Impact of foliar application of zinc and iron on summer green gram (Vigna radiata L.)

Introduction

Green gram (Vigna radiata L.) is the key grain legumes cultivated extensively in India owing to its high protein content (20-25%), short term, and suitability in multiple cropping systems. Despite its importance, national productivity remains relatively low as compared to its genetic potential. Key reason for short production is widespread micronutrient deficiency, particularly zinc and iron (Singh and Sachdev, 2017) [23] nearly 48-50% of soils in india suffer from zinc deficiency (Alloway, 2009) [2] . Iron deficiency is commonly occur in calcareous and alkaline soils, leading to interveinal chlorosis and impaired physiological activity (Marschner, 2012) [18] . Micronutrient deficiency not only reduces yield but also lowers grain nutritional quality, contributing to hidden hunger among human populations (Cakmak et al., 2017) [7] Foliar fertilization is increasingly recognized as a corrective and supplementary nutrient management strategy that enhances nutrient-use efficiency and minimizes soil-related losses (Fernández and Brown, 2013) [15] . Additionally, micronutrients are required for plant growth. Plant reproduction and the synthesis of growth-promoting hormones depend on zinc (Patel et al., 2017) [19] . Zn is vital for the functioning of the many enzymes, including tryptophan syntheses, dehydrogenases, and superoxide dismutase. Zinc deficiency leads to deficiencies in the production of RNA and proteins. Zinc-deficient plants therefore contain less protein (Singh et al., 2018) [24] . Zinc fertilizer encourages root and shoot growth throughout the growing season, increasing seed yield, according to research by Rengel (2001) [22] . The method of micronutrient application was observed to positively influence plant growth and lead to the increase in seed yield. Most of the nation's agricultural lands suffer from zinc deficiency. Reduced leaves, delayed growth, chlorosis, and spikelet sterility are all symptoms of a zinc deficiency. These differences make plants more susceptible to different biotic and abiotic stressors. One of the micronutrients found in plants, zinc is necessary for a number of enzymatic functions. Usually, metals are used to activate enzymes. It has been demonstrated that zinc increases crop productivity almost as much as major nutrients do. Zinc is involved in the synthesis of tryptophan, protein, and nucleic acid, among other aspects of auxin metabolism. Furthermore, it promotes nitrogen fixation and root nodulation in leguminous crops and helps plants absorb phosphate and nitrogen (Patel et al., 2013) [20] .

Physiological Role of Iron and Zinc in Green Gram 2.1 Role of Iron (Fe)

Iron plays a critical role in:  Chlorophyll synthesis  Electron transport chain (cytochromes, ferredoxin)  Respiration and photosynthesis  Nitrogen fixation in legumes  Enzyme activation Iron deficiency results in interveinal chlorosis of young leaves, reduced photosynthesis, and lower biomass production (Marschner, 2012) [18] . In legumes like green gram, iron is essential for nitrogenase enzyme activity in root nodules, thereby influencing biological nitrogen fixation (Fageria and Baligar, 2008) [12] .

Role of Zinc (Zn)

Zinc is involved in:  Auxin synthesis (IAA metabolism)  Protein and nucleic acid synthesis  Enzyme activation (dehydrogenases, carbonic anhydrase)  Membrane integrity  Carbohydrate metabolism Zn deficiency causes stunted growth, small leaves, delayed maturity, and poor seed set (Broadley et al., 2007) [5] . Zinc also improves nodulation and enhances nitrogen assimilation in pulses (Singh and Sachdev, 2017) [23] .

Concept and Mechanism of Foliar Nutrition

Foliar fertilization denotes to the use of nutrient solutions directly onto plant leaves through spraying. Nutrient uptake occurs via:  Cuticular penetration  Stomatal absorption  Diffusion across epidermal cells Efficiency depends on spray concentration, environmental conditions (humidity, temperature), leaf age, and surfactants (Zhang and Brown, 1999) [31] .

