The use of oil palm biomass as fertilizer and its potency in agroforestry systems for peatland rehabilitation

Oil palm biomass is one of the most abundant wastes in Indonesia. The biomass can be used as fertilizer for increasing plant growth, such as paddy Inpara-2 variety and peatland rehabilitation. The study on the application of oil palm biomass as fertilizer on paddy Inpara-2 growth and its potency in agroforestry systems for accelerating peatland rehabilitation is limited. This study aimed to analyze the application of oil palm-based fertilizers on paddy Inpara-2 and investigate the scientific literature on the use of oil palm biomass as fertilizer in agroforestry systems for peatland rehabilitation. The method used was a completely randomized design with a factor (oil palm-based fertilizer) and scientific literature from the search engine database. Application of micro-lignocellulose 1% resulted in the best paddy germination percentage (100%), abnormal sprout percentage (0%), maximum growth potential (100%), mean germination time (1.95 days), seedling survival rate (100%), and seedling height (13.67 cm). We found 993 articles on oil palm biomass as fertilizer in supporting peatland rehabilitation and only three articles (0.003%) used the agroforestry system as the selected approach. Application of oil palm biomass as fertilizers can accelerate paddy Inpara-2 variety growth, and agroforestry system application could accelerate peatland rehabilitation.


Introduction
Deforestation and degradation in the peat have led to ecological damage that is caused by logging activities (both legal and illegal logging), industrial plantation, peatland conversion to agriculture, recurrent fires, artificial drainage canals, poverty incidence, land use policy, and governance [1].[2] reported 2,492,527 ha of degraded areas that need restoration.Peatland revegetation faces challenges 1315 (2024) 012001 IOP Publishing doi:10.1088/1755-1315/1315/1/012001 2 such as low fertility growing medium, high acidity, and containing toxic compounds for plants [3].Therefore, one of the alternative ways to improve peatland fertility and accelerate rehabilitation can be applied through adaptive species planting and fertilizer application.
Paddy (Oryza sativa L.) has become one of the most important plants in the world.[4] reported that paddy is the staple food for >50% of the world's population and has become one of the most important food crops in the developing world.Indonesian Center of Rice Research (ICCR) has released many varieties of paddy.One of the varieties is the Inpara-2 variety.This variety is included in tidal swamp rice and has approximately 6.0 t/ha [5].Even though this variety can grow in peatland, it still needs fertilizers to improve the growth and yield production of this variety.
The increase in palm oil production in recent years has impacted the production of palm oil waste.In 2017, the production of palm oil waste reached 4,319,820 tons [6].Oil palm biomass generally contains high organic matter, impacting environmental pollution [7].Oil palm biomass can be processed and used for various things, including plant fertilizer.In addition to overcoming the accumulation of waste, it was processing oil palm biomass into fertilizer to minimize the use of chemical fertilizers [8].Economically and ecologically, using oil palm biomass as fertilizer can be a good solution for the palm oil industry's sustainable management in the future.This is supported by the increasing demand for fertilizer as a form of plant organic intake [9].Therefore, research on the utilization of oil palm biomass for fertilizer and its potency in agroforestry systems for peatland rehabilitation is necessary.

Paddy growth
2.1.1.Fertilizers preparation.Oil palm biomass was used to form two types of fertilizers: micro-carbon and micro-cellulose.Micro-carbons consist of activated and non-activated micro-carbons that have been proceeded in the Chemical Laboratory of the Centre for Standardization of Sustainable Forest Management Instrument.Carbon microfiber was obtained by the carbonization process of palm oil biomass, which produces 34% of the yield.The carbonization product was then divided for KOH activation and non-activation, then subsequently filtered with a size of 100 mesh.Micro-cellulose consists of micro-lignocellulosic and micro-crystalline cellulose.Lignocellulose microfiber was extracted using chemical materials such as NaOH, H2O2, and HCOOH.The extraction process also used an autoclave and water bath, then washed with distilled water.Micro-crystalline cellulose was obtained by micro-lignocellulosic hydrolysis for 24 hours using H2SO4, then washed with distilled water till neutral pH (pH = 7).

Seeds preparation.
This research used a seed of the Paddy Inpara-2 variety.The seed was obtained from the Indonesian Center for Rice Research, Subang.Seeds were selected by soaking them in water, floating seeds were removed, and drowned seeds were used for this research.The seed was then soaked in water for 24 hours.This research has 16 levels of treatment and control.The sample was repeated four times so that every petri dish had five seeds.The whole used seed was 340 seeds or 8.5 grams of seed.The weight of the seed was counted by the weight of 1000 seeds calculation of paddy, which was 25 grams [5].

