oil palm bulletin 53 (november 2006) p. 1 - 24 opflsim3...

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ABSTRACT

The OPFLSIM models (Oil Palm Flowering Simulator versions 1 and 2) are mathematical process-type models that simulate oil palm flowering and bunch yield at successive nodes, mainly on the basis of endogenous feedback loops postulated to regulate inflorescence and fruit bunch production. A third model, OPFLSIM3, has now been produced that takes more account of the effect of external factors on flowering and yield cycles than did the previous versions. OPFLSIM3 also contains several other features simulating aspects of palm behaviour that were not previously catered for.

The construction and use of the new model is described together with examples of output and comparisons with field data.

ABSTRAK

Model OPFLSIM (Oil Palm Flowering Simulator versi 1 dan 2) adalah model simulasi hasil dan pengeluaran bunga sawit jenis matematik secara berturut-turut mengikut peringkat berdasarkan teori bahawa lingkaran maklum balas dalaman mengawal pengeluaran bunga dan buah sawit. Model ketiga, OPFLSIM3, yang telah dikeluarkan sekarang mengambil kira kesan luaran yang mempengaruhi pengeluaran bunga dan pusingan hasil yang tidak ada pada versi sebelum ini. OPFLSIM3 juga mengandungi ciri lain berkaitan simulasi perlakuan pokok sawit yang tidak diambil kira sebelum ini.

Pembinaan dan penggunaan model baru dihuraikan bersama contoh-contoh output dan perbandingan dengan data ladang.

Keywords: o�l palm, s�mulat�on modell�ng, seasonal cycles, flowering, yield.

INTRODUCTION

The o�l palm computer models OPFLSIM1 and 2 (O�l Palm Flower�ng S�mulator vers�ons 1 and 2) were developed to simulate flowering, and flowering plus bunch yield respectively, on a node-

by-node bas�s (Henson and Jones, 2005a,b). They represent updates/extens�ons of the model of Jones (1997) in which the underlying concepts were first formal�zed. The models have, as the�r core, two internal feedback loops that regulate inflorescence sex determination and abortion. Briefly, the development of bunches, and perhaps also male inflorescences, results, in the models in stress signals that act at specific sensitive nodes, to regulate sex differentiation and inflorescence abortion. While the nature of the s�gnals �s unknown, the�r product�on is related to bunch load. This reflects observations that when the current y�eld �s low, the format�on of female flowers is favoured and the level of abort�on �s low, so result�ng later �n a h�gher y�eld. Then the converse s�tuat�on w�ll apply. The result, �n the absence of any external confound�ng factors, �s a regular cycl�ng �n bunch y�eld. Such cycles commonly d�splay an annual per�od�c�ty, result�ng �n peaks and troughs �n y�eld that have �mportant econom�c repercuss�ons.

Although the prev�ous vers�ons of OPFLSIM perm�t a w�de range of �nternal factors l�kely to influence yield cycling to be investigated, and allow appl�cat�on of some man�pulat�ve treatments, they largely neglect effects of the external env�ronment. External factors, part�cularly water supply, must exerc�se an �mportant role �n regulat�ng the �nternal cycles s�nce an annual per�od�c�ty �s ma�nta�ned. However, as w�th the �nternal factors, there �s scant knowledge of how such regulat�on �n the plant works. Nevertheless, the concept of stress s�gnals can aga�n be appl�ed, w�th adverse cond�t�ons such as drought, pest attacks or low rad�at�on hav�ng s�m�lar effects to those of h�gh bunch loads on future y�elds. In add�t�on, changes �n bunch s�ze, such as those result�ng from var�able poll�nat�on, may also contr�bute to the y�eld cycles.

NEWFEATURESOFOPFLSIM3

The new opt�ons �n OPFLSIM3 are of two k�nds. The first provides additional flexibility to alter var�ous developmental processes that, �n the previous models, were fixed. The second provides for external stresses of water deficit, inadequate poll�nat�on and loss of leaf area (by prun�ng or

Oil Palm Bulletin 53 (November 2006) p. 1 - 24

OPFLSIM3–AnImprovedOilPalmSeasonalFloweringandYieldSimulationModel

IanEHenson*

* Malaysian Palm Oil Board, P. O. Box 10620, 50720 Kuala Lumpur, Malaysia.

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pests) to be appl�ed, and to �nteract w�th the �nternal regulat�on. The poll�nat�on opt�on also allows for calculat�on of the bunch components, so that o�l and kernel y�elds can be est�mated. The object�ve has been to produce a more hol�st�c model with greater flexibility and capability for s�mulat�ng observed y�eld cycles. In add�t�on to operat�ng as a self-conta�ned model, OPFLSIM3 can also be harnessed as a feeder module for the dry matter product�on model, OPRODSIM (Henson, 2005; 2007).

New Options Affecting Developmental Processes

These are g�ven �n the�r order of presentat�on when runn�ng the QBas�c vers�on of the model. For those opt�ons reta�ned unchanged from the earl�er model vers�ons, reference can be made to the OPFLSIM Technical Manual and the Users’ Guide (Henson and Jones, 2005b,c).

Planting density. The prev�ous vers�ons assumed a plant�ng dens�ty of 148. Th�s may be var�ed �n the new model.

Presence of stress-generating male inflorescences. The earl�er models followed the procedure of Jones (1977) in allowing for male inflorescences to be present and act�ve at any of the 10 stress-generat�ng fronds (convent�onally, fronds 20 to 29). However, males d�e shortly after anthes�s, w�th pollen shedding lasting only a maximum of four to five days (Hartley, 1977). Thus, any stress �nduced by males is likely to be confined to the earlier stress-generating fronds, probably the first four only (des�gnated by default as fronds 20 to 23), allow�ng for var�at�on �n rate of male development. Older fronds, wh�ch may have subtended act�ve males earl�er, no longer contr�bute to the stress-sum and are therefore re-ass�gned a zero stress score. The range of fronds allowed to conta�n act�ve males can be var�ed �f requ�red and can d�ffer w�th respect to the�r effects on sex rat�o and abort�on.

Effects of palm age on the node(s) at which inflorescence gender is determined. There �s st�ll much uncerta�nty about the cr�t�cal node or nodes at which the sex of inflorescences is determined, w�th results vary�ng �n d�fferent stud�es. Corley (1976) assembled data that indicated that specific stages of inflorescence development were attained progress�vely earl�er �n older palms. Thus, the stage of initiation of the first bract (considered to precede sex determ�nat�on) occurred at frond –24 �n 1.5-year-old palms and frond –29 �n 27.5-year-old palms. There was a significant linear trend (Figure 1), that can be used opt�onally �n the model to change the position of specified gender-sensitive node(s) (GSN1) as the palms age. Over a 30-year per�od,

th�s adjustment amounts to a change at wh�ch a specific stage is attained of about six nodes. The age-related trends appear to be s�m�lar for d�fferent developmental events (Figure 1).

Figure 1. Changes with palm age in the frond position at which the spikelets and the first bract subtending

them are initiated.

Notes: Data for seedl�ng (i.e. sexually-produced) palms are from Corley (1976) and for clones (mean of seven clones) from Corley et al. (1995). The regress�ons (om�tt�ng clones) for spikelets and first bract are significant at P<0.01 and <0.05, respect�vely.

