Overview on leafy (Pak Choy) vegetable industry and vertical soilless culture application for Pak Choy production in Malaysia

Rosie Laiza Henny @ Stephen; Januarius Gobilik.

Transactions on Science and Technology, 9(4), 204 - 222.

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ABSTRACT
The agriculture industry plays a significant role in the well-being of Malaysia’s economy. It provides jobs for more than 1566 thousand people and contributes 7.1% to the gross domestic product (GDP). The vegetable industry, however, is lagging behind other agricultural industries, such as oil palm, rubber, and tea. The demand for vegetables in Malaysia increased from 1.58 million metric tonnes (MT) in 2010 to 2.4 million MT in 2020, but the production was only 0.1 million MT in 2010, 1.01 million MT in 2015, and 1.7 million MT in 2020. The trade balance deficit in 2021 stood at Ringgit Malaysia (RM) 3.37 billion. The vegetable industry is under pressure from rising population, shortage of resources, and post-COVID-19 pandemic impacts. Vertical farming (VF) of vegetables is widely promoted worldwide, including Malaysia, to increase production. In VF, the vegetables are produced in environmentally controlled multi-storey buildings with different vegetables at different levels, and at any level, the vegetables are cultivated using vertical farming systems (VFSs). In that way, the production per unit area is said to be maximal. However, is Malaysia’s leafy (Pak Choy) vegetable industry agronomically ready to embark on VF and VFS? There is a concern about business failure associated with promoting VF and VFS without sufficient knowledge and skills in agronomy about VF and VFS based on the local scenarios. Hence, the present paper aims to review the leafy vegetable industry, specifically Pak Choy production in Malaysia, to assess its readiness to apply VF and VFS to better the direction of future research projects. Keywords used for the search of relevant information in Science Direct, World Wide Science, Google Scholar, Google, and online newspapers were Malaysia plus vertical farming, hydroponic systems, column hydroponic system, agriculture sector, agriculture 4.0, precision agriculture, soilless culture, leafy vegetable industry, and Pak Choy production. The articles and reports obtained were reviewed. Based on the review, the leafy industry in Malaysia, specifically the Pak Choy production, is not yet agronomically ready to venture into VF and VFS, although VF and VFS have gained attention. The agronomic information about VF and VFS based on the local scenarios is still lacking. Local farmers have little guidance for operating VF and VFS. It is understood that VF is an expensive venture and will be relatively unknown to many farmers, but even the agronomic information related to VFS, which is just about the system used in VF, is seldom published. Of the many designs of VFSs in Malaysia, the Column Hydroponic System (CHS) has a markedly higher vegetable yield per unit area. Thus, more research on CHS is needed, and its agronomic and technical information should be published for the local vegetable farmers to use to mitigate the supply shortage and the high foreign exchange of leafy vegetables in Malaysia.

KEYWORDS: Brassica vegetable industry; vertical farming; vertical soilless culture system; hydroponic systems; column hydroponic system



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REFERENCES
  1. Ahmad, A. 2021. Interactive: Young Entrepreneurs Thriving on Aquaponic Farming (https://www.thestar.com.my/news/nation/2021/04/03/interactiveyoungentrepreneurs-thriving-on-aquaponic-farming). Last accessed on 02 November 2021.
  2. Al-Kodmany, K. 2018. The vertical farm: A review of developments and implications for the vertical city. Buildings, 8(2), 24.
  3. Anonymous. 2019. Sabah Green Sanctuary (https://www.sabahgreensanctuary.com/). Last accessed on 07 November 2021.
  4. Anonymous. 2020. Agriculture Sector (https://www.trade.gov/knowledgeproduct/malaysia-agricultural-sector). Last accessed on 07 June 2021.
  5. Anonymous. 2021. Malaysia/ Imports and Exports/ World/ Cabbages, Cauliflowers, Kohlrabi, Kale/ Value (US$) and Value Growth, YoY (%)/ 2009–2020 (https://trendeconomy.com/data/h2/Malaysia/0704). Last accessed on 22 July 2021.
  6. Anonymous. 2022a. Overview of Global Bok Choy Market (https://www.tridge.com/intelligences/bok-choy/import). Last accessed on 26 April 2022.
  7. Anonymous. 2022b. Vertical Hydroponic – A Basic Introduction (https://www.trees.com/gardening-and-landscaping/vertical-hydroponics). Last accessed on 29 December 2022.
