Effect of Beneficial Microbes on Macronutrient Uptake and Oil Palm Seedling Growth in Peat Soil

Peat soil has low fertility due to low content of macronutrients, such as N, P, K, Ca, & Mg. Efforts that can be made to increase nutrient availability and nutrient uptake for plants on peatlands are the utilization of beneficial microbes such as endophytic bacteria and arbuscular mycorrhizae. This study aims to identify the role of endophytic bacteria and arbuscular mycorrhizae applied to peat soil media to help increase macronutrient uptake and the growth of oil palm seedlings (main nursery). This study was conducted in June – December 2022. The peat soil sample was collected from oil palm plantations located in Siak Regency, Riau, with coordinates 0°45′22″ N, 101°44′27″ E. The experimental design used in this study was a completely randomized design (CRD) with 8 treatments and 5 replicates. The treatment given in this study was a variation of beneficial microbes with zeolite as the carrier. Beneficial microbes used in this study were arbuscular mycorrhizae, namely Glomus sp, and endophytic bacteria, i.e. Burkholderia cenocepacia and Pseudomonas fluorescens. Parameters observed in this study were plant growth (every 1 month) and leaf nutrient (6 months after planted). The results of this study indicated that the consortium application of endophytic bacteria and arbuscular mycorrhizae was the best treatment which was shown to have the best growth of oil palm seedlings compared to all treatments with plant height increment of 55.5 cm; stem diameter increment of 34.3 mm; and the number of fronds addition as many as 11 fronds. This is also supported by macronutrients content in the leaves of oil palm seedlings such as N, P, and K.


Introduction
Indonesia's peatlands, which total 13.4 million hectares [1], are the fourth-largest peatlands in the world, behind those of Canada, Russia, and the United States.Sumatra (35%), Kalimantan (32%), and Papua (30%) are the three main islands where the majority of the peatlands are found.The remaining 3% is dispersed over a small area in Sulawesi [2].Peatlands 1308 (2024) 012029 IOP Publishing doi:10.1088/1755-1315/1308/1/012029 2 formed under anaerobic conditions in swamps.Peatlands have an organic content of more than 50% and are accumulated crop residues [3].Peatlands have low fertility such as low macro and micro nutrient contents.Other problem that can arise in peatlands are irreversible drying, low pH, low nutrient availability for plants, ash content and water management [4], and the presence of phenolic acids which are toxic to plants [5].
Efforts that can be made to increase sub-optimal land productivity, especially for nutrient availability and nutrient uptake for plants on peatlands, are the utilization of beneficial microbes such as endophytic bacteria and arbuscular mycorrhizae.Utilization of beneficial microbes that are applied in a consortium can support in the decomposition process of organic matter which can form humus consisting of simple C compounds, humic acids, humin acids, and fulvic acids [6], where these acids are a source of negative charge and binding sites for nutrients such as phosphate and potassium [7].Endophytic bacteria are one of the helpful microbes that contribute to promoting plant growth in a variety of ways, including by fixing nitrogen; solubilizing phosphate & potassium; and generating IAA [8].biofertilizer with active ingredients from endophytic bacteria Burkholderia cenocepacia and Pseudomonas fluorescens able to increasing the available nutrients for plants so as to support increased oil palm production [9].Arbuscular mycorrhiza plays a important role in helping plants grow by improving their capacity to absorb nutrients like N, P, K, Ca, and Mg from the soil.[10].This is in accordance with the research results of that the application of arbuscular mycorrhizae can increase the availability of phosphorus so as to increase the growth of oil palm seedlings planted on peat soils [11] [12].Utilization of these microorganisms can be one of the solutions and alternatives for developing and optimizing agricultural activities on peatlands, considering that the two beneficial microbes are potential biological resources that do not have a negative impact on the environment.The presence of endophytic bacteria and arbuscular mycorrhizae in plants can play a positive role in supporting plant growth such as increasing the availability of macro and micro nutrients [12] [13].