Fron

dnu

mbe

r

Seasonal variation in the position of stress-generating nodes. The frond numbers at wh�ch inflorescences anthesize and at which bunches develop can vary apprec�ably both w�th t�me and between palms, as a result of changes �n the per�od between frond emergence and anthes�s (Chang et al., 1993; Lamade et al., 1998). The cause of th�s var�able development rate �s uncerta�n but �s most l�kely related to abort�on, wh�ch �n turn depends on seasonal cond�t�ons, and can show annual cycl�ng (Lamade et al., 1998). Hence, an annual trend can be used �n OPFLSIM3 to alter the pos�t�on of the stress-generat�ng nodes/frond numbers �n the model, w�th the ampl�tude of the annual change selectable up to a max�mum of s�x fronds.

Long-term variation in mean bunch weight. By default, the model uses a standard age-dependent curve to spec�fy the mean bunch fresh we�ght (MBWT) used to calculate FFB y�eld. Wh�le MBWT can vary w�th plant�ng mater�al, the curve, based on the data of Chow and Jamaludd�n (1995) has proven su�table for produc�ng real�st�c y�elds �n comb�nat�on w�th the trends �n bunch number. However, to make the model more flexible and to take account of the rec�procal relat�onsh�p generally found between bunch number and MBWT (Figure 2), prov�s�on has been made to reduce the latter �f bunch number �s h�gh, and vice versa. Th�s �s effected v�a the parameter FEMREG, wh�ch sets the upper

Oil Palm Bulletin 53

1 A full listing of abbreviations is given in Appendix 1.

Changes in critical frond positions with age

1st Bract (seedlings)1st Bract (clones)

Spikelets (seedlings)Spikelets (clones)

Yearsafterplanting

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limit to the percentage of female inflorescences, and hence, bunch number. The non-l�near relat�onsh�p shown �n Figure 2 �s used to relate bunch number to we�ght. A cho�ce �s prov�ded both to vary FEMREG (as �n OPFLSIM2) and to l�nk MBWT to �t. The h�gher the FEMREG sett�ng, the lower w�ll be the MBWT (Figure 3). Th�s opt�on �s �ndependent of the short-term cycling �n MBWT descr�bed next.

generat�ng nodes (SGNs). Breure and Corley (1992) found MBWT to be negat�vely related to fruiting activity w�th a lag of about 10 months, suggest�ng that development of the bunch was most sens�t�ve at around fronds +5 to +10, roughly s�m�lar to the abort�on-sens�t�ve stage. The magn�tude of the effect can be var�ed and �s d�scussed �n more deta�l �n another paper deal�ng w�th the use of OPFLSIM3 as a s�nk module w�th�n the OPRODSIM model (Henson, 2007).

The second, though less mechan�st�c opt�on, �s to �mpose an annual seasonal trend as when vary�ng the SGNs, aga�n w�th prov�s�on to vary the ampl�tude of the effect. Th�s �s also descr�bed elsewhere (Henson, 2007).

Option to specify gender-specific abortion thresholds. There �s some ev�dence that the sens�t�v�ty to abort�on d�ffers between male and female inflorescences, with the latter being more sens�t�ve (Corley, 1976). Prev�ous s�mulat�ons w�th OPFLSIM2 (Henson and Jones, 2005b) actually resulted �n the oppos�te behav�our (males be�ng more abort�on-prone), expla�ned �n terms of an �nteract�on between gender and abort�on cycles. In OPFLSIM3, �t �s poss�ble to spec�fy separate abort�on thresholds for male and female inflorescences or opt for equal sens�t�v�ty for both (the default case).

Alternatives for defining the strength of stress signals and their relationships to bunch load and male inflorescences. Prev�ous OPFLSIM vers�ons use arbitrary and fixed stress scores based on the inflorescence type and so give equal weighting at all SGNs. They make no allowance for changes �n the b�omass or ass�m�late use by the bunches as they develop. Wh�lst the use of such scores has proved to be a workable approach, a better method m�ght be to use a more quant�tat�ve and var�able stress measure such as fru�t�ng act�v�ty (Broekmans, 1957; Corley and Breure, 1992), or the current bunch and male inflorescence assimilate requirements.

The new model therefore, has several opt�ons for generat�ng stress-sums. In add�t�on to the previous use of scores based on inflorescence type and number (default), there are two add�t�onal opt�ons, namely:(a) stress-sums based on the product of bunch

number and MBWT, w�th the latter adjusted to reflect the current bunch load (standing bunch b�omass). Th�s opt�on presumes that males have no effect; and

(b) as for (a) but w�th an add�t�onal stress contr�but�on based on the number of male inflorescences.

Mea

nbu

nch

fresh

wei

ght

(kg)

Figure 2. Relationships between single bunch weight and bunch number for three sites in Peninsular

Malaysia.

Note: Adapted from Figure 38 of Henson and Jones (2005b). The regress�on �s for the pooled data.

MBWT vs. bunch number at three sites

Short-term variation in mean bunch weight. In add�t�on to long-term changes, MBWT can also vary seasonally (e.g. Henson and Mohd Tayeb, 2004). OPFLSIM3 provides two specific options to impose short-term var�at�on �n MBWT wh�le, �n add�t�on, MBWT will also be affected by water deficit and poll�nat�on level, should these factors be �ncluded �n the s�mulat�on (see below).

The first option is to relate future MBWT to the stress be�ng generated currently at the stress-

OPFLSIM3 – An Improved Oil Palm Seasonal Flowering and Yield Simulation Model

Bunch number (palm-1 yr-1)

Figure 3. Changes with palm age in single mean bunch weight (MBWT) with adjustment for bunch numbers

using four values of the FEMREG parameter.

Note: The standard curve (produced us�ng FEMREG = 1) �s based on the data of Chow and Jamaludd�n (1995).

MBW

T(k

g)

Mean bunch fresh weight

Months after planting

FEMREG0.80.91.01.1

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The above adjustment of MBWT �s ach�eved by d�v�s�on w�th a scal�ng factor (16.9), to ensure that the resultant mean stress-sums and hence, the sex rat�o, are s�m�lar �n magn�tude to those produced us�ng the scor�ng system.

These two alternat�ve opt�ons can be used to determ�ne the stress-sums affect�ng both abort�on and gender or gender alone. In the latter case, abort�on w�ll be regulated by the convent�onally-generated stress scores.

Option to output inflorescence data at different frond positions. By default, the presence and sex of each inflorescence is recorded at frond 20 where anthesis �s assumed to occur. It �s now poss�ble to spec�fy the frond at wh�ch sex �s to be output, enabl�ng changes �n sex rat�o and abort�on of each node �n�t�at�on cycle to be tracked as the palm grows. Data from such an analys�s allow the percentage abort�on of female and male inflorescences to be separately assessed. The inflorescence data can be stored and output for any frond position or a specific stage such as at the first gender-determining node, the last gender-determ�n�ng node, or the node �mmed�ately follow�ng the abort�on-sens�t�ve node.

Option to vary the rate of node production by individual palms. In the default case, all the s�mulated palms �n the populat�on have �dent�cal rates of node production as defined by a standard equation (Henson and Jones, 2005b). In the field, �nd�v�dual palms can show substant�al d�fferences �n node product�on rate (NPR). In th�s opt�on, NPR �s var�ed us�ng a random number generat�on. The 30-year mean NPR of �nd�v�dual palms can vary cons�derably (e.g. from 16 to up to 40 palm-1 yr-1), although the mean for a populat�on of 10 palms �s much less var�able, be�ng close (typ�cally ± 4 palm-1 yr-1) to the mean default value.

