Growth Test of Three Types of Legume Cover Crops Commonly Used in Oil Palm Plantation

Legume cover crops (LCC) in oil palm plantations aim to protect the soil from direct sunlight, suppress weed growth, suppress erosion, maintain soil moisture and increase soil fertility. Cover crops such as Mucuna bracteate (Mb), Pueraria javanica (Pj), and Calopogonium mucunoides (Cm) are commonly used in oil palm plantations. Nowadays, the superior cover crop seeds are limited. However, all of the cover crop seeds spread in the market are coming from unlicenced farms. As consequence, the seed quality and the purity are questioned. It is important to conduct research to identify the quality of those there LCC seeds. Germination methods used in the laboratory tests were the method of on paper (UDK), between-paper test (UAK), and soil media test. An experimental design completely randomized was used. The results showed that the germination percentage of Pj, Mb, dan Cm with the UDK method are 29%, 22%, and 4%; the UAK method are 33%, 41%, and 5%; meanwhile, the growth percentage of Pj, Mb, and Cm are 47%, 53%, and 7% respectively.


Introduction
Legume cover crops (LCC) in oil palm plantations serve to support the optimal growth and development of oil palm, especially in creating a better microenvironment during the immature period.The planting of LCC in oil palm plantations aims to protect the soil from direct sunlight, suppress weed growth, suppress surface erosion, maintain soil moisture, and increase soil fertility [1].The type of LCC usually has specific growth characteristics such as Mucuna bracteate (Mb), Pueraria javanica (Pj), Calopogonium mucunoides (Cm) commonly used to support immature oil palm.
Mucuna bracteate (Mb), Pueraria javanica (Pj), Calopogonium mucunoides (Cm) can grow fastly, are easy to grow with low input, are tolerant of pests and diseases, and have deep roots [2].The deep roots of legumes can improve soil physical properties and produce high litter as humus that decomposes slowly thus increasing soil fertility.Legume roots can fix nitrogen from the air [3].The root characteristics of Mucuna bracteata are taproots like other legumes, brownish white, spread above the soil surface.This plant also has fresh pink root nodules and relatively very many, round in shape and very varied in diameter between 0.2-2.0cm.The root growth rate is quite high so that at the age of more than three years the main roots can reach a length of 3 m.Pueraria javanica has a role as a plant that can increase soil fertility, this plant is a type of legume that quickly spreads because it has the advantage of binding the element N (nitrogen) which is needed by immature main plants, also this legume lowers soil temperature during drought [4].Likewise, the roots of Calopogonium mucunoides plants have root nodules that allow this type of symbiosis with rhizobium to form root branches resembling threads.This makes it easier for plants to absorb water in the soil.Root hairs will respond by bending the roots to reach the depth of the roots which ranges from 1-2 m because most of these root nodules tether N from free air [5,6,1].
For decades oil palm plantations obtained legume seeds from imports in bulk form.The large domestic demand has certainly affected the availability of seeds.The question then arises as to whether the quality of the seeds received in the country is following existing regulations in Indonesia.It is reported that there is a lot of deterioration in the quality of these legume seeds in the field.Many seeds with germination percentages below 50% were found.
In general, superior seeds are seeds that have passed through laboratory tests following the requirements and carried out by experts and the final results show their advantages when compared to other varieties.Germination testing can estimate the quality of the seed.Germination can be defined as the ability of a seed to bloom or the development of vital parts of the embryo to grow normally in an appropriate environment.The normal germination process will go through a series of germination attributes, namely root candidates, stem candidates, and leaves.Although seed germination is influenced by many factors, including seed quality, dormancy, seed treatment, and environmental factors which are the most dominant [7,8].Seed quality testing of the three LCCs is an important thing to do, so that information on the level of seed quality is obtained.According to the International Seed Testing Association (ISTA) (2017) in conducting seed quality testing, the media or substrates used include paper, sand, and organic growing media.For this reason, research was conducted on the quality test of Mucuna bracteata, Pueraria javanica, Calopogonium mucunoides seeds commonly circulated in Indonesia using several testing methods.