  8. Baiyin, B., Tagawa, K., Yamada, M., Wang, X., Yamada, S., Yamamoto, S. & Ibaraki, Y. 2021. Effective of substrate flow rate on nutrient uptake and use efficiency in hydroponically grown swiss chard (Beta vulgaris L. ssp. cicla ‘Seiyou Shirokuki’). Agronomy, 11, 2050.
  9. Baudoin, W. O. & Zabeltiz, C. H. R. 2002. Greenhouse construction for scale farmer in tropical regions. Acta Horticulturae, 578, 171-179.
  10. Beacham, A. M., Vickers, L. H. & Monaghan, J. M. 2019. Vertical farming: a summary of approaches to growing skywards. Journal of Horticultural Science and Biotechnology, 94(3), 277-283.
  11. Benton, J. Jr. 2014. Complete Guide for Growing Plants Hydroponically. Boca Raton: CRC Press.
  12. Birkby, J. 2016 Vertical farming. ATTRA Sustainable Agriculture, IP516, 1-12.
  13. Boomgrow. 2022. Boomgrow (https://www.linkedin.com/company/boomgrow). Last Accessed on 29 December 2022.
  14. Cartea, M. E., Lema, M., Francisco, M. & Velasco, P. 2011. Basic Information on Vegetable Brassica Crops. In: Sadowsky, J. & Kole, C. (Eds.). Genetics, Genomics and Breeding of Vegetable Brassicas (1st edition). Boca Raton: CRC Press.
  15. Chin, C. F. 2020. The impact of food supply chain disruptions amidst covid-19 in Malaysia. Journal of Agriculture, Food System, and Community Development, 9(4), 161-163.
  16. CityFarm Malaysia. 2021. Hydroponic A and B Liquid Fertilizer for Leafy Greens (https://cityfarm.my/products/hydroponics-fertilizer). Last accessed on 09 October 2021.
  17. CityFarm Malaysia. 2022a. Pak Choy (https://cityfarm.my/collections/pak-choy). Last accessed on 25 April 2022.
  18. CityFarm Malaysia. 2022b. 4 Level Plant Factory with Artificial Light (PFAL) Module (https://cityfarm.my/collections/all-hydroponic-setup/products/custom-setup). Last accessed on 12 October 2022.
  19. CityFarm Malaysia. 2022c. Germination and Growing Media (https://cityfarm.my/collections/growing-media-1). Last accessed on 29 December 2022.
  20. Ding, X., Jiang, Y., Zhao, H., Guo, D., He, L., Liu, F., Zhou, Q., Nandawi, D., Hui, D. & Yu, J. 2018. Electrical conductivity of nutrient solution influenced photosynthesis, quality, and antioxidant enzyme activity of Pakchoi (Brassica campestris L. ssp. chinensis) in a Hydroponic System. PLoS ONE, 13(8), e0202090.
  21. Dardak, R. A. 2015. Transformation of Agricultural Sector in Malaysia through Agricultural Policy (https://ap.fftc.org.tw/article/818). Last accessed on 26 May 2021.
  22. Dayangku, S. 2021. It Took this Malaysian Smart Farm 5 Years to Find an Ideal Method to Grow Pesticide-Free Vegetable (https://vulcanpost.com/753391/boomgrow-malaysia-smart-farm-organic-vegetable-delivery/). Last accessed on 29 December 2022.
  23. Department of Agriculture (DOA). 2020. Vegetables and Cash Crop Statistics Malaysia 2020 (https://fliphtml5.com/flqg/suyx/basic). Last accessed on 11 July 2022.
  24. Department of Agriculture (DOA). 2021. Vegetables and Cash Crop Statistic Malaysia 2021 (http://www.doa.gov.my/index/resources/aktiviti_sumber/sumber_awam/maklumat_pertanian/perangkaan_tanaman/statistik_tanaman_sayur_tanaman_kontan_2021.pdf). Last accessed on 06 January 2023.
  25. Department of Statistic Malaysia (DOSM). 2020a. Current Population Estimates, Malaysia, 2020 (https://www.dosm.gov.my/v1/index.php?r=column/cthemeByCat&cat=155&bul_id=OVByWjg5YkQ3MWFZRTN5bDJiaEVhZz09&menu_id=L0pheU43NWJwRWVSZklWdzQ4TlhUUT09#:~:text=The%20growth%20rate%20of%20Citizens,to%2029.7%20million%20in%202020). Last accessed on 30 December 2022.
