The tobacco variety (Nicotiana tabacum L. ‘Yunyan 87’) was used in this study, which has good disease resistance, coordinated dehydration and drying, and is easy to bake. The field experiment was conducted in Lanshan County, Yongzhou City, Hunan Province, China (25.18°N, 112.18°E) from March to August 2024. The specific location is shown in Figure 1 . The annual average temperature in this area is 18°C to 19 °C, the annual precipitation is 1400 to 1600 millimeters, and the annual sunshine hours are 1400 to 1600 hours. The climate data from March to August, including temperature, precipitation and hydrothermal index are shown in Figure 2 . The basic physicochemical properties and the microelement content of the soil (0–20 cm) were as follows: pH, 6.73; organic matter (OM), 65.97 mg/kg; alkali-hydrolysable nitrogen (AN), 229.10 mg/kg; available phosphorus (AP), 102.81 mg/kg; available potassium (AK), 355.85 mg/kg; total nitrogen (TN), 3.64 g/kg; total phosphorus (TP), 2.42 g/kg; total potassium (TK), 6.63 g/kg; chloride ion (Cl^-), 5.74 mg/kg; boron (B), 3.69 (mg/kg); available SiO₂, 6.98 mg/kg; manganese (Mn), 38.92 mg/kg; iron (Fe), 357.89 mg/kg; nickel (Ni), 3.21mg/kg; copper (Cu), 2.08 mg/kg; zinc (Zn), 9.14 mg/kg.

Tobacco was transplanted on March 27, 2024, the lower leaves were harvested on June 26, 2024, the middle leaves were harvested on July 15, 2024, and the upper leaves were harvested on August 1, 2024. The apical part was excised 2–3 weeks prior to floral anthesis, and basal leaf removal was implemented when 30–50% of the central inflorescence had reached bloom stage, ultimately retaining 18 functional leaves per plant through systematic defoliation. In order to ensure the growth and development of plants, high ridge cultivation was adopted during transplantation, covered with plastic film. During the period of plant growth, leaf diseases and leaf eating pests were controlled, and solar insecticidal lamps were installed in the field.

Five experimental treatments were established, CK is no fertilization, S0 is normal fertilization, S50 is normal fertilization+750 kg/ha Si fertilizer, S100 is normal fertilization+1500 kg/ha Si fertilizer and S200 is normal fertilization+3000 kg/ha Si fertilizer. The plant spacing and row spacing are 50 × 120 cm. Three replicates were set up for each treatment, with each replicate area of 4 m × 8.4 m, and each treatment was randomly distributed.

The Si fertilizer used contains SiO₂ 50%, CaO 12%, MgO 0.7%, Fe₂O₃ 2.3%, organic matter 10%, humic acid 6% and other trace elements 3%. Fertilizer application refers to Table 1 . The nutrient input of each treatment was 185.4 kg/ha of N, 127.5 kg/ha of P₂O₅, and 430.5 kg/ha of K₂O.

Soil samples ranging from 0–20 cm were gathered from 10 random sites within each plot on March 15, 2024 and after visible plant residues and stones were removed. The soil samples were air-dried, pulverized, and sieved through 2 mm and 0.0149 mm screens for subsequent analysis, including pH, OM, HN, AP, AK, TN, TP, TK, Cl^-, B, available SiO₂, Mn, Fe, Ni, Cu, Zn.

At the flower budding stage and button stage of tobacco, 10 plants with consistent growth and no pests or diseases were randomly selected from each plot. The 3rd, 6th, and 9th leaves were selected from top to bottom for SPAD value measurement. Agronomic traits such as plant height (cm), stem circumference (cm), effective leaves (leaves/plant), maximum leaf length (cm), maximum leaf width (cm), and maximum leaf area (cm²) were recorded for each treatment. At the maturating stage of tobacco, the harvested mature tobacco leaves were baked and divided into three parts, including upper leaves (the 1st to 6th leaves), middle leaves (the 7th to 12th leaves), and lower leaves (the 13th to 18th leaves). Physical properties including leaf length (cm), leaf width (cm), leaf area (cm²), single leaf weight (g), density of leaf(g/m²), leaf moisture content (%), leaf midrib proportion (%), thickness (mm) and opening degree (%) were measured. After physical property assessment, economic traits such as yields, output value, and average price, proportion of high-quality tobacco leaves and proportion of medium to high-quality tobacco leaves were evaluated. Then, the tobacco samples were ground into fine powders for chemical composition analysis, including total sugar, reducing sugar, total N, nicotine, K, chlorine, starch, and protein. At the same time, 10 plants with consistent growth and no pests or diseases were randomly selected from each plot. The plants were dug out, cleaned, and divided into five parts: roots, stems, upper leaves, middle leaves, and lower leaves. Biomass and nutrient content for each part were subsequently measured.

