r i ed according t o t h e volume of water o f f t a k e necessary during w e t

weather cond i t ions , as determined by observat ions i n s i t u .

While the width o r i n t e n s i t y of t h e f i e l d d r a i n s can be v a r i e d according

t o circumstances, t h e depth of t hese d r a i n s must no t exceed 75 cm,

otherwise t h e r e i s a r i s k of acce le ra t ed ox ida t ion of t he p y r i t i c l aye r

during dry weather condi t ions.

The main requirements i n the management of ac id su lpha te s o i l s i s t h a t

t h e wa te r t ab le should be r a i s e d and maintained above t h e p y r i t i c l aye r

f o r as long as poss ib l e . To achieve t h i s , t h e main d r a i n s must be

blocked a t va r ious p o i n t s along t h e i r l eng th by w e i r s . These may be

b u i l t by using s o i l bags, i . e . s o i l packed i n used f e r t i l i z e r bags, o r

by t h e cons t ruc t ion of s l u i c e ga t e s . From experience, t hese w a t e r re-

t e n t i o n blocks are b e s t constructed next t o t h e c u l v e r t s a t a p o i n t

c l o s e t o where t h e c o l l e c t i o n d r a i n s m e e t t he main d ra in . A t t h i s loca-

t i o n t h e c u l v e r t f a c e w i l l a ss i s t i n minimizing water leakages through

t h e blocks. Normally t h e wa te r t ab le i n a c i d su lpha te areas i s main-

t a ined a t about 60 cm from t h e s o i l su r f ace .

With t h e l o c a t i o n of t h e water r e t e n t i o n blocks as desc r ibed , i t w i l l

u sua l ly be unnecessary t o p l ace any more blocks i n t h e f i e l d d ra ins .

However, i n s i t u a t i o n s where t h e s lope of t he land i s uneven, i t may be

necessary t o p l ace s o i l bags a t va r ious p o i n t s along the f i e l d d r a i n s t o

maintain t h e wa te r t ab le .

I n many s i t u a t i o n s , d e s p i t e placement of water r e t e n t i o n blocks, t he

w a t e r t a b l e i s no t expected t o remain a t t h e required l e v e l throughout

t h e year because of seasonal dry weather. I n p r a c t i c e , t he w a t e r t a b l e

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w i l l f l u c t u a t e , though i d e a l l y water should be v i s i b l e i n t h e f i e l d

d r a i n s throughout t he yea r . From obse rva t ions , t he w a t e r t a b l e can be

maintained a t a reasonable l e v e l f o r up t o a month i n t o the dry season,

bu t t h i s w i l l l a r g e l y depend on s o i l t e x t u r e and s t r u c t u r e .

The f l u c t u a t i n g wa te r t ab le does no t completely prevent oxidat ion. During

t h e r a iny pe r iods , ac id accumulation i n the ground w a t e r i s decreased by

r e g u l a r p r e c i p i t a t i o n and removal of a c i d s through the d r a i n s . The prob-

l e m becomes acu te during prolonged dry s p e l l s when f r e s h water i s not

a v a i l a b l e and t h e ac id concen t r a t ion inc reases p rogres s ive ly owing t o

evapo-transpirat ion and accentuated ox ida t ion of p y r i t e .

I n p r a c t i c e , t h e problem of a c i d i t y build-up i s minimized by p e r i o d i c

f l u s h i n g of t h e d r a i n s during the wet season, which i s achieved by open-

ing up t h e s l u i c e g a t e s and s o i l blocks. Well be fo re t h e end of t h e w e t

season, when r a i n f a l l i s s t i l l v i r t u a l l y assured, t he s l u i c e g a t e and

blocks are set i n place. Fresh water i s then allowed t o build-up again

t o t h e required l e v e l , be fo re t h e d ry s p e l l sets i n . One t o two f lush-

ings during the wet season are normally adequate.

