Okra is an important vegetable crop with high nutritional and economic value. Various approaches have been attempted to increase its production, including foliar fertilisers. This study aims to determine the optimal time to apply foliar fertiliser in a day to improve the final yield in Abelmoschus esculentus L. var. Torpedo and evaluate okra’s growth and yield responses by integrating foliar fertiliser as supplementary fertiliser with granule fertiliser in a controlled environment. The study was conducted in a rain shelter under a randomised complete block design with 3 blocks comprising 3 replications within each block. The treatments involved a combination of foliar and granule application at different timings: sunrise, midday, and dusk, and solely granule fertiliser at labelled recommended rates. The control group was treated with only granule fertiliser at the same rate as the combined foliar and granule application. The study found that the application of foliar fertiliser during dusk (6–7 p.m.) showed a higher trend of potential yield, which revealed the potential of dusk foliar fertiliser application timing as the optimal timing for foliar fertilisation. The study also demonstrated that incorporating liquid foliar fertiliser with granular fertiliser can enhance nutrient uptake and promote plant growth, leading to a more sustainable farming practice by reducing inorganic soil granule fertilisers. The potential yield under the combined fertiliser treatments was 5% to 20% higher when compared to experiment control while comparable to the conventional fertiliser application treatment, despite using 45% less nitrogen. Therefore, the study suggests that farmers integrate foliar and soil fertilisation methods to achieve optimal crop yield production and promote sustainable farming.

• Abbasi, F. F., Baloch, M. A., Zia-ul-hassan, Wagan, K. H., Shah, A. N., & Rajpar, I. (2010). Growth and yield of okra under foliar application of some new multinutrient fertilizer products. Pakistan Journal of Agriculture: Agricultural Engineering Veterinary Sciences, 26(2), 11–18.

• Afe, A. I., & Oluleye, F. (2017). Response of okra (Abelmuschus esculenthus L. Moench) to combined organic and inorganic foliar fertilizers. International Journal of Recycling of Organic Waste in Agriculture, 6, 189–193. https://doi.org/10.1007/s40093-017-0166-6

• Ajayi, E. O., Adeoye, I. B., & Shittu, O. A. (2017). Economic analysis of intercropping okra with legumes. Journal of Agricultural Sciences, 62(2), 193–202. https://doi.org/10.2298/JAS1702193A

• Alshaal, T., & El-Ramady, H. (2017). Foliar application: From plant nutrition to biofortification. Environment, Biodiversity and Soil Security, 1, 71–83. https://doi.org/10.21608/JENVBS.2017.1089.1006

• Anwar, F., Qadir, R., & Ahmad, N. (2020). Cold pressed okra (Abelmoschus esculentus) seed oil. In M. F. Ramadan (Ed.), Cold pressed oils (pp. 309-314). Academic Press. https://doi.org/10.1016/B978-0-12-818188-1.00027-X

• Bassi, R., & Dall’Osto, L. (2021). Dissipation of light energy absorbed in excess: The molecular mechanisms. Annual Review of Plant Biology, 72, 47–76. https://doi.org/10.1146/annurev-arplant-071720-015522

• Bindraban, P. S., Dimkpa, C., Nagarajan, L., Roy, A., & Rabbinge, R. (2015). Revisiting fertilisers and fertilisation strategies for improved nutrient uptake by plants. Biology and Fertility of Soils, 51, 897–911. https://doi.org/10.1007/S00374-015-1039-7

• Cangsong, Z., Pengcheng, L., Miao, S., Chaoyou, P., Xinhua, Z., Huiping, G., Shuai, L., Yukun, q., Helin, D., & Xueke, Y. (2018). 叶面施氮对棉花根系吸收硝态氮的影响 [Effects of foliar nitrogen applications on the absorption of nitrate nitrogen by cotton roots]. Cotton Science, 30(4), 338–343. https://doi.org/10.11963/1002-7807.ZCSDHL.20180703

• Chen, X., Yao, Q., Gao, X., Jiang, C., Harberd, N. P., & Fu, X. (2016). Shoot-to-root mobile transcription factor HY5 coordinates plant carbon and nitrogen acquisition. Current Biology, 26(5), 640–646. https://doi.org/10.1016/J.CUB.2015.12.066

• Cui, J., Lei, B., & Liu, H. (2019). Effect of daily light integral on plant growth and development. Acta Horticulturae Sinica, 46(9), 1670–1680.

