Physiological Performance of Oil Palm Inflorescences (Elaeis guineensis Jacq) After Drought Stress on 3 Different Soil Types in Central Kalimantan

Oil palm is a plantation crop that requires an amount of rainfall ranging from 1,750–2,500 mm/year as a condition for good growth. Long dry conditions will have an impact on decreasing productivity. Water deficit can cause growth stagnation and if it occurs continuously can cause irreversible physiological changes in plants, resulting in death. This study aims to study the relationship between water deficit events and the flowering physiology of oil palm plants in 3 soil types in Central Kalimantan. This study is explorative in nature with a quantitative descriptive research method using 3 types of soil: mineral, peat, sand; and 2 plant ages: Young (=7 years) and Prime (> 7 years) and each observation plot consisted of 10 trees selected systematically 5 x 5. The results showed that the occurrence of water deficit had different effects on several phases of FFB formation in phase of sex differentiation & leaf initiated on mineral soil, phase of sex differentiation & female inflorescence on peat and phase of sex differentiation, female inflorescence & inflorescence abortion on sandy soil in the Young plant category. The Prime category occurs in the ripeness, anthesis & inflorescence abortion phases on mineral soils, the anthesis & inflorescence abortion phases on peat and the inflorescence abortion & female inflorescence phases on sandy soils. Apart from the stages of FFB formation, the incidence of water deficit also affects the position of the appearance of bud inflorescences, female & male inflorescences anthesis, male inflorescences receptive & male inflorescences post anthesis, black fruit and red fruit in each soil type and plant category.


Introduction
Oil palm productivity is strongly influenced by many factors such as soil nutrient reserves, nutrient supply, field management, climate, plant material and fertilization [1].Climatic factors play a crucial role for the cultivation of oil palm plants starting from the growing requirements to the FFB harvest stage.Oil palm is a plantation cultivation plant that requires an amount of rainfall ranging from 1,750 -2,500 mm/year and evenly distributed throughout the year, without months or dry periods [2,3] as a condition for good growth.Adequate water availability will support optimal growth and development of oil palm.This is because oil palm plants are sensitive to drought stress events [4], where the frequency of occurrence is strongly influenced by climate anomalies such as El Nino events.[5] reported the 2015 El Nino event which caused a long period of drought that impacted the growth and decreased productivity of oil palm due to water deficit [6,7].The water deficit is calculated based on the balance of soil and plant water using the Tailez method [8], where the balance of groundwater is influenced by water availability, rainfall and evapotranspiration.Water deficit can cause growth stagnation and if it lasts for a long time can cause irreversible (irreversible) physiological changes in plants and can result in death.In general, the response of oil palm plants when experiencing a water deficit is characterized by spear leaves that do not open ≥ 3 per tree.The effect of this water deficit is closely related to the ability of the soil to bind water (water holding capacity) which varies for each type of soil.In 2015, most areas of Indonesia experienced a longer dry season than usual, including Central Kalimantan.This study aims to study the impact of the relationship between water deficit events on the Inflorescencesing physiology of oil palm plants in 3 soil types in Central Kalimantan.

Experimental Site
The study was carried out an commercial plantation of PT Sawit Sumbermas Sarana Tbk.Located in Selangkun Estate (SGE), 2 0 25'42.72"S, 111 0 32'56.19"E and Rungun Estate (RGE), 2 0 23'16.36"S, 111 0 31'47.85"E Kotawaringin Barat Regency, Central Kalimantan province, Indonesia (Table 1).Both site has a tropical humid climate with the peak rainy season occurrs in April and December, with a monthly mean rainfall of 232.1 mm month -1 (averages from 2012 to 2020), and a drier season from June to September, with a monthly mean rainfall of 157.3 mm month -1 (averages from 2012 to 2020) for Selangkun Estate, while Rungun Estate has a peak rainy season occurs in April and November-December with a monthly mean rainfall of 183.9 mm month -1 (averages from 2012 to 2020), and a drier season from June to September, with a monthly mean rainfall of 120.1 mm month -1 (averages from 2012 to 2020).The beginning of the experimental period was recorded from November 2015 to April 2018, with annual rainfall was 3177 mm (SGE), 2757 mm (RGE) in 2016 and 2824 mm (SGE), 2274 mm (RGE) in 2007.To evaluate drought extent during experimental period, climatic water balance (CWB) was calculated as rainfall minus potential evapotranspiration (Table 2 and 3), where potential evapotranspiration (mm month) was calculated according FAO guidelines [9].

