Lettuce (Lactuca sativa L.) is a popular salad vegetable belonging to the family compositae having chromosome number 2 n=18. Leaf lettuce (Lactuca sativa var. crispa), head lettuce (Lactuca sativa var. capitata), stem lettuce (Lactuca sativa var. aspergina) and Cos or Romanian lettuce (Lactuca sativa var. longifolia) are the four basic forms of lettuce. Lettuce is an excellent source of vitamins and minerals. Its nutritional composition per 100 g is as follows: Vit A (276 IU), Vit B1 (0.057 mg), Vit B2 (0.15 mg), Vit B6 (0.082 mg), Vitamin C (3.7 mg), Vitamin K (102.3 µg), calcium (35 mg), iron (1.24 mg) and magnesium (13 mg). The high cellulose content (1.1 g/100 g) of leaves facilitates digestion of food. Throughout the globe, lettuce consumption and production have increased since late 20^th century. In present day, China is the leading producer of lettuce occupying 4% of world total production. In India, lettuce is grown in smaller area (Majid et al., 2021). Lettuce is a cool season crop and shows high growth rates in between 15 and 18°C. Extreme temperature i.e., 30°C for a few days will cause bolting in lettuce which makes the leaves bitter in taste and making it unmarketable. In field, lettuce shows good production in soils with a pH of 6.0 to 6.8. Light-textured soils are ideal for early spring harvest. Leafy vegetables like lettuce require continuous supply of mineral nutrients such as calcium which is a principal function in plants to facilitate nutrient transfer, a component of cell walls, neutralize acidic intracellular environments, boost plant resistance to pathogens and allow for more upright stems. Calcium content in Indian soil varies according to agro-climatic zones. In most instances, most of the calcium is lost through leaching and farmers add calcium sources in the form of gypsum to minimize the losses, but in major lettuce producing areas like Punjab and Haryana, the soils are alkaline and calcareous, however due to high pH and carbonate levels, the calcium content can’t be released into the soil solution. This reduced availability when combined with low organic matter and poor aeration in intensively farmed sandy loams and therefore, the use of highly soluble nano-calcium in the form of foliar application is essential so that the nutrient is easily available to the plants during the short growth period.
       
However, excessive usage of fertilizer and insufficient organic matter have resulted in negative consequences such as decreased soil fertility, soil erosion, air permeability and water retention capacity, widespread malnutrition, negative effects on soil health particularly in acidic soils, food taste, food poisoning and pesticide residue and water erosion and pollution and health hazards. Therefore, there is a need to implement a potential agro-technique or innovation such as nanotechnology to achieve the concept of sustainable agriculture (Manisankar et al., 2022). Nano-fertilizer is required in less quantity and it delivers nutrients at the right place and right time, so it reduces the chemical load of fertilizers on the soil and increases nutrient use efficiency as compared to traditional methods of fertilizers application (Acharya et al., 2024). The application of nanotechnology formulation to the input of agricultural crops is one of the proposed tools for sustainable intensification (Chandini et al., 2019). To enhance fertilizer absorption and nutrient usage effectiveness, nano-fertilizers which contain larger surface areas and particle sizes that are smaller than those of plants’ roots and leaves are a potential alternative. Absorption rates of nano-fertilizers by plants can be enhanced through combinations with organic materials while reducing nutrient loss as well as lowering environmental contaminations (Sharma et al., 2022). As there is better nutrient use efficiency and reduced nutrient loss, nano-fertilizers enhances yield and nutritional quality of crops (Iqbal, 2019).  Additionally, foliar application of minerals in the form of nano-fertilizers provides a means of rapidly correcting plant nutrient deficiencies as it helps in controlling crop growth rate, root development and available to the plant more efficiently (Hu et al., 2020). The advantages of foliar application of calcium fertilizers is ensured balanced nutrition for enhancing vegetative growth and plant biomass, while mitigating accumulation of harmful nitrates in leafy greens (Thajeel and Bayati, 2026) application of ca-fertlizers prevents tip burn which is very undesirable in leafy greens and salad crops, adequate calcium increases the shelf life by stabilizing the cell membranes. The use of nano fertilizers in small quantities that directly feed into the plant metabolism, will provide farmers an added benefit of increasing yield and quality.

