rfnam Revista Facultad Nacional de Agronomía Medellín Rev. Fac. Nac. Agron. Medellín 0304-2847 2248-7026 Facultad de Ciencias Agrarias - Universidad Nacional de Colombia 10.15446/rfnam.v74n1.85335 Artículos Effects of the sludge application at different concentrations on growth and production of rice ( Oryza sativa L.) using a water channel underneath soil surface Efectos de la aplicación de lodos a diferentes concentraciones sobre el crecimiento y producción de arroz ( Oryza sativa L.) utilizando un canal de agua establecido por debajo de la superficie del suelo 0000-0002-5788-5773 Effendi AR Arman 1 0000-0001-8311-1416 Zuhry Elza 1 0000-0002-8621-0986 Ariani Erlida 1 Department of Agrotechnology, Faculty of Agriculture, Universitas Riau, Pekanbaru, Indonesia. arman.effendi@lecturer.unri.ac.id, elsazuhry@yahoo.com, erlida.ariani@yahoo.co.id Department of Agrotechnology Faculty of Agriculture Universitas Riau Pekanbaru Indonesia arman.effendi@lecturer.unri.ac.id elsazuhry@yahoo.com erlida.ariani@yahoo.co.id Jan-Apr 2021 74 1 9395 9401 02 04 2020 29 10 2020 This is an open-access article distributed under the terms of the Creative Commons Attribution License ABSTRACT

Indonesia's strategies are focus on improving food production using environmentally-friendly measures in its agricultural development. This research was designed in accordance with the national strategies on increasing the productivity of rice using efficient water while reducing methane emissions from rice fields. A low rice yield is obtained when the conventional anaerobic methods (flooded soil) are used. Additional to the water, sludge from palm oil factories was also applied. This research aimed to establish a proper concentration of sludge to increase the productivity of rice sown in aerobic condition with the water level at 5 cm below soil surface. The study was conducted by making experiments with 5 levels. Waste sludge from palm oil factories was applied on the soils tested with concentrations of 0 t ha-1, 10 t ha-1, 15 t ha-1, 20 t ha-1 and 25 t ha-1. Height of the plant, total number of tillers, number of productive tillers, number of filled grains, percentage of filled grains, weight of 1000 grains and weight of filled grain per plot were studied. Application of 25 t ha-1 organic sludge showed a high level of productivity increasing the total number of tillers, the number of productive tillers and weight of filled grain per plot.

 RESUMEN

Las estrategias de Indonesia para desarrollar su agricultura se centran en mejorar la producción utilizando medidas respetuosas con el medio ambiente. Esta investigación fue diseñada de acuerdo con las estrategias nacionales para incrementar la productividad del arroz y un uso eficiente del agua mientras se reducen las emisiones de metano de los cultivos de arroz. El bajo rendimiento de arroz en los campos que emplean métodos convencionales se debe al suelo inundado (anaerobio). Además del uso eficiente del agua, también se aplicaron lodos residuales de las fábricas de aceite de palma. Esta investigación tiene como objetivo establecer una concentración adecuada de lodos para aumentar la productividad del arroz cultivado en condición aeróbica con el nivel de agua a 5 cm por debajo de la superficie del suelo. Se realizaron experimentos con 5 niveles. Los tratamientos que se probaron involucraron aplicación de lodos residuales de fábricas de aceite de palma con concentraciones de 0 t ha-1, 10 t ha-1, 15 t ha-1, 20 t ha-1 and 25 t ha-1. Parámetros como la altura de la planta, número total de retoños, número de retoños productivos, número de granos llenos, porcentaje de granos llenos, peso de 1000 granos y peso de arroz molido seco fueron estudiados. La aplicación de 25 t ha-1 de lodos orgánicos mostró un alto nivel de productividad al incrementar el número total de retoños, el número de retoños productivos y el peso del arroz molido seco.