Germination test.
The germination test was conducted using petri dishes on the germinator.Watering was done periodically using 15 mL of distilled water according to the moisture of the growing medium on the petri dish.The petri dishes were arranged in the germinator and then periodically rolled every 24 hours so that every petri dish had the same environmental condition.
2.1.5.Data collection and analysis.The parameters were observed for 21 days.The observed parameters were germinated seeds, abnormal sprout, normal sprout, seedling height, survival seedling, and root length.The collected data was then analyzed based on germination parameters, such as abnormal sprout percentage (ASP), germination percentage (GP), mean germination time (MGT), maximum growth potential (MGP), and seedling survival rate (SSR).
The germination test was calculated using the Analysis of Variance (ANOVA) test.The ANOVA was carried out to identify the influence of the treatment on the observed parameters.The result that had a significant influence was continued with the Duncan Multiple Range Test (DMRT).

Literature review
The research was conducted in June 2023.Harzing's Publish or Perish is software for retrieving and analyzing the reference's academic citation.The data was collected from 2013 to 2023.The search keywords used were "peatland rehabilitation", "oil palm biomass", and "micro-fertilizers".We downloaded The Research Information Systems (RIS), and then analyzed it using VOSviewer software to determine the mapping visualization and keyword density [10].

Paddy growth
The result shows that the application of micro-fertilizers significantly affects all germination test parameters.It indicates that all treatments had enhancing mechanisms for paddy growth performance.The DMRT test result is described in Table 1.The DMRT test result in Table 2 shows that the ML1%, ML5%, and ML7% treatments affected in the highest GP with an average value of 100%.This result is higher than the C treatment but like the DMRT test result.For the abnormal sprout percentage, the MT5%, MT7%, ML1%, ML3%, ML5%, ML7%, and MK7% treatments resulted in the lowest ASP with an average value of 0%, and this result is lower than the C treatment but similar.The MNT3% and MNT7% treatments resulted in the fastest MGT with an average value of 1.84 days, which is faster than the C but similar according to the DMRT test result.For the MGP, the ML1%, ML5%, ML7%, and MK7% treatments influenced in the highest MGP with an average value of 100.00%, which is higher than the C but similar.The ML1%, ML5%, ML7%, and C treatments resulted in the highest SSR with an average value of 100%.The ML1% treatment resulted in the highest seedling height with an average value of 13.67 cm, which is higher than the C and significantly different.The ML7% treatment resulted in the highest root length with an average value of 9.90 cm, it is higher than the C but similar according to the DMRT test result.

Literature review
Oil palm biomass-based micro-fertilizers are rarely used for peatland rehabilitation in Indonesia.Based on the study result (Table 3), only three articles use fertilizers from oil palm biomass.The result of the VOSviewer mapping showed there is no research on the utilization of oil palm biomass-based microfertilizers for peatland rehabilitation.Figure 2 shows that no micro-fertilizers appear in the VOSviewer mapping result.Only fertilizers, organic fertilizers, and synthetic fertilizers are found in the VOSviewer mapping result.

Paddy growth
The germination test measures the seed quality and ability to raise the vital parts of the embryo to normal growth in a suitable environmental condition [14].Germination is the first stage of the seeded plant growth.[15] described that the germination stage is when the dormant embryo undergoes several physiological changes so that it sprouts.The parameters used in the germination growth are seedling survival rate, abnormal sprout percentage, and germination percentage.

Germination percentage.
Germination percentage measures the seed's ability to grow and produce normally in optimum conditions.[16] described that the result of germination percentage indicated the number of seeds that could produce normal sprouts from the sown seeds in a certain period.The result shows that the ML1%, ML5%, and ML7% could produce high GP for paddy.Micro-lignocellulose consists of chemical compounds, such as lignin, cellulose, hemicellulose, inorganic matter, and extractives demanded by the plants.So, the sprout maintained normal growth in Micro-lignocellulose treatments.[17] reported that the neat PVA/chitosan and PVA/chitosan/LCNFs consisted of three dominant elemental components.Those were C (35.56-66.21%), O (27.09-30.80%), and N (37.17-38.08%).

