Study of porang (Amorphophallus muelleri blume) as intercrops in oil palm immature plants

The porang plant is one of the products being considered as an intercrop in the oil palm plantation. Specifically on smallholder oil palm plantations, the study’s objective was to investigate the ecological and financial aspects of porang growing as an intercrop in an oil palm intercropping system. This study was put together using approaches from farming analysis and descriptive analysis of literature studies. The study’s findings indicate that a number of characteristics, including the amount of solar radiation received, the acidity of the soil, and the soil’s moisture (during wet and dry seasons), must be taken into account for porang to produce at its highest level as an intercrop. In the meantime, the outcomes of the farming analysis demonstrate that it is possible to grow porang plants as intercrops during the Immature plant period.


Introduction
The size of the oil palm plantation area offers significant possibilities for diversification into other oil palm-related sources of income.Intercropping is one method of diversity that can be used.When carried out correctly and precisely, the intercropping pattern for oil palms is more profitable than the monoculture system.The benefits of oil palm intercropping include increased land productivity, producing various goods, increased yields, enhanced soil fertility, reduced erosiveness, cost savings on production facilities, and less chance of failure.Up to now, intercropping of oil palm crops has been done often, including rice, corn, and soybeans.
Apart from these commodities, porang plants also have the potential to be used as intercrops for immature oil palm plantations.Porang (Amorphophallus muelleri Blume.) has various benefits and a relatively high tuber-selling value because of the various benefits.Porang tubers contain high glucomannan, which can be processed into various types of food and industrial materials and is good for health.Porang plants produce very high output with little maintenance cost and very low failure rate.In addition, the porang plant, which does not require much maintenance, is the main attraction for farmers to make porang one of their agricultural commodities [1].
The enthusiasm of farmers to make porang a cover crop in oil palm plantations is increasing along with the government's attention to the development of porang as a potential commodity that can contribute to the country's foreign exchange earnings and improve the welfare of farmers.The export value of porang in 2020 reached 1.47 trillion, with the actual planting area of porang based on mapping

Chinese Ocra 560 plants
This research is a desk study conducted for 6 (six) months from the start of the research, starting in December 2022.The desk study was conducted at the Indonesian Oil Palm Research Institute (IOPRI), North Sumatra.Meanwhile, field observations of porang cultivation were carried out on porang farms owned by smallholders in Langkat District.
Descriptive analysis is especially used in the comparison of aspects of the agronomic feasibility of porang to grow optimally without causing negative effects on the main crop (in this case, oil palm).The growth requirements and production of the porang will be compared with the soil conditions and microclimate of immature palm.In addition, the same thing was also done for the other intercrops in Table 1.Furthermore, a descriptive analysis was also carried out to compare the economic and agronomic aspects of the oil palm and the intercrops listed in Table 1.

Agronomic Suitability of Porang as an Intercrop for Oil Palm
The agronomic suitability of porang as intercrops in oil palm plantations are presented in Table 2 below.Meanwhile, comparisons of the ecological suitability of porang as an intercrop and other intercrops are presented in Table 3.Based on Table 2 and Table 3, the porang has potential to be developed as an intercrop for oil palm plantations.However, several agronomic parameters need to be considered to obtain maximum porang production: the intensity of solar radiation, soil acidity, and soil moisture.Immature plant <1 oil palm plants can transmit 80% of the incoming sunlight.At Immature plant 1-2 it transmits 60% and at Immature plant 2-3 it transmits 40% of sunlight.Meanwhile, in yielding plants, it is 13-40% [5,9].See Fig. 3.
Suitable, but it is more profitable to develop porang plants at the mature plant phase.

Neutral pH around 6-7 [1]
Oil palm is generally planted at pH 5-6.5 [6] Suitable, but needs treatment to improve soil pH if porang is planted in plantation areas with pH <6 to maximize porang production.

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The soil water content required for porang plant growth should not be less than 40% field capacity [1] Oil palm plants are planted on land with a minimum monthly rainfall of 60 mm/month or around 30% of field capacity [8] -Suitable but needs to be ensured that the area planted with porang does not experience drought.-Porang should be used as an intercrop in oil palm plantation centers that are not prone to drought.Or avoid planting porang in the dry months of June-August.Based on the research in oil palm plantation in Jambi, the air temperature around the immature palm is higher than that of mature palm (Figure 1).The lowest average diurnal temperature at immature palm is around 27 o C, while the highest average temperature is 35 o C.Meanwhile, the maximum solar radiation intensity obtained by oil palm in immature phase is 600 W/m 2 or 80% of the maximum solar radiation intensity, around 800-1000 W/m 2 .
The ecological conditions of immature palm are not optimal for porang because porang will grow and produce optimally in the temperature range of 25-30 o C and solar radiation intensity of 40-60%.Under these conditions, it should be shaded when planting porang as an intercrop.Porang is a shadeplant, so without shade, it will experience some symptoms of heat stress, and its products will be lower than porang plants with shade [9].Some literature showing that porang needs shade is presented in Table 4. Based on Table 4, shade has a positive effect on porang productivity.The optimal shade for porang is 40-60%.Shade can be in shade plants or artificial shade such as a paranet.The porang will produce tubers and katak, tuber roots which function as storage of carbohydrates, both have economic value.According to research, at the age of one year or during first dormancy, usually, 50-200 g of tubers will be produced.Furthermore, in the second year, 250-1350 g of tubers will be produced.Meanwhile, in the third year, 450-3350 g of tubers will be produced [11].Related to the intercropping system with oil palm, in the second year, porang tubers can begin to be harvested, especially plants with tubers that are quite large.The rest can be harvested in the third year when the oil palm plantations enter the final phase of immature plant.
Furthermore, no information has been obtained regarding the impact of porang on soil conditions and immature palm performance.Based on previous research, it is known that the intercropping pattern does not affect the overall soil fertility parameters (Table 5).Several parameters were observed, such as C-organic, C/N, Phosphorus (P), Calcium (Ca), and Magnesium (Mg).Soil nutrient contents in the intercropping system had higher values than the control.Meanwhile, the content of Nitrogen (N) and Potassium (K) is the same value [5].However, the values of pH, cation exchange capacity (CEC), and base saturation (KB) in the intercropping plots were lower than the control plots (without intercrops).Source: [5] Furthermore, based on observations on vegetative growth (plant height, number of fronds, and stem diameter), it is known that intercropping system does not reduce the vegetative performance of immature palm.The average palm height was 134 -136 cm, the number of fronds was 14, and the diameter of the hump was 4.2 cm [5].
Table 5 indicates that there are no competition for the absorption of nutrients between oil palm and intercrops [5].The critical thing in this intercropping technique is to pay attention to the performance of the main crop and intercrops.Previous research states that it is necessary to optimize land management through certified seeds, weed removal, pruning, and sufficient fertilization to increase plant growth and productivity.If land management and cultivation techniques are applied optimally, the annual oil palm production can reach 12 tonnes/ha.

