Effect of foliar application of nano zinc and nano copper on the growth, yield and economics of cowpea (Vigna unguiculata L.)

Introduction

Agriculture sector is one of the most important sectors which plays a major role in ensuring food and nutritional security around the world. Green revolution was a major leap in meeting the food requirements of the rising population around the globe through the intensive use of irrigation, fertilizers, agrochemicals and short duration high yielding dwarf varieties etc. which ultimately led to an increase in world food production. However, the adverse impacts of green revolution became evident in the later years. Intensive use of chemical fertilizers led to the deterioration of soil health and the quality of underground water. Eutrophication, nutrient imbalances and other environmental hazards occurred as a result of improper and unscientific management of conventional fertilizers (Alshaal and El-Ramady, 2017) [3] . Cowpea is well-known for its ability to withstand dryness. It is also known as black-eyed pea or southern pea. The shadowing effect of its broad, drooping leaves preserves soil moisture. It can be used as a vegetable, food, feed, fodder, forage and green manuring. In the semi-arid tropical regions of Asia, Africa, Southern Europe, Central America, and South America, it is a vital food legume. Worldwide, the use of cowpeas as food, fodder, and a raw resource for numerous industries is increasing. Cowpea, also referred to as vegetable meat, is a valuable source of vitamins, minerals, and protein for a healthy diet.4.3 g protein, 2.0 fibre, 8.0 g carbohydrate, 74 mg phosphorus, 2.5 mg iron, 13.0 mg vitamin C and 0.9 mg minerals, etc. are present in 100 g of green tender pods (Damoar K, Sharma RK, Maida P, 2020) [6] . India has low pulse production and productivity as pulses are cultivated mainly on marginal and submarginal soils with inadequate management techniques (Ponniya Vijay, Anil Choudhary K, 2015) [24] . India is the world's biggest importer and user of pulses. With 2,745.28 tonnes production, Uttar Pradesh is the top cowpea producer. India's productivity of pulses (764 kg ha -1 ) is significantly lower than the global average (848 kg ha 1 ). Overall area cultivated for pulses remains almost unchanged at 22 to 24 million hectares, with a production that has remained relatively constant at 12 to 14 million tonnes. Legumes are crops that are fond of phosphorus, and is necessary for the development of seeds, nodules, and flower initiation. Zinc is a major micronutrient that is crucial to the growth and development of plants. In developing countries, Zn deficiency occurs due to inadequate supply of micronutrient. Several research findings also reported that, considerable increment in the yield of the crop is due to the application of Zn fertilizers. In India, despite the availability of high-yielding varieties such as 'Kashi Kanchan', cowpea productivity remains below its potential due to several production constraints, among which micronutrient deficiencies are particularly significant. zinc and copper are essential micronutrients involved in numerous physiological and biochemical processes, including enzyme activation, photosynthesis, protein synthesis, reproductive development, and biological nitrogen fixation. Deficiencies of these nutrients are widespread in Indian soils and adversely affect crop growth, yield, and quality. Conventional micronutrient fertilizers often exhibit low nutrient use efficiency because of fixation, leaching, and limited plant availability. Recent advances in nanotechnology have opened new opportunities for improving nutrient management in agriculture. Nano-fertilizers possess unique properties such as high surface area, enhanced reactivity, and improved nutrient delivery, which can increase nutrient use efficiency while reducing environmental losses. Although positive effects of nano zinc and nano copper have been reported in several crops, information regarding their combined and individual effects on cowpea under the agro-climatic conditions of Uttar Pradesh remains limited. Considering the low productivity of cowpea, widespread zinc and copper deficiencies, and the potential benefits of nano-fertilizers, the present study was undertaken to evaluate the effect of foliar application of nano zinc and nano copper on the growth, yield, quality, and economics of cowpea cultivation.

