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