Location and Experimental Design
The research was carried out in June -December 2022.Sampling of peat soil was carried out in an oil palm plantation, Siak Regency, Riau with coordinates 0 o 45'22'' N, 101 o 44'27'' E. The greenhouse experiment was conducted at the Greenhouse, Indonesian Oil Palm Research Institute Bogor Unit.Laboratory analysis was carried out at the Chemical Laboratory, Indonesian Oil Palm Research Institute Bogor Unit.The materials used were the 3-month-old Dura x Pisifera Simalungun variety of oil palm seeds from PPKS Medan; arbuscular mycorrhizae inoculums (Glomus sp.); isolate Burkholderia cenocepacia and Pseudomonas fluorescens.While the tools used are polybags, measuring instruments, plastic, and scales.The experimental design used in this study was a completely randomized design (CRD) with eight (8) treatments (Table 1).The treatment given was a variety of beneficial microbes with zeolite as carrier.The peat soil used will be sterilized using gamma radiation Co-60 at a dose of 25 kGy for 8 hours.The purpose of the peat sterilization is to remove or sterilize the peat media from the original microbes.Some of the sterile peat samples were analysed at the Chemical Laboratory, Indonesian Oil Palm Research Institute Bogor Unit.
Oil palm seedlings planted in peat soil media are uniform in size and age of seedling.Peat planting media that has been sterile will be put in polybag 40 cm x 50 cm with a peat media capacity of 20 kg/polybag.Beneficial microbes are inoculated onto the zeolite as carrier.Zeolite that has been inoculated is given as much as 50 g/seed to peat media.Inoculation is done by applying the zeolite to the root area of the oil palm seeds.Watering the oil palm seedlings is done by providing water up to field capacity or around 1.5 -2 liters per day [14].Fertilizer application is carried out using the main nursery fertilizer recommendations [15].

Observation Parameters
Parameters observed are plant height (cm); number of fronds, stem diameter (mm), and plant nutrient uptake.Observation of the growth of oil palm seedlings was carried out for 1-6 BST.The nutrient absorption analysis was carried out at 6 BST with leaf samples from the 3 rd frond.The parameters for the nutrient absorption analysis were N, P, K, Ca, and Mg.Data were tested statistically using Duncan's New Multiple Range Test (DNMRT) at the 5% level and analysis of variance.

Characteristic of Sterile Peat Soil Before Treatment
The results of the chemical analysis of sterile peat soil before treatment are presented in Table 2. below and are compared with the assessment criteria for the results of the analysis of the soil chemical properties [16].The analysis' findings revealed that the peat soil used in this study had a pH of 2.9 and was part of the very acid category.The very acidic conditions of the peat soil used are caused by the accumulation of organic matter in an anaerobic environment, where these conditions will form organic acids [17].As a result of the organic matter that has accumulated in peat soil, the organic C value in peat soil is included in the very high range.The availability of nutrients that plants can absorb, however, will depend on the acidity of the soil; generally speaking, the more acidic the soil, the less readily available nutrients are, particularly for macronutrients.The total N content in the peat soil used in this study is included in the very high of 1.0%.Even though the total N value is very high, the available nitrogen in the peat will be small because the available nitrogen will be used by microbes to decompose the organic matter in the peat soil [18].The Total P and K content in peat soil is included in the very high, namely 65 mg/100g and 99 mg/100g respectively.However, high Total P and K values may not necessarily be absorbed well by plants because they are not in the form of P and K available.Lowering P and K available can be caused by peat still in the process of decomposition, causing peat soil to become poor in P and K available [19].The Ca & Mg content obtained from the analysis results were 14.5 me/100g and 5 me/100g which were included in the high.

Growth of Vegetative Oil Palm Seedling (Main Nursery)
Observation of plant height in oil palm seedlings was observed every month until 6 months after planting (MAP) in the main nursery (Table 3.).Based on the results of observations, it was known that the treatment given in this study had a positive impact on increasing plant height compared to controls with a significant difference at the end of the observation (5 -6 MAP).Treatment with a combination of arbuscular mycorrhizae and endophytic bacteria applications B. cenocepacia and P. fluorescens (P7) gave the best results compared to the other treatments with the plant height increment (6 -1 MAP) of 55.5 cm.Based on Table 3, it shows that the application of beneficial microbes in a consortium (P5 -P7) is able to provide better results than single application (P2 -P4).The difference in the effectiveness of the combined or single application was seen at 5 MAP where at that time there was a significant difference, whereas in months 1 -4 MAP there was not significantly difference between the two application methods.The results of observing the effect of the application of beneficial microbes on the stem diameter of the oil palm seedling are presented in Table 4. Based on these results it shows that the application of beneficial microbes has a significantly different effect.The treatment application in this study has a tendency to improved a better stem diameter compared to the control with the best treatment obtained in the combination of arbuscular mycorrhizae and endophytic bacteria applications B. cenocepacia and P. fluorescens (P7) with the stem diameter increment (6 -1 MAP) of 34.3 mm.Similar to plant height, significant differences in the stem diameter began to be seen at 5 MAP until the end of the study.Whereas at the beginning of the study (1 -4 MAP) there was not significantly difference between the two application methods.Parameters of the number of frond oil palm seedlings affected by the application of beneficial microbes observed once a month are presented in Table 5.In general, the treatment given in this study gave significantly different results compared to the control in the number of frond.The beneficial microbes application treatment began to show a significantly different effect when the oil palm seedlings were aged 5 MAP until the end of the study, whereas at the age of 1 -4 MAP the results did not show a significant difference in all treatments.
After being observed for six months, in general the growth parameters of oil palm seedlings that had been applied to beneficial microbes statistically were able to produce a significant increment of plant height, stem diameter, and number of fronds addition compared to the control.Increased plant growth occurred when the oil palm seedlings were 5 MAP which could be due to the early vegetative period of the oil palm seedlings still using the supply of nutrients found in the endosperm.Oil palm seeds begin to carry out photosynthetic activities and absorb nutrients from the soil when the supply of nutrients in the endosperm begins to decrease.With the application of beneficial microbes it can help absorb plant nutrients on peat soil media which has low nutrient availability.This is evident from the findings of observations of vegetative growth, which show that application of beneficial microbes can lead to better growth outcomes, as evidenced by increases in plant height, stem diameter, and the number of fronds compared to controls of 11-23%, 23-37%, and 14-16%, respectively.Based on the combination of treatments, it showed that the beneficial microbes applied in a consortium were able to produce better improvements compared to the single one.This is because the beneficial microbes that are applied in a consortium are able to provide complementary or alternate roles in supporting the growth of oil palm seedlings.The endophytic bacteria B. cenocepacia and P. fluorescens function as plant growth-promoting rhizobacteria (PGPR), which can improve the vegetative development of plants [9].This increase in plant vegetative growth results from the association of endophytic bacteria with plants, which promote plant growth through a variety of mechanisms, including the production of phytohormones, biological N fixation, mineral and nutrient solubilization, increased root volume, and systemic induction of pathogen resistance [20] [21].Arbuscular mycorrhizae also has an important role in increasing plant growth, which can help increase the ability to absorb nutrients even in low nutrient soil conditions [22] [23].

