Zinc (Zn) and iron (Fe) are among the micronutrients humans need. However, the main food sources in developing countries such as Malaysia have low micronutrients, making it insufficient to supply the minimum daily requirement. Foliar fertilization is one of the most effective and safe ways to enrich important micronutrients in plants. This study investigated variations in Zn and Fe sources to evaluate the effects of individual Zn and Fe foliar applications on growth, dry matter, and nutrient uptake by lettuce (Lactuca sativa). Based on the result, the application of Zn and Fe in the form of sulfate salt showed a lower toxicity effect in terms of growth and dry matter of plants than Fe and Zn in the form of ethylenediaminetetraacetic acid (EDTA). In terms of Zn uptake, it was found that there was a significant difference observed compared to the control, especially when 3 kg/ha Zn was applied, regardless of whether it was in the form of sulfate or EDTA. Furthermore, there was an increase in Fe uptake observed with increased Zn application. In contrast, the Fe application showed no difference in Fe intake compared to the control. It was found that there is a decrease in Zn uptake observed with increasing application of Fe rate. Sufficient Fe content is already available in the soil, and plants only take up what is needed for growth.

• Barrameda-Medina, Y., Montesinos-Pereira, D., Romero, L., Ruiz, J. M., & Blasco, B. (2014). Comparative study of the toxic effect of Zn in Lactuca sativa and Brassica oleracea plants: I. Growth, distribution, and accumulation of Zn, and metabolism of carboxylates. Environmental and Experimental Botany, 107, 98-104. https://doi.org/10.1016/j.envexpbot.2014.05.012

• Buturi, C. V., Mauro, R. P., Fogliano, V., Leonardi, C., & Giuffrida, F. (2021). Mineral biofortification of vegetables as a tool to improve human diet. Foods, 10(2), 223. https://doi.org/10.3390/foods10020223

• Connolly, E. L., & Guerinot, M. L. (2002). Iron stress in plants. Genome Biology, 3(8), reviews1024.1. https://doi.org/10.1186/gb-2002-3-8-reviews1024

• Department of Agriculture. (2021). Vegetables and cash crop statistics Malaysia 2021. DOA. http://www.doa.gov.my/index/resources/aktiviti_sumber/sumber_awam/maklumat_pertanian/perangkaan_tanaman/statistik_tanaman_sayur_tanaman_kontan_2021.pdf

• Doolette, C. L., Read, T. L., Li, C., Scheckel, K. G., Donner, E., Kopittke, P. M., Schjoerring, J. K., & Lombi, E. (2018). Foliar application of zinc sulphate and zinc EDTA to wheat leaves: Differences in mobility, distribution, and speciation. Journal of Experimental Botany, 69(18), 4469–4481. https://doi.org/10.1093/jxb/ery236

• El-Jendoubi, H., Vázquez, S., Calatayud, A., Vavpetiˇc, P., Vogel-Mikuš, K., Pelicon, P., Abadía, J., Abadía, A., & Morales, F. (2014). The effects of foliar fertilization with iron sulfate in chlorotic leaves are limited to the treated area. A study with peach trees (Prunus persica L. Batsch) grown in the field and sugarbeet (Beta Vulgaris L.) grown in hydroponics. Frontiers in Plant Science, 5, 2. https://doi.org/10.3389/fpls.2014.00002

• Hochmuth, G. (2011). Iron (Fe) nutrition of plants: SL353/SS555, 8/2011. EDIS, 2011(8). https://doi.org/10.32473/edis-ss555-2011

• Kyu, H. H., Pinho, C., Wagner, J. A., & Brown, J. C. (2016). Global and national burden of diseases and injuries among children and adolescents between 1990 and 2013: Findings from the global burden of disease 2013 study. JAMA Pediatrics, 170(3), 267-287. https://doi.org/10.1001/jamapediatrics.2015.4276

• Ministry of Health. (2017). Recommended nutrients intake (RNI) for Malaysia: A report of the technical working group on nutritional guidelines. MOH. https://hq.moh.gov.my/nutrition/wp-content/uploads/2017/05/FA-Buku-RNI.pdf

• Munirah, N., Lah, M. K. C., Nordin, M. N., Khandaker, M. M., Mat, N., & Jahan, M. S. (2015). The effects of zinc application on physiology and production of corn plants. Australian Journal of Basic and Applied Sciences, 9(5), 161-165.

• Rouphael, Y., & Kyriacou, M. C. (2018). Enhancing quality of fresh vegetables through salinity eustress and biofortification applications facilitated by soilless cultivation. Frontiers in Plant Science, 9, 1254. https://doi.org/10.3389/fpls.2018.01254

• Rout, G. R., & Sahoo, S. (2015). Role of iron in plant growth and metabolism. Reviews in Agricultural Science, 3, 1-24. https://doi.org/10.7831/ras.3.1

• Rugeles-Reyes, S. M., Filho, A. B. C., Lopez Aguilar, M. A., & Silva, P. H. S. (2019). Foliar application of zinc in the agronomic biofortification of arugula. Food Science and Technology, 39(64), 1011-1017. https://doi.org/10.1590/fst.12318

• Uchida, R. (2000). Essential nutrients for plant growth: Nutrient functions and deficiency symptoms. In J. A. Silva & R. Uchida (Eds.), plant nutrient management in Hawaii’s soils approaches for tropical and subtropical agriculture (pp. 31-55). University of Hawaii Press.

• Vadlamudi, K., Upadhyay, H., Singh, A., & Reddy, M. (2020). Influence of zinc application in plant growth: An overview. European Journal of Molecular and Clinical Medicine, 7(7), 2321-2327.

• Wessells, K. R., & Brown, K. H. (2012). Estimating the global prevalence of zinc deficiency: Results based on zinc availability in national food supplies and the prevalence of stunting. PLOS One, 7(11), e50568. https://doi.org/10.1371/journal.pone.0050568

• White, P. J., & Broadley, M. R. (2009). Biofortification of crops with seven mineral elements often lacking in human diets – Iron, zinc, copper, calcium, magnesium, selenium and iodine. New Phytologist, 182(1), 49–84. https://doi.org/10.1111/j.1469-8137.2008.02738.x

• Zahed, Z., Kumar, S. S., Mahale, A. G., Krishna, J. R., & Mufti, S. (2021). Foliar micro-nutrition of vegetable crops - A critical review. Current Journal of Applied Science and Technology, 40(7), 1-12. https://doi.org/10.9734/cjast/2021/v40i731322

• Zahra, N., Hafeez, M. B., Shaukat, K., Wahid, A., & Hasanuzzaman, M. (2021). Fe toxicity in plants: Impacts and remediation. Physiologia Plantarum, 173(1), 201–222. https://doi.org/10.1111/ppl.13361

• Zarcinas, B. A., Ishak, C. F., McLaughlin M. J., & Cozens, G. (2004). Heavy metals in soils and crop in Southeast Asia. Environmental Geochemistry and Health, 26, 343-357. https://doi.org/10.1007/s10653-005-4669-0

• Zou, C., Du, Y., Rashid, A., Ram, H., Savasli, E., Pieterse, P.J., Ortiz-Monasterio, I., Yazici, A., Kaur, C., Mahmood, K., Singh, S., Le Roux, M. R., Kuang, W., Onder, O., Kalayci, M., & Cakmak. I. (2019). Simultaneous biofortification of wheat with zinc, iodine, selenium, and iron through foliar treatment of a micronutrient cocktail in six countries. Journal of Agricultural and Food Chemistry, 67(29), 8096-8106. https://doi.org/10.1021/acs.jafc.9b01829