• Delhon, P., Gojon, A., Tillard, P., & Passama, L. (1996). Diurnal regulation of NO3− uptake in soybean plants IV. Dependence on current photosynthesis and sugar availability to the roots. Journal of Experimental Botany, 47(7), 893–900. https://doi.org/10.1093/JXB/47.7.893

• Department of Statistic Malaysia. (2018). Supply and utilization accounts selected agricultural commodities, Malaysia 2014-2018. DOSM. https://www.dosm.gov.my/portal-main/release-content/supply-and-utilization-accounts-selected-agricultural-commodities-malaysia-2014-2018

• Department of Statistic Malaysia. (2020). Supply and utilization accounts selected agricultural commodities, Malaysia 2016-2020. DOSM. https://www.dosm.gov.my/portal-main/release-content/supply-and-utilization-accounts-selected-agricultural-commodities-malaysia-2016-2020

• Department of Statistic Malaysia. (2021). Supply and utilization accounts selected agricultural commodities, Malaysia 2017-2021. DOSM. https://www.dosm.gov.my/portal-main/release-content/supply-and-utilization-accounts-selected-agricultural-commodities-malaysia-2017-2021

• Fageria, N. K., Filho, M. P. B., Moreira, A., & Guimarães, C. M. (2009). Foliar fertilization of crop plants. Journal of Plant Nutrition, 32(6), 1044–1064. https://doi.org/10.1080/01904160902872826

• Fernández, V., & Brown, P. H. (2013). From plant surface to plant metabolism: the uncertain fate of foliar-applied nutrients. Frontiers in Plant Science, 4, 289. https://doi.org/10.3389/fpls.2013.00289

• Fernández, V., Gil-Pelegrín, E., & Eichert, T. (2021). Foliar water and solute absorption: An update. The Plant Journal, 105(4), 870–883. https://doi.org/10.1111/TPJ.15090

• Fernández, V., Sotiropoulos, T., & Brown, P. H. (2013). Foliar fertilization: Scientific principles and field practices. International Fertilizer Industry Association.

• Gooding, M. J., & Davies, W. P. (1992). Foliar urea fertilization of cereals: A review. Fertilizer Research, 32, 209–222. https://doi.org/10.1007/BF01048783

• Hofmann, L. C., Koch, M., & de Beer, D. (2016). Biotic control of surface pH and evidence of light-induced H+ pumping and Ca2+-H+ exchange in a tropical crustose coralline alga. PLOS One, 11(7), e0159057. https://doi.org/10.1371/journal.pone.0159057

• Jusoh, M., Ramlee, S. I., Pydi, F. I., Mazlan, N. A., Berahim, Z., Muhamad Mujab, A. A., Sinniah, U. R., Yeoh, J. P. S., Khalid, K., & Yaapar, M. N. (2023). Specific sound frequency improves intrinsic water efficiency in rice leaf by imparting changes in stomatal dimensions. Pertanika Journal of Tropical Agricultural Science, 46(2), 439–457. https://doi.org/10.47836/PJTAS.46.2.05

• Kandasamy, S., Weerasuriya, N., Gritsiouk, D., Patterson, G., Saldias, S., Ali, S., & Lazarovits, G. (2020). Size variability in seed lot impact seed nutritional balance, seedling vigor, microbial composition and plant performance of common corn hybrids. Agronomy, 10(2), 157. https://doi.org/10.3390/AGRONOMY10020157

• Khor, S. C. (2022). Growth, yield and fruit quality improvement of okra (Abelmoschus esculentus L.) through vegetative CO2 enrichment derived from grey oyster mushroom respiration (Pleurotus pulmonarius (Fr.) Quél) [Unpublished Master’s thesis]. Universiti Putra Malaysia.