  26. Department of Statistic Malaysia (DOSM). 2020b. Selected Agricultural Indicator, Malaysia, 2020 (https://www.dosm.gov.my/v1/index.php?r=column/cthemeByCat&cat=72&bul_id=RXVKUVJ5TitHM0cwYWxlOHcxU3dKdz09&menu_id=Z0VTZGU1UHBUT1VJMFlpaXRRR0xpdz09). Last accessed on 13 April 2022.
  27. Department of Statistic Malaysia (DOSM). 2021. Selected Agricultural Indicator, Malaysia, 2021 (https://www.dosm.gov.my/v1/index.php?r=column/cthemeByCat&cat=72&bul_id=TDV1YU4yc1Z0dUVyZ0xPV0ptRlhWQT09&menu_id=Z0VTZGU1UHBUT1VJMFlpaXRRR0xpdz09). Last accessed on 06 January 2023.
  28. Despommier, D. 2010. The Vertical Farm: Feeding the World in the 21st Century. New York: Picador.
  29. Despommier, D. 2019. Vertical farms, building a viable indoor farming model for cities. In: Martin-Moreau, M. & Ménascé, D. (Eds.). Urban Agriculture: Another Way to Feed Cities. Aubervilliers: Institut Veolia.
  30. Digital News Asia. 2020. MaGIC’s GAP Cohort 4 Startups Post Revenue Growth of 53% (https://www.digitalnewsasia.com/entrepreneurial-nation/magics-gap-cohort-4-startups-post-revenue-growth-53). Last accessed on 23 May 2021.
  31. Drakes, D., Briercliffe, T., Lightfoot-Brown, S., Arnold, D. & Mackay, N. 2001. The Use and Disposal of Growing Media – Summary of Current Practice (https://www.hse.gov.uk/pesticides/pesticides-registration/data-requirements-handbook/fate/resources/use-disposal-growing-media-adas.pdf). Last accessed on 29 December 2022.
  32. Eigenbrod, C. & Gruda, N. 2015. Urban vegetable for food security in cities: A review. Agronomy for Sustainable Development, 35, 483-498.
  33. Fajar Saintifik. 2022. Indoor Farming-Plant Factory (https://fajar.com.my/indoor-farming/plant-factory/). Last accessed on 06 May 2022.
  34. Federal Agricultural Marketing Authority (FAMA). 2021. Memperkukuhkan Industri Sayur-Sayuran dan Buah-Buahan serta Memulihkan Industri Kelapa (https://www.fama.gov.my/documents/20143/64638/Bab+6+-+Memperkukuhkan+Industri+Sayur-sayuran+dan+Buah-buahan+serta+Memulihkan+Industri+Kelapa.pdf/bad0fcab-44f5-397a-781c-4098a9c6b590). Last accessed on 29 December 2022.
  35. Food and Agriculture Organization (FAO). 2013. Good Agricultural Practices for Greenhouse Vegetable Crops: Principles for Mediterranean Climate Areas. Rome: Food and Agriculture Organization (FAO) of The United Nations.
  36. Gobilik, J., Rechard, C. T., Maludin, A. J., Alam, M. A. & Benedick, S. 2021. Efficacy of column hydroponic system for increasing growth and yield of Pak Choy (Brassica rapa L.) per unit area. Transactions on Science and Technology, 8(1), 7-24.
  37. Goh, D. 2019. John-Hans Oei on How Cultiveat is Revolutionising Agriculture in Malaysia (https://www.augustman.com/my/amselect/john-hans-oei-on-how-cultiveat-is-revolutionising-agriculture-in-malaysia/). Last accessed on 02 November 2021.
  38. Gohler, F., HeiBner, A. & Schmeil, H. 1989. Control of Water and Nutrient Supply in Greenhouse Vegetable Production by Means of Hydroponic Systems. Acta Horticulturae, 260, 237-246.
  39. Gomez-Merino, F. C. & Trejo-Tellez, L. I. 2012. Nutrient Solution for Hydroponic Systems. In Hydroponics: A Standard Methodology for Plant Biological Researches. Rijeka: InTech.
  40. He, J., Qin, L. & Chow, W. S. 2019b. Impacts of LED spectral quality on leafy vegetables: productivity closely linked to photosynthetic performance or associated with leaf traits. International Journal Agricultural and Biological Engineering, 12(6), 16-25.