Macronutrient Content in Oil Palm Seedling Leaves
Macronutrient content in oil palm seedlings leaves obtained by analysis of nutrient in leaves is presented in Table 6.The results of the analysis of variance showed that beneficial microbes had a significant effect on N, P, K, Ca, and Mg compared to controls.The highest N, P, and K was produced by the P7 treatment with values, respectively 4.27%, 0.74%, and 1.84% compared to the control, while the best Ca and Mg was obtained in the P6 treatment, namely with sequential values of 0.67% and 0.33%.Based on the treatment of beneficial microbes applications carried out as a consortium or individually, the further test results were not significantly different, but the consortium application was able to provide better macronutrient compared to a single application.Arbuscular mycorrhizae, endophytic bacteria B. cenocepacia and P. fluorescens has the main function in supporting plant growth, namely as a phosphate solubilizing microbes.These microbes play a role in secreting certain types of organic acids so that P bound to metal elements such as Ca, Al, and Fe can be released [24] [25].Thus, phosphorus that was previously unavailable to plants becomes more available to plants and can be absorbed to support their growth.Arbuscular mycorrhizae also has another important role, namely being able to grow plants by increasing the ability of plants to utilize nutrients in the soil such as N, P, K, Ca and Mg [10].This is consistent with the results of the study that the P4 -P7 treatment had higher N, P, K, Ca, and Mg absorption values compared to the treatment that did not apply arbuscular mycorrhizae.Increased nutrient uptake is also influenced by the role of endophytic bacteria B. cenocepacia and P. fluorescens.These two bacteria are plant growth-promoting rhizobacteria (PGPR) which has the ability to N-fixation [10] [24], potassium solubilizing [26], and produce growth substances Indole Acetic Acid (IAA), which can increase plant growth and root proliferation [9] [21].

Conclusion
The consortium application of endophytic bacteria and arbuscular mycorrhizae, which was shown to have the best growth of oil palm seedlings compared to all treatments, was the best treatment, according to the study's findings.Plant height increased by 55.5 cm, stem diameter increased by 34.3 mm, and the number of fronds increased by as many as 11 fronds.This is also corroborated by the presence of macronutrients like N, P, and K in the leaves of oil palm seedlings.Because beneficial bacteria can promote oil palm seedling growth and nutrient absorption in peat soil medium, the study's findings suggest that their application may have a positive effect.

Table 1 .
Combination of beneficial microbes treatments.

Table 2 .
Chemical properties of sterile peat soil before treatment.

Table 3 .
Plant height of oil palm seedling (main nursery) at 1 -6 MAP.
*) The Duncan's new multiple range test at = 0.05 finds no statistically significant difference between means in the same column and following the same letter.
*) The Duncan's new multiple range test at = 0.05 finds no statistically significant difference between means in the same column and following the same letter.

Table 6 .
Macronutrient content in oil palm seedlings leaves at 6 MAP. ) The Duncan's new multiple range test at = 0.05 finds no statistically significant difference between means in the same column and following the same letter. *