Abnormal sprout percentage.
An abnormal sprout is a sprout that does not show the sprouting potential to grow into a normal plant if they planted in the optimum media [18].The pathogen carried by the seeds can cause an abnormal sprout.[19] described that the early symptoms shown by the abnormal sprout were yellowing on the leaf tips, then spreading to almost the entire leaf, then drying up, and some of the leaves fell off.This study shows that the MT5%, MT7%, ML1%, ML3%, ML5%, ML7%, and MK7% treatments produced the lowest abnormal sprout percentage with a value of 0%.The MT5% and MT7% had low abnormal sprout percentages because no sprout survived on the observation day.It is shown by the result of survival seedlings in the MT5% and MT7% treatment was 0%.
All concentrations in micro-lignocellulose treatments (ML1%, ML3%, ML5%, and ML7%) resulted in the lowest abnormal sprout percentage with a value of 0%.This result shows that micro-lignocellulose could provide conditions for the sprout to grow abnormally.Micro-lignocellulose still had the nutrition needed by the sprout and did not have toxic compounds that could damage the sprout and disturb the sprout growth.[17] reported that the neat PVA/chitosan and PVA/chitosan/LCNFs consisted of three dominant elemental components, such as C (35.56-66.21%), O (27.09-30.80%), and N (37.17-38.08%).
The MK7% treatment also produced the lowest abnormal sprout percentage with a value of 0%.MK7% treatment consisted of 7% of microcrystalline cellulose.Microcrystalline cellulose (MCC) has unique characteristics such as biodegradability, high mechanical properties, large surface area, etc [20].The large surface area of MCC helps this material to perform its ability to bond and or adsorb some materials such as water.[21] reported that one of the most important features of adsorbents is their surface area and porosity.The possible nutrition in the MK7% treatment was thought to be bonded by microcrystalline cellulose particles and helped it efficiently adsorbed by the plant.

Seedling survival rate.
The seedling survival rate shows the seedling ability to survive for a longer time until the observation day.This study shows that the ML1%, ML5%, ML7%, and C treatments affected in the highest SSR with an average value of 100%.This result shows that the micro lignocellulose that consisted in the ML1%, ML5%, and ML7% treatment could maintain the seedling survival rate.Micro-lignocellulose had completed chemical compounds, such as lignin, cellulose, hemicellulose, extractives, and inorganic matter demanded by the plants.So, the seedling could survive for longer periods than the other treatments.[17] reported that the neat PVA/chitosan and PVA/chitosan/LCNFs had three dominant elemental components, which were C (35.56-66.21%), O (27.09-30.80%), and N (37.17-38.08%).

Literature review
Harzing's Publish or Perish software was used to retrieve scientific articles, utilizing various search engines including Google Scholar, PubMed, and Crossref.According to [22], Google Scholar indexes the web as part of the World Wide Web (www) search engine, without language range limits or restrictions on keywords per search.It also covers a wide range of journals [23].[24] notes that PubMed effectively searches numerous keywords with no fee for open access.Crossref can be used for searching the articles based on the digital object identifier (DOI) [24] leading to a substantial finding related article.
The use of keywords facilitates the identification of related articles by indicating the research scope and article topics.The articles that were difficult to find in this study were caused by rarely used keywords in search engines.[25] emphasizes that the frequency of keyword usage correlates with the specificity and ease of finding articles.
The VOSviewer was instrumental in visualizing keywords, using colored circles for labeling and analysis of the relationship between keyword categories.[26] reported that the circle size in the VOSviewer indicates a positive relationship regarding the occurrence of keywords in the title and abstract.Larger font sizes and circles indicate more frequents keywords appearances [27].

Conclusions
The micro-fertilizers application significantly affects all parameters on the paddy germination test.Application of micro-lignocellulose 1% resulted in the best germination for paddy (100%), which resulted in 13.67 cm of seedling height, 1.95 days of mean germination time, 100% of seedling survival rate, 0% of abnormal sprout percentage, and 100% of maximum growth potential.It was found that 993 articles on oil palm biomass as fertilizer in supporting peatland rehabilitation and only three articles (0.003%) used the agroforestry system as the selected approach.Application of oil palm biomass as fertilizers can accelerate paddy Inpara-2 variety growth, and agroforestry system application could accelerate peatland rehabilitation.

Figure 1 .
Figure 1.The effect of oil palm biomass-based fertilizers on the germination test parameters

Figure 2 .
Figure 2. VOSviewer results on research of oil palm biomass utilization for peatland rehabilitation

Table 1 .
Recapitulation of ANOVA test for germination test a (ns): the treatments had no significant effect at the 5% test level with the P-value > 0.05, (*): the treatments had a significant effect at the 5% test level with the P-value < 0.05

Table 2 .
Recapitulation of DMRT test for germination test

Table 3 .
Data on scientific articles