  41. He, J., Qin, L., Teo, L. J. L. & Choon, T. W. 2019a. Nitrate accumulation, productivity and photosynthesis of Brassica alboglabra grown under low light with supplemental LED lighting in the tropical greenhouse. Journal of Plant Nutrition, 42(15), 1740-1749.
  42. Heath, T., Zhu, Y. & Shao, Z. 2012. Vertical Farm: A High-Rise Solution to Feeding the City? Shanghai: Council on Tall Buildings and Urban Habitat (CTBUH) 2012 9th World Congress.
  43. Herr, I., & Buchler, M. W. 2010. Dietary constituents of broccoli and other cruciferous vegetables: implication for prevention and therapy of cancer. Cancer Treatment Reviews, 36(5), 377-383.
  44. Hussain, A., Iqbal, K., Aziem, S., Mahato, P. & Negi, A. K. 2014. A review on the science of growing crops without soil (soilless culture) – A novel alternative for growing crops. International Journal of Agriculture and Crop Sciences, 7(11), 833-842.
  45. Kalantari, F., Tahir, O. M., Lahijani, A. M. & Kalantari, S. 2017. A review of vertical farming technology: a guide for implementation of building integrated agriculture in cities. Advanced Engineering Forum, 24, 76-91.
  46. Kalantari, F., Tahir, O. M., Joni, R. A. & Fatemi, E. 2018. Opportunities and challenges in sustainability of vertical farming: a review. Journal of Landscape Ecology, 11(1), 35-60.
  47. Kang, J. H., Kumar, S. K., Atulba, S. L. S., Jeong, B. R. & Hwang, S. J. 2013. Light intensity and photoperiod influence the growth and development of hydroponically grown leaf lettuce in a closed-type plant factory system. Horticulture, Environment, and Biotechnology, 54(6), 501-509.
  48. Khedr, A. F., Kishk, S. S. & Zedan, M. I. 2022. Impact of “A” frame angle design on hydroponic system production. Misr Journal of Agricultural Engineering, 39(3), 391-408.
  49. Kozai, T. 2018. The Next Generation Indoor Vertical Farms. In: Kozai, T. (Ed.). Smart Plant Factory. Singapore: Springer.
  50. Lawlor D.W. 2002. Limitation to Photosynthesis in Water‐stressed Leaves: Stomata vs. Metabolism and the Role of ATP. Oxford Journals, Annals of Botany, 89, 871-885.
  51. Looi, C. B. 2018. CityFarm’s Jayden Koay: Let the Lettuce Bloom, Even When There’s Little Room (https://cityfarm.my/blogs/cityfarm-press-release/astro-awani-cityfarms-jayden-koay-let-the-lettuce-bloom-even-when-theres-little-room). Last accessed on 29 December 2022.
  52. Maludin, A. J., Lum, M. S., Lassim, M.M. & Gobilik, J. 2020. Optimal plant density, nutrient concentration and rootzone temperature for higher growth and yield of Brassica rapa L. ‘Curly Dwarf Pak Choy’ in raft hydroponic system under tropical climate. Transactions on Science and Technology, 7(4), 78-188.
  53. MARDI. 2014. MARDI Perkenal Teknologi Pertanian Menegak (https://blogmardi.wordpress.com/2014/03/03/mardi-perkenal-teknologi-pertanian-menegak/). Last accessed on 06 January 2023.
  54. Miwil, O. 2022. Ranau Quake Victim Helping Community Trough Hydroponic Farming (https://www.nst.com.my/news/nation/2022/06/809196/ranau-quake-victim-helping community-through-hydroponic-farming). Last accessed on 16 August 2022.
  55. Nate, L. 2021. Do You Have Enough Natural Light for Plants (https://www.geturbanleaf.com/blogs/lighting/enough-lighting-for-plants). Last accessed on 09 July 2022.
  56. Nemali, K. S. & Van Iersel, M. W. 2004. Light intensity and fertilizer concentration in estimating optimal fertilizer concentration from water-use efficiency of wax begonia. HortScience, 39, 1287-1292.