New Options for Applying External Stress

Three external factors likely to influence the flowering and yield cycles are presently simulated. They are soil water deficit (reflecting the influence of ra�nfall and evaporat�ve demand), poll�nat�on efficiency (affecting fruit set, MBWT and bunch components) and defol�at�on stress (such as may result from pest attack or over-prun�ng).

The water deficit and pollination routines are descr�bed elsewhere (Henson, 2007) and so are only discussed briefly here.

Soil water deficit. To run th�s rout�ne, an external data file is required containing the mean fractional

ava�lable so�l water (FASW) for each node cycle. Th�s �s a measure of the water ava�lable for plant uptake w�th�n the root�ng zone. F�les have been prepared for two s�tes, each cover�ng a 30-year per�od. One is for an inland site with only a mild water deficit wh�le the other �s for a s�te that has a severe annual dry period lasting three or more months. More files cover�ng other s�tes may be added �n future.

FASW �s used to mod�fy both the sex rat�o and percentage abort�on. F�rstly, �t affects the level of FEMREG, the parameter govern�ng the sens�t�v�ty of gender determ�nat�on to stress (Henson and Jones, 2005a) and, secondly, the value of a water stress factor termed WSSUM. The latter adds to the stress scores, ABSUM and SEXSUM, that regulate inflorescence abortion and sex determination, respect�vely. In add�t�on, WSSUM �s also used to regulate the mean bunch we�ght.

The equat�ons relat�ng FEMREG and WSSUM to FASW are based on that of Taylor et al. (1978), deta�ls of wh�ch are g�ven �n Henson (2007).

Pollination efficiency. Th�s rout�ne prov�des a cho�ce of four standard cond�t�ons affect�ng the pollen supply and fru�t set. Alternat�vely, users can set the cond�t�ons themselves by enter�ng the appropriate regression coefficients relating the percentage fru�t set to the number of anthes�z�ng male inflorescences. The model then adjusts this tentat�ve fru�t set value to allow for the rat�o of anthesizing males to females. The final or adjusted fru�t set �s used to calculate the fru�t/bunch and other component rat�os and to der�ve a new MBWT by reference to the standard, age-related value. Further deta�ls are g�ven �n Henson (2007).

An add�t�onal value of the poll�nat�on rout�ne �s an ab�l�ty to der�ve the mesocarp o�l and kernel contents, the o�l and kernel y�elds and the�r nom�nal extract�on rates. These can also be obta�ned �n the absence of poll�nat�on stress by select�ng the non-l�m�t�ng case.

Defoliation stress. This routine is a modification of the frond prun�ng treatment conta�ned �n OPFLSIM1 and 2. The approach �s s�m�lar to that �n the prev�ous vers�ons except that the number of pruned fronds, previously fixed at 20, can be varied, while the max�mum stress score per pruned frond that �s perm�tted (prev�ously 0.5, th�s be�ng added to the scores generated at the SGNs) has been �ncreased to one. As before, the node �n�t�at�on number at wh�ch prun�ng �s done may be selected by the user.


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OUTPUT FILES

The model outputs up to nine data files, two of which are optional. The files are:

(i) OPTIONS. This file lists the options and parameter values selected each t�me the model is run. (Other file types list identifiers, date and t�me of run and a few other key parameter values only.) Either the file run name or the date and t�me of the run can be used to relate this file to other files output at the same time.

(ii) FLOWIN. This file contains the raw flowering data for the s�mulated palm populat�on (i.e. %female, %hermaphrod�te, %male, %aborted) for each node that �s �n�t�ated, together w�th the der�ved var�ables, bunch number per hectare (BN), male inflorescence number per hectare (MINH), raw BARMAX and MARMAX (bunch and male inflorescence assimilate requ�rements, respect�vely, the values of wh�ch are der�ved from the b�omass at matur�ty), and MBWT. It also g�ves the days after plant�ng (DAP) at the t�me of �n�t�at�on of each node and the t�me �nterval (�n days) between the �n�t�at�on of success�ve nodes (days per node, or DPN). All the data are based on 148 palms ha-1 and any adjustment for d�fferent plant�ng dens�t�es �s carr�ed out later and allowed for �n subsequent files.

The FLOWIN file can be used in the model OPRODSIM to generate further sink data (Henson, 2007).

(iii) FLOW1. This file is derived from FLOWIN and, with the exception of the inflorescence data, l�sts the same var�ables, aga�n node-by-node, together w�th TARMAX, the sum of BARMAX and MARMAX. However, the values reflect the total stand�ng b�omass present rather than the final biomass at maturity as in FLOWIN. Th�s results �n the data be�ng smoothed out over nodes and t�me to g�ve a more cont�nuous pattern.

(iv) FLOW2. This file holds monthly data derived from FLOW1. When the poll�nat�on opt�on �s selected, add�t�onal bunch component var�ables are l�sted together w�th the o�l and kernel y�elds.

(v) FLOW3. This file holds annual data derived

from FLOW2. The provision for two file types depend�ng on use of the poll�nat�on opt�on, also appl�es as for FLOW2.

(vi) FLOW4. This file contains the equivalent raw (un-smoothed) data to those �n FLOW1 and �s presented for reference only.

(v��) STRESUMS. Th�s l�sts for each node the stress scores affect�ng abort�on and sex determ�nat�on. In add�t�on to the core stress-sums, ABSUM and SEXSUM, the add�t�onal stresses generated when �mpos�ng water deficit and defoliation (WSSUM and DEFOL, respect�vely) are also l�sted.

(viii) CYCLES. This is an optional file, also produced by OPFLSIM2. It l�sts any cycl�c trends selected, g�v�ng the non-cycl�c and cycl�c node product�on �nterval (DPN) and the equ�valent month number after plant�ng, for each newly �n�t�ated node. In add�t�on, �f cycl�ng of SGNs has been requested, the file gives the frond position of the first SGN.

(ix) NODEPROD. This is another optional file, used to d�splay the mean node product�on rate for each palm as well as the mean for the populat�on. It would generally be called only �f the palm-var�able node product�on rate opt�on were exerc�sed.

EXAMPLES OF OUTPUT

Examples of output from the model will be confined here to the features un�que to �t. For aspects common to other OPFLSIM vers�ons, the OPFLSIM Technical Manual and the Users’ Guide (Henson and Jones, 2005b,c) should be consulted. Also, only a br�ef treatment is accorded here to the water deficit and poll�nat�on opt�ons, as these are fully documented elsewhere (Henson, 2007).

The Default Case

Us�ng the standard default parameters �n Table 1 results �n peaks �n bunch number and bunch b�omass product�on of approx�mately annual frequency (Figures 4a and 5a). S�m�lar output can also be obta�ned w�th OPFLSIM2 us�ng the same parameter sett�ngs. The levels and patterns of bunch production reflect that of a well managed and fert�l�zed s�te w�th a good year-round water supply. Wh�le the general patterns accord well w�th field observations (Figures 4b-d; 5b-d), the mean product�on levels (bunch numbers and total y�eld) produced by the model were less than at the best s�te (Coastal), but greater than at the poorer ones. Such d�fferences can be accounted for �n terms of both MBWT and number, and adjustment �n the model of the former, as descr�bed �n the next paragraph, enables the model to be tailored for specific sites.


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TABLE 1. SET OF STANDARD PARAMETER VALUES USED IN OPFLSIM3*

Input parameter Standard value Permitted range Notes

1 Number of nodes s�mulated 770 1 to 770 Represents palm growth �n terms of number of new nodes produced. The 770 cycles equate to approx�mately 30 years’ growth.

2 Number of palms s�mulated (palm populat�on)

10 120 to 200 10 to 20 are generally sufficient.