Microsoft Excel 2019 software was used to sort out data, and they were statistically analyzed using analysis of variance (ANOVA) in SPSS version 22.0 software (IBM, Chicago, USA). The significant difference among treatments was calculated by the least significant difference (LSD) and was considered significant when p< 0.05. 

To investigate the impact of different Si fertilizer application rates on the growth of tobacco at different stages, agronomic traits including plant height, stem circumference, effective leaf number, maximum leaf length, and maximum leaf width were measured during the flower bud stage and button stage of tobacco. Results showed that, compared with S0, the plant height of S50, S100, and S200 during the flower bud stage of tobacco significantly increased by 6.05%, 16.57%, and 9.74%, respectively ( Table 2 ). Similarly, during the button stage, this phenomenon also occurred. Compared with S0, the tobacco plant height significantly increased under Si fertilizer treatment, with increases of 15.38%, 16.35%, and 19%, respectively ( Table 2 ). This indicated that Si fertilizer significantly increased the height of tobacco plants. It is worth noting that for tobacco leaves, under Si fertilizer treatment, the maximum leaf length and maximum leaf area of tobacco in the flower bud stage were significantly increased; interestingly, the maximum leaf length of tobacco during the button stage significantly increased by 7.78%, 9.6%, and 6.03%, respectively, while the maximum leaf area was showed the same trend ( Table 2 ). Compared with S0, the maximum leaf width of S200 has significantly increased, with an increase of 7.12% and 15.57% in the flower bud stage and button stage, respectively ( Table 2 ). This indicated that the application of Si fertilizer significantly promoted the growth of tobacco leaves. The effective number of tobacco leaves were increased, with significant increases of 10.20% and 13.33% in S50 and S100 during the bud stage, respectively ( Table 2 ). However, Si fertilizer had no significant effect on the stem circumference of tobacco. In summary, Si fertilizer promotes the growth and development of tobacco leaves and plants.

The SPAD value of tobacco leaves was measured during the bud stage and dome stage. The results indicated that, at the flower bud stage, compared with S0, Si improved the SPAD value of tobacco, and the SPAD value of tobacco leaves in S100 was significantly increased. At the button stage of tobacco, there was no significant difference among the treatments ( Figure 3 ). Collectively, Si was significantly impacted the SPAD value of tobacco in the early stage.

During maturating stage of tobacco, the biomass of different parts of tobacco were measured, it indicated that Si fertilizer was significantly increasing the biomass of various parts of tobacco. Compared with the control, Si fertilizer significantly increased the biomass of tobacco plants, with S50, S100, and S200 significantly increasing by 26.53%, 19.95% and 19.50%, respectively ( Table 3 ). Among the upper leaves, lower leaves, stems, and roots of S50 showed the highest growth, increasing by 17.74%, 20.35%, 28.31% and 48.91%, respectively ( Table 3 ). It is interesting that the middle leaves showed the most significant increasing in S200, reaching 55.32g ( Table 3 ). Overall, these results indicated that Si fertilizer significantly increased the biomass of various parts of tobacco.

In order to investigate the effect of different Si fertilizer application rates on the nutrient content of tobacco, the accumulation of N, P, and K in various parts of tobacco was measured. These results indicated that compared with S0, the N accumulation in S50, S100 and S200 were increased by 31.14%, 22.16%, and 14.66%, respectively ( Figure 4A ). However, among Si treatment, the N accumulation of the lower leaves, stems, and roots in S50 showed the most significantly improvement, which were increased by 27.30%, 142.48%, and 50.15%, respectively ( Figure 4A ). This data indicated that Si was significantly influence the nitrogen content of tobacco, and the application rate of 750kg/ha Si fertilizer has the most significant effect on nitrogen accumulation in tobacco.

Research on tobacco P content found that compared with S0, there was no significant differences in P accumulation of plant and lower leaves in S50, S100, and S200 ( Figure 4B ). The P accumulation of roots in S50, S100 and S200 were increased by 56.04%, 38.98%, and 29.14%, respectively ( Figure 4B ). In contrast, the P accumulation of upper leaves of S200 were significantly decreased by 56.72%, while the P accumulation of stem of S200 were significantly increased by 32.13%; and on middle leaves, S50 was significantly decreased by22.66% ( Figure 4B ). These results indicated that Si fertilizer significantly changed P accumulation content of tobacco.

The application of Si significantly increased the K accumulation in various parts of the tobacco. Compared with S0, the K accumulation in S50, S100 and S200 were significantly increased by 28.08%, 28.30%, and 25.51%, respectively ( Figure 4C ). Interestingly, the K accumulation of upper leaves in S50, S100 and S200 were no significant difference, the K accumulation of middle leaves in S50, S100 and S200 were significantly increased by 18.86%, 36.18%, and 59.54%, respectively; similarly, the K accumulation of lower leaves and stem were significantly increased ( Figure 4C ). The K accumulation of roots in S50, S100 were significantly increased by 55.40%, 50.32%, and 20.83%, respectively, reaching0.59 g/plant and 0.58 g/plant ( Figure 4C ). In summary, the nutrient content of plants was significantly affected by Si fertilizer, and the application rate of moderate Si fertilizer (750–1500 kg/ha) is better.

