Modelling Oil Palm Yield Based on Source and Sink

摘要

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 overesti-mation 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 sufficientproduction 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 sexratio 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 If the latter, then 'excess' assimilate (i.e. that remaining after sink requirements have been met) may be stored and withdrawn later to support bunch growth when sink demand exceeds source supply.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.