 Keywords: Aerobic Anaerobic Sludge Rice Water channel Palabras clave: Aerobio Anaerobio Lodo Arroz Canal de agua

Rice is a vital commodity in Indonesia as it is a basic food in the people diet. Food security in this country is highly dependent on the availability of this grain. Indonesia's population is in continuous growth, which implies to improve the rice productivity otherwise, the rice supply will be adversely affected. Currently, Indonesia is importing to meet its own rice supply. As a mandatory action, innovative cultivation techniques of rice must be considered to reduce the dependence on the other countries (Wardani et al., 2019).

Indonesia's strategy to improve the national agriculture is to incorporate a cleaner production considering the environmental issues. This strategy adopted by Indonesian government must be accompanied with efficient use of water as well as reduction of methane emission from rice fields (Leimona et al., 2015). Other measures include the use of organic fertilizers (Amjad et al., 2016).

Sludge is the waste of processes from wastewater treatment, which in this case is from palm oil factories. The process of waste treatment in palm oil factories consists in decomposition by bacterias. The bacterias can break down molecules and transform complex chemical structures into simpler ones and accelerate the absorption of nutrition in plants (Widiastuti et al., 2019). The sludge is stored in a waste pool and can be recommended for use as an organic fertilizer (Khairuddin et al., 2016).

Sludge derived from wastes of palm oil factories can be used as compost due to its humus and trace element contents. Application of sludge in soils can improve its fertile. Sludge taken from an anaerobic pool contains elements of nitrogen (0.047%), calcium (0.111%), phosphorus (0.004%), carbon (0.016%), magnesium (0.09%), and potassium (0.161%). Meanwhile, an aerobic pool contains elements of nitrogen (0.041%), calcium (0.145%), phosphorus (0.003%), carbon (0.012%), magnesium (0.083%) and potassium (0.131%). Fertilizers that have solidified from the liquid waste can be a supplement of an organic fertilizers and at the same time are environmentally friendly (Dwi et al., 2009). Pandapotan et al. (2017) evaluated the use of these sludge in an Ultisol. They found that a concentration of 21.25 t ha-1 can increase pH level of soil, C-organic, and the presence of phosphorus can improve its absorption in plants and the growth of the corn.

This research aimed to establish a proper concentration of sludge to increase the productivity of rice in aerobic using a water channel at 5 cm below soil surface.

MATERIALS AND METHODS

The research was conducted in rice fields of Parent Seed Center Institution in Padang Marpoyan, Pekanbaru city, Riau province, Indonesia. It has a temperature between 27-34 °C, is wet and has flat topography. This study brings together the previous research that was done in the field from June until October 2019.

The sludge chemical characterization indicated a total nitrogen 750 mg L-1, phosphorus 18 mg L-1, potassium 2,270 mg L-1, magnesium 615 mg L-1 , calcium 439 mg L-1, boron 7.6 mg L-1, iron 46.5 mg L-1, manganese 2.0 mg L-1 copper 0.89 mg L-1 and zinc 2.3 mg L-1 (Lang, 2007).

Preparation of experiment field

The experiment field was carried out in a muddy soil by and was prepared by a semi-mechanical method using tractor and manual work. The soil was broken down into smaller particles and was flooded with water about 21 days removing weed completely. The land was set up according to research plan setting the height of water at 5 cm below the soil surface with 2 m interval between channels.

Dosage treatment of organic sludge fertilizer

According to the 5 different levels of organic sludge from waste of palm oil factories, 15 squares (3 m2 each) were prepared in the fields with 3 replications. G0=0 t ha-1; G1=10 t ha-1; G2=15 t ha-1; G3=20 t ha-1; G4=25 t ha-1 were the five levels evaluated.

Preparation of seeds and seed bed

Batang Piaman was the only variety of rice seeds used in the research, which is known for its great adaptability in low altitude areas. Seed bed was set up close to the experiment fields with an area of 5 m2, 0.5 kg of compost was spread at 1 t ha-1. It was kept in moisture conditions before the seedlings were sown. The seedling were soaked in water for 2 days before planting. The floating seeds indicated bad quality and were discarded while ones that sank were used. The seeds were then cleaned and dried before they were sown and distributed evenly on the seed bed.

Planting seeds

The seedlings were transferred at 12 days after sowing, which were carefully removed to avoid to damage the roots. Then, these were planted in their respective plots about 2 cm deep. They were sown at 25 cm distance resulting 48 seedlings in each square.