To explore the impact on the fertilize use efficiency, the utilization efficiency of N, P and K were measured, we found that Si increased the fertilizer use efficiency. Compared to S0, the N use efficiency of S50, S100 and S200 were increased by 43.71%, 31.10%, and 27.42%, respectively ( Figure 4D ). And the K use efficiency of S50, S100 and S200 were improved by 44.25%, 44.63%, and 40.25%, respectively ( Figure 4F ). While there was no significant difference among the treatments in P use efficiency ( Figure 4E ).

In order to elucidate the impact of Si on economic characteristics, five indicators including yield, output value, average price, proportion of high-quality tobacco leaves and proportion of medium to high-quality tobacco leaves were studied. The results showed that compared with S0, the yields of S50, S100 and S200 were increased by 15.70%, 13.32%, and 17.00% respectively; similarly, the output values were increased by 30.76%, 23.14%, and 21.39% respectively ( Table 4 ). In addition, the proportion of high-quality tobacco leaves and medium to high-quality tobacco leaves were both the highest in S50, which were 80.11% and 94.75%, respectively, the average price of S50 was significantly increased by 13.08% compared to S0 ( Table 4 ). These results indicated that Si increased the yield and output value of tobacco, improved economic benefits. Furthermore, the effect of moderate Si fertilizer application is better.

In order to study the effect of Si on tobacco quality, the physical properties of the upper, middle, and lower leaves of tobacco were tested, including single leaf weight, density of leaf, leaf moisture proportion, leaf midrib proportion, opening degree, thickness, leaf length, leaf width and leaf area. On upper leaves, compared with S0, the single leaf weight in S50, S100 and S200 were increased by 25.17%, 11.55%, and 10.86%, respectively; and the leaf length of tobacco were significantly increased by 7.99%, 8.84%, and 6.56%, respectively; but the density of leaves was decreased by 6.08%, 9.12%, and 18.80%, respectively, S200 was significantly decreased to 108.42 g/m² ( Table 5 ). Data showed that Si promoted the growth of upper tobacco leaves, reduce tobacco density, and improved tobacco quality. Compared with S0, the leaf midrib proportion in S50 and S100 were decreased by 10.53% and 2.40%, respectively, while the leaf midrib proportion of S200 was increased by 3.95% ( Table 5 ). This indicate that high application of Si fertilizer actually increased the stem content of upper leaves, which is not conducive to improving the usability of tobacco leaves.

On middle leaves, compared with S0, the leaf midrib proportion of S50, S100 and S200 were decreased by 19.96%, 8.58%, and 11.12%, respectively; the leaf width was increased by 7.97%, 5.58%, and 14.74%, respectively, S200 was significantly increased to 19.20 cm; similarly, the leaf area was increased by 9.75%, 8.12%, and 19.35%, respectively ( Table 5 ). This indicates that Si can promote the growth of tobacco leaves in the middle, reduce the stem content of tobacco leaves, and then increase yield.

The lower leaves of tobacco were impacted by Si. On lower leaves, compared with S0, the leaf midrib proportion of S50, S100 and S200 were increased by 7.48%, 12.50%, and 10.40%, respectively; the leaf length in S50, S100 and S200 were increased by 9.30%, 4.12%, and 7.44%, respectively, S50 was significantly increased to 54.87 cm; the leaf area in S50, S100 and S200 were increased by 14.56%, 5.49%, and 14.81%, respectively ( Table 5 ). In summary, Si affected the physical properties of tobacco leaves, promoted the growth of tobacco leaves, and increased the availability of upper and middle leaves. However, high usage of Si fertilizer actually increased the leaf midrib proportion.

Similarly, in order to investigate the effect of Si on the quality of tobacco, chemical indicators of tobacco leaf from different parts were tested. The results indicate that Si fertilizer improved the applicability of tobacco leaves. On the upper leaves, compared with S0, the content of reducing sugar in S50 was significantly increased by 15.21%, while S100 and S200 were significantly decreased by 13.92% and 21.93%, respectively; the K content of S50, S100 and S200 were significantly increased by 6.42%, 12.10%, and 11.56%, respectively; the chlorine content and the ratio of reducing sugar to total sugar of S50 were significantly increased by 20.44% and 19.09%, respectively; the nicotine content of S200 was significantly increased by 13.99%; while the total sugar, starch content and the ratio of total sugar to nicotine of S200 were significantly decreased