Advantages of Foliar Nutrition

 Rapid correction of deficiencies  Higher nutrient-use efficiency  Reduced fixation in soil  Smaller nutrient doses required Foliar fertilization is especially effective when root uptake is limited due to adverse soil conditions (Fernández and Brown, 2013) [15] .

Impact of Foliar Zinc Practice on Growth and Yield

Foliar Zn application significantly improves:  Height of plant  Leaf area index  Content of chlorophyll  Dry matter accumulation Angmo et al. (2022) [3] investigated the influence of zinc fertilization on green gram performance through an experiment involving four zinc levels: 0, 5, 10, and 15 kg/ha. They showed that applying zinc up to 10 kg/ha directed to a noticeable improvement in plant growth and yield. Plants grew taller and produced more pods per plant, while the 1000-seed weight also increased. These improvements ultimately resulted in higher yield of seed as well as greater stover yield. Krishna et al. (2022) [16] conducted a study on green gram during Zaid season of 2021 at SHUATS, Prayagraj. The experiment included three zinc levels 10, 12, and 15 kg/ha. Among these, the use of zinc at 15 kg/ha produced the best growth by the time of harvest. Plants reached a height of 44.08 cm and developed about 6.04 branches/plant. The dry matter accumulation was also higher (6.20 g per plant), along with a greater no. of nodules (6.33 per plant). In addition, the crop growth rate was recorded at 2.62 g m⁻² day⁻¹ under this treatment. Dhinagaran et al. (2021) [11] found that green gram achieved significantly higher pods per plant (28.46), seeds per pod (13.5), test weight (3.48 g), seed yield (950 kg/ha), and stover yield (1,520 kg/ha) when ZnSO₄ was applied to the soil at 25 kg/ha after incubating it with 125 kg vermicompost in a 1:5.

Effect of Foliar Iron Application

Foliar Fe sprays correct chlorosis and enhance chlorophyll synthesis. Dhayal et al. (2025) [10] described significant improvement in pods per plant and grain yield with foliar Fe application. Iron improves:  Nitrogen metabolism  Photosynthetic efficiency  Root nodulation  Enzyme activity Improved iron nutrition enhances vegetative growth and reproductive development (Marschner, 2012) [18] . Choudhary et al. (2018) [9] informed the effect of mungbean to foliar use of iron in Jobner condition and found that the grain yield was significantly increased (28.5%) with use of 0.5% FeSO 4 at branching with flowering over control, whereas straw yield was recorded 15.6% higher with 0.5% FeSO4 at branching and 20.8% higher with the foliar practice same at branching + flowering stage over control Soni et al. (2020) [27] performed an experiment at Mahatma Gandhi Chitrakoot Gramodaya Vishwavidyalaya in Chitrakoot, Satna (M.P.), Soni and colleagues examined how foliar sprays of zinc and iron influenced mung bean yields. Their findings showed no significant impact on height of plant, nodules per plant, or branches per plant. Kumawat et al. (2006) [17] reported that soil application of iron at 25 kg FeSO₄ per hectare was statistically comparable to a foliar spray of 0.5% FeSO₄ combined with 0.1% citric acid applied at the branching and flowering stages. Both treatments produced significantly higher seed & straw yields of summer mungbean compared with the control. Chaurasia et al. (2024) [8] showed that the improvements in growth parameters of greengram under combined input management, including micronutrients, indicating that iron may enhance nodulation and nitrogen fixation when integrated with biological inputs such as Rhizobium. Since iron supports the nitrogenase activity and energy transfer, adequate iron nutrition contributes to stronger nodulation and better growth of plant. This supports the inclusion of parameters of growth such as crop height of crop, branches per plant, dry matter accumulation (DMA), and nodulation parameters when evaluating iron interventions in green gram.