Experimental Design
This study is exploratory in nature using a quantitative descriptive research method of 3 types of soil: Mineral, Peat, Sand; and 2 plant age categories: Young (<= 7 years) and Prime (> 7 years) with each observation block consisting of 10 trees selected systematically using the 5 x 5 method.Observation parameters such as emergence and number of Inflorescences buds, Observations were made every month to observe the number of bud Inflorescencess, female Inflorescencess, male Inflorescencess, receptive female Inflorescencess, anthesis male Inflorescencess, post anthesis male Inflorescencess, black fruit and red fruit are carried out in each observation point every month and marked on the object of observation and the frond where the object appears.Observations and the experimental period were carried out after the drought stress event occurred in November 2015 to 2017.

Climatic Conditions
Based on estate data for the 2012-2018 period, it can be seen that in 2015 both the Selangkun Estate (SGE) and the Rungun Estate (RGE) had the lowest rainfall (Table 2).The total rainfall for SGE is 1916 mm/year and RGE is 1694.5 mm/year.This amount is predicted to affect the vegetative and generative growth and development of oil palm plants.Oil palm produces optimally when rainfall is more than 2000 mm per year which is evenly distributed, meaning that there are no dry months, and rainfall is at least 150 mm per month to offset the amount of evapotranspiration [8].Based on CWB calculations, it shows that the incidence of water deficit took place from August to October 2015 in SGE of 293.0 mm, while in RGE the occurrence of water deficit occurred longer, namely from July to October 2015 of 492.4 mm.Whereas in 2016 and 2017 in both SGE and RGE there were no water deficits due to the fact that the annual rainfall has increased and was higher compared to 2015.Drought stress that occurred in 2015 will have an impact over a long period of time on this component.production.This is due to drought stress conditions which are very sensitive to affect processes such as determining the sex of Inflorescencess or abortion in the early stages of Inflorescences formation which require several months or years before the fruit ripens [10,11] and causes cleavage activity.and cell enlargement decreases so that growth conditions in plant tissues are hampered [12].

Effect of Drought Stress on Inflorescencesing Physiology
Drought stress in 2015 showed a significant effect on the decrease in the number of female Inflorescencess, anthesis male Inflorescencess, and the number of aborted Inflorescencess and fruits until 2017 (Table 4), while the number of bunches tended to increase even though it was not statistically significant.The high number of anthesis male Inflorescencess and the high number of aborted Inflorescencess and fruits in 2016 showed a fairly high response of plants to environmental stress.This is because water deficit will have a negative impact on the sex differential of oil palm, increasing the number of female Inflorescences abortions and inhibiting plant growth [13].Fruit growth and development will follow the same pattern and the combination is related to environmental stress problems which will affect variations in fruit development and the ripening process [14].In 2017 or the second year after the occurrence of drought stress began to show improvement marked by an increase in the number of receptive female Inflorescencess and a decrease in the number of aborted Inflorescencess and fruits, even though statistical analysis was not significant.The effect of drought stress on peatlands tends to be lower compared to other soil types which is characterized by a lower number of male Inflorescencess and fruit abortions than mineral and sand soil types.This is presumably due to the availability of water in peat soils which ranges from 100 -1,300% of their dry weight [15] and is sufficient during the dry season compared to mineral and sand soils.The development of black fruit (FFB aged 1 to 4 months) on young plants also looks better and more significant than prime age plants and is still in the normal range.However, young plants during the bunch development period had a significant correlation with higher abortion rates so that the failure rate of bunch formation was higher than prime age plants.The condition of occurrence of drought stress is closely related to the amount of soil water content that can be absorbed by plant roots or plant water available (PWA), whose value is strongly influenced by climatic factors such as the amount of rainfall and the rate of evapotranspiration.Based on the results of this study (Figure 1) it shows that PWA has an effect one month before harvest (BSP) or (late ripeness stage), 8-13 BSP (anthesis and inflorescence abortion stages) in mineral soil types with prime age plants, whereas in Young age affects 33-34 BSP (leaf initiated stage) and 29-30 BSP (end of sex differentiation stage and early stage of inner, outer and bract initiated process).In peat soil types with prime age plants, PWA has an effect on 8-14 BSP (anthesis and inflorescence abortion stages), while on young plants it has an effect on 18-20 BSP (female inflorescence stages), 24-26 BSP (inner, outer and bract initiated process) and 31-32 BSP (sex differentiation stage).In sandy soil types with prime age plants, it affects 8-14 BSP (anthesis and inflorescence abortion stages), while in young plants it affects 14 BSP (inflorescence abortion stages), 16-18 BSP (female inflorescence stages) and 30 BSP (the final stage of the sex differentiation phase) Figure 1.Graph of the relationship between plant water available and the number of bunches in each soil type and oil palm age group