Maintenance of rice plants

Weed control was performed twice at 20 days after planting (DAP) and at 40 DAP. Using a single application during planting phase of Curater 3G (17 kg ha-1) pests were prevented.

The irrigation management was planned to keep the depth of the water channels at 5 cm below soil surface with 2 m between channels (Figure 1). The level of water in the channels remained stable under soil surface because the inlet and outlet sluice gate were conditioned.

Rice crop in field. Water channels set at 5 cm below ground surface.

The fields were drained upon entering the ripening of seedlings, which was about 2 weeks before harvesting stage.

Harvesting stage

When almost all of the rice turned yellow (80%) was the criteria used to harvest. It was carried out in each plot. Every treatment was done in triplicated i.e, each treatment had 3 plots.

After harvesting was concluded, filled grains were dried for 3 days or until the water content was less than 14%, then were weighed and analyzed.

 Parameters of observation

The height of plant was established by measuring the length of the plant from the surface of soil to the farthest tip of leaf. The measuring was taken once at the end of the vegetative phase.

Total number of tillers; every stem in each unit of experiment was counted.

Number of productive tillers: each tiller that produces panicles at harvesting time for each sample.

The age of plant in each unit of experiment was carried out during harvesting time. It was done by counting the total number of growing days from the planting time to harvesting time.

Number of filled grains per panicle was counted along with the counting of rice production from the same sample in each plot.

Weight of 1000 grains (g) was done together with the counting of rice production. The weight of 1000 grains had approximately 14% water content. The sample was taken from every unit in the experiment.

Weight of filled grain per plot with approximately 14% water content (kg).

 Statistical analysis

Results were expressed as mean±standard deviation of three repetitions. The assays were compared by using one-way analysis of variance (ANOVA), followed by Duncans New Multiple Range Test post-hoc test, with statistical significance (P<0.05). All statistical analyses were performed using IBM SPSS software.

RESULTS AND DISCUSSION

Application of organic sludge in different concentrations had an effect on the total number of tiller and productive tiller but it did not affect the height and age of the rice plants (P<0.05) (Table 1).

of the few changes on the plant development on height of plant, number of total tillers, number of productive tillers and harvesting age.

Application of 25 t ha-1 of organic sludge showed the highest plant height (116.45 cm); however, there was not significant differences with the other concentrations of organic sludge. The height of Batang Piaman variety was not affected by different concentrations of sludge fertilizer. This is probably because the fertility level of the soil is the same, causing few changes on the plant development. The characteristics of the lowland rice plant height of the Batang Piaman variety are not influenced by the relatively small differences in soil environment. Plant height could differ if the plant is planted in environments with different properties.The difference in soil environment caused by the treatment of various doses of organic sludge fertilizer can not significantly affect the growth of plant height because the different doses of organic sludge fertilizer applied do not cause significant changes in the soil environment. According to Huang et al. (1996) the genetic factor of Batang Piaman rice controls the height when the differences in the soil environment are not wide; the rice plants usually have 4-6 vertical nodes whose height is highly influenced by the qualitative gene and quantitative portrait loci. Also, Sasaki et al. (2002) stated that the length of internodes in rice plant is controlled by a gene that is expressed in every node, meaning that the lengthening of rice stem is coordinated in every node.

Application of 25 t ha-1 of organic sludge produced the highest number of tillers (27.10) and the highest number of productive tillers (15.26), which was different from the other treatments, being 25 t ha-1 the highest concentration. Organic sludge contains trace elements of nitrogen, calcium, phosphorus, carbon, magnesium, and potassium, all necessary components to improve the soil fertility. Macro elements found in sludge of palm oil factories can increase the number of productive tillers when these macro-elements are proportionately applied. The rise in the number of tillers after the use of organic sludge at 25 t ha-1, showed that trace elements contribute to metabolism process, especially calcium which activates a number of enzymes in the process (Maryam and Amiri, 2014). The formation of tillers is influenced by the availability of nitrogen element. This substance is important given that stimulates their growth. In addition, nitrogen plays a crucial role in the vegetative growth as well as in the formation of productive tillers. Phosphorus-trace element is essential in rice plant particularly in its initial stage of growth. During this phase, phosphorus stimulates the formation of roots and multiplication of roots and tillers. Element phosphorus is fundamental in the growth of plants. This element supports plants in their flowering stage (De Groot et al., 2003). According to Enstone et al. (2003), a plant will grow well when all the necessary elements are available in enough quantities and in a state that can be absorbed by the plant itself.