Materials and Methods

A field experiment was conducted during the Kharif season 2025 at the Vegetable Research Farm, Department of Vegetable Science, Chandra Shekhar Azad University of Agriculture and Technology (CSAUA&T), Kanpur, Uttar Pradesh, India. The experimental site is situated at 26°49′ N latitude, 80°30′ E longitude, and an altitude of 133 m above mean sea level. The region experiences a humid subtropical climate with an average annual rainfall of 750-800 mm. The soil of the experimental field was sandy clay loam in texture, slightly alkaline in reaction (pH 7.7), low in organic carbon (0.45%) and available nitrogen (210.3 kg ha⁻¹), medium in available phosphorus (13.5 kg ha⁻¹), and rich in available potassium (251.6 kg ha⁻¹). The experiment was laid out in a Randomized Block Design (RBD) with eight treatments and three replications using the vegetable cowpea variety 'Kashi Kanchan'. Seeds were sown on 23 July 2025 at a spacing of 45 cm × 15 cm using a seed rate of 25 kg ha⁻¹. A recommended basal fertilizer dose of 30:60:80 kg N:P₂O₅: K₂O ha⁻¹ was applied through urea, single superphosphate, and muriate of potash, respectively. Seeds were treated with carbendazim at 2.5 g kg⁻¹ seed before sowing. The treatments consisted of: T₁-100% RDF (control); T₂-RDF + Nano Zn (50 ppm); T₃-RDF + Nano Cu (50 ppm); T₄-RDF + Nano Zn (50 ppm) + Nano Cu (50 ppm); T₅-RDF + ZnSO₄ (1%); T₆-RDF + CuSO₄ (1%); T₇-RDF + ZnSO₄ (1%) + CuSO₄ (1%); and T₈-RDF + Kashi Sookshma Shakti micronutrient mixture (0.5%). Foliar sprays were applied twice, at 30 and 45 days after sowing (DAS), corresponding to the vegetative growth and flowering initiation stages, respectively. Standard agronomic practices were followed throughout the crop growth period. Gap filling, thinning, weeding, irrigation, and plant protection measures were carried out as required. Green pods were harvested manually in five pickings at weekly intervals from 48 to 70 DAS. Observations were recorded on growth, phenological, yield, shelf life, and economic parameters. Included plant population, plant height, and number of branches per plant,days to 50% flowering and days to first fruit initiation. number of pods per plant, pod length, pod girth, number of seeds per pod, pericarp weight, pod yield per plant, pod yield per plot, and green pod yield per hectare. Shelf life of pods at room temperature was recorded as a quality parameter. Economic analysis was carried out by estimating gross returns, net returns, and benefit-cost ratio for each treatment.

Results and Discussion

Growth Parameters

Foliar application of nano zinc and nano copper significantly influenced the growth of cowpea. Among all treatments, the combined application of nano zinc and nano copper (T₄) recorded the maximum plant height of 31.39 cm and 60.94 cm at 30 and 60 DAS, respectively, which was significantly higher than the control (23.89 cm and 54.22 cm). Similarly, T₄ produced the highest number of branches per plant (10.55) at 50 DAS. The superior growth performance under nano nutrient application may be attributed to enhanced nutrient absorption, enzyme activation, auxin synthesis, and improved photosynthetic activity. Nanoformulations exhibited greater effectiveness than conventional ZnSO₄ and CuSO₄ treatments owing to their higher bioavailability and efficient foliar uptake.

Phenological Characters

The foliar application of micronutrients significantly affected flowering and fruit initiation. Treatment T₄ recorded the earliest 50% flowering (43.10 days) and first fruit initiation (47.77 days), whereas the control required 52.88 and 58.10 days, respectively. The enhanced nutrient availability under nano treatments may have accelerated physiological and metabolic processes responsible for reproductive development, resulting in earlier flowering and fruit set.

Pod Yield

Pod yield was significantly influenced by the different treatments.