Material and Methods
The research was conducted at the Soil Physics Laboratory and Plastic House of Indonesian Oil Palm Research Institute Jl.Brigjen Katamso No.51, Kp.Baru, Medan Maimun, Medan City, North Sumatra.The research was conducted from October to November 2022.The tools used include sprayers, Petri dishes, scissors, digital scales with 1/1000 accuracy, trays, ovens, desiccators, and aluminum cups.Then the materials used include seeds of Mucuna bracteata, Pueraria javanica, Calopogonium mucunoides, filter paper, soil, and organic fertiliser.Tests were conducted to determine the percentage of seed moisture content, germination, and vigor of the three LCCs.The seeds of the three LCC species were obtained from the EMU (Environmental Management Unit) of PT Mustika Sembuluh 1, Wilmar Group, Central Kalimantan based on sample packaging without seed description information.
The observation of LCC seed weight between Mb and Pj and Cm is different, this is done considering the clear size of each LCC where for seeds with small size the seed weight is calculated based on the weight of 1000 seeds, while for large seeds using the weight of 100 seeds.The initial tests carried out on the samples were observations of the weight of 1000 seeds and testing of the moisture content of the seeds.Observation of the weight of 1000 seeds was carried out by randomly taking seeds in the sample population and then counting 1000 seeds to be weighed with 3 times repetition.The moisture content testing of LCC Mucuna bracteata, Pueraria javanica, and Calopogonium mucunoides was carried out based on the provisions of ISTA 2017.Seed preparation of Mucuna bracteata was prepared with approximately 10 grains, Pueraria javanica, and Calopogonium mucunoides 100 grains which were counted manually and then put into an aluminum cup with 4 times repetition.The seeds were crushed first before being put into the oven.The seeds of Mucuna bracteata, Pueraria javanica, and Calopogonium mucunoides were then weighed, and the fresh weight was recorded.The prepared seeds were put into the specified oven at 130 0 C for 1 hour, 2 hours, 3 hours, and 4 hours.After that, the seeds were put into a desiccator for 35 minutes, and the dry weight is calculated.The calculation of moisture content is expressed as a percentage based on the weight for each replicate with the formula: Description: M1 is the weight in grams (to a minimum of three decimal places) of the container and lid; M2 is the weight in grams (to a minimum of three decimal places) of the container, lid, and contents before drying; M3 is the weight in grams (to a minimum of three decimal places) of the container, lid, and contents after drying.
The next test is testing the quality of seeds in the laboratory including germination, vigor index, and germination rate using the test method on paper (UDK) and test between papers (UAK) in Petri dishes with filter paper media.The prepared filter paper has been cut to adjust the shape of the Petri dish.The number of Mucuna bracteata seeds was 50, while the number of Pueraria javanica and Calopogonium mucunoides seeds used for each Petri dish was 100.Each LCC was repeated 4 times.The filter paper in the Petri dish was first moistened with water until it did not drip, then each seed was placed on the filter paper in an orderly manner.Mucuna bracteata seeds were scarified first by cutting one edge of the seed using nail scissors.Furthermore, seed spraying was carried out every morning and evening every day.The calculation of seed germination is based on the percentage of total normal sprouts observed on the first and last count days of observation.The calculation of the vigor index is based on the percentage of normal sprouts on the first count day of observation, while the germination rate is calculated based on the percentage of normal sprouts per etmal (24 hours) until the last count.Seeds are said to germinate with the criteria that a radicle has appeared at a minimum of 2 mm (millimeters) (ISTA, 2017).The criteria for normal germination of seeds are when the length of the plumula and radicle is fully formed with proportional growth.In addition, seed quality testing was also carried out in the field to test the growing power of Mucuna bracteata, Pueraria javanica, and Calopogonium mucunoides.Growth power testing was carried out in the Plastic House using trays that had been filled with sifted soil media, then added with bioneensis biofertilizer 25 grams/kg of soil.In each tray then placed 25 seeds of the three LCCs with a repetition of 3 times.Observations of germination were calculated based on the percentage of sprouts that grew on the tray until the last day of observation.Observations were stopped when no seeds were found growing during the observation.