Applying organic sludge in different concentrations did not affect the harvesting time of rice plant. The harvesting period is influenced more by genetic factors rather than different environments (different concentrations of organic sludge). This also supports that the Batang Piaman rice takes between 105-117 days to harvest (Indonesian Agency for Agricultural Research and Development, 2003). Also, Islam et al. (2015) support this statament that heritability value of the harvesting stage of rice plants is 81.81, which is classified as high and indicates that the harvesting age is more determined by genetic rather than environment.

According to Table 2, application of organic sludge in different concentrations impacted the parameter of quantity of filled grains in each tiller and grain yield from each plot but it did not affect the percentage of filled grains and the weight of 1000 grains (P<0.05).

of the sludge applications at different concentrations on number of filled grains in each tiller, weight of 1000 grains and grain yield in each plot.

The highest number of filled grains from each tiller resulting using 25 t ha-1 of organic sludge was 125.69 grains, which was different from other treatments. Filled grains are derived from a compound of assimilates resulting from the photosynthesis process that must be supported by the availability of trace elements in soil. These trace elements such as nitrogen, calcium, phosphorus, carbon, magnesium, and potassium come from organic sludge.

Trace elements contained in organic sludge work simultaneously to form the higher filled grains from each tiller. Nitrogen synthesizes amino acid and protein in the rice plant. Phosphorus transports the results of metabolism process in the plant stimulating the flowering and pollination processes and the formation of roots and seeds. Potassium participates in the process of photosynthesis, transporting the results of assimilation process, enzymes and minerals including water. Calcium plays a role in the arrangement of chlorophyll, which is needed by enzymes in the metabolism of carbohydrate, and strengthen meristem cells. In the meantime, magnesium is a major component in the buildup of chlorophyll, which determines the speed of photosynthesis/ formation of carbohydrate runs as well as transporting Phosphate (Tränkner et al., 2018).

Different concentrations of organic sludge did not impact the percentage of filled grains in each tiller in the rice plants. The content of filled grains is determined by the result of photosynthesis (carbohydrate) in the stem and leaves which is then transferred and deposited inside the grains. It means, the percentage of filled grains did not show a response regard to the environment of the soil but it was heavily influenced by genetic factors. Manalu et al. (2017) stated that the score of the percentage filled grains is 70.6 (high) indicating a dominant influence by genetic factors rather than environmental factors.

The different concentrations of organic sludge did not show significant impact on the weight of 1000 grains. It was not influenced by environmental factors but more readily affected by genetic factors. This is in accordance to characteristic of Batang Piaman rice, in which the weight of 1000 grains is less than 27 g (Indonesian Agency for Agricultural Research and Development, 2003). Fan et al. (2006) reported that the weight of 1000 grains were mainly controlled by the Quantitative Trait Loci (QTL). Dou et al. (2016) further expressed that the weight characteristic of 1000 grains was influenced by each variety.

Application organic sludge at 25 t ha-1 resulted heavier in weight of filled grain per plot (3.99 kg) compared to the other treatments. The higher yield in each plot was due to some supporting factors such as the total number of tillers, number of productive tillers and number of grains for each tiller, which showed a high number applying 25 t ha-1 of organic sludge. According to Amjad (2016), to find the accurate portion of fertilizer, the concentration should establish based on the amount of trace element available in soil; therefore, the growth of rice plant could be optimal.

CONCLUSIONS

Based on the data, different doses of organic sludge fertilizer affected the total number of productive tillers and the productive ones, number of filled grains and seed weight in each plot. In general, the total number of tillers and the productive ones, number of filled grains and weight of seeds in each plot is proportional to the increase in the various doses of organic sludge fertilizer. The higher doses of the sludge, the higher increase in the total number of tillers and the productive ones, number of filled grains, and seed weight in each plot. The 25 t ha-1 of organic sludge fertilizer could increase the seed weight by 66.25% compared to that with no organic sludge fertilizer added.

