Rice husk ash (RHA), palm oil mill effluent (POME) sludge, and decanter cake can be utilized as compost to reduce environmental pollution. This research attempted to investigate the effect of RHA addition to palm oil-based compost in boosting the nitrogen (N) uptake and the growth of Brassica oleracea var. alboglabra L. (Chinese kale plant). Two categories of compost treatment were prepared in this study: Treatment 1 (control) and Treatment 2 [consisting of 10% (wt/wt) of RHA]. Both treatments were composted for 60 days until it was matured. The temperature and pH of the composts were recorded daily throughout the study. The treatments were analyzed for moisture, water-holding capacity, and nutrient content. The Chinese kale plant was grown in growing media and applied with Treatment 1 and Treatment 2 composts. The progress of plant growth was tracked every week. Based on the analysis, Treatment 2 exhibited a higher temperature and pH profile than Treatment 1. Meanwhile, the contents of N, P, and K were higher in Treatment 1 compost. However, Treatment 2 compost had higher silicon (Si) content, moisture content, and water-holding capacity. Based on the field test study carried out on the Chinese kale plant, the N uptake, and the growth of the plant, were found to be significantly higher when applied with Treatment 2 compost compared to Treatment 1 by 19% to 31% and 13% to 53%, respectively. It was proven that the addition of 10% RHA managed to provide an adequate amount of Si, moisture content, and water-holding capacity in Treatment 2 compost that can enhance the N uptake and improve the growth of the Chinese kale plant in this study.

• Adam, S., Ahmad, S. S. N. S., Hamzah, N. M., & Darus, N. A. (2016). Composting of empty fruit bunch treated with palm oil mill effluent and decanter cake. In Regional Conference on Science, Technology and Social Sciences (RCSTSS 2014) (pp. 437–445). Springer, Singapore. https://doi.org/10.1007/978-981-10-0534-3_43

• Alfaro, M. A., Rosolem, C. A., Goulding, K. W. T., & Wang, H. (2017, January 25-27). Potassium losses and transfers in agricultural and livestock systems [Paper presentation]. Proceedings for the Frontiers of Potassium Science Conference, Rome, Italy. https://www.apni.net/wp-content/uploads/2020/05/IPNI-FOPS-2017-Proceedings.pdf

• ASTM D2980-02. (2002). Standard test method for volume weights, water-holding capacity, and air capacity of water-saturated peat materials. ASTM International. https://doi.org/10.1520/D2980-02

• ASTM D4442-16. (2016). Standard test methods for direct moisture content measurement of wood and wood-based materials. ASTM International. https://doi.org/10.1520/D4442-16

• Babaso, P. N., & Sharanagouda, H. (2017). Rice husk and its applications: Review. International Journal of Current Microbiology and Applied Sciences, 6(10), 1144–1156. https://doi.org/10.20546/ijcmas.2017.610.138

• Biyada, S., Merzouki, M., Dėmčėnko, T., Vasiliauskienė, D., Ivanec-Goranina, R., Urbonavičius, J., Marčiulaitienė, E., Vasarevičius, S., & Benlemlih, M. (2021). Microbial community dynamics in the mesophilic and thermophilic phases of textile waste composting identified through next-generation sequencing. Scientific Reports, 11, 23624. https://doi.org/10.1038/s41598-021-03191-1

• Di Mola, I., Cozzolino, E., Ottaiano, L., Nocerino, S., Rouphael, Y., Colla, G., El-Nakhel, C., & Mori, M. (2020). Nitrogen use and uptake efficiency and crop performance of baby spinach (Spinacia oleracea L.) and lamb’s lettuce (Valerianella locusta L.) grown under variable sub-optimal N regimes combined with plant-based biostimulant application. Agronomy, 10(2), 278. https://doi.org/10.3390/agronomy10020278

• Dinh, T. H., Watanabe, K., Takaragawa, H., Nakabaru, M., & Kawamitsu, Y. (2017). Photosynthetic response and nitrogen use efficiency of sugarcane under drought stress conditions with different nitrogen application levels. Plant Production Science, 20(4), 412–422. https://doi.org/10.1080/1343943X.2017.1371570

• Erwin, J., & Gesick, E. (2017). Photosynthetic responses of swiss chard, kale, and spinach cultivars to irradiance and carbon dioxide concentration. HortScience, 52(5), 706–712. https://doi.org/10.21273/HORTSCI11799-17

• Gao, L., Lu, Z., Ding, L., Guo, J., Wang, M., Ling, N., Guo, S., & Shen, Q. (2018). Role of aquaporins in determining carbon and nitrogen status in higher plants. International Journal of Molecular Sciences, 19(1), 35. https://doi.org/10.3390/ijms19010035

• Hayawin, Z. N., Astimar, A. A., Ropandi, M., Faizah, J. N., & Hamid, F. A. (2016). Rapid composting of oil palm biomass by using aerobic thermophilic composter. Palm Oil Engineering Bulletin, 119, 19–26.

