Effect of humic acid on oil palm seed germination

Humic acid is an extract from organic materials that can enhance root development to accelerate the absorption of nutrients and water, thereby increasing plant growth. This study aims to determine the role of humic acid to increase the initial growth of oil palm seedlings. This study used a completely randomized design (CRD) with four treatments to test the optimum doses of humic acid, namely 0% (control), 0.5% (P1), 1% (P2), and 1.5% (P3). Each treatment used 22 oil palm seeds. Seedlings were soaked in humic acid according to treatment for one hour, then grown for seven days. Observations were made every day until the 7th day on the parameters of hair length, radicle length, and number of lateral roots. Data analysis used the analysis of variance test (ANOVA) with the Tukey HSD follow-up test (p>95%). Humic acid treatment at a dose of 1% showed significant results in increasing the number of lateral roots by 110% compared to the control. Humic acid can be an alternative growth regulator to induce the growth of oil palm roots.


Introduction
Oil palm (Elais guineensis Jacq) is one of the main crops in Indonesia with a significant increase in cultivated land.The annual demand for oil palm seeds in Indonesia is estimated to reach 120 million, but existing seed producers can only provide 60-70 million seeds per year.The process of germinating oil palm seeds is quite difficult because the seeds have a hard shell and are dormant.This dormancy condition requires the seeds to be treated to break the dormancy.Humic acid is one type of active ingredient in organic fertilizers that is widely developed both as an organic soil conditioner and a biostimulant [12].
Humic acid is the result of biological and chemical degradation of organic materials over millions of years.Humic acid is one type of active ingredient in organic fertilizers that is widely developed both as an organic soil conditioner and a biostimulant.Generally, humic acid is produced from low-rank coals.Currently, there is a development in the formulation of humic acid products, one of which is the addition of materials that can increase the effectiveness of the product.
Liquid fertilizer by-product (PSNC) that can be used to enrich humic acid fertilizer formulations and replace water as a solvent, thereby increasing manufacturing process efficiency towards zero waste and beneficial for improving plant growth and productivity [2].In this study, a humic acid formulation using PSNC as a water substitute solvent was conducted through bioassay using oil palm seedlings.This research aims to improve the initial growth of oil palm seedlings by providing humic acid.

Liquid fertilizer by-product (PSNC) Humic Acid Production
The production of PSNC humic acid formula was carried out in the Biochemistry Laboratory of Oil Palm Reasearch Institute (IOPRI) Bogor Unit, referring to the standard operating procedures (SOP) with modifications on the type of solvent used [2].The raw materials, consisting of lignite, sodium hydroxide, potassium hydroxide, and seaweed, were added to the extraction tank, and then the liquid fertilizer byproduct (PSNC) obtained from PT Pupuk Kalimantan Timur was added as a solvent until the specified volume was reached.The mixture of raw materials and PSNC was homogenized until evenly distributed.Air was circulated into the mixture as aeration, then heated to a temperature of 95°C for 1 hour.Aeration and stirring were carried out during heating.The resulting extraction was added with 1% (v/v) phosphoric acid until reaching a pH of 9-10, and then left for 24 hours.Filtration was carried out to obtain 2 product phases, solid and liquid.This resulted in the final product of liquid humic fertilizers.

Palm oil seedling bioassay
Humic acid is used as a biostimulant to stimulate the growth of oil palm seedlings.This experiment used a completely randomized design with four treatments of humic acid 0%, 0.5%, 1%, and 1.5% in 22 units of oil palm seedlings as replicates.Prior to the application of humic acid, oil palm seedlings were selected and their plumule and radicle were measured.The oil palm seeds used had an average plumule and radicle of 8-10 mm and 12-15 mm.Furthermore, the oil palm seeds were soaked according to the treatment for 1 hour [5], then aired for 30 minutes.Germination was carried out on trays with wet cotton media for seven days.Humidity is maintained by spraying aquadest (150-200 mL per day) periodically for each treatment.During the oil palm germination process, a 2 g/L fungicide solution was sprayed on the 4th day to prevent mold growth [4].Observation of seedling growth was carried out including the length of the plumule, the length of the radicle, and the number of lateral radicles on day 0 to day 7. Seedling growth gain was calculated by looking at the comparison between the growth on day 0 and day 7. Data analysis used ANOVA with Tukey HSD as a follow-up test (p>95%).

PSNC humic acid characterization and formula quality test
The characterization results of PSNC obtained from PT. Pupuk Kalimantan Timur are presented in Table 1.The PSNC sample has a basic pH of 9.27.The PSNC sample has a content of N, P, and K elements of 2.66%, 356.80 ppm, and 1.76%, respectively.Compared to the liquid waste of palm oil factories, Raja et al. [10] reported that fermented palm oil mill effluent with 7% bentonite added to EM4 showed the highest N content at 9,167 ppm, while the highest P and K content was observed with 3% bentonite addition, namely 20.1 ppm and 742 ppm, respectively.In addition, the NH3 and Cl content in the PSNC sample is 3.35% and 0.11%, respectively.
The quality of the humic acid formula of PSNC was analyzed according to the criteria in the Ministry of Agriculture Regulation No. 1 of 2019 concerning the quality standards for organic fertilizer, biological fertilizer, and soil conditioner.This testing was carried out to determine the quality of the humic prototype fertilizer formulated with PSNC.The results of the product quality test for the PSNC sample can be seen in Table 2. Based on these standards, the concentration of humic compounds in liquid products must be at least 10%.The test results showed that the PSNC liquid humic acid contained 15.97% humic compounds.Liquid humic acid have a very low sodium content of 0.56%, and this product has a basic pH of 9.5.Heavy metals such as As, Hg, Pb, Cd, and Ni are known to be very low.The content of Cr heavy metal is 13.22 ppm for liquid PSNC humic acid.