Based on the result of the research, the researchers suggest that the cultivation of rice plant can develop in fields where the water channel is at 5 cm below soil surface using organic sludge at 25 t ha-1. For future research, it is recommended to increase the doses of organic sludge fertilizer, in order to obtain optimal yields using different rice varieties in dissimilar soil environments.

 ACKNOWLEDGEMENT

The researchers would like to thank to the Rector of Riau University (Prof. Dr. Ir. Aras Mulyadi), the chairman of Institution of Research and Community Service (Prof. Dr. Almasdi Syahza, SE. MP), and the Dean of Faculty of Agriculture, Riau University (Dr. Ir. Syafrinal, MS) for the encouragement and support given to facilitate the conduct of this research. A sincere gratitude should also be expressed to the General Directorate of Higher Education which provided the funding for this research by Directorate of Research and Community Service.

 REFERENCES Amjad AA, Radovich TJK, Nguyen HV, Uyeda J, Arakaki A, Cadby J, Paull R, Sugano J and Teves G. 2016. Organic fertilizers - from basic concepts to applied outcomes. Chapter 4: Use of organic fertilizers to enhance soil fertility. pp. 85-108. In: Larramendy ML (ed.). Plant Growth, and Yield in a Tropical Environment. doi: 10.5772/62529 Amjad AA Radovich TJK Nguyen HV Uyeda J Arakaki A Cadby J Paull R Sugano J Teves G 2016 Organic fertilizers - from basic concepts to applied outcomes. Chapter 4: Use of organic fertilizers to enhance soil fertility 85 108 Larramendy ML Plant Growth, and Yield in a Tropical Environment 10.5772/62529 De Groot CC, Marcelis LFM, Boogaard R, Kaiser WM and Lambers H. 2003. Interaction of nitrogen and phosphorus nutrition in determining growth. Plant and Soil 248: 257-268. doi: 10.1023/A:1022323215010 De Groot CC Marcelis LFM Boogaard R Kaiser WM Lambers H 2003 Interaction of nitrogen and phosphorus nutrition in determining growth Plant and Soil 248 257 268 10.1023/A:1022323215010 Dou F, Soriano J, Tabien RE and Chen K. 2016. Soil texture and cultivar effects on rice (Oryza sativa L.) grain yield, yield components and water productivity in three water regimes. PLoS ONE 11(3):12 doi: 10.1371/journal.pone.0150549 Dou F Soriano J Tabien RE Chen K 2016 Soil texture and cultivar effects on rice (Oryza sativa L.) grain yield, yield components and water productivity in three water regimes PLoS ONE 11 3 12 12 10.1371/journal.pone.0150549 Dwi N, Wahyu A and Andrian E. 2009. Kajian potensi pemanfaatan limbah sludge kolam anaerob dan aerob pengolahan limbah pabrik kelapa sawit. Agroteknose 4(2): 39-45. http://36.82.106.238:8885/jurnal/index.php/ATS/article/view/88 Dwi N Wahyu A Andrian E 2009 Kajian potensi pemanfaatan limbah sludge kolam anaerob dan aerob pengolahan limbah pabrik kelapa sawit Agroteknose 4 2 39 45 http://36.82.106.238:8885/jurnal/index.php/ATS/article/view/88 Enstone DE, Peterson CA and Ma F. (2003). Root endodermis and exodermis: structure, function, and responses to the environment. Journal of Plant Growth Regulation 21: 335-351. doi: 10.1007/s00344-003-0002-2 Enstone DE Peterson CA Ma F 2003 Root endodermis and exodermis: structure, function, and responses to the environment Journal of Plant Growth Regulation 21 335 351 10.1007/s00344-003-0002-2 Fan C, Xing Y, Mao H, Lu T, Han B, Xu C, Li X and Zhang Q. 2006. GS3, a major QTL for grain length and weight and minor QTL for grain width and thickness in