The study was conducted at Vegetable Research Farm of Lovely Professional University, Phagwara, during winter season. The experiment was laid out in factorial randomized block design (FRBD) with three replications and ten treatments. The seedlings of lettuce variety Iceberg and Grand rapid were raised in pro-trays during the 2^nd week of September using soilless growing media (Cocopeat, Vermicompost and Perlite, 2:1:1) and transplanted at a spacing of 45x30cm during 1^st week of November 2021 on raised beds to provide proper aeration, drainage and ease of other intercultural operations such as weeding. The experimental plot have sandy loam type of soil, where previously bottle gourd was cultivated. Prior to transplantation, the soil sample was collected and tested for initial physico-chemical properties and found that, the pH was 6.45, electrical conductivity was 0.232 (S/m), organic carbon content was 0.622% and the NPK composition of the soil was 210:20.02:190 kg/ha. A complete dosage of potassium and phosphorous and 50% of nitrogen were applied at the time of transplanting. Thereafter at 15 days interval, plants were sprayed (thrice) with Ca nano-fertilizers as foliar application as per the treatments (C₀: 0 ppm, C₁: 10 ppm, C₂: 20 ppm, C₃: 30 ppm and C₄: 40 ppm). Light irrigation was given right after transplanting of the seedlings; at the 20^th day after transplantation, water soluble NPK fertilizer 19:19:19 was sprayed @ 3g/l water. Five plants were selected randomly from each plot and tagged to record the data on growth and yield attributes. The growth parameters were recorded at an interval of 15 days, starting from 30 days after transplanting until harvesting. Harvesting was done when the leaves were firm and tender. The various parameters of yield, quality and economics were estimated after the harvesting of the tender leaves. Ascorbic acid content of the fresh leaves were measured following 2,6-dichlorophenol indophenol dye technique, chlorophyll index was measured using a SPAD-502 meter at the time of harvesting, chlorophyll content was estimated using spectrophotometric method and observing the supernatant under 645 and 663 nm wavelength as suggested by Sadasivam and Manickam  (1992) and Slamet et al., (2017), TSS was measured using a refractometer and dry matter was determined by using the formula i.e.,
 

 

 
All the data recorded on various parameters were subjected to statistical analysis using OPSTAT software. The statistical significance was tested by F value and the critical difference (CD) was calculated at 5% level of significance.

The foliar application of Ca nano-fertilizer at regular interval  had a significant influence on the growth, yield, quality and B:C of lettuce cultivation, the data of which is presented in Table 1, 2, 3 and 4 respectively. The results obtained from the experiment are discussed under suitable headings.

Effect of foliar application of Ca nano-fertilizers on growth parameters of lettuce
 