3 Plant�ng dens�ty 148 120 to 200 Palms per hectare.

4 Youngest frond generat�ng gender stress-�nduc�ng s�gnal

20 17 to 25

Number�ng of fronds follows the standard procedure whereby frond 1 �s the youngest fully-expanded frond. Fronds younger than frond 0 are g�ven consecut�vely negat�ve, and older fronds, consecut�vely pos�t�ve numbers. Fronds are numbered �n reverse order to that of node cycles.

Frond number at the end of the sex determ�n�ng stage can be the same as that at the start, �n wh�ch case. gender w�ll be determ�ned at a s�ngle frond pos�t�on.

5 Oldest frond with live male inflorescences affect�ng gender

23 Parameter 4 + 3 to parameter 4 + 9

6 Oldest frond generat�ng gender stress-�nduc�ng s�gnal

29 Parameter 4 + 9

7 Youngest frond generat�ng abort�on-�nduc�ng s�gnal

20 17 to 25

8 Oldest frond with live male inflorescences affect�ng abort�on

23 Parameter 7 + 3 to parameter 7 + 5

9 Oldest frond number generat�ng abort�on-�nduc�ng s�gnal

25 Parameter 7 + 5

10 Ampl�tude of seasonal var�at�on �n stress-generat�ng nodes

3 0 to 6

11 Youngest frond determ�n�ng gender -11 -28 to –4

12 Oldest frond determ�n�ng gender -11 -28 to –4

13 Frond at abort�on-sens�t�ve stage 10 5 to 15

14 Mean bunch we�ght cycl�ng ampl�tude 0 0 to 10 -

15 Initial node inflorescence status 0 0,1,2 or 3 0 = aborted; 1 = male; 2 = hermaphrod�te; 3 = female.

16 Female regulat�ng factor (FEMREG) 1 0.1 to 1.5 Determ�nes the upper l�m�t for % female inflorescences.

17 FEMREG equat�on Polynom�al polynom�al or l�near

Polynomial gives better fit.

18 Hermaphrod�te product�on gap zero 1 to 10 The opt�on ex�sts to exclude hermaphrod�tes.

19 Stress threshold for abort�on 35 0 to 50 Appl�es to both sexes.

20 Male inflorescence stress signal score 1 0 to 1 -

21 Bas�s for generat�ng sex-sums - - Inflorescence class and number.

22 Random stress factor level 35 0 to 50 -

23 Frond number to output sex 20 -29 to 30 Assumed to be at anthes�s.

24 Random node product�on rate None - -

25 Select�on of external stresses None - Three external stress factors can be s�mulated.

Oil Palm Bulletin 53 OPFLSIM3 – An Improved Oil Palm Seasonal Flowering and Yield Simulation Model

Note: *Modified from Table 1 of Henson and Jones (2005b).

}

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In test�ng the new opt�ons of the model, the defaults l�sted �n Table 1 were used, unless otherw�se stated.

Stress Generation by Male Inflorescences

Prev�ous model vers�ons allowed for the poss�ble presence of stress-generat�ng male inflorescences at any of the 10 stress-generating fronds. By default, OPFLSIM3 assumes no l�ve males beyond frond 23. The effects of restr�ct�ng the occurrence of l�ve males are shown �n Figure 6. As m�ght be expected, progress�vely exclud�ng males at the older fronds �ncreased the mean bunch b�omass product�on (BBP) and bunch numbers, although w�th less effect on the latter. Surpr�s�ngly, there was also a phase sh�ft �n the peaks, w�th the loss of males at late frond numbers result�ng �n extended cycle lengths (Figure 7).

Dependence of Sex Determination on Palm Age

As seen �n Figure 1, the specific stages of floral morphology appear to be reached progress�vely earl�er as the palms age. The consequences of th�s were tested assum�ng d�fferent values for the average pos�t�on at wh�ch gender �s assumed to be determ�ned. The effects on bunch y�eld, here measured over 23 years, were qu�te small, the ma�n effect be�ng an �ncrease �n the cycle length and hence, a phase sh�ft. Th�s was most apparent when the mean node for gender determ�nat�on was set early, at node (frond) –23 (Figure 8).

Seasonal Variation in the Position of Stress-Generating Nodes

Vary�ng the pos�t�on of the SGNs w�ll effectively change the rate of inflorescence and/or bunch development, and result �n altered cycle lengths. Such var�able development rates have been observed �n several stud�es (Corley, 1977; Chang et al., 1993; 1995; Lamade et al., 1998). When comb�ned w�th the standard default sett�ngs of other model parameters, an �ncrease �n the ampl�tude of SGN cycl�ng resulted �n less regular cycl�ng of bunch numbers (Figure 9), although the long-term mean bunch y�eld was not much affected. Vary�ng the SGN pos�t�ons �s one of two opt�ons �n the model that can influence bunch development rate, the other be�ng �nduc�ng seasonal var�at�on �n the rate of node, and hence frond, product�on, an opt�on also present �n OPFLSIM2.

Long-Term Variation in Mean Bunch Weight

Th�s opt�on allows the age-related trend �n mean bunch we�ght to respond to bunch number, thus s�mulat�ng the rec�procal relat�onsh�p normally

Bunc

hnu

mbe

r(p

alm

-1m

th-1)

Bunc

hnu

mbe

r(p

alm

-1m

th-1)

Bunc

hnu

mbe

r(p

alm

-1m

th-1)

Bunc

hnu

mbe

r(p

alm

-1m

th-1)

Figure 4. (a) Monthly bunch number production simulated by OPFLSIM3 using default parameter settings, compared with data for three field sites

(b), (c), (d) of varying productivity.

Notes: To fac�l�tate compar�son the scales on each ax�s are standardized. For origins and details of the field data, see Henson and Mohd Tayeb (2004).


(a)

(b)

(c)

(d)

Bunchnumberperpalmonapeatsite

Monthsafterplanting

Bunchnumberperpalmonacoastalsite

Monthsafterplanting

Bunchnumberperpalmonainlandsite

Monthsafterplanting

Bunchnumber:OPFLSIM3

Monthsafterplanting

8

BBP

(kg

palm

-1m

th-1)

BBP

(kg

palm

-1m

th-1)

BBP

(kg

palm

-1m

th-1)

BBP

(kg

palm

-1m

th-1)

Figure 5. As for Figure 4 but showing bunch biomass production (BBP).

Note: The mean bunch component values from the model and the s�tes over the per�ods shown were:

‘Site’ Bunch number MBWT BBP (palm-1 yr-1) (kg) (t ha-1 yr-1)

Model 16.20 14.63 16.36Peat s�te 20.39 9.27 13.28Coastal s�te 14.44 16.77 16.21Inland s�te 9.60 16.43 11.94

Bunc

hnu

mbe

r(ha

-1m

th-1)

BBP

(kg

palm

-1m

th-1)

Figure 6. Effects on (a) bunch number and (b) bunch biomass production (BBP) of varying the number of stress-generating nodes (SGNs) at which live male inflorescences can occur.


(a) Bunchbiomassproduction:OPFLSIM3

Monthsafterplanting Monthsafterplanting

Bunchbiomassproductiononapeatsite(b)

(c) Bunchbiomassproductiononacoastalsite Bunchbiomassproductiononaninlandsite(d)

Monthsafterplanting Monthsafterplanting

(a) Bunchnumber

NumberofSGNspermittingmales

Bunchbiomassproduction

NumberofSGNspermittingmales

(b)1500

1450

1400

1350

190

180

170

9

Figure 7. Effects on cycles in (a) bunch number and (b) bunch biomass production (BBP) of restricting live male inflorescences to the first four (last male at Frond 23) or to all ten (last male at Frond 29) stress-generating fronds.