rice, encodes a putative transmembrane protein. Theor Appl Genet 112: 1164-71. doi: 10.1007/s00122-006-0218-1 Fan C Xing Y Mao H Lu T Han B Xu C Li X Zhang Q 2006 GS3, a major QTL for grain length and weight and minor QTL for grain width and thickness in rice, encodes a putative transmembrane protein Theor Appl Genet 112 1164 1171 10.1007/s00122-006-0218-1 Huang N, Courtois B, Khush G. et al. 1996. Association of quantitative trait loci for plant height with major dwarfing genes in rice. Heredity 77(1): 130-137. doi: 10.1038/hdy.1996.117 Huang N Courtois B Khush G. 1996 Association of quantitative trait loci for plant height with major dwarfing genes in rice Heredity 77 1 130 137 10.1038/hdy.1996.117 Indonesian Agency for Agricultural Research and Development. 2003. Description of batang piaman rice varieties. Jakarta Selatan, Indonesia. http://www.litbang.pertanian.go.id/varietas/452/ . Retrieved 23 November 2020. Indonesian Agency for Agricultural Research and Development 2003 Description of batang piaman rice varieties Jakarta Selatan Indonesia http://www.litbang.pertanian.go.id/varietas/452/ 23 November 2020 Islam M, Raffi S, Hossain M and Hasan A. 2015. Analysis of genetic variability, heritability and genetic advance for yield and yield associated traits in some promising advanced lines of rice. Progressive Agriculture 26(1): 26-31. doi: 10.3329/pa.v26i1.24511 Islam M Raffi S Hossain M Hasan A 2015 Analysis of genetic variability, heritability and genetic advance for yield and yield associated traits in some promising advanced lines of rice Progressive Agriculture 26 1 26 31 10.3329/pa.v26i1.24511 Khairuddin M, Zakaria A, Isa I, Jol H, Rahman W and Salleh M. 2016. The potential of treated palm oil mill efluent (POME) sludge as an organic fertilizer. AGRIVITA Journal of Agricultural Science 38(2): 142-154. doi: 10.17503/agrivita.v38i2.753 Khairuddin M Zakaria A Isa I Jol H Rahman W Salleh M 2016 The potential of treated palm oil mill efluent (POME) sludge as an organic fertilizer AGRIVITA Journal of Agricultural Science 38 2 142 154 10.17503/agrivita.v38i2.753 Lang L. 2007. Treatability of palm oil mill effluent (POME) using black liquor in an anaerobic treatment process. Thesis for the Master Degree of Science. Universitas Sains Malaysia. Malaysia Lang L 2007 Treatability of palm oil mill effluent (POME) using black liquor in an anaerobic treatment process Master Degree of Science Universitas Sains Malaysia Malaysia Leimona B, Amaruzaman S, Arifin B, Yasmin F, Hasan F, Agusta H, Sprang P, Jaffee and Frias J. 2015. Indonesia's 'Green Agriculture' Strategies and Policies: Closing the gap between aspirations and application. Occasional Paper 23. Nairobi: World Agroforestry Centre. http://apps.worldagroforestry.org/sea/Publications/files/occasionalpaper/OP0003-15.pdf Leimona B Amaruzaman S Arifin B Yasmin F Hasan F Agusta H Sprang P Jaffee Frias J 2015 Indonesia's 'Green Agriculture' Strategies and Policies: Closing the gap between aspirations and application Occasional Paper 23 Nairobi World Agroforestry Centre http://apps.worldagroforestry.org/sea/Publications/files/occasionalpaper/OP0003-15.pdf Manalu VMP, Wirnas D, and Sudarsono D. 2017. Karakter seleksi pada generasi awal untuk adaptasi padi terhadap cekaman suhu tinggi (selection characters in early generation for adaptation of rice to high temperature stress). Indonesian Journal of Agronomy 45(2): 109-11. doi: 10.24831/jai.v45i2.12938 Manalu VMP Wirnas D Sudarsono D 2017 Karakter seleksi pada generasi awal untuk adaptasi padi terhadap cekaman suhu tinggi (selection characters in early generation for adaptation of rice to high temperature stress) Indonesian Journal of Agronomy 45 2 109 111 10.24831/jai.v45i2.12938 Maryam JM and E. Amiri. 