| Summary: | The demand for palm oil is expected to increase due to the increase in world population.
However, climate change poses significant challenges to the production of oil palm as
its output can be directly affected by abiotic stress, especially water and temperature
stress. Potassium (K) is a crucial element in oil palm plantation as it is directly involved
in the crop physiological processes. Thus this research was designed to determine how
the use of the evapotranspiration replacement (ER) method and potassium fertiliser could
be used to alleviate water and heat stress in oil palm seedlings. In tile first experiment,
four irrigation regimes [100% ER (well -watered), 75% ER (moderate water stress), 50%
ER (high water stress), and 25% ER (severe water stress)] were used to investigate the
effect of different water stress regimes on the physiology of 4-montlls old oil palm
seedlings. Results showed that severe water stress decreased vegetative plant growth,
plant water status, leaf gas exchange, water use efficiency (WUE), and fv/fm (maximwn
efficiency of photosystem II), but the malondialdehyde (MDA) and proline levels of oil
palm seedlings were increased. In the second experiment, tluee levels of potassium rates
(Kl, K2, and K3) with five times applications (170, 340, and 510 kg KCI ha "), (480
960, and 1440 kg KCI ha") (170,340, and 510 kg KCI ha-I), (960, 1920, and 2880 KCI
kg ha "), and (960, 1920, and 2880 kg KCI ha-I) under three different levels of water
stress (100% ER, 75% and 25% ER) were exposed on oil palm seedlings to identify the
best rate of potassium fertiliser under water stress application and to understand the
interaction between drought impacts and potassium application on oil palm seedlings.
The result revealed that water stress hampered the growth of oil palm seedlings. As
potassium fertiliser rates increased, no significant differences in the physiology of the
seedlings were observed except for height, net photosynthesis, and intercellular C02 (C).
However, the biochemical properties (proline, soluble sugars, and phenolics) of oil palm
seedling increased by 50%, 60%, and 55% while MDA decreased by 40% compared to
control when the application ofK was doubled. Yet, there were no significant differences
by applying double rate and triple rate of K. There was also an interaction between
different water treatment levels and the rate of potassium fertiliser on the height, C; and
flavonoid level of oil palm seedlings. In the third experiment, three types of potassium fertiliser (KCI; Potassium chloride, K2S04; Potassium s Ilphate and KN03: Potassium
nitrate) with a double rate of K under three levels of wat r stress (100% ER, 75% ER,
and 25% ER) were exposed to oil palm seedlings to investigate the influence of
potassium source in minimizing water stress effects in this crop. It was found that as the
level of water reduced, the RGR (relative growth rate), LAR (leaf area ratio), L WR (leaf
weight ratio) and SLA (specific leaf area) of oil palm seedlings reduced, but the value
of R:S (root: shoot ratio) improved. The result also revealed that K2S04 increased the
leaf gas exchange and fvlfm as well as reducing the leaf temperature compared to KCI
and KN03. There was an interaction between water stress and the source of K on
respiration rate and electrolyte leakage. K2S04 also reduced the biochemical properties
of oil palm seedlings. In the last experiment, the study was designed to investigate the
effect of elevated temperature on the physiology of oil palm seedlings, to examine the
combination of heat and water stress as well as to explore the potential of potassium
fertiliser in alleviating these stresses. Oil palm seedlings were treated with six regimes:
A (well-watered + control amount of KCI + 30°C), B (well-watered + control amount of
KCI + 32°C), C (moderate water stress + double rate of K2S04 + 30°C), D (moderate
water stress + double rate of K2S04 + 32°C), E (severe water stress + double rate of
KN03 + 30°C) and F (severe water stress + double rate of KN03 + 32°C). The results
showed heat stress decreased vegetative plant growth, plant water status, and increased
leaf temperature. The effects were exacerbated by the combination of water stress.
However, there was no significant effect of high temperature on the leaf gas exchange,
WUE, fv/fm, SPAD chlorophyll value, and biochemical properties of the palms. The level
of MDA, proline, soluble sugar, and lipid peroxidation only greatly increased under
severe water stress. The present study suggests that only the growth of oil palms
seedlings is sensitive to the 2°C rise, but not leaf gas exchange and biochemical
attributes. Potassium fertiliser can play protective role during moderate water stress
under ambient temperature, thus supplying 75% water from soil field capacity, and
doubling K2S04 on oil palm seedlings under water scarcity is recommended. From this
project, it can be concluded that the application of the evapotranspiration replacement
method and potassium fertiliser were able to alleviate the abiotic stress in oil palm
seedlings.
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