Combined Foliar Practices of Zinc and Iron

Combined foliar usage of Zn and Fe produces synergistic effects. Farooq et al. (2025) [14] informed that combined application increased grain yield and micronutrient absorption more than single nutrient application. Synergistic effects include:  Improved enzyme activation  Better chlorophyll formation  Enhanced nutrient translocation  Increased seed micronutrient density Combined application supports agronomic biofortification (Welch and Graham, 2004; White and Broadley, 2009) [29,30] Barla et al. (2023) [4] performed an experiment to evaluate the impact of iron and zinc foliar and soil applications on summer mungbean output, nutritional content, and quality. They found that foliar spraying of 0.5% zinc sulfate and 0.5% iron sulfate at the start of flowering-combined with the standard fertilizer dose (RDF) and farmyard manure-delivered optimal results. This approach yielded the top seed production (521 kg/ha) and stover output (1307 kg/ha), plus the highest gross income (Rs 36,470/ha) and net income (Rs 8,020/ha), achieving a benefitcost ratio of 1.28. Soni et al. (2020) [27] investigated foliar zinc and iron applications impact on mungbean productivity at Mahatma Gandhi Chitrakoot Gramodaya Vishwavidyalaya, Chitrakoot, Satna (M.P.). Results showed significant gains in yield attributes, particularly pods per plant with a 0.5% FeSO4 application at flowering initiation.

Effect on Yield Attributes

Foliar Fe and Zn significantly enhance:  No. of pods per plant  Seeds per pod  100-seed weight  Grain yield  Straw yield Improvement is attributed to enhanced photosynthesis and carbohydrate translocation to developing pods (Fageria and Baligar, 2008) [12] .

Effect on Nutrient Uptake and Biofortification

Foliar Zn and Fe increase micronutrient concentration in grains. Agronomic biofortification through foliar fertilization is considered an effective strategy to address micronutrient malnutrition (Cakmak, 2008) [6] . Higher Zn and Fe density in green gram seeds contributes to improved human nutrition (FAO, 2024) [12] .

Factors Affecting Foliar Efficiency

 Stage of application (flowering stage most responsive)  Concentration of spray solution  Frequency of spraying  Environmental conditions  Use of surfactantsExcess concentration may cause leaf scorching (Fernández and Brown, 2013) [15] .

Economic Feasibility

Foliar application requires low quantities of micronutrients, making it cost-effective. Yield gains often outweigh the cost of micronutrient sprays, particularly under Zn-deficient soils.