Note: Mean values for the two cases are �ncluded �n Figure 6.

Bunc

hnu

mbe

r(ha

-1 m

th-1)

BBP

(tha

-1m

th-1)

Figure 8. Effects on bunch number cycles of allowing the gender-sensitive node (GSN) to vary with palm age.


Bunchnumber(a)

Bunchbiomassproduction

Months

Months

Bunchnumbers;averageGSN=-23

Bunc

hnu

mbe

r(ha

-1 m

th-1)

Months

(b)

10

Figure 9. Effects on bunch number cycles of introducing seasonal cycling in the position of stress-generating nodes (SGN), with three amplitudes (a, b, c) of SGN cycles compared with the

non-cycling (constant) control.

Bunc

hnu

mbe

r(ha

-1 m

th-1)

Bunc

hnu

mbe

r(ha

-1 m

th-1)

Bunc

hnu

mbe

r(ha

-1 m

th-1)


Bunchnumber;SGNamplitude=1(a)

Months

Bunchnumber;SGNamplitude=3(b)

Months

(c) Bunchnumber;SGNamplitude=6

Months

11

observed between bunch number per palm and MBWT.

From the relat�onsh�p between MBWT and bunch number g�ven for pooled data �n Figure 2, �t �s poss�ble from the�r product to calculate the total bunch y�eld. Plott�ng the total y�eld aga�nst bunch number (Figure 10) shows the former to be greatest at �ntermed�ate bunch numbers and so below the max�mum we�ghts. As the mean bunch number �s v�rtually a l�near funct�on of FEMREG, max�mum BBP occurs w�th �ntermed�ate FEMREG values, and peaks at FEMREG < 1.0 (Figure 11).

Us�ng the long-term MBWT var�able opt�on together w�th FEMREG prov�des a conven�ent means of s�mulat�ng s�tes w�th d�fferent y�eld potent�al, d�fferences that are often expressed �n terms of both bunch number and MBWT (e.g. Figure 5).

Short-Term Variation in Mean Bunch Weight

Short-term changes �n MBWT appear to be seasonally related and may be a consequence e�ther of the cycl�ng �n bunch load (Breure and Corley, 1992), seasonal changes in pollination efficiency (Donough et al., 1996; Rao and Law, 1998) or var�at�on �n water supply. The regulat�on of MBWT via fruiting activity, pollination level, water deficit or as a result of an artificially imposed annual trend, �s descr�bed elsewhere (Henson, 2007).

Gender-Specific Abortion Thresholds

The effects of assum�ng d�fferent levels of sens�t�v�ty to abort�on by male and female inflorescences are illustrated in Figure 12. Female inflorescence numbers increased curvilinearly as the female abort�on threshold (i.e. the stress level above wh�ch abort�on occurs) was ra�sed, and were l�ttle affected by the male threshold. In contrast, male numbers were dependent on both the female and the male thresholds, w�th a marked �nteract�on be�ng �nd�cated at low and moderate male thresholds. For the extreme case, when the female abort�on threshold was set to zero, result�ng �n 100% abort�on of females, ne�ther males nor females were recorded at anthes�s. Th�s effect can be accounted for �n the follow�ng way. W�th complete abort�on, no females surv�ved to produce bunches and hence, the stress-sum generated by the SGNs remained low. This resulted in all the inflorescences becom�ng female, s�nce the stress-sum affect�ng gender rema�ned below the female threshold. Hence, no males were �n�t�ated. The product�on of males thus becomes dependant on the extent to wh�ch the stress s�gnal allows females to be formed. The extent to wh�ch abort�on var�es w�th gender

can be further exam�ned us�ng the opt�on descr�bed below, to output sex at d�fferent frond pos�t�ons.

Testing Alternatives for Generating Endogenous Stress Signals

The method used �n the prev�ous OPFLSIM models to generate the stress-sums determ�n�ng gender and abort�on �nvolved us�ng scores based on the number and type of inflorescence/bunch present at the SGNs. Th�s can be cr�t�c�sed for be�ng too crude and fa�l�ng to take account of changes �n s�nk strength due to changes �n bunch s�ze and/or for giving too much weight to male inflorescences as sources of stress. Methods to mod�fy the latter have already been addressed.

The use of bunch load as the determ�nant of stress affect�ng both abort�on and gender, resulted �n bunch numbers and y�elds dur�ng the early years of product�on be�ng spur�ously h�gh (Figure 14a). Th�s �s because the bunch load �n the early years �s low (due to low bunch we�ghts) and, thus, so too are the stress-sums when these are based on bunch b�omass (Figure 13). It can be argued that the generat�on of stress, result�ng from bunch load, w�ll partly depend on ass�m�late supply and the extent to wh�ch th�s caters to the demands of the bunch s�nks. Source act�v�ty �n the early years may be restr�cted by �ncomplete canopy cover, so result�ng �n greater stress generat�on per un�t bunch we�ght. Thus, even the small bunches, such as occur on young palms, may be act�ve stress sources. Th�s can be better allowed for by assuming inflorescence/bunch number (h�gh �n young palms), rather than mass, to be �n�t�ally more �mportant �n determ�n�ng stress generat�on.

In general, the use of opt�ons �nvolv�ng bunch b�omass resulted �n less regular y�eld patterns than d�d the use of scores that emphas�ze bunch number (Figure 14). As shown �n Table 2, of the four opt�ons �nvolv�ng b�omass, bas�ng SEXSUM on bunch b�omass plus male-generated scores, and ABSUM on scores alone (male and female), resulted �n mean y�elds be�ng most s�m�lar to the default (i.e. all score) method.

Output of Inflorescence Status at Different Frond Positions

Follow�ng Jones (1997), the standard model outputs the proportions of inflorescence types present at frond number 20, wh�ch �s assumed to be the frond at wh�ch anthes�s occurs. In OPFLSIM3, inflorescence types and number can be examined at d�fferent stages of growth by request�ng the output at any frond pos�t�on. By runn�ng the program several times, the history of inflorescence development can


12

Variation in the Rate of Node Production by Individual Palms

Th�s opt�on allows the rate of node product�on (equ�valent to frond product�on rate) to vary for �nd�v�dual palms w�th the max�mum poss�ble range, though not the mean, specified by the value of a factor termed RFR. Three examples of such var�at�on, d�ffer�ng �n degree, are shown �n Figure 17, wh�le Figure 18a shows the relat�onsh�p between the mean NPR and the random factor, RF2, the max�mum range of wh�ch �s set by RFR.

Vary�ng �nd�v�dual palm NPR had only a m�nor effect on total BBP produced over all nodes (wh�ch var�ed by no more than 1% from the control), but

be traced and, from the data, the abort�on of male and female inflorescences separately assessed.

Figure 15 g�ves two examples of changes �n inflorescence numbers following sex determination and abort�on. Dur�ng the �nterval between these events and after abort�on, the percentages are relat�vely constant; any var�at�on be�ng due to the random factor used to generate the stress-sums. In the present examples, the analysis is simplified by the om�ss�on of hermaphrod�tes.

The data obta�ned allow the percentage abortion of male and female inflorescences to be separately assessed. Summary results for the examples �n Figure 15 are g�ven �n Table 3. The same (default) abort�on threshold sett�ng of 35 was used for both sexes. The results confirm other output from th�s and earl�er vers�ons of OPFLSIM that males are more prone to abort.

