Effects of Water Stress on the Physiological Processes and Water Use Efficiency in Oil Palm

Malaysia is currently the major producer of palm oil in the world with a total production of crude palm oil of about 15 million tonnes in 2005. This major commercial crop in Malaysia covers an area of about 4 million hectares of agricultural land. Due to its important role, various research and development are still on going to improve and to ensure the sustainability of this industry. In this physiological study of oil palm, focus was given to two different environments and palm age. In the first experiment, physiological evaluation was done on two different planting materials namely the commercial DxP and PS1.1 dwarf palms. This PS1.1 planting material is expected to be shorter, higher yielding, more compact and with desirable fruit qualities. The seedlings were raised in large polybags filled with topsoil. Experiments were initially done at Green House I that was located near the UPM Hydroponics and later, at Green House II situated at the UPM Agriculture Park. Various physiological parameters were studied to compare the performance of both genotypes and their responses to soil drying. Four replicates of ten seedlings per treatment were used. Among the parameters studied were gas exchange, chlorophyll fluorescence, vegetative growth, chlorophyll content, root:shoot ratio, soil moisture and leaf sugar analysis. Based on vegetative measurements, DxP seedlings had 34% longer rachis length than PS1.1 and were 29% taller. The leaves of DxP seedlings had higher relative water content and moisture content as compared to PS1.1. As water is essential for cell growth, this may be one of the factors that enable the DxP seedlings to grow faster. The leaf chlorophyll content was slightly higher in the DxP as compared to PS1.1 seedlings. Fluctuations in leaf sugar contents were found in both genotypes in response to soil drying. DxP seedlings had significantly higher water use efficiency (WUE) (p<0.05) and showed vigorous growth as compared to PS1.1. The PS1.1 seedlings showed higher photosynthetic rate and higher evapotranspiration rate as compared to DxP. PS1.1 seedlings had similar root:shoot ratio as DxP. Both photosynthetic rate and stomatal conductance were reduced in response to soil drying. In the second experiment, the study was carried out at the ESPEK Tanjung Genting, Sintuk located in North Kedah. The site was chosen because of the seasonal dry period that occurred at the end of the year and ends in the first quarter of the following year (Dec to Mac). Comparisons of physiological responses were done between irrigated and non-irrigated palms. Two treatments with three replicates of 16-recorded palms per replicate were used. A total of 96 DxP oil palms planted in July 2000 were involved in this study. Irrigation was done using the drip system, where the Netafim drip tape was aligned at one side of the planting rows. A higher photosynthetic rate or gas exchange response to CO2 concentration was observed in the irrigated palms as shown by the ACi curve. But there was no significant response of both irrigated and control palms to the different light intensities. The leaf moisture content of irrigated palms was higher than the control, but the relative water content and chlorophyll content were lower than control. No statistically significant difference was found in the canopy study, such as the leaf area index and light interception. The instantaneous WUE in the field study showed better response in the irrigated palms as compared to control. Based on chlorophyll fluorescence, palms in the control plots showed lower PSII efficiency. In the first year harvesting, the FFB yield in the irrigated plots was 10% higher than control.

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