Research Gaps and

References

1. Alloway BJ. Zinc in soils and crop nutrition. Brussels: International Zinc Association; 2008.
2. Alloway BJ. Soil factors associated with zinc deficiency. Environmental Geochemistry and Health. 2009;31:537-548.
3. Angmo P, Mondal AK, Phogat M, Kumar S, Rai AP. Effect of phosphorus and zinc interaction on performance of green gram (Vigna radiata L. Wilczek). Legume Research. 2022;45(10):1303-1308.
4. Barla S, Sahoo HK, Patra BP. Effect of soil and foliar application of zinc and iron on yield, nutrient content and quality of summer mungbean. International Journal of Environment and Climate Change. 2023;13(9):2099-2104.
5. Broadley MR, White PJ, Hammond JP, Zelko I, Lux A. Zinc in plants. New Phytologist. 2007;173:677-702.
6. Cakmak I. Enrichment of cereal grains with zinc. Plant and Soil. 2008;302:1-17.
7. Cakmak I, McLaughlin MJ, White PJ. Zinc for better crop production and human health. Plant and Soil. 2017;411:1-4.
8. Chaurasia J, et al. Effect of micronutrients, rhizobium, salicylic acid, and effective microorganisms on growth and yield of green gram (Vigna radiata) in Nepal. Heliyon. 2024.
9. Choudhary H, Yadav LR, Yadav MR, Kantwa R, Kumawat R. Growth and productivity of mungbean varieties under foliar application of iron in semi-arid eastern plain zone of Rajasthan. International Journal of Chemical Studies. 2018;6(5):2269-2274.
10. Dhayal BC, Shukla UN, Singh U. Response of mungbean to zinc and iron application. Annals of Agricultural Research. 2025;46(2):181-188.
11. Dhinagaran M, Indirani R, Pandian PS, Gurusamy A, Kannan P. Effect of organic fortified zinc on growth and yield of green gram (Vigna radiata L. Wilczek) in typic chromustert. Journal of Applied and Natural Science. 2021;13(4):1166-1171.
12. Fageria NK, Baligar VC. Micronutrients in crop production. Advances in Agronomy. 2008;77:185-268.
13. Food and Agriculture Organization. The state of food security and nutrition in the world. Rome: FAO; 2024.
14. Farooq H, Ishtiaq R, Babar H. Enhancing zinc and iron biofortification in mungbean. Scientific Reports. 2025;15:10974.
15. Fernández V, Brown PH. From plant surface to plant metabolism: Foliar nutrient fate. Frontiers in Plant Science. 2013;4:289.
16. Krishna BM, Kumar HS, Priyanka G, NAIL M, Umesha C. Influence of boron and zinc on growth and yield of green gram (Vigna radiata L.). The Pharma Innovation Journal. 2022;11(3):1674-1678.
17. Kumawat RN, Rathore PS, Pareek N. Response of moongbean to S and Fe nutrition grown on calcareous soil of Western Rajasthan. Indian Journal of Pulses Research. 2006;19(2):228-230.
18. Marschner H. Mineral nutrition of higher plants. 3rd ed. London: Academic Press; 2012.
19. Patel HB, Shah KA, Barvaliya MM, Patel SA. Response of green gram (Vigna radiata L.) to different level of phosphorus and organic liquid fertilizer. International Journal of Current Microbiology and Applied Sciences. 2017;6(10):3443-3451.
20. Patel HR, Patel HF, Maheriya VD, Dodia IN. Response of kharif green gram (Vigna radiata L.) to sulphur and phosphorus fertilization. Bioscan. 2013;8(1):149-152.
21. Rashid MH, Jahan I, Islam MS. Foliar zinc application enhances yield of mungbean. Fundamental and Applied Agriculture. 2024;9(2):59-64.
22. Rengel Z. Genotypic differences in micronutrient use efficiency in crops. Communications in Soil Science and Plant Analysis. 2001;32(7-8):1163-1186.
23. Singh B, Sachdev A. Management of micronutrient deficiencies in pulses. Indian Journal of Agronomy. 2017;62:123-130.
24. Singh R, Singh P, Singh V, Yadav RA. Effect of phosphorus and PSB on growth parameters, yield, quality and economics of summer green gram (Vigna radiata L.). International Journal of Chemical Studies. 2018;6(4):27982803.
25. Singh R, Singh V, Singh P, Yadav RA. Effect of phosphorus and PSB on yield attributes, quality and economics of summer green gram (Vigna radiata L.). Journal of Pharmacognosy and Phytochemistry. 2018;7(2):404-408.
26. Solanke GN, Puri AN, Adsul PB. Effect of micronutrient application on green gram. International Journal of Research in Agronomy. 2024;7:143-148.
27. Soni J, Kushwaha HS. Effect of foliar spray of zinc and iron on productivity of mungbean (Vigna radiata L. Wilczek). Journal of Pharmacognosy and Phytochemistry. 2020;9(1):108-111.
28. Srivastava S, Singh S, Mohan M. Influence of boron and zinc on green gram. International Journal of Research in Agronomy. 2025;8:94-97.
29. Welch RM, Graham RD. Breeding for micronutrients in staple crops. Journal of Experimental Botany. 2004;55:353364.
30. White PJ, Broadley MR. Biofortification of crops with mineral elements. New Phytologist. 2009;182:49-84.
31. Zhang H, Brown PH. Foliar nutrient absorption mechanisms. Journal of Plant Nutrition. 1999;22:17471764.