6 Discussion

The profound in f luence of proper water management on t h e p r o d u c t i v i t y of

o i l palms grown on a c i d su lpha te s o i l s may be a s soc ia t ed with improve-

ments i n condi t ions s u i t a b l e f o r r o o t development. With a r a i s e d water-

t a b l e , t h e secondary and t e r t i a r y roots are gene ra l ly concentrated c l o s e

t o t h e w a t e r t a b l e and primary r o o t s t h a t p e n e t r a t e t o g r e a t e r depths

during t h e d r i e r per iods produce upward-growing secondaries and ter t i -

aries. When t h e wa te r t ab le recedes during dry weather, r o o t s a r e appar-

e n t l y a b l e t o p r o l i f e r a t e through less t o x i c areas i n t h e moist ac id

horizon t o reach t h e w a t e r t a b l e below. I n c o n t r a s t , i n f r e e l y drained

a c i d su lpha te s o i l s , few r o o t s can p e n e t r a t e t h e apparent ly less d i f f e r -

e n t i a t e d ac id horizon t o reach t h e wa te r t ab le . Primary r o o t s t h a t happen

t o p e n e t r a t e t he a c i d i c horizon produce very few secondaries and te r t i -

aries and are usua l ly s tun ted due t o excessive s o i l a c i d i t y . Root spread

i s a l s o much r e s t r i c t e d and t h e bulk of r o o t s are concentrated c l o s e t o

the bole of t h e palm. Consequently, o i l palms grown i n f r e e l y drained

a c i d su lpha te s o i l s are u n t h r i f t y and f r equen t ly e x h i b i t symptoms of

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moisture stress and m u l t i p l e d e f i c i e n c i e s .

Reservations had previously been expressed on t h e r i s k of i ncu r r ing H2S

t o x i c i t y problems owing t o anaerobic condi t ions brought about by main-

t a i n i n g a high wa te r t ab le over prolonged pe r iods . However, i n f i e l d

p r a c t i c e i t i s r a r e l y p o s s i b l e t o maintain a cons t an t wa te r t ab le and

l e v e l s f l u c t u a t e throughout t h e year depending on r a i n f a l l d i s t r i b u t i o n .

Hence, no problems with H2S t o x i c i t y have been encountered over t h e l as t

f i f t e e n yea r s and i t appears u n l i k e l y t h a t such a problem w i l l occur i n

the fo re seeab le f u t u r e .

I n a d d i t i o n t o proper water management, a r a t i o n a l manuring programme

must b e implemented i f palm y i e l d s are t o be optimized. Bunch ash, de-

r i v e d from burning empty o i l palm f r u i t bunches, i s used almost exclu-

s i v e l y as t h e source of potash i n a c i d su lpha te areas. I ts h igh ly alka-

l i n e r e a c t i o n con t r ibu te s t o pH improvements i n the t o p s o i l . S tud ie s

have a l s o shown t h a t bunch ash improved s o i l moisture r e t e n t i o n proper-

t i e s , t h i s being a s soc ia t ed with p a r t i a l d e s t r u c t i o n of t he crumb s t r u c -

t u r e i n t h e t o p s o i l (Yeow e t a l . 1977).

7 Conclusion

There i s a r e l a t i o n s h i p between o i l palm y i e l d s and the depth a t which

t h e a c i d i c horizon occurs . Acidic horizons below 90 cm have v i r t u a l l y no

e f f e c t on palm y i e l d s . On t h e o t h e r hand, where the a c i d i c l a y e r s occur

w i t h i n 60 cm of t h e s o i l su r f ace , y i e l d l e v e l s w i l l be reduced. Fortu-

n a t e l y , such areas of s eve re a c i d i t y are usua l ly discont inuous and rec-

lamation of ac id su lpha te areas as a whole f o r o i l palm c u l t i v a t i o n i s

h igh ly economic.

The recommended drainage p a t t e r n , with t h e l o c a t i o n of water r e t e n t i o n

blocks a t s t r a t e g i c p o i n t s as descr ibed, has improved t h e y i e l d perform-

ance of o i l palms considerably over many years.. I t i s now envisaged t h a t

t h e r e are r e l a t i v e l y few problems with t h e growth of o i l palms on ac id

su lpha te s o i l s provided t h a t t h e p y r i t i c horizon i s no t too shallow and

t h e areas do no t experience prolonged d ry s p e l l s .

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Acknowledgements

The authors wish to record their appreciation to Mr. R. Shepherd,

Director of Research, H&C Research and Advisory Scheme, for reviewing

the paper. They would also like to record their thanks to MIS. Harrisons & Crosfield (M) Sdn. Bhd., for their kind permission to publish this

paper.

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