Effect of Drought Stress on Inflorescencesing Physiology
Water deficit conditions will have an impact on some of the nutrients dissolved in the soil solution with the help of water becoming unavailable so that they cannot be absorbed by plants.The K content of leaves decreased in proportion to the amount of water deficit that occurred and correlated with the production of the number of fronds, where the optimum K content of leaves to maintain a fixed number of 24 fronds was 1.1% [16].The number of initiations of Inflorescencesing in oil palm is highly dependent on the production rate of fronds, where the number will decrease following the number of fronds produced [17].The initiation rate of fronds will directly determine the number of potential Inflorescencesing [18].because in each axil of an oil palm frond there is an embryo of a Inflorescences.The initiation rate of fronds is greatly affected by drought [19,20], where drought causes the leaf opening rate to decrease rapidly [19] resulting in accumulation of unopened leaves in the middle of the plant canopy [21,22].
This can be seen from the observations in this study where the emergence of Inflorescencess and fruit experienced a shift in the number pattern of midribs due to delayed opening of new leaves in response to water pressure, and stomatal opening was strongly influenced by a deficit in air vapor pressure (VPD) and ground water availability [23,6].On mineral soils, both prime and young plants show a delay in the appearance of Inflorescences buds, male and female Inflorescencess, which generally appear in the range of fronds that are younger than the 17th frond [24] to shift to older fronds.from the 20th frond (Figure 2).This phenomenon occurred consistently from 3 months after drought stress (BAWD) to 25 BAWD for prime age plants, whereas in young plants it still occurred until the 28th BAWD observation.The same thing also happened in peat soils for both prime and young plants, but the effect only started to occur at 9 BAWD.On peat soils with prime age plants, a vacancy in the number of male and female Inflorescencess was found for ±5 months at 22-26 BAWD, while at young ages it occurred for ±3 months (12-14 BAWD) with only Inflorescences buds appearing (Figure 3).The impact of drought stress was most obvious on sandy soils with prime age plants, where for ± 9 months (6-14 BAWD) no Inflorescences buds were found, while at a relatively young age it only had an impact on the shift in the number of fronds on the emergence of Inflorescences buds at 7 BAWD and 27 BAWD.BAWD (Fig. 4).The sex ratio (ie the ratio of the number of female Inflorescencess to the total number of Inflorescencess) is strongly influenced by sex determination and the tendency to abort female or male Inflorescencess [25], and its value can be affected by water deficits [21,25,26].Changes in sex ratio were seen in mineral soils with prime age plants not showing the appearance of receptive female Inflorescencess for ± 12 months, namely from 5-27 BAWD and 22-24 BAWD, whereas in young age the impact was relatively shorter, lasting for ± 5 months in 6 -10 BAWD and 20-24 BAWD (Figure 5).A similar phenomenon also occurs in sandy soils for both prime and young plants with an almost similar pattern, where at prime age it occurs for ±10 months (3-12 BAWD) and ±5 months (22-26 BAWD) while at young age it occurs for ±5 months (4-8 BAWD) and ±7 months (10-16 BAWD) (Figure 7).A different pattern occurs in peat soil where in prime age plants there is no consistent appearance of receptive female Inflorescencess for ± 3 months, namely at 8-10 BAWD, 12-14 BAWD and 18-20 BAWD, whereas at young age it tends to only occur at the beginning only ie 4-6 BAWD (Figure 6).In general, the maturity time of FFB (calculated from anthesis until harvest) varies from 140-180 days, depending on both genetic and environmental factors [27,28].Mature FFB will generally be found on frond number ± 31 or on fronds older [14].The results of observations in all types of soil, both prime and young, found the phenomenon of red fruit (fruit ready for harvest and/or  8).On peat soils with prime age plants occur at 11, 13-21 and 25-27 BAWD, whereas at young age it occurs almost in all months of observation (Figure 9).In sandy soil with prime age plants it occurs at 3-21 BAWD, while at young ages it occurs at 3, 15-21 and 27 BAWD (Figure 10).The process of allocating assimilation to the fruit formation process can be stopped due to lack of water and/or radiation received by the oil palm so that it becomes one of the causes of bunch failure apart from poor pollination quality [29,30].Under conditions where water is sufficient, about 10-12% of assimilation is allocated to roots [14], whereas under conditions of water stress, assimilation to roots can reach up to 35% [31,32].Assimilation allocation to Inflorescencesing (male and female Inflorescencess) and bunches will not occur until the need for vegetative production is met [31].This causes the FFB which is in the midrib which is older than the 31st frond to be immature.This phenomenon is found in mineral soils for both prime and young plants, on peat soils at prime age, it occurs at 11, 15 and 17 BAWD, whereas at a young age, the shift in frond number occurs up to 27 BAWD.In sandy soils with prime age plants, this phenomenon occurs from 3-19 BAWD, whereas in young ages it occurs at 3-9 BAWD and 15-27 BAWD.In addition, in young plants on both mineral and peat soils, hermafrodit fruit was found at 3, 19, 23-25 BAWD for mineral soils, while peat soils at 3-7 BAWD and 27 BAWD (Figure 9).In sandy soil, both prime and young plants did not find hermafrodit fruit (Figure 10).This phenomenon is consistent with the results of the correlation between PWA at each Inflorescencesing stage, especially at the inner, outer and bract initiated process stages and the sex differentiation stage (Figure 1) on mineral and peat soils.