• Hisham, N. E. B., & Ramli, N. H. (2020). Incorporation of rice husk ash with palm oil mill wastes in enhancing physicochemical properties of the compost. Pertanika Journal of Tropical Agricultural Science, 44(1), 221–236. https://doi.org/10.47836/pjtas.44.1.13

• Hisham, N. E. B., & Ramli, N. H. (2019). Effect of rice husk ash on the physicochemical properties of compost. Indonesian Journal of Chemistry, 19(4), 967–974. https://doi.org/10.22146/ijc.39704

• Hock, L. S., Baharuddin, A. S., Ahmad, M. N., Hassan, M. A., Shah, U. K. M., Rahman, N. A. A., Abd-Aziz, S., & Shirai, Y. (2009). Physicochemical changes in windrow co-composting process of oil palm mesocarp fiber and palm oil mill effluent anaerobic sludge. Australian Journal of Basic and Applied Sciences, 3(3), 2809–2816.

• Irvan, Rahman, M., Anwar, D., Trisakti, B., & Daimon, H. (2019). Production of compost from non-shredded empty fruit bunches mixed with activated liquid organic fertilizer in tower composter. Malaysian Journal of Analytical Science, 23(1), 138–146. https://doi.org/10.17576/mjas-2019-2301-17

• Khairuddin, M. N., Zakaria, A. J., Isa, I. M., Jol, H., Nazri Wan Abdul Rahman, W. M., & Salleh, M. K. S. (2016). The potential of treated palm oil mill effluent (POME) sludge as an organic fertilizer. Agrivita, 38(2), 142–154. https://doi.org/10.17503/agrivita.v38i2.753

• Krishnan, K., Ngerong, A. A., Ahim, K., Ahmed, O. H., Ali, M., Omar, L., & Musah, A. A. (2021). Mitigating potassium leaching from muriate of potash in a tropical peat soil using clinoptilolite zeolite, forest litter compost, and chicken litter biochar. Agronomy, 11(10), 1900. https://doi.org/10.3390/agronomy11101900

• Lumbanraja, S., Nainggolan, H., & Sitohang, C. (2019). Improving porosity of glycerol-plated silica from rice husk silica. Journal of Chemical Natural Resources, 1(2), 88–97. https://doi.org/10.32734/jcnar.v1i2.1257

• Majbar, Z., Lahlou, K., Ben Abbou, M., Ammar, E., Triki, A., Abid, W., Nawdali, M., Bouka, H., Taleb, M., El Haji, M., & Rais, Z. (2018). Co-composting of olive mill waste and wine-processing waste: An application of compost as soil amendment. Journal of Chemistry, 2018, 7918583. https://doi.org/10.1155/2018/7918583

• Maurel, C., Boursiac, Y., Luu, D. T., Santoni, V., Shahzad, Z., & Verdoucq, L. (2015). Aquaporins in plants. Physiological Reviews, 95(4), 1321–1358. https://doi.org/10.1152/physrev.00008.2015

• Nizar, M. K., Isharudin, M. I., Jamil, A. Z., & Hazandy, A. H. (2018). Influence of treated palm oil mill effluent sludge on maize (Zea mays) growth performance and gas exchange. Sains Malaysiana, 47(5), 961–969. https://doi.org/10.17576/jsm-2018-4705-11

• Onwonga, R. N., Chepkoech, C., Wahome, R. G., Jensen, H. H., & Freyer, B. (2017, September 20-22). Synchronizing legume residue nutrient release with kale (Brassica oleracea var. acephala) uptake in a nitisol of Kabete, Kenya [Paper presentation]. International Research on Food Security, Natural Resource Management and Rural Development 2017, Bonn, North Rhine-Westphalia, Germany. https://backend.orbit.dtu.dk/ws/portalfiles/portal/134276995/ Paper_til_Tropentag_sept_2017_1075.pdf

• Oviedo‐ocaña, E. R., Hernández‐gómez, A. M., Ríos, M., Portela, A., Sánchez‐torres, V., Domínguez, I., & Komilis, D. (2021). A comparison of two‐stage and traditional co‐composting of green waste and food waste amended with phosphate rock and sawdust. Sustainability, 13(3), 1109. https://doi.org/10.3390/su13031109

• Phonphuak, N., & Chindaprasirt, P. (2015). Types of waste, properties, and durability of pore-forming waste-based fired masonry bricks. In F. Pacheco-Torgal, P. B. Lourenco, J. A. Labrincha, S. Kumar, & P. Chindaprasirt (Eds.), Eco-efficient masonry bricks and blocks (pp. 103–127). Woodhead Publishing. https://doi.org/10.1016/B978-1-78242-305-8.00006-1

• Purbajanti, E. D., Slamet, W., Fuskhah, E., & Rosyida. (2019). Effects of organic and inorganic fertilizers on growth, activity of nitrate reductase and chlorophyll contents of peanuts (Arachis hypogaea L.). In IOP Conference Series: Earth and Environmental Science (Vol. 250, No. 1, p. 012048). IOP Publishing. https://doi.org/10.1088/1755-1315/250/1/012048

• Ramli, N. H., Hisham, N. E. B., Said, F. M., Hisham, N. E. B., & Olalere, O. A. (2019). The role of wood vinegar in enhancing the microbial activity and physicochemical properties of palm oil-based compost. Pertanika Journal of Tropical Agricultural Science, 42(4), 1391–1403.

