Early growth of porang (Amorphophallus oncophyllus) with planting distance adjustment under oil palm plantation

Porang (Amorphophallus oncophyllus) thrive under shaded conditions and has been planted under plantations. As oil palm plantations area in Aceh is growing; the effect of shading under oil palm plantation has not been previously reported. The material used is bulbil from the porang plant. Meanwhile, the oil palm stands used were 8-10 years old with the canopy covering >80% of the land. The experimental design used is a Completely Randomized Block Design with the treatment of spacing settings of 40 x 40 cm; 75 x 75 cm; 80 x 80 cm; 90 x 90 cm and 100 x 100 cm. Experiments were conducted in four replicates. Data were analysed using One Way Anova, followed by posthoc Tukey HSD test. Results shows that the spacing had a significant effect on its growth, especially the age of shoot emergence, plant height, stem diameter and number of leaves. The age of budding which allows early shoots to appear is at a spacing of 40 x 40 cm, as well as the plant height parameters at observations 4, 5, 6 and 7 WAP. Meanwhile, at the age of 8 and 9 WAP, the best plant height growth was at 80 x 80 cm spacing.


Introduction
Porang (Amorphophallus oncophyllus) is wildly found in tropical forests and widely cultivated in Indonesia.Other related species of porang including iles-iles, suweg, and walur.Those species' share common characteristics such as small to massive terrestrial plants, herbaceous, tuberous, tuber depressed globose, saucer-shaped [1].The leaves are compounds, smooth, wavy and hairless, and the stems are patterned.Porang's distinctive feature are the presence of bulbyl on its leaves and colour of tubers which is yellow to orange [2].
Porang considered to have the highest economic value compared to for mentioned species, due to its high glucomannan content [3][4][5].It is reported that porang has the highest glucomannan content compared to suweg, iles-iles and walur [6].Diverse function of glucomannan reported in food, pharmaceutical, cosmetics and chemical industries [7].In 2019 alone, porang's total exports were 11.170 tons to countries mainly China, Vietnam and Thailand.Porang highly regarded for its precious glucomannan [8].
Porang are very adaptive to shades.In fact, its optimum growth is proposed to be at 40% shades.A. oncophyllus has been reported to cultivated under sengon (Paraserianthes falcataria), coffee, clove, durian, mangosteen plants [9,10].However, planting porang under shades of oil palm plantation in Bireuen Regency has never been previously reported.Shading affected oxalate compounds accumulated in bulbs or porang, also act as determinant of the glucomannan.Calcium oxalate accumulation reported 3 times higher on unshaded plants compared to shaded plants, thus, determining the quality [11,12].
The practice of porang cultivation under productive plant stands is not popular in Aceh; moreover under oil palm stands.While vast area of oil palm plantation in Aceh makes it a potential to applied.However, knowledge on alternative land use by planting A. oncophyllus as intercrops on oil palm plantation.Moreover, the information on adaptive ability of A. oncophyllus under oil palm stands has not been widely studied.

Material and methods
The research was conducted in smallholder community-owned oil palm plantations with the plant age range between 8-10 years.The research location was in Bukit Sudan Village, Peusangan Siblah Krueng Subdistrict, Bireuen Regency, Aceh Province from April to August 2023.The research site altitude is at 100-200 m above sea level.The oil palm plants used as the object of research applied a planting distance of 8 x 8 m, and followed the direction of the slope.The soil order is Ultisol with a Typic Paleudults sub order (USDA 2010) with parent material dominated by andesite rocks.The soil texture in the topsoil (0-0.15m depth) in the research area is classified as sandy loam, with a special characteristic of having an argillic horizon with clay content between 19-37%.

Materials and tools
The material used is bulbil from the porang plant with dimensions of 3 cm to 12 cm.Meanwhile, the oil palm stands used were 8-10 years old with the canopy covering >80% of the land.The measurements of covering percentage were conducted using luxmeter (Smart Luxmeter Versi 1.0.8), and percent coverage was calculated by measuring sunlight intensity under oil palm stands compared to that of outside oil palm stands.Oil palm stands have a density of 110 trees/ha or with a spacing of 9 m x 9 m.The equipment used in this study included stationery, hoe, rope meter, machete, protractor, hygro-thermometer, bucket, analytical scale, used paper, plastic, lux meter, bamboo.

Research design
The experimental design used is a Completely Randomized Block Design with the treatment of spacing settings, namely J1 = 40 x 40 cm; J2=75 x 75 cm; J3=80 x 80 cm; J4 = 90 x 90 cm and J5 = 100 x 100 cm.The number of repetitions in this treatment is 4 times test.

Research implementation
Planting holes are made with a depth of 10 cm-15 cm and a width of 15 cm x 15 cm.The spacing used for porang plants is in accordance with the treatment.Manure and NPK were put into the planting hole at a dose of 5 tons/ha and 350 kg/ha.Manure in the planting hole is left for 7 days to decompose more completely.Porang plants were maintained by weeding once a week and during the experiment there was no additional irrigation other than rain water.Environmental factors observed were the intensity of sunlight, air temperature in the stand, and humidity.
Maintenance of porang plants includes weed control and fertilization.Weed control is done manually by weeding around the plants.Weed control does not use herbicides because herbicides can interfere with the growth of porang plants.
Observations on porang plants were carried out by vegetative observation once a week.Vegetative observations included measurements of: age of shoots appear, plant height, stem diameter, number of leaves and canopy area.
Age of shoot appear was observed by recording the first appearance of shoots that penetrated the soil surface after the first day of planting.Plant height.Plant height was measured after the leaves begins to bloom from the base of the stem to the tip of the branching leaves.Measurements are carried out every 1 week for 9 weeks.The diameter of the rod was measured using a caliper.Measurements were made by measuring the diameter at the bottom of the stem, in the middle and under the lowest petiole, then averaged.The number of leaves is counted on plants that have fully grown leaf organs.
The growth and development of porang plants is known by doing the F test.If the results of the F test are significantly different, a further honest significant difference (HSD) test is carried out at a 5% confidence interval to determine the difference between treatments.Data processing was carried out using the Statistical Analysis System (SAS).

