Although fruit bunch production by oil palm is often considered to be mostly dependent upon the ability of the plant to produce assimilates, the availability of an adequate sink is also of importance in optimizing yield. The model OPRODSIM initially simulated yield based on the assimilates remaining after the requirements of vegetative growth had been met, in accordance with an ‘overflow’principle. Using this ‘source-limited’approach (i.e. yield dependent only on source supply), sink limitations (in the form of adequate numbers of pollinated female inflorescences) are ignored, leading to a possible overestimation of yield. This paper describes an attempt to produce a more holistic model in which both source and sink combine to determine yield. The source depends on the canopy gross assimilation rate while the sink capacity is defined by the number of fertile female inflorescences and the size of the resulting fruit bunches. As pollination is essential for normal bunch development, a sufficient production of male inflorescences is also required as a pollen source. Inflorescence production is simulated using a routine based on the model OPFLSIM, which determines inflorescence gender and development node-by-node for a population of palms. The sex ratio and abortion rate of inflorescences are dependent on a variety of factors including palm age, bunch load, the position of gender- and abortion-sensitive nodes in relation to the apex, and external stresses. Pollination, sexual homogeneity (i.e. fully female versus hermaphrodite inflorescences), palm age, current bunch number and bunch load combine to determine the weight of each bunch. The product of bunch number and weight constitutes the ‘sink demand’. Actual yield depends on which factor – source or sink – is the most limiting. If the latter, then ‘excess’ assimilate (i.e. that remaining after sink requirements have been met) may be stored and withdrawn later to support bunch growth when sink demand exceeds source supply. However, limits are placed by the model on the maximum storage capacity (which is related to the standing trunk biomass). The model calculates parameters either on a daily or node-by-node basis and produces monthly and annual yield summaries. Examples are given comparing source, sink and combined estimates of yield for both non-stress conditions and for limiting conditions of water deficit and inadequate pollination.
Penghasilan tandan sawit walaupun lazim dikatakan bergantung sepenuhnya pada keupayaan pokok untuk menghasilkan asimilat, kehadiran sinki yang mencukupi juga penting bagi memperoleh hasil maksimum. Bagi model OPRODSIM, pada asalnya hasil disimulasi berasaskan baki asimilat setelah keperluan pertumbuhan tampang berlaku seiring dengan prinsip ‘limpahan’.Dengan kaedah ‘sinki terhad’, segala penghad sinki diabaikan menjurus kepada lebihan anggaran hasil. Artikel ini menerangkan langkah untuk menghasilkan versi yang lebih holistik yang menggabungkan kedua-dua sumber dan sinki bagi penentuan hasil. Sinki bergantung pada kadar asimilasi kanopi kasar manakala keupayaan sinki didefinisikan sebagai bilangan mayang betina subur dan potensi saiz tandan buah. Memandangkan pendebungaan perlu untuk perkembangan normal, penghasilan mayang jantan yang cukup perlu sebagai sumber debunga. Penghasilan mayang disimulasi dengan menggunakan rutin berasaskan model OPFLSIM yang mengenal pasti jantina mayang dan perkembangan dari nod ke nod bagi sesuatu populasi sawit. Nisbah jantina dan kadar keguguran mayang bergantung pada pelbagai faktor termasuk umur pokok, beban tandan, kedudukan jantina dan nod yang sensitif terhadap keguguran berkaitan dengan apek dan faktor tekanan luaran. Pendebungaan, keseragaman seksual (iaitu betina sepenuhnya berbanding mayang hermafrodit), umur pokok, bilangan tandan semasa dan beban tandan sama-sama menentukan potensi berat setiap tandan. Bilangan Oil Palm Bulletin 54 (May 2007) p. 27 – 51 28 potensi tandan dan berat menghasilkan ‘permintaan sinki’. Hasil sebenar bergantung pada faktor sumber atau sinki dan ini paling terhad. Sekiranya terhad, kelebihan asimilat (iaitu baki selepas keperluan sinki telah dipenuhi) boleh disimpan dan dikeluarkan kemudian bagi menyokong pertumbuhan tandan apabila permintaan sinki melebihi bekalan sumber. Bagaimanapun, had terletak pada keupayaan penyimpanan maksimum (yang berkaitan dengan jisim batang). Model mengira parameter berdasarkan harian atau nod ke nod dan menghasilkan rumusan hasil secara bulanan dan tahunan. Contoh diberi untuk membandingkan sumber, sinki dan anggaran gabungan hasil bagi kedua-dua keadaan tekanan dan keadaan kekurangan air serta pendebungaan.