• Lin, L., Li, Z., Yu, L., Wang, H., & Niu, Z. (2020). Photosynthetic responses to interaction of light intensity and CO2 concentration and photoinhibition characteristics of two apple canopy shapes. Acta Horticulturae Sinica, 47(11), 2073–2085.

• Mehraj, H., Taufique, T., Mandal, M. S. H., Sikder, R. K., & Jamal Uddin, A. F. M. (2015). Foliar feeding of micronutrient mixtures on growth and yield of okra (Abelmoschus esculentus). American-Eurasian Journal of Agricultural and Environmental Sciences, 15(11), 2124–2129. https://doi.org/10.5829/idosi.aejaes.2015.15.11.12615

• Niu, J., Liu, C., Huang, M., Liu, K., & Yan, D. (2020). Effects of foliar fertilization: A review of current status and future perspectives. Journal of Soil Science and Plant Nutrition, 21, 104–118. https://doi.org/10.1007/S42729-020-00346-3

• Oprica, D. I., Cioroianu, T. M., Lungu, M., & Badea, I. A. (2014). A new eco-friendly foliar fertilizer with bone glue suitable for crops of maize and sunflower. Revista de Chimie, 65(1), 1–7.

• Patelou, M., Infante, C., Dardelle, F., Randewig, D., Kouri, E. D., Udvardi, M. K., Tsiplakou, E., Mantecón, L., & Flemetakis, E. (2020). Transcriptomic and metabolomic adaptation of Nannochloropsis gaditana grown under different light regimes. Algal Research, 45(101735). https://doi.org/10.1016/J.ALGAL.2019.101735

• Peirce, C. A. E., McBeath, T. M., Priest, C., & McLaughlin, M. J. (2019). The timing of application and inclusion of a surfactant are important for absorption and translocation of foliar phosphoric acid by wheat leaves. Frontiers in Plant Science, 10, 1532. https://doi.org/10.3389/fpls.2019.01532

• Prajwal Kumar, G. K., Lalitha, B. S., Somashekar, K. S., & Sannagoudar, M. S. (2018). Effect of foliar applied nutrients on soil chemical properties and nutrient uptake of baby corn (Zea mays L.). International Journal of Chemical Studies, 6(2), 2087–2089.

• Quintana, J., Bernal, M., Scholle, M., Holländer-Czytko, H., Nguyen, N. T., Piotrowski, M., Mendoza-Cózatl, D. G., Haydon, M. J., & Krämer, U. (2022). Root-to-shoot iron partitioning in Arabidopsis requires IRON-REGULATED TRANSPORTER1 (IRT1) protein but not its iron(II) transport function. The Plant Journal, 109(4), 992–1013. https://doi.org/10.1111/TPJ.15611

• Rai, S., Singh, P. K., Mankotia, S., Swain, J., & Satbhai, S. B. (2021). Iron homeostasis in plants and its crosstalk with copper, zinc, and manganese. Plant Stress, 1, 100008. https://doi.org/10.1016/J.STRESS.2021.100008

• Reynolds, J. F., & Thornley, J. H. M. (1982). A shoot:root partitioning model. Annals of Botany, 49(5), 585–597. https://doi.org/10.1093/OXFORDJOURNALS.AOB.A086286

• Sakuraba, Y., & Yanagisawa, S. (2018). Light signalling-induced regulation of nutrient acquisition and utilisation in plants. Seminars in Cell and Developmental Biology, 83, 123–132. https://doi.org/10.1016/J.SEMCDB.2017.12.014

• Schönherr, J., & Schreiber, L. (2004). Size selectivity of aqueous pores in astomatous cuticular membranes isolated from Populus canescens (Aiton) Sm. leaves. Planta, 219, 405–411. https://doi.org/10.1007/S00425-004-1239-0