At 30, 45 and 60 DAT, the maximum plant height, number of leaves per plant and leave area were recorded in Ca nano-fertilizer @ 40 ppm (C₄) i.e., 16.63 cm, 33.76 leaves and 383.50 cm² respectively followed by Ca nano fertilizer @ 30 ppm (C₃) i.e., 16.17 cm, 31.19 leaves and 355.00 cm² respectively, whereas the minimum value was observed in C₀ i.e., 14.57cm, 24.66 leaves and 245.00 cm² respectively. The maximum plant height, number of leaves and leaf area in the treatment C₄ might be due to adequate supplies of Ca that leads to the well-formed and healthy leaves. Calcium (Ca) is one of the main constituents of cell walls in plants and plays an extremely significant role in producing plant tissues and it enables plants to grow better. The result is in close conformity with the findings of Merghany et al., (2019) who reported that foliar application of higher concentration of NPK nano-fertilizer on cucumber proves beneficial for its growth. Among the variety, V₂ (Grand Rapid) was found significantly superior over V₁ (Iceberg) in terms of plant height, number of leaves and leaf area i.e., 15.51 cm, 29.83 leaves and 383.50 cm² respectively. The higher plant height in V₂ (Grand rapid) over V₁ (iceberg) might be because of the varietal characteristic of having loose leaf and exceptionally fast-growing habit. The result is in support with the findings of Ramaskevicine et al., (2017), where they found superior plant height in the variety, Grand Rapid over ‘Austrache Gel’. The result of interaction effect of Ca nano fertilizer and varieties were found significant for all the growth parameters irrespective of the growth stages. Among the treatment combinations, the maximum plant height was found in the treatment C₄V₁ (Ca nano-fertilizer @ 40 ppm + Iceberg) i.e., 16.70 cm, which was also found at par with the treatments C₃V₁ and C₄V₂ i.e., 16.57 cm each. The maximum number of leaves per plant and leaf area were found in the treatment C₄V₂ i.e., 33.88 leaves and 383.5 cm² respectively, followed by C₄V₁ i.e., 33.64 leaves and 377.33 cm² respectively.  While the minimum plant height, number of leaves per plant and leave area i.e., 14.20 cm, 22.53 leaves and 245.00cm² respectively were observed in C₀V₁ (Ca nano-fertilizer@ 0ppm + iceberg). The maximum number of leaves in the treatment combination C₄V₂ might be due to the adequate supply of calcium nano fertilizers through foliar spray leading to increased synthesis of chlorophyll which in turn increase the metabolic reaction and photosynthesis. This result is also supported by the finding of Yassen et al., (2017), who reported that foliar application of higher concentration of SiO₂ nano fertilizer on cucumber proves beneficial for number of leaves. Ramaskevicine et al., (2017) also reported significant differences in varietal performances of lettuce to foliar application of Nitrate nano-fertilizer. The maximum leaf area in the treatment C₄V₂ might be due to foliar application of Ca nano fertilizers that helps in protein synthesis and regulating the effect of photosynthesis. The result is supported by the findings of Khanm et al., (2017), where they found superior leaf area with higher concentration of ZnO nano-fertilizers and ZnSO₄.
 
Effect of foliar application of Ca nano-fertilizers on yield parameters of lettuce
 
The maximum fresh weight of leaves, yield per plot and yield per hectare (t) were recorded in foliar application of Ca nano-fertilizer @ 40 ppm (C₄) i.e., 126.83g, 2.54 kg and 9.40 t respectively followed by Ca nano fertilizer @ 30 ppm (C₃) i.e., 115.33g, 2.31 kg and 8.54 t respectively. While, the minimum values were observed in C₀ i.e., 98.17 g, 1.96 kg and 7.27 t respectively. Calcium plays a vital role of in meristem growth, cell elongation and nutrient uptake which enhance the vegetative growth and leads to a greater number of leaves. Foliar application of these nutrients might have helped plants in maintaining vigor of the plant, increased uptake of nutrients and more photosynthesis and other metabolic activities leading to more rapid growth, optimizing the yield. The result is supported by the findings of Palmqvis et al., (2017), where they found an increase in leaf growth rate with application of Fe₂O₃ nanoparticles. Tameemi et al., (2019), also found superior fresh weight of leaves with higher concentration of chelated iron nano-fertilizers. Maximum fresh biomass was also observed from optimum ZnO nano-particles application @ 10 mg/kg soil on lettuce (Jiangbing et al., 2017). Salama et al., (2022) also reported superior yield per plot with foliar application of higher concentration of MnO₂ nano-fertilizer. Among the variety under study, V₂ (Grand Rapid) was found significant over V₁ (Iceberg) in terms of fresh weight of leaves (g), yield per plot (kg) and yield per hectare (t) i.e., 112.67 g, 2.25 kg and 8.35 t respectively. The superiority of fresh weight in V₂ (Grand Rapid) over V₁ (Iceberg), might be due to varietal characteristics of having rapid growth and loose leaves, more number of leaves and broader leave size.  Among the treatment combinations, the maximum fresh weight (g), yield per plot and yield per hectare (t) was found in the treatment C₄V₁ i.e., 127.00 g, 2.54 kg and 9.41 t respectively followed by C₄V₂ i.e., 126.67 g, 2.53 kg and 9.38 t respectively. While the minimum fresh weight of leaves i.e., 97.67g was observed in C₀V₁. The significantly higher yield per hectare in the treatment combination C₄V₂ might be due to the morphological characters of the variety and optimum concentration of calcium nano-fertilizer which had helped to stabilize cell walls structures, ensuring proper overall health and growth leading to increased number of leaves and leaf weight which in turn results to higher yield.
 