Effect of PSNC humic acid to the growth of palm oil seedling
The results of the germination of oil palm after seven days showed a significant difference in the parameter of lateral root growth, while the length of plumule and radicle did not show any difference in Figure 1.Stimulation of germination, growth, and development of oil palm can be done through several approaches, namely heat treatment and hormone treatment.Ani [1] reported that soaking Leucaena leucocephala seeds in water with an initial temperature of 60-70oC for 10-12 minutes can break dormancy and produce a germination rate of 75%.The use of ethephon can also break dormancy because ethephon can stimulate enzyme activation for germination.Herrera et al. [6] reported that the use of 0.6% ethephon concentration for 48 hours on oil palm seeds can result in germination of 88% if preceded by soaking using 98% sulfuric acid for 10 minutes.Based on the information given, the length of the plumule of oil palm seedlings treated with humic acid (HA) at concentrations of 0.5%, 1%, and 1.5% did not show a significant increase compared to the control on day 7 of germination in Figure 2A.The length of plumule for all treatments increased gradually and was lower than the control in Figure 2B.Therefore, it can be concluded that the application of humic acid at concentrations of 0.5%, 1%, and 1.5% did not have a significant effect on the increase of plumule length in oil palm seedlings compared to the control.The effect of humic acid immersion on the increase in the length of oil palm seedling radicle is shown in Figure 3A.On day 0, the length of radicles in each treatment and control was different, namely 10.69 mm (HA 0.5%), 11.52 mm (HA 1%), and 11.90 mm (HA 1.5%), while for the control it was 11.58 mm.On day 7, the length of plumula in the HA 0.5%, HA 1%, HA 1.5%, and HA 0% treatments were 15.41 mm, 15.55 mm, 15.77 mm, and 15.77 mm, respectively in Figure 3A.The results of the variance analysis showed no significant difference between each treatment and the control.The increase in plumula length was 4.05 mm, 3.45 mm, 3.32 mm, and 3.59 mm for HA 0.5%, HA 1%, HA 1.5%, and HA 0%, respectively in Figure 3B.These results indicate that humic acid at concentrations of 0.5%, 1%, and 1.5% did not significantly affect the increase in oil palm plumula length compared to the control.The effect of humic acid soaking on the increase of lateral root number in oil palm seedlings is shown in Figure 4A.On day 0, the length of the radicle for each treatment and control was different, namely 4.12 (HA 0.5%), 2.63 (HA 1%), and 2.56 (HA 1.5%), while for control it was 2.10.On day 7, the number of lateral roots for HA 0.5%, HA 1%, HA 1.5%, and HA 0% treatments were 6.14, 5.86, 4.68 and 4.27 in Figure 4A.The results of the variance analysis show a significant difference in the HA 1% treatment compared to the control.The increase in the number of lateral roots for each treatment was 1.73, 2.77, 1.82, and 1.95 for HA 0.5%, HA 1%, HA 1.5%, and HA 0% in Figure 4B.These results indicate that humic acid at a concentration of 1% can increase the number of lateral roots in oil palm seedlings compared to control.Humic acid 1% significantly increased the number of lateral roots.These results are consistent with previous studies showing that humic acid can promote cell division in roots and alter their architecture, particularly in root hairs and lateral roots.Humic acid can induce H+-ATPase on the root plasma membrane [3] & [7].Arabidopsis which was applied with Ascophyllum nadusum biostimulant dose of 3% showed faster root growth [8].Base extract from Sargassum sp.dose of 1.5% also showed the highest number of shoots and roots.

Conclusion
The results showed that humic acid treatment from the PSNC formulation at a dose of 1% could increase the growth of oil palm seed roots, so that it could be used as an alternative growth regulator to induce rooting of oil palm.

Figure 2 .
Figure 2. Effect of humic acid on the increase in plumule length (A) and plumule length (B) of oil palm sprouts.Bars represent the average plumula length parameters with significant values indicated by letters above each bar, P < 0.05.HA 0%: control, HA 0.5%, HA 1%, and HA 1.5%

Figure 3 .
Figure 3.Effect of humic acid on the increase in radicle length (A) and radicle length (B) of oil palm sprouts.Bars represent the mean of the radicle length parameter with significant values indicated by letters above each bar, P < 0.05.HA 0%: control, HA 0.5%, HA 1%, and HA 1.5%

Figure 4 .
Figure 4. Effect of humic acid on the increase in the number of lateral roots (A) and the increase in the number of lateral roots (B) of oil palm sprouts.Bars represent the mean of root growth parameters with significant values indicated by letters above each stem, P < 0.05.HA 0%: control, HA 0.5%, HA 1%, and HA 1.5%