Results and Discussion
The three of LCC seeds tested in this research are Mucuna bracteata, Pueraria javanica, and Calopogonium mucunoides, had no known shelf life, seed origin, seed moisture content, and germination.For this reason, the initial observation carried out was to determine the character of the three seeds in terms of seed weight and seed moisture content.The seed weight of each LCC species is presented in Table 1.
The function of calculating seed weight is intended to determine the number of seeds in units of weight.This is very important for calculating the estimated seed requirements that will be needed before seedling preparation until planting LCC in the field.There are factors that affect the weight of the seed, which includes variety factors and environmental factors [9].The decrease in seed weight can be caused by the length of storage, warehouse pest attacks, excessive drying during seed processing, and poor growth of the parent material [10].
Seed water content testing was carried out at a high temperature of 130 o C with a range of baking times of 1 hour, 2 hours, 3 hours, and 4 hours.The results of the test on the seeds of Mucuna bracteata, Pueraria javanica, and Calopogonium mucunoides showed that the calculation of the percentage of constant seed water content was obtained at a high-temperature oven for 2 hours on Mucuna bracteata seeds, 3 hours for Pueraria javanica seeds, and 4 hours for Calopogonium mucunoides seeds with a calculated percentage of the water content of 12.1%; 11.5%; and 11.0%, respectively (Table 2).The variation in the calculation of the percentage of water content is thought to be the influence of the seedcrushing process before the oven is carried out.The seeds that belong to the type of hard seeds (legume), (1) there are indications that during the preparation period with scarification and crushing, the seeds absorb the surrounding water due to hygroscopic properties [11,12].Germination testing of Mucuna bracteata, Pueraria javanica, and Calopogonium mucunoides in Petri dishes was observed every day until the 14th day.Based on Figure 1, it is known that Mucuna bracteate seeds began to germinate at the first observation (1 day after planting) at UAK and UDK, Pueraria javanica seeds began to germinate at 1 HST at UAK and 2 HST at UDK, while Calopogonium mucunoides seeds began to germinate at the observation of 2 HST both at (UDK) and (UAK).This shows that there is faster germination in UAK when compared to (UDK), this is also based on the ability of the UAK method to maintain moisture in a Petri dish.In the process of germination, water absorption will activate embryonic cells in the seeds, so that water absorption will accelerate germination [13].Water absorbed by the seed is useful for softening the seed coat which will cause the embryo and endosperm to expand.Further development of the endosperm can result in rupture or tearing of the seed coat.Seeds germinated under optimal conditions in Petri dishes show three phases of water absorption [14].Phase 1 is the initial phase of water absorption that takes place as a result of the attraction of water molecules due to the large potential matrix of the cell wall and other materials contained in the cell.Then the stagnation phase, this phase is called phase 2, dormant seeds or dead seeds will remain in this phase [15].Phase 3 will occur enzymatic reactions and some metabolic processes begin immediately.The test results of germination, vigor index, and germination rate of the three LCCs show that germination is in line with the vigor index and germination rate.Based on Table 3, it can be seen that UAK obtained a higher germination rate, vigor index, and germination rate when compared to UDK.However, the germination rate of Mucuna bracteata, Pueraria javanica, and Calopogonium mucunoides in this test was low, ranging from 4-37%.The results of previous studies state that good germination for seeds of annual horticultural crops is above 70%, in line with that the characteristics of good seeds are seeds that have high germination and have a high percentage of life [16].Growth ability testing with soil media is intended to form a suboptimal to optimal seed growth environment.In the test of growing power, Mucuna bracteate seeds were also scarified first.The seeds of the three types of LCC were given a soaking treatment using water with a duration of 2 hours and 4 hours then the seeds were planted in a tray placed in a Plastic House.Based on the test results, it was found that the first seed to grow at 1 HST was the seed with 2 hours and 4 hours of soaking, while the seed without soaking treatment grew at 2 HST (Figure 2).This may indicate that soaking for 2 hours or 4 hours can accelerate seed germination, especially Cm and Pj seeds.According to [17], seed soaking treatment serves to soften the seed coat and facilitate the process of water absorption by seeds so that physiological processes in seeds can take place for the germination process and make it easier for seeds to break their dormancy and start growing.The highest growth ability was shown by Mb seeds at 53% without soaking, Cm seeds with 7% growth ability in the 4-hour soaking treatment, and PJ showed a growth ability of 47% with 2-hour soaking.Soaking seeds can generally increase seed germination in the field as shown in Cm and Pj.However, this was not the case for Mb seeds where the germination decreased with the length of soaking time.This is due to the scarification treatment carried out previously.Scarification by opening the seed coat on one side will accelerate the entry of water in the embryo and endosperm, soaking treatment causes water-saturated seeds.According to [18] seed treatments such as scarification or chemically provide the best growth rate because the water and oxygen needed for germination can enter the seed without obstruction so that the seeds can germinate, the longer the seeds are soaked, the greater the entry of water into the seed endosperm, thus allowing the seeds to germinate quickly but there are certain limits to the length of soaking because if it is too long to soak the seeds will experience decay and damage.

Conclusion
Testing the quality of legume cover crops (LCC) seeds that are commonly circulated is important because it will determine the success of the planting process in oil palm plantation.Laboratory testing of 3 LCC Mucuna bracteata, Pueraria javanica, and Calopogonium mucunoides seeds from unidentified sources resulted in germination rates of 29-37%; 22-28%; and 4-5%, respectively, which are categorized as low.While testing the growing power of the three LCC 47% (Pj) with soaking treatment 2 hours before planting, 53% (Mb) scarification without soaking treatment, and 7% (Cm) with soaking treatment 4 hours before planting.

Acknowledgment
This research was carried out with the cooperation of various parties.

Table 3 .
Germination, vigor index, and germination rate of three LCCs on paper test and between- Thanks to IOPRI for all the support to the author.PT Mustika Sembuluh I, Wilmar Group, Central Kalimantan for providing LCC seeds.Iqbal Ramadhan and Icaq Dwi Prasetyo, students of the certified independent study internship program (MSIB) Batch III for technical research and data collection.Colleagues of Soil Science and Agronomy IOPRI.