2014. Effect of nitrogen and potassium on yield and yield components of rice cultivar 'Hashemi'. Indian Journal of Fundamental and Applied Life Sciences 4(4):417-42. https://www.cibtech.org/J-LIFE-SCIENCES/PUBLICATIONS/2014/Vol-4-No-4/JLS-061-63-DEC-ACCEPT-5-Amiri%20and%20Jalali%20Moridani,%202014.pdf Maryam JM E. Amiri 2014 Effect of nitrogen and potassium on yield and yield components of rice cultivar 'Hashemi' Indian Journal of Fundamental and Applied Life Sciences 4 4 417 442 https://www.cibtech.org/J-LIFE-SCIENCES/PUBLICATIONS/2014/Vol-4-No-4/JLS-061-63-DEC-ACCEPT-5-Amiri%20and%20Jalali%20Moridani,%202014.pdf Pandapotan CD, Mukhlis and Marbun P. 2017. Pemanfaatan limbah lumpur padat (sludge) pabrik pengolahan kelapa sawit sebagai alternatif penyediaan unsur hara di tanah ultisol (utilization of solid sewage (sludge) palm oil mills as an alternative supply of nutrients in ultisol). Jurnal Agroekoteknologi FP USU 5(2): 271- 276. https://talenta.usu.ac.id/joa/article/view/2538 Pandapotan CD Mukhlis Marbun P 2017 Pemanfaatan limbah lumpur padat (sludge) pabrik pengolahan kelapa sawit sebagai alternatif penyediaan unsur hara di tanah ultisol (utilization of solid sewage (sludge) palm oil mills as an alternative supply of nutrients in ultisol) Jurnal Agroekoteknologi FP USU 5 2 271 276 https://talenta.usu.ac.id/joa/article/view/2538 Sasaki A, Ashikari M, Ueguchi-Tanaka M, Itoh H, Nishimura A, Swapan D, et al. (2002). Green revolution: a mutant gibberellin-synthesis gene in rice. Nature 416(6882): 701-702. doi: 10.1038/416701a Sasaki A Ashikari M Ueguchi-Tanaka M Itoh H Nishimura A Swapan D 2002 Green revolution: a mutant gibberellin-synthesis gene in rice Nature 416 6882 701 702 10.1038/416701a Tränkner M, Tavakol E and Jákli B. 2018. Functioning of potassium and magnesium in photosynthesis, photosynthate translocation and photoprotection. Physiologia Plantarum 163(3): 414-431. doi: 10.1111/12747 Tränkner M Tavakol E Jákli B 2018 Functioning of potassium and magnesium in photosynthesis, photosynthate translocation and photoprotection Physiologia Plantarum 163 3 414 431 10.1111/12747 Wardani C, Jamhari, Hardyastuti S and Suryantini A. 2019. Determinant of Rice Consumption: Evidence From Panel Data in Indonesia. International Journal of Mechanical Engineering and Technology (IJMET) 10(5): 160-168. http://www.iaeme.com/MasterAdmin/Journal_uploads/IJMET/VOLUME_10_ISSUE_5/IJMET_10_05_016.pdf Wardani C Jamhari Hardyastuti S Suryantini A 2019 Determinant of Rice Consumption: Evidence From Panel Data in Indonesia International Journal of Mechanical Engineering and Technology (IJMET) 10 5 160 168 http://www.iaeme.com/MasterAdmin/Journal_uploads/IJMET/VOLUME_10_ISSUE_5/IJMET_10_05_016.pdf Widiastuti L, Sulistiyanto Y, Jaya A, Yusurum J and Neneng L. 2019. Potensi mikroorganisme sebagai biofertilizer (potential of microorganisms as biofertilizer). EnviroScienteae 15(2): 226. doi: 10.20527/es.v15i2.6957 Widiastuti L Sulistiyanto Y Jaya A Yusurum J Neneng L 2019 Potensi mikroorganisme sebagai biofertilizer (potential of microorganisms as biofertilizer) EnviroScienteae 15 2 226 226 10.20527/es.v15i2.6957