  57. Ng, C. 2016. What it Means to be a farming smallholder in Malaysia. UTAR Agriculture Science Journal, 2(1), 40-48.
  58. Nguyen, T. P. D., Tran, T. T. H. & Nguyen, Q. T. 2019. Effect of light intensity on the growth, photosynthesis and leaf microstructure of hydroponic cultivated spinach (Spinacia oleracea L.) under a combination of red and blue LEDs in house. International Journal of Agricultural Technology, 15(1), 75-90.
  59. Nguyen, T. P. D., Vu, N. T., Nguyen, Q. T., Tran, T. T. H., Cao, P. B., Kim, I. S. & Jang, D. C. 2022. Quality of hydroponic cultivated spinach (Spinacia oleracea L.) affected by the light intensity of red and blue LEDs. Sains Malaysiana, 51(2), 473-483.
  60. OECD. 2016. Safety Assessment of Transgenic Organism in the Environment. Paris: OECD Publishing.
  61. Oztekin, G. B., Uludag, T. & Tuzel, Y. 2018. Growing spinach (Spinacia oleracea L.) in a floating system with different concentrations of nutrient solution. Applied Ecology and Environmental Research, 16(3), 3333-3350.
  62. Parks, S. & Murray, C. 2011. Leafy Asian Vegetables and Their Nutrition in Hydroponics (https://www.dpi.nsw.gov.au/__data/assets/pdf_file/0007/385576/Leafy-Asian-veg-final-Low-Res.pdf). Last accessed on 08 May 2021.
  63. Penang Institute. 2020. Penang Agricultural Policy Report (https://penanginstitute.org/wp-content/uploads/2020/10/Penang-Agricultural-Policy-report-final.pdf). Last accessed on 08 June 2021.
  64. Priadi, D. & Nuro, F. 2017. Seedling production of Pak Choy (Brassica rapa L.) using organic and inorganic nutrients. Biosaintifika, 9(2), 217-224.
  65. Priadi, D., Wibowo, H. & Mulyaningsih, E. S. 2019. The growth optimization of Pak Choy (Brassica rapa L. var. chinensis) in household-scale aquaponic system. Jurnal Biodjati, 4(2), 175-183.
  66. Prieto, K. R., Echaide-Aquino, F., Huerta-Robles, A., Valerio, H. P., Macedo-Raygoza, G., Prado, F. M., Medeiros, M. H. G., Brito, H. F., da Silva, I. G. N., Cunha Felinto, M. C. F., White Jr., J. F., Di Mascio, P. & Beltran-Garcia, M. J. 2017. Endophytic bacteria and rare earth elements; promising candidates for nutrient use efficiency in plants. In: Hossain, M.A., Kamiya, T., Burritt, D.J., Phan Tran, L.S., Fujiwara, T. (Eds.). Plant macronutrient use efficiency: Molecular and Genomic Perspectives in Crop Plants. London: Academic Press.
  67. Rabu, M. R. & Muhammad, R. M. 2015. The Potential of Urban Farming Technology in Malaysia: Policy Intervention (https://ap.fftc.org.tw/article/965). Last accessed on 06 March 2021.
  68. Rahman, Y. 2012. MARDI Vertical Farming Research Institute (https://mdrxa.wordpress.com/architecture/mardi-vertical-farming/). Last accessed on 28 May 2021.
  69. Rakow, G. (2004). Species origin and economic importance of Brassica. In: Pua, E. C., Douglas, C. J. (Eds.) Brassica: Biotechnology in agriculture and forestry (Vol. 54) (https://doi.org/10.1007/978-3-662-06164-0_1). Berlin: Springer.
  70. Refarmers. 2016. ZipGrow Vertical, Easy, Efficient (https://wfghub.blob.core.windows.net/b4fdb68b97a83cff3fbe67337909f932/ZipGrow-Vertical-Easy-Efficient2016_65rjn.pdf). Last accessed on 06 January 2023.
  71. Resh, H. M. 2013. Hydroponic Food production: A Definitive Guidebook for the Advanced Home Gardener and the Commercial Hydroponic Grower (7th edition). Florida: CRC Press.
  72. Sakamoto, M. & Suzuki, T. 2015. Effect of root-zone temperature on growth and quality of hydroponically grown red leaf lettuce (Lactuca sativa L. cv. Red Wave). American Journal of Plant Science, 6, 2350-2360.