Technical Recommendation for Oil Palm-Porang
As explained in the previous sub-chapter, the oil palm crop intercropping system has an area of about 60% of the total planting area that can be used for intercropping.The oil palm-porang intercropping system is shown in Figure 3. Assuming that the porang spacing is 50 x 50 cm, the total number of porang trees is 19,800-20,000 in 1 ha of oil palm land.
Porang planting can be done 1-3 months after the oil palm are planted in the field.Considering the rainfall pattern in the central areas of oil palm plantations, which are dominated by equatorial and monsoonal rainfall, the porang planting schedule can follow the schedule in Figure 4. Assuming oil palm planting is carried out in December-January, land preparation for porang can be conducted in areas with equatorial rain types in May-July.Meanwhile, the smallholders can prepare the cultivation of porang in January for areas with monsoonal types of rain.The suggested cultivation techniques for porang as intercrops for immature palm are as follows [20]: 3.2.1.Land Processing.Land processing that needs to be done is as follows: Soil tillage is absolutely necessary, especially in densely textured land areas.

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Apply dolomite is necessary because most of soil in Indonesia has low pH.

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Apply organic fertilizers include cattle manure, leaves and fruit and vegetable waste, husks, and bran.

Planting. It includes the following process:
• Planting time.Seedlings from tubers can be planted directly in the field at the start of the rainy season.In the other hand, seeds from seeds, small katak, and leaf cuttings require a nursery process and then wait for the right time to be planted in the field.• The ideal planting hole depth for porang is around 10 cm.
• The recommended ideal spacing is 50 cm x 50 cm, with a population of 19,800 to 20,000 trees per ha.• Planting seeds from tubers is done by turning them over, or they will not stay the same, different from katak.Planting katak is utilizing spies; katak cannot be turned over so that porang can grow.Then for seeds, cuttings, and small katak, do the seeding first.

Shade.
Porang can produce more optimally if planted under tree stands/artificial shade with an intensity of 40-60%.However, due to the economic aspect and the consideration that the canopy of immature palm will continue to grow, it is unnecessary to use artificial shade.

Maintenance.
• Weed control is carried out in 2 ways: manually by clearing the weed or using mulch.The use of mulch helps prevent weed growth in porang.

• Fertilization recommendations [3]:
o Basic fertilizer: compost or manure 5-10 tonnes/ha depending on soil organic matter conditions.o Applied evenly on the bunds.o On average, farmers only use inorganic fertilizers, namely Urea and NPK Phonska.
Urea needs 300 kg/ha, and NPK Phonska is 200 kg/ha.Fertilizer application is made by sowing/immersing around the stem.The application is given at the first planting time as essential fertilizer, and the next fertilizer application is made once a year (early rainy season).

Harvesting
• Harvesting of porang is carried out based on its purpose, whether to sell the tubers or used as seeds for re-cultivation.
• Harvesting porang tubers is done during the dry season.The right time to harvest is after the plants have experienced at least three vegetative periods and two dormant periods (see Figure 4).
• Harvesting katak can be done at the age of 6 months after planting.

Conclusion
The study on the ecological aspects of porang as an intercrop during the immature palm showed that optimum productivity of porang will be achieved by considering several factors, particularly the intensity of solar radiation, soil acidity, and soil moisture (wet and dry seasons).The results of an agronomic study showed that the air temperature and solar irradiance conditions in an immature palm plantation were not optimal for porang, so it required shading.The consequence is a significant increase in investment costs.Therefore, further economic study is needed to determine the feasibility of porang as an intercrop in oil palm plantations.

Acknowledgment
We extend our gratitude and appreciation to The Indonesian Oil Palm Plantations Fund Management Agency (BPDPKS) for funding the research project.The support has played an important role in the successful execution of this study (Contract No. PRJ-59/DPKS/2021).

Figure 1 .Figure 2 .
Figure 1.Air temperature conditions under oil palm stands in the immature and mature phase (source: [7])

Figure 3 .
Figure 3.A simple scheme for oil palmporang intercrop

Figure 4 .
Figure 4. Porang planting and harvesting schedule in the oil palm-porang intercropping system.Porang tubers can be harvested when they are dormant in year 2 and 3 (soil tillage indicates in blue bar, vegetative phase in green, and dormant in red).

Table 1 .
The commodity and total area of intercrops were reviewed and compared in the study

Table 2 .
Agronomic suitability of porang plants as intercrops in oil palm plantations

Table 3 .
Agronomical suitability for some intercrops for oil palm plantation

Table 4 .
Some literature showing the relationship between shading and porang productivity