Concluding
Oil palm is sensitive to drought stress because one of its growth requirements requires water in large quantities and evenly distributed throughout the year.Drought stress in 2015 showed a significant effect on the decrease in the number of female Inflorescencess, anthesis male Inflorescencess, and the number of aborted Inflorescencess and fruits until 2017.In young plants, drought stress during the development of bunches is significantly correlated with the abortion rate so that the failure rate of cluster formation higher than the prime age plants.Plant water available has an effect one month before harvest (BSP) or (late ripeness stage), 8-13 BSP (anthesis and inflorescence abortion stages) on mineral soil types with prime age plants, while at a young age it has an effect on 33-34 BSP (leaf initiated stage) and 29-30 BSP (end of sex differentiation stage and beginning of inner, outer and bract initiated process).In peat soil types with prime age plants, PWA has an effect on 8-14 BSP (anthesis and inflorescence abortion stages), while on young plants it has an effect on 18-20 BSP (female inflorescence stages), 24-26 BSP (inner, outer and bract initiated process) and 31-32 BSP (sex differentiation stage).In sandy soil types with prime age plants, it affects 8-14 BSP (anthesis and inflorescence abortion stages), while in young plants it affects 14 BSP (inflorescence abortion stages), 16-18 BSP (female inflorescence stages) and 30 BSP (the final stage of the sex differentiation phase).Another impact that arises is a shift in the number of fronds for the appearance of Inflorescencess and red fruits, a slowdown in fruit maturity in all types of soil and plant age and young plants in both mineral and peat soils found hermafrodit fruits.

Figure 2 .Figure 3 .
Figure 2. Graph of frond number of emergence of Inflorescences buds, male Inflorescencess and female Inflorescencess on mineral soils of prime age plants (above) and young plants (below)

Figure 4 .
Figure 4. Graph of frond number of Inflorescences buds, male and female Inflorescencess in sandy soil, prime age plants (top) and young plants (bottom)

Figure 5 .Figure 6 .Figure 7 .
Figure 5. Graph of frond number of emergence of anthesis male Inflorescencess, post anthesis male Inflorescencess and receptive female Inflorescencess on mineral soils of prime age plants (top) and young plants (bottom)

Figure 8 .Figure 9 .Figure 10 .
Figure 8. Graph of frond number of black fruit, red Inflorescences and hermafrodit fruit on mineral soils of prime age plants (top) and young plants (bottom)

Table 1 .
Research Locations

Table 2 .
Total Rainfall and Rainy Days

Table 3 .
Rainfall, Monthly Water Deficit in Experimental Locations

Table 4 .
Average generative parameters (per tree) during 2016-2017 was on a frond that was younger than the 17th frond, namely at 7, 19 and 27 BAWD on mineral soils with prime age plants, whereas at young age it occurs in almost all months of observation except at 9 and 17 BAWD (Figure 10 before harvest