Results and discussion
The results of the field experiment showed that bulbil porang planted on April, 2023 grew slowly, because at the time of planting there were fluctuations in the dry-rainy season.Rain at the study site occurred in April-July under the wet rain category.Porang's bulbil porang takes one month from planting to shoots germination.Santosa et al [13] stated that porang have four phases of growth cycle: dormant phase, stem and root growth phase, tuber initiation and filling phase, and old phase.The initial stage of its growth is generally noted when shoots appear above the soil surface with a height of about 3 cm.The condition of water availability in the first month of planting was categorised as a dry month, characterised by rainfall below 50 mm.This condition caused the late formation of porang shoots.Adequate water availability was met in the second and third months after planting, where rainfall increased to 165 mm per month for 2 consecutive months.Water availability strongly influences the early growth of porang plants, considering that other climatic parameters such as air temperature, air humidity and solar irradiation are relatively not different.

Porang Growth
Based on the results of analysis of variance on porang growth parameters (Table 1), spacing treatment on initial growth of porang under oil palm stands had a significant effect on parameters of budding age, plant height, stem diameter and number of leaves observed at 4 weeks after planting (WAP) -9 WAP.The fastest porang shoots appeared at the age of 31.5 DAP (J3 and J4), then at 39.5 DAP (J1), 46.5 DAP (J2) and 52.5 DAP (J5) (Figure 1).Based on the results of this study, the shoots appear age of porang plants is considered normal.
According to [14], shoots began to appear between 1-6 WAP, meaning that shoot germination from tubers took longer than porang's germination from bulbil.Hidayat et al. [15] stated that at 46 days after planting, the growth power of iles-iles from tuber reached >91%.
Plant height was measured after the leaves began to bloom from the base of the stem to the tip of the branching leaves.Measurements were carried out every 1 week for 13 weeks.Based on the post hoc Tukey HSD test, porang at spacing of 40x40 cm (J1) gave the best average plant height at plant age 4-7 WAP compared to porang height growth at other spacings.However, at the age of 8 and 9 WAP, treatment with a spacing of 90x90 cm (J4) showed the highest growth (Table 2).The phenology and rate of development of a plant depend on climatic factors such as temperature, day length, and water supply.The intensity of sunlight was measured using a lux meter with units of cal/cm2.In oil palm stands, the average monthly light intensity is between 634 -768 cal/cm 2 .While the average daily temperature for 4 months in oil palm stands ranged from 27.33 o C -27.92 o C in one full day of sunlight.
Mutaqin et al [16] said that temperatures above 30 o C are critical factors for various types of plants when protein compounds tend to be released and cannot return or when enzymes cannot function.However with respect to photosynthesis, as measured by the amount of biomass accumulated, most plants show a wide range of tolerances.Temperatures between 25 o C -35 o C shows a relatively good influence on the amount of growth.During the study, oil palm stands had an average daily humidity ranging from 81.18% -83.55%.Humidity describes the content of water vapor in the air.Water is a more important factor in crop production than any other environmental factor.Water plays an important role because it can transport nutrients from the soil to the roots and forwarded to other parts of the plant body.The photosynthesis process will decrease if 30% of the water content in the leaves is lost, then the photosynthesis process will stop if the water loss reaches 60%.
Parameters of stem diameter and number of leaves have a strong correlation with the growth of porang plant height.The stem diameter was measured at the age of 6 WAP -9 WAP (Figure 2, 3, 4 and 5), while the number of leaves was measured at the age of 7 WAP.The results of analysis of variance showed that consistently at the age of 6-8 WAP, the stem diameter was the highest and significantly different in the J1 spacing treatment, followed by J2, J3, J4 and J5 respectively.Meanwhile, at the age of 9 WAP, the largest stem diameter was at J2, J1, J4, J3 and J5 respectively (Figure 5).At the age of 7-9 weeks after planting, the growth of the number of leaves fluctuated and was influenced by the plant spacing.Moreover, pests such as wild boar and monkeys found on the study area affecting the plant observation results, i.e. smaller stem diameter observed on J5 at 6 to 8 WAP (Figure 6,7 and 8), and lower leaves number at 7 to 8 WAP (Figure 6 and 7).The analysis results showed that the highest number of leaves was obtained in porang plants with J3 plant spacing treatment, followed by J1, J4, J2 and J4, respectively (Figure 8).

Conclusion
From the initial data obtained, it can be concluded that porang shows good adaptability under oil palm stands.The spacing of Porang had a significant effect on its growth, especially the age of shoot emergence, plant height, stem diameter and number of leaves.On the parameters of stem diameter and number of leaves, quite varied results were obtained.

Table 1 .
Climatic conditions of the research location during the study.