To extend the results �n Table 3, tests were run using sex-specific abortion thresholds. Obtaining output for four frond pos�t�ons, namely, GSN + 1, the abort�on-sens�t�ve node (AbSN), AbSN + 1 and frond 20, is adequate for calculating sex-specific abortion. The mean of the values at the first two pos�t�ons g�ves the pre-abort�on levels and at the last two, the post-abort�on level. The d�fference between the two sets represents the number aborted and can be expressed as a percentage of the pre-abort�on number. Figure 16 shows how changes �n the male sens�t�v�ty to abort�on determ�ne wh�ch sex suffers most abort�on. The response to the male abort�on threshold proved h�ghly sens�t�ve.

Mea

nbu

nch

fresh

wei

ght(

kg)

Figure 10. Relationships between mean bunch fresh weight (MBWT), bunch biomass production (BBP) and bunch number.

Note: Data for MBWT versus bunch number are pooled from Figure 2 w�th BBP der�ved as the product of bunch number per hectare x MBWT x 0.53, where 0.53 represents the fract�on of dry matter �n FFB.

BBP

(tha

-1y

r-1)

Figure 11. Changes in bunch biomass production (BBP) with FEMREG, obtained using the option to link mean

bunch weight with bunch number.


MBWTandBBPvs.bunchnumber

Bunchnumber(palm-1yr-1)

Bunc

hbi

omas

spr

oduc

tion

(tha

-1y

r-1)

BBPvs.FEMREG

FEMREG

13

%fe

mal

es

%fe

mal

es

%m

ales

%m

ales

%a

borti

on

%a

borti

on

Figure 12. Effects of varying sex-specific abortion thresholds on the proportions of female, male and aborted inflorescences.

Notes: Data are means for 770 node �n�t�at�on numbers (c. 30 year’s growth). Each graph shows the effect of vary�ng the female or male abort�on threshold us�ng three levels of male (MAb) or female (FAb) threshold.


Effectoffemaleabortionsettingonfemaleinflorescences

FemaleABORTsetting

Effectofmaleabortionsettingonfemaleinflorescences

MaleABORTsetting

Effectoffemaleabortionsettingonmaleinflorescences

Effectofmaleabortionsettingonmaleinflorescences

FemaleABORTsetting MaleABORTsetting

Effectoffemaleabortionsettingontotalabortions

FemaleABORTsetting

Effectofmaleabortionsettingontotalabortions

MaleABORTsetting

(a) (b)

(c) (d)

(e) (f)

14

the y�eld per un�t t�me (e.g. annual y�eld) was significantly affected (Figure 18b), as m�ght be expected from the changes �n the relat�onsh�p between node number and t�me,

Some effects on peak cycles of vary�ng �nd�v�dual palm NPR are shown �n Figure 19. The peak frequency can be e�ther �ncreased or decreased depending on RF2, there being a significant negative relat�onsh�p (P < 0.001) between mean cycle lengths and RF2.

External Stress Options

Of the three external factors that may be examined with the model, the water deficit and poll�nat�on rout�nes are descr�bed elsewhere (Henson, 2007). Hence, only the defol�at�on opt�on w�ll be dealt w�th here.

The defol�at�on stress opt�on �n OPFLSIM3 �s a development of the frond prun�ng treatment �ncluded �n prev�ous OPFLSIM vers�ons. It can be regarded as s�mulat�ng e�ther the effects of pest attack or of over-prun�ng. Defol�at�on resulted �n a transient reduction in female inflorescences and, hence, bunch number (Figure 20) and an �ncrease �n males and abort�on (Figure 21). Defol�at�on also induced a phase shift in the flowering and, hence, bunch number cycle (Figure 20), but whether or not th�s occurs depends on the t�m�ng of the fol�age loss. This effect was first observed by Jones (1997) in his original flowering model, and has practical �mpl�cat�ons for the �nterpretat�on of frond prun�ng experiments in the field.

In general, the defol�at�on effects are qu�te trans�ent and, as �solated events, have l�ttle effect

TABLE 2. ThE ChOICE OF OPTIONS USED TO GENERATE STRESS-SUMS AND ThEIR EFFECTS ON BUNCh NUMBER AND BUNCh BIOMASS PRODUCTION*

SEXSUM based on: ABSUM based on:

Bunch number Bunch biomass production

palm-1 yr-1 % of option 1

t ha-1 yr-1 % of option 1

1 scores scores 14.7 100 17.36 100

2abunch b�omass

bunch b�omass 17.6 119.7 18.76 108.1

2b scores 16.2 110.2 18.26 105.2

3abunch b�omass plus male scores

bunch b�omass plus male scores

17.6 119.7 18.59 107.1

3b scores 15.7 106.8 17.57 101.2

Note: *Data are means over 21 years from the 3rd to 23rd year after plant�ng.

on the long-term y�eld, w�th a 9% reduct�on �n BBP be�ng the max�mum observed �n a ser�es of 21 tests.

DISCUSSION AND CONCLUSIONS

Some of the �mprovements proposed on release of OPFLSIM1 and 2 have now been �ncorporated �nto the new model, w�th the a�m of produc�ng a more hol�st�c and versat�le tool. The add�t�onal rout�nes aim to enhance flexibility and cater for external as well as �nternal cond�t�ons. As well as operat�ng as an �ndependent model, OPFLSIM3 may also be �nterfaced w�th the dry matter product�on model, OPRODSIM, to prov�de a means of regulat�ng bunch product�on based on both source and s�nk capac�ty. In add�t�on, the prov�s�on �n OPFLSIM3 for conduct�ng a full bunch component analys�s perm�ts the add�t�onal assessment of o�l and kernel y�eld as well as that of the�r potent�al extract�on rates.

A major uncerta�nty �n the present model and �ts predecessors concerns the relat�onsh�p between bunch load and stress generat�on, w�th both the nature and mode of act�on of the stress s�gnal(s) yet to be identified. Two possibilities have been mooted (Corley and Breure, 1992), e�ther a s�gnal produced by the develop�ng embryos and hence, related to seed number, or a s�gnal related to the s�nk demand by bunches and hence, dependent on ass�m�late supply and growth, part�cularly the rate of format�on of l�p�ds, wh�ch have the h�ghest ass�m�late requ�rement of the bunch const�tuents.

If ass�m�late �s the controll�ng factor, then the probable need to take account of both the supply as well as the demand for ass�m�lates by develop�ng bunches cons�derably compl�cates the �ssue. Wh�le


}}

15

rough quant�tat�ve relat�onsh�ps can be der�ved between future y�elds and current bunch load est�mated from harvest we�ghts (Corley and Breure, 1992), these may have to be adjusted �n the l�ght of any changes �n the ass�m�late supply and supply/demand rat�o, such as are l�kely to occur w�th palm age and env�ronment. It �s proposed that l�m�ted source supply �n the early years (due to �ncomplete canopy cover) may render the bunch load alone an �nappropr�ate �nd�cator of stress s�gnal strength.

A further compl�cat�on �s that abort�on and sex determ�nat�on may be subject to d�fferent controls. Th�s �s �mpl�ed �n the model wh�ch, based on observat�ons of de Berchoux and Gascon (1965), l�m�ts the frond pos�t�ons generat�ng abort�on stress to the early stages of bunch development [see Corley (1977) and Jones (1997) for further d�scuss�on]. As

Figure 13. Comparison of stress-sums affecting (a) abortion (ABSUM) and (b) gender (SEXSUM), generated using stress scores alone or bunch biomass plus male scores.