The highest pod yield was recorded under T₄ (Nano Zn + Nano Cu), with 428.66 g plant⁻¹, 16.20 kg plot⁻¹, and 171.43 q ha⁻¹, representing a substantial increase over the control (278.75 g plant⁻¹, 10.50 kg plot⁻¹, and 111.11 q ha⁻¹). Among the individual nano treatments, nano zinc performed better than nano copper. The higher yield under combined nano application may be attributed to improved vegetative growth, enhanced photosynthetic efficiency, greater nutrient use efficiency, and better translocation of assimilates towards developing pods. Pod weight was also significantly increased by nano nutrient application. The maximum pod weight of 132.66 g per 10 pods was recorded under T₄, followed by T₅ (129.99 g) and T₂ (129.21 g), whereas the control recorded the lowest value (118.63 g). The increase in pod weight reflects improved carbohydrate accumulation and efficient utilization of photosynthates during pod development.

Shelf Life

Shelf life of fresh cowpea pods was significantly improved by nano nutrient application. The combined foliar application of nano zinc and nano copper (T₄) recorded the longest shelf life (5.20 days), compared with 4.10 days in the control. Improved membrane stability, reduced moisture loss, and enhanced antioxidant enzyme activity under nano micronutrient treatments may have contributed to better post-harvest quality and prolonged shelf life.

Conclusion

The present study demonstrated that foliar application of nano zinc and nano copper significantly improved growth, yield attributes, yield, quality, and economic returns of cowpea. Among the different treatments, the combined application of nano zinc (50 ppm) and nano copper (50 ppm) proved most effective, recording the highest plant height, number of branches, pods per plant, pod dimensions, pericarp weight, seeds per pod, and pod yield. The treatment also enhanced post-harvest shelf life and resulted in the highest net returns and benefit-cost ratio. Nanoformulations consistently outperformed conventional zinc and copper sources, indicating superior nutrient use efficiency and bioavailability. Therefore, foliar application of nano zinc (50 ppm) and nano copper (50 ppm) at 30 and 45 DAS can be recommended as an efficient and economically viable micronutrient management strategy for enhancing productivity, quality, and profitability of cowpea cultivation in Central plains of Uttar Pradesh.