• Rastogi, M., Nandal, M., & Khosla, B. (2020). Microbes as vital additives for solid waste composting. Heliyon, 6(2), e03343. https://doi.org/10.1016/j.heliyon.2020.e03343

• Rios, J. J., Martínez-Ballesta, M. C., Ruiz, J. M., Blasco, B., & Carvajal, M. (2017). Silicon-mediated improvement in plant salinity tolerance: The role of aquaporins. Frontiers in Plant Science, 8, 948. https://doi.org/10.3389/fpls.2017.00948

• Román, P., Martínez, M. M., & Pantoja, A. (2015). Farmer’s compost handbook: Experiences in Latin America. Food and Agriculture Organization of the United Nations.

• Sapie, S., Jumali, S. S., Mustaffha, S., & Pebrian, D. E. (2019). Analysis of POME discharge quality from different mill in Perak, Malaysia: A case study. In IOP Conference Series: Earth and Environmental Science (Vol. 327, No. 1, p. 012022). IOP Publishing. https://doi.org/10.1088/1755-1315/327/1/012022

• Schaller, J., Cramer, A., Carminati, A., & Zarebanadkouki, M. (2020). Biogenic amorphous silica as main driver for plant available water in soils. Scientific Reports, 10, 2424. https://doi.org/10.1038/s41598-020-59437-x

• Sharma, D., Varma, V. S., Yadav, K. D., & Kalamdhad, A. S. (2017). Evolution of chemical and biological characterization during agitated pile composting of flower waste. International Journal of Recycling of Organic Waste in Agriculture, 6, 89–98. https://doi.org/10.1007/s40093-017-0155-9

• Sharma, N. K., Singh, R. J., & Kumar, K. (2012). Dry matter accumulation and nutrient uptake by wheat (Triticum aestivum L.) under poplar (Populus deltoides) based agroforestry system. International Scholarly Research Notices, 2012, 359673. https://doi.org/10.5402/2012/359673

• Siddika, A., Mamun, M. A. Al, Alyousef, R., & Mohammadhosseini, H. (2021). State-of-the-art-review on rice husk ash: A supplementary cementitious material in concrete. Journal of King Saud University - Engineering Sciences, 33(5), 294–307. https://doi.org/10.1016/j.jksues.2020.10.006

• Teuber, O., Samarappuli, D., & Berti, M. (2020). Nitrogen and sulfur fertilization in kale and swede for grazing. Agronomy, 10(5), 619. https://doi.org/10.3390/agronomy10050619

• Theeba, M., Bachmann, R. T., Illani, Z. I., Zulkefli, M., Husni, M. H. A., & Samsuri, A. W. (2012). Characterization of local mill rice husk charcoal and its effect on compost properties. Malaysian Journal of Soil Science, 16(1), 89–102.

• Wang, M., Ding, L., Gao, L., Li, Y., Shen, Q., & Guo, S. (2016). The interactions of aquaporins and mineral nutrients in higher plants. International Journal of Molecular Sciences, 17(8), 1229. https://doi.org/10.3390/ijms17081229

• Wang, Y., Zhang, X., Liu, H., Sun, G., Song, S., & Chen, R. (2022). High NH4+/NO3− ratio inhibits the growth and nitrogen uptake of Chinese kale at the late growth stage by ammonia toxicity. Horticulturae, 8(1), 8. https://doi.org/10.3390/horticulturae8010008

• Wijitkosum, S., & Jiwnok, P. (2019). Effect of biochar on chinese kale and carbon storage in an agricultural area on a high rise building. AIMS Agriculture and Food, 4(1), 177–193. https://doi.org/10.3934/agrfood.2019.1.177

• Xiang, Y., Zou, H., Zhang, F., Qiang, S., Wu, Y., Yan, S., Wang, H., Wu, L., Fan, J., & Wang, X. (2019). Effect of irrigation level and irrigation frequency on the growth of mini Chinese cabbage and residual soil nitrate nitrogen. Sustainability, 11(1), 111. https://doi.org/10.3390/su11010111

• Yin, M., Li, X., Liu, Q., & Tang, F. (2022). Rice husk ash addition to acid red soil improves the soil property and cotton seedling growth. Scientific Reports, 12, 1704. https://doi.org/10.1038/s41598-022-05199-7

• Yousaf, M., Bashir, S., Raza, H., Shah, A. N., Iqbal, J., Arif, M., Bukhari, M. A., Muhammad, S., Hashim, S., Alkahtani, J., Alwahibi, M. S., & Hu, C. (2021). Role of nitrogen and magnesium for growth, yield and nutritional quality of radish. Saudi Journal of Biological Sciences, 28(5), 3021–3030. https://doi.org/10.1016/j.sjbs.2021.02.043