Abs

umSe

xsum

noted by Corley (1977), th�s favours a hormonal, as opposed to an ass�m�late-l�nked, abort�on-stress s�gnal and co-�nc�dentally accounts for the poor s�mulat�on of early y�eld when both abort�on and sex rat�o were assumed dependant on bunch load (Figure 14, opt�on 2a).

Yet a further unknown factor �s whether male inflorescences contribute to stress generation. This does not appear to have been the subject of any pract�cal �nvest�gat�ons. Wh�le the dry mass of males �s cons�derably lower than that of a bunch, males at anthes�s exh�b�t a marked peak �n resp�rat�on (Dufrene, 1989; Henson and Chang, 2000) that could be �nd�cat�ve of a sudden h�gh ass�m�late demand, wh�ch may then provoke a trans�ent stress s�gnal. The model presently prov�des the opt�ons of e�ther �gnor�ng males or moderat�ng the�r effects.


ABSuM

Nodeinitiationnumber

SEXSuM

Nodeinitiationnumber

(a)

(b)

16

Figure 14. Comparison of bunch biomass production (BBP) patterns resulting from the use of three alternative options for formulating stress-sums affecting abortion and gender.

Note: See text for further deta�ls.

BBP

(tha

-1m

th-1)

BBP

(tha

-1m

th-1)

BBP

(tha

-1m

th-1)


Methodsofstressgeneration-Scoresvs.option2a

Months

Methodsofstressgeneration-Scoresvs.option2b

Months

Months

Methodsofstressgeneration-Scoresvs.option3b

17

%o

ftot

alin

flore

scen

cec

lass

es%

oft

otal

inflo

resc

ence

cla

sses

Figure 15. Two examples of changes in inflorescence status during palm growth obtained using the option to output inflorescence data at different frond numbers.

Notes: The gender-sens�t�ve (GSN) and abort�on-sens�t�ve (AbSN) nodes (frond numbers) are �nd�cated. Data are means for 740 node �n�t�at�on numbers.


TABLE 3. CALCULATION OF ThE PERCENTAGE ABORTION OF MALE AND FEMALE INFLORESCENCES FROM MEAN VALUES OUTPUT AT DIFFERENT FROND NUMBERS

Gender-sensitive node

Inflorescence class

Mean % pre-abortion

Mean % post-abortion

% abortion of initial inflorescences1

-28 Male 42.6 36.2 15.02

Female 57.4 51.7 9.93

Aborted 0 12.1 -

-11

Male 44.7 35.6 20.30

Female 55.3 52.0 5.96

Aborted 0 12.4 -

Note: 1Calculated as [(mean % pre-abort�on - mean % post-abort�on)/(mean % pre-abort�on)] * 100.

GSN=-28;AbSN=+10

GSN=-11;AbSN=+10

Frondnumber

Frondnumber

(a)

(b)

18

Figure 16. Effect of male inflorescence abortion threshold on the percentage of aborted female, aborted male and total aborted inflorescences.

Notes: The female abort�on threshold was held constant at 30. Default values were used for all the other �nput var�ables.

%o

fabo

rted

inflo

resc

ence

Figure 17. Variation between individual palms in the relative mean annual rate of node production, generated during three random runs of the model, where SD is the standard deviation per run.

Notes: For all runs the factor RFR was set to 0.5. The node product�on rates (NPR) are the means of 440 nodes. Relative refers to the NPR as a fract�on of the mean rate obta�ned �n the absence of random var�at�on.

Nod

epr

oduc

tion

rate

(p

alm

-1y

r-1)

BBP

(tha

-1y

r-1)

Figure 18. Relationships between (a) the mean node production rate and the mean random factor, RF2, and (b) the mean bunch biomass production (BBP) and RF2.

Notes: The factor RFR, controll�ng the m�n�mum and max�mum poss�ble RF2, was held constant at 0.5. The control represents the absence of any palm-to-palm var�at�on �n the node product�on rate.


Effectofmaleabortionthreshold

Maleabortionthreshold

Rela

tive

NPR

(pal

m-1

yr-1

)

Variationinmeannodeproductionrate

Nodeproductionratevs.RF2

RF2

BBPperannumvs.RF2

RF2

(a) (b)

Palm

19

Figure 19. Three examples of bunch number patterns produced using variable individual palm node production rates (NPR) versus a control with standard NPR.

Bunc

hnu

mbe

r(ha

-1m

th-1)

Bunc

hnu

mbe

r(ha

-1m

th-1)

Bunc

hnu

mbe

r(ha

-1m

th-1)


Months

Inflorescencenumbers:variableNPR<control

Inflorescencenumbers:variableNPR=control

Months

Inflorescencenumbers:variableNPR>control

Months

(a)

(b)

(c)

20

Figure 20. Response of bunch number to defoliation at times (defined by the node initiation number) indicated by arrows.

Notes: Twenty fronds per palm were removed at the t�mes �nd�cated by the arrows. Controls were unpruned.

Bunc

hnu

mbe

r(ha

-1m

th-1)

Bunc

hnu

mbe

r(ha

-1m

th-1)

Bunc

hnu

mbe

r(ha

-1m

th-1)


Palmsdefoliatedatnodeinitiationnumber480

Monthsafterplanting


Monthsafterplanting


Monthsafterplanting

t

t

t

(a)

(b)

(c)

21

Other new opt�ons are prov�ded �n the model that attempt to �mprove the s�mulat�on of palm behav�our, such as bunch load regulat�on of s�ngle bunch we�ght, bunch number-�nduced moderat�on of long-term mean bunch we�ght, var�at�on between palms �n node product�on rate, age-dependent changes �n the node(s) at wh�ch sex �s determ�ned and d�fferent�al sens�t�v�ty to abort�on by male and female inflorescences. Again, for many of these processes, there are but l�m�ted data or understand�ng of the factors that control them.

More �nformat�on �s also requ�red concern�ng factors affect�ng the stage or node at wh�ch gender �s determ�ned. Stud�es �nd�cate th�s can be very w�de and hence, the default values used �n the model are from node –28 to node –4. There �s also

Figure 21. Effects of defoliation on (a) male inflorescence numbers and (b) abortion.

Notes: Twenty fronds per palm were removed at the t�mes �nd�cated by the arrows. Controls were unpruned.

%m

ales

%a

borti

on

ev�dence (Corley et al., 1995) for there be�ng two stages, centred at around nodes –25 and –5 (though poss�bly earl�er �n some mater�als), at wh�ch gender is influenced, with sex change being possible at the second, later, stage. Th�s process rema�ns to be modelled effect�vely and, at present, �t �s the latest node specified that determines when gender is fixed �n OPFLSIM3.

Several stud�es have �nd�cated the l�kely importance of rates of inflorescence and bunch development on the seasonal y�eld patterns (Corley, 1977; Chang et al., 1993; 1995; Lamade et al., 1998). Such effects are catered for by the opt�on to seasonally vary the pos�t�on of the stress-generat�ng nodes, so shorten�ng or lengthen�ng the �nterval between node �n�t�at�on and anthes�s. Add�t�onally,


Malecycles:Defoliatedatnodeinitiationnumber480

Abortion:Defoliatedatnodeinitiationnumber480

Nodecycle

Nodecycle

t

t

(a)

(b)

22

a seasonal cycle �n the frequency of node product�on can be �ntroduced.