  73. Savvas, D., Gianquinto, G., Tuzel, Y. & Gruda, N. 2013. Soilless culture. In: Baudoin, W., Nono-Womdim, R., Lutaladio, N., Hodder, A., Castilla, N., Leonardi, C., de Pascale, S., Qaryouti, M. and Duffy, R. (FAO Plant Production and Protection Paper 217). Good agricultural practices for greenhouse vegetable crops: Principles for Mediterranean climate areas. Rome: Food and Agriculture Organization (FAO) of The United Nations.
  74. Shaharudin, A. A. 2020. Protecting the Agriculture Sector During the COVID-19 Crisis (https://www.krinstitute.org/assets/contentMS/img/template/editor/200330%20Views_Agri%20COVID-19_EN.pdf). Last accessed on 29 December 2022.
  75. Shamshiri, R., Kalantari, F., Ting, K. C., Thorp, K. R., Hameed, I. A., Weltzien, C., Ahmad, D. & Shad, Z. M. 2018. Advances in greenhouse automation and controlled environment agriculture: a transition to plant factories and urban agriculture. International Journal of Agricultural and Biological Engineering, 11(1), 1-22.
  76. Shao, Y., Heath, T. & Zhu, Y. 2016. Developing an economic estimation system for vertical farms. The International Journal of Agricultural and Environmental Information Systems, 7(2), 26-52.
  77. Singh, H. & Dunn, B. 2021. Building a Vertical Hydroponic Tower (https://extension.okstate.edu/fact-sheets/building-a-vertical-hydroponic-tower.html). Last accessed on 09 March 2021.
  78. Storey, A. 2016. Pros and Cons of Hydroton (Clay Pebbles) in Hydroponic (https://university.upstartfarmers.com/blog/pros-cons-hydroton-hydroponics). Last accessed on 07 October 2021.
  79. Takeshima, H. & Joshi, P. K. 2019. Protected Agriculture, Precision Agriculture and Vertical Farming: Brief Reviews of Issues in the Literature Focusing on the Developing Region in Asia. Washington: International Food Policy Research Institute.
  80. Tan, V. 2021. Price Hike of Vegetables in Malaysia Due to Weather, Labour Shortage and Production Costs, Say Farmers (https://www.channelnewsasia.com/asia/malaysia-vegetable-price-hikes-2345001). Last accessed on 19 April 2022.
  81. Tao, M. 2019. Top 25 Vertical Farming Companies (https://roboticsandautomationnews.com/2019/05/03/top-25-vertical-farming-companies/22181/). Last accessed on 06 January 2023.
  82. Thomas, B. M. & Awadh, D. G. 2020. Light quality and photoperiod influence crop growth, productivity and produce quality in hydroponic vegetables production. Acta Horticulture, 1273, 271-280.
  83. Touliatos, D., Ian, C. D. & Martin, M. 2016. Vertical Farming Increases Lettuce Yield Per Unit Area Compared to Conventional Horizontal Hydroponics. Food and Energy Security, 5(3), 184-191.
  84. United Nations (UN). 2019. How Certain Are the United Nations Global Population Projections (https://www.un.org/en/development/desa/population/publications/pdf/popfacts/PopFacts_2019-6.pdf). Last accessed on 29 December 2022.
  85. Velazquez-Gonzalez, R. S., Garcia-Garcia, A. L., Ventura-Zapata, E., Barceinas-Sanchez, J. D. O. & Sosa-Savedra, J. C. 2022. A review on hydroponics and the technologies associated for medium and small-scale operation. Agriculture, 12, 646.
  86. Wang, Y. & Folta, K. M. 2013. Contributions of green light to plant growth and development. American Journal of Botany, 100(1), 70-78.
  87. Wiggins, Z. D., Akaeze, O., Nandwani, D. & Witcher, A. 2020. Substrate Properties and Fertilizer Rates on Yield Responses of Lettuce in a Vertical Growth System. Sustainability, 12, 6465.
  88. World Health Organization (WHO). 2021. COVID-19 Situation Reports for Malaysia (https://www.who.int/malaysia/emergencies/covid-19-in-malaysia/situation-reports). Last accessed on 30 April 2021.
  89. Zainudin, A. 2019. Percepat Tempoh Tuaian (https://www.hmetro.com.my/xpresi/2019/09/499150/percepat-tempoh-tuaian). Last accessed on 02 November 2021.
  90. Zhou, J., Li, P. & Wang, J. 2022. Effect of light intensity and temperature on the photosynthesis characteristics and yield of lettuce. Horticulturae, 8, 178.