Effect of foliar application of Ca nano-fertilizers on quality parameters of lettuce
 
The maximum ascorbic acid content, chlorophyll index, chlorophyll content, TSS ÚBrix and dry matter were found in foliar application of Ca nano-fertilizer @ 40 ppm (C₄) i.e., 4.18 mg/100 g, 40.33, 0.68 mg/ml, 6.00°Brix and 13.41% respectively; while the minimum values were recorded in C_0­ for all parameters i.e., 0.41, 19.50, 0.58 mg/ml, 4.85°Brix and 10.47% respectively. Among varieties, V₂ has superior content of ascorbic acid, chlorophyll index, chlorophyll content, TSS and dry matter i.e., 0.45 mg/100 g, 32.83, 0.64 mg/ml, 5.61°Brix and 12.83% respectively. Among treatment combinations, the maximum ascorbic acid content and TSS were obtained in the treatment combination C₄V₁, i.e., 4.71 mg/100 g and 6.00°Brix respectively. Helaly  et al. (2021) also found increased in the levels of ascorbic acid with the treatment of nano-nitrogen. The maximum chlorophyll index, chlorophyll content and dry matter were found in C₄V₂ i.e., 32.83, 0.71 mg/ml and 14.21% respectively. While, the minimum values were observed in C₀V₁, i.e., 19.23, 0.54 mg/ml and 8.12% respectively.
 
Economics
 
The economic analysis was carried out after harvesting of produce considering the prevailing prices of all the inputs in the market. The lowest cost of cultivation (Rs. 93,140.00/ha), gross return (Rs 2,17,037.04) and net income (Rs. 1,23,897.04) were recorded in C₀V₁ whereas, the highest cost of cultivation, gross income and net income were recorded in C₄V₂ i.e., Rs. 1,12,956.00/ha, Rs. 3,00,246.91/ha and Rs 1,87,290.91/ha respectively, which was followed by C₄V₁ i.e., Rs. 1,12,916 /ha, Rs.2,82,222.22/ha and Rs. 1,69,306.22/ha respectively. The highest benefit cost ratio was observed in C₄V₂ i.e., 1.66, followed by in C₁V₂ i.e., 1.63. While the lowest B:C ratio was observed in C₀V₁ i.e., 1.33. Highest net income obtained from C₄V₂ might be due to higher marketable yield resulting to higher gross return. The higher net income in the treatment C₄V₂ has resulted to higher B:C ratio. The comparatively higher cost of cultivation in rest of the treatment other than C₀V₁ was due to higher inputs. 

The perusal from this study showed that foliar application of Ca nano-fertilizer promotes the performance of lettuce in terms of all the parameters under study and thus it can be concluded that, for obtaining better growth, higher yield with better quality and higher returns of lettuce, Ca nano-fertilizers as a foliar spray @ 40 ppm along with the recommended dosage of fertilizers may be recommended to farmers under Punjab condition. However, since the result is based on one year observations, need of continuous effort was felt to standardize the use of Ca nano- fertilizer as foliar application in lettuce.

The present study was supported by the School of Agriculture, Lovely Professional University.
 
Disclaimers
 
The views and conclusions expressed in this article are solely those of the authors and do not necessarily represent the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect losses resulting from the use of this content.
 

The authors declare that there are no conflicts of interest regarding the: publication of this article. No funding or sponsorship influenced the design of the study, data collection, analysis, decision to publish, or preparation of the manuscript.