The prev�ous model, OPFLSIM2, was able to reproduce annual y�eld patterns at several s�tes after the appropr�ate adjustment of �nput parameters, but difficulty was met in simulating shorter-term yield var�at�on (Henson and Jones, 2005a). Th�s �s st�ll problemat�c but the s�mulat�ons can be �mproved �f the s�te y�eld potent�al �s taken �nto account by adjustment of the var�able FEMREG, and �f, �n add�t�on, the opt�on �s taken to relate s�ngle bunch we�ght to bunch number.

ACKNOWLEDGEMENT

I am most grateful to Chang, K C and Dr L H Jones for the�r pat�ent read�ng of the manuscr�pt and for percept�ve comments lead�ng to �ts �mprovement.

REFERENCES

BREURE, C J and CORLEY, R H V (1992). Fru�t�ng act�v�ty, growth and y�eld of o�l palm. II. Observat�ons �n untreated populat�ons. Experimental Agriculture, 28: 111-121.

BROEKMANS, A F M (1957). Growth, flowering and y�eld of the o�l palm �n N�ger�a. J. West African Institute for Oil Palm Research, 2: 187-220.

CHANG, K C; RAO, V; HASNUDDIN, M Y and ZAKARIA, A (1993). The role of developmental times of inflorescences in the seasonal flowering behav�our of o�l palm. Unpubl�shed manuscr�pt. 14 pp.

CHANG, K C; RAO, V; HASNUDDIN, M Y and ZAKARIA, A (1995). Inflorescence abortion and flowering cycles in oil palm. Proc. of the 1993 PORIM International Palm Oil Congress - Agriculture Module. PORIM, Bang�. p. 519-524.

CHOW, C S and JAMALUDDIN NASIR (1995). Expected Malays�an palm o�l product�on �n 1996 and observat�ons on age effects �n some o�l palm y�eld components. PORIM Bulletin No. 31: 16-21.

CORLEY, R H V (1976). Inflorescence abortion and sex determ�nat�on. Chapter 4. Oil Palm Research (Corley, R H V; Hardon, J J and Wood, B J eds.). Elsev�er, Amsterdam. p. 37-54.

CORLEY, R H V (1977). O�l palm y�eld components and y�eld cycles. International Developments in Oil Palm (Earp, D A and Newall, W eds.). Incorporated Soc�ety of Planters, Kuala Lumpur. p. 116-129.

CORLEY, R H V and BREURE, C J (1992). Fru�t�ng act�v�ty, growth and y�eld of o�l palm. I. Effects of fru�t removal. Experimental Agriculture, 28: 99-109.

CORLEY, R H V; NG, M and DONOUGH, C R (1995). Effects of defol�at�on on sex d�fferent�at�on �n o�l palm clones. Experimental Agriculture, 31: 177-189.

de BERCHOUX, C and GASCON, J P (1965). Character�st�ques vegetat�ves de c�nq descendances d’Elaeis guineensis Jacq. Prem�eres donnes b�ometr�ques. Relat�ons entre d�vers caracteres et la product�on. Oleagineux, 20: 1-7.

DONOUGH, C R; CHEW, K W and LAW, I H (1996). Effect of fru�t set on OER and KER: results from stud�es at Pamol Estates (Sabah) Sdn Bhd. The Planter, 72: 203-219.

DUFRENE, E (1989). Photosynthese, consommation en eau et modelisation de la production chez le palmier a huile (Elae�s gu�neens�s Jacq.). Doctoral thes�s, Un�vers�te de Par�s-Sud Centre d’Orsay. 154 pp.

HARTLEY, C W S (1977). The Oil Palm. 2nd ed�t�on. Longman, London. 806 pp.

HENSON, I E (2005). OPRODSIM, a versat�le, mechan�st�c s�mulat�on model of o�l palm dry matter product�on and y�eld. Proc. of the PIPOC 2005 International Palm Oil Congress – Agriculture Conference. MPOB, Bang�. p. 801-832.

HENSON, I E (2007). Modell�ng o�l palm y�eld based on source and s�nk. Oil Palm Bulletin. In press.

HENSON, I E and CHANG, K C (2000). O�l palm product�v�ty and �ts component processes. Advances in Oil Palm Research. Volume 1. MPOB, Bang�. p. 97-145.

HENSON, I E and JONES, L H (2005a). OPFLSIM1 and 2: Seasonal oil palm flowering models based on endogenous mechan�sms. Proc. of the PIPOC 2005 International Palm Oil Congress – Agriculture Conference. MPOB, Bang�. p. 772-800.

HENSON, I E and JONES, L H (2005b). Modelling Flowering and Seasonal Yield Cycles of Oil Palm. Simulation Models for Teaching and Research. Technical Manual. MPOB, Bang�. 97 pp.

HENSON, I E and JONES, L H (2005c). Modelling Flowering and Seasonal Yield Cycles of Oil Palm. Simulation Models for Teaching and Research. Users’ Guide. MPOB, Bang�. 36 pp.


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HENSON, I E and MOHD TAYEB, D (2004). Seasonal var�at�on �n y�eld and developmental processes �n an o�l palm dens�ty tr�al on a peat so�l. I. Y�eld and bunch number components. J. Oil Palm Research Vol. 16 No. 2: 88-105.

JONES, L H (1997). The effects of leaf prun�ng and other stresses on sex determ�nat�on �n the o�l palm and the�r representat�on by a computer s�mulat�on. J. Theoretical Biology, 187: 241-260.

LAMADE, E; BONNOT, F; PAMIN, K and SETYO, I E (1998). Quant�tat�ve approach of o�l palm phenology �n d�fferent env�ronments for La Me

Del� and Yangamb� Del� mater�als - �nvest�gat�ons in the inflorescence cycles process. Proc. of the 1998 International Oil Palm Conference. Nusa Dua, Bal�, Indones�a. p. 287-301.

RAO, V and LAW, I H (1998). The problem of poor fru�t set �n parts of East Malays�a. The Planter, 74: 463-483.

TAYLOR, M A W; THIRUGNANASAMBANTHAR, S and STILL, D C (1978). Hydrolog�cal aspects of agr�cultural plann�ng and �rr�gat�on des�gn. Hydrological Procedure No. 20. Dra�nage and Irr�gat�on D�v�s�on, M�n�stry of Agr�culture, Malays�a. p. 31.


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Appendix 1

List of Abbreviations Used in Text

ABSUM Sum of stress un�ts affect�ng abort�on

AbSN Abort�on-sens�t�ve node

BARMAX Bunch assimilate requirement based on female inflorescence production

BBP Bunch b�omass (dry matter) product�on

BN Bunch number (per ha)

DAP Days after plant�ng

DPN Days between �n�t�at�on of success�ve nodes

DEFOL Stress-sum generated by defol�at�on

FASW Fract�onal ava�lable so�l water

FEMREG Female inflorescence regulating factor

FFB Fresh fru�t bunches

Fab Female inflorescence abortion threshold

GSN Gender-sens�t�ve node

Mab Male inflorescence abortion threshold

MARMAX Male inflorescence assimilate requirement based on male inflorescence production

MBWT Mean bunch fresh we�ght

MINH Male inflorescence number per hectare

NPR Node product�on rate

RFR Scal�ng factor affect�ng perm�tted range of var�at�on �n RF2

RF2 Random�zat�on factor affect�ng �nd�v�dual palm node product�on rate

SEXSUM Sum of stress units affecting inflorescence gender

SGN Stress-generat�ng nodes

TARMAX Total assimilate requirement for males and bunches based on inflorescence production

WSSUM Sum of stress units generated by soil water deficit


oil palm bulletin 53 (november 2006) p. 1 - 24 opflsim3...

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