• Schreinemachers, P., Simmons, E. B., & Wopereis, M. C. S. (2018). Tapping the economic and nutritional power of vegetables. Global Food Security, 16, 36–45. https://doi.org/10.1016/J.GFS.2017.09.005

• Sebilo, M., Mayer, B., Nicolardot, B., Pinay, G., & Mariotti, A. (2013). Long-term fate of nitrate fertilizer in agricultural soils. Proceedings of the National Academy of Sciences of the United States of America, 110(45), 18185–18189. https://doi.org/10.1073/pnas.1305372110

• Shahid, M. R., Amjad, M., Ziaf, K., Jahangir, M. M., Ahmad, S., Iqbal, Q., & Nawaz, A. (2013). Growth, yield and seed production of okra as influenced by different growth regulators. Pakistan Journal of Agricultural Sciences, 50(3), 387–392.

• Simarmata, T., Prayoga, M. K., Setiawati, M. R., Adinata, K., & Stöber, S. (2021). Improving the climate resilience of rice farming in flood-prone areas through Azolla biofertilizer and saline-tolerant varieties. Sustainability, 13(21), 12308. https://doi.org/10.3390/su132112308

• Sinclair, S. A., & Krämer, U. (2012). The zinc homeostasis network of land plants. Biochimica et Biophysica Acta - Molecular Cell Research, 1823(9), 1553–1567. https://doi.org/10.1016/J.BBAMCR.2012.05.016

• Thakur, P., & Kumar, P. (2020). Leaching losses of micronutrient: A review. Biological Forum - An International Journal, 12(2), 13–21.

• Toh, L. S., Jusoh, M., Fleming, A., Muhamad Mujab, A. A., Berahim, Z., & Yaapar, M. N. (2022, September 13-15). The potential of temporal sundown foliar application in promoting growth of leafy crop (pak choi) and fruit crop (okra) [Poster presentation]. 32nd Malaysian Society of Plant Physiology (MSPP) Conference 2022, Kedah, Malaysia.

• United States Department of Agriculture. (2019). Okra, raw. USDA. https://fdc.nal.usda.gov/fdc-app.html#/food-details/169260/nutrients

• Xin, H., PanWei, Z., ChuanYu, D., YuPing, Z., QiRong, S., & Wei, C. (2009). 弱光下硝铵比对小白菜氮吸收和碳氮分配的影响 [Effects of nitrate/ammonium ratio on nitrate absorption and distribution of carbon and nitrogen in pakchoi growing under low light intensity]. Acta Pedologica Sinica, 46(3), 452–458. https://doi.org/10.11766/trxb200711120311

• Xu, J., Guo, Z., Jiang, X., Ahammed, G. J., & Zhou, Y. (2021). Light regulation of horticultural crop nutrient uptake and utilization. Horticultural Plant Journal, 7(5), 367–379. https://doi.org/10.1016/J.HPJ.2021.01.005

• Yaapar, M. N. (2017). The control of stomatal properties in rice (Oryza sativa L.) and their influence on photosynthetic performance [Unpublished Doctoral dissertation]. The University of Sheffield.

• Yin, Y., Li, S., Liao, W., Lu, Q., Wen, X., & Lu, C. (2010). Photosystem II photochemistry, photoinhibition, and the xanthophyll cycle in heat-stressed rice leaves. Journal of Plant Physiology, 167(12), 959–966. https://doi.org/10.1016/J.JPLPH.2009.12.021

• Zhang, A., Liu, C., Chen, G., Hong, K., Gao, Y., Tian, P., Peng, Y., Zhang, B., Ruan, B., Jiang, H., Guo, L., Qian, Q., & Gao, Z. (2017). Genetic analysis for rice seedling vigor and fine mapping of a major QTL qSSL1b for seedling shoot length. Breeding Science, 67(3), 307–315. https://doi.org/10.1270/JSBBS.1619