References

1. Abdel-Aziz HMM, Hasaneen MNA, Omer AM. Effect of foliar application with nano zinc and nano copper on cowpea under water stress. Journal of Plant Nutrition. 2018;41(12):1547-1558.
2. Alloway BJ. Zinc in soils and crop nutrition. 2nd ed. Brussels and Paris: International Zinc Association and International Fertilizer Industry Association; 2008.
3. Alshaal T, El-Ramady H. Foliar application: from plant nutrition to biofortification. Environmental Biodiversity Soil Security. 2017;1:71-83.
4. Balachandrakumar V, Sowmiya K, Shofiya M, Gopika K, Nithika M. Impact of nano DAP and Zn EDTA on cowpea growth and yield. International Journal of Plant & Soil Science. 2024;36(6):317-326.
5. Borkakati K, Roy SS, Bhattacharyya P, Talukdar AJ, Bhattacharya SS. Copper nanoparticles enhance photosynthesis, biological nitrogen fixation and growth of cowpea. Journal of Trace Elements in Medicine and Biology. 2019;56:66-74.
6. Damoar K, Sharma RK, Maida P. Response of cowpea (Vigna unguiculata L.) varieties under Malwa region of Madhya Pradesh. Journal of Pharmacognosy and Phytochemistry. 2020;9(2):1749-1753.
7. DeRosa MC, Monreal C, Schnitzer M, Walsh R, Sultan Y. Nanotechnology in fertilizers. Nature Nanotechnology. 2010;5:91.
8. Directorate of Economics and Statistics. statistics database. Government of India; 2023.
9. Dimkpa CO, Bindraban PS. Fortification of micronutrients for efficient agronomic production: A review and outlook for the future. Agronomy for Sustainable Development. 2016;36:1-26.
10. Food and Agriculture Organization. FAOSTAT statistical database. Rome: FAO; 2021.
11. Fageria NK, Barbosa Filho MP, Moreira A, Guimarães CM. Foliar fertilization of crop plants. Journal of Plant Nutrition. 2009;32(6):1044-1064.
12. Food and Agriculture Organization. World food and agriculture statistical yearbook. Rome: FAO; 2022.
13. Gad El-Hak SH, Ahmed SE, Moustafa YMM. Effect of nanoparticles of copper and zinc application on growth, yield and chemical components of cowpea plants grown in sandy soils. Pakistan Journal of Biological Sciences. 2020;23(10):1282-1293.
14. Giller KE. Nitrogen fixation in tropical cropping systems. 2nd ed. Wallingford (UK): CABI Publishing; 2001.
15. Hall AE. Breeding for adaptation to drought and heat in cowpea. European Journal of Agronomy. 2004;21(4):447454.
16. Haruna IM, Aliyu L. Yield and economic returns of sesame (Sesamum indicum L.) as influenced by poultry manure, nitrogen and phosphorus at Samaru, Nigeria. Elixir Agriculture. 2011;39:4884-4887.
17. Indian Council of Agricultural Research. Annual report 2025-26. New Delhi: ICAR; 2025.
18. Khot LR, Sankaran S, Maja JM, Ehsani R, Schuster EW. Applications of nanomaterials in agricultural production and crop protection: A review. Crop Protection. 2012;35:64-70.
19. Kumari P, Kumari N, Kumari V, Kumar V, Singh SK. Synergistic effect of nano zinc and nano copper on growth, yield and quality of cowpea. Journal of Pharmacognosy and Phytochemistry. 2021;10(2):345-352.
20. Marschner H. Mineral nutrition of higher plants. 3rd ed. London: Academic Press; 2012.
21. Mustafa N, Safdar ME, Asif M, Javaid MM, Farooq N, Ghaffar A, et al. Impact of nano zinc oxide foliar application on physiology, yield and quality of cowpea. Pakistan Journal of Agricultural Research. 2021;34(3):487-496.
22. Ministry of Agriculture and Farmers Welfare. Directorate of pulses development annual report 2021-2022. Government of India; 2022.
23. Prasad TNVKV, Sudhakar P, Sreenivasulu Y, Latha P, Munaswamy V, Raja Reddy K, et al. Effect of nanoscale zinc oxide particles on germination, growth and yield of peanut. Journal of Plant Nutrition. 2012;35(6):905-927.
24. Ponniya V, Choudhary AK, Dass A, Bana RS, Rana KS, Rana DS, et al. Improved crop management practices for sustainable pulse production: An Indian perspective. Indian Journal of Agricultural Sciences. 2015;85:747-758.
25. Salim SS, Shimi GJ, Pillai S, Sheeja KR, Shruthy ON. Effect of foliar application of nano-N and nano-Zn on growth and yield attributes in bush type vegetable cowpea [Vigna unguiculata Subsp. unguiculata (L.) Verdcourt]. The Pharma Innovation Journal. 2023;12(5):1073-1076.
26. Singh MV. Micronutrient nutritional problems in soils of India and improvement for human and animal health. Indian Journal of Fertilisers. 2009;5(4):11-26.
27. Singh V, Kumar S, Tiwari S. Nano micronutrient application in cowpea: Current status and future prospects. Journal of Plant Nutrition. 2022;45(4):512-528.
28. Vandana Nandal, Solanki M. Zn as a vital micronutrient in plants. Journal of Microbiology, Biotechnology and Food Sciences. 2021;11(3):4026.
29. Yruela I. Copper in plants: acquisition, transport and interactions. Functional Plant Biology. 2009;36(5):409-430.
30. Zhao L, Lu L, Wang A, Zhang H, Huang M, Wu H, et al. Nanobiotechnology in agriculture: Use of nanomaterials to promote plant growth and stress tolerance. Journal of Agricultural and Food Chemistry. 2020;68(7):1935-1947.