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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

    260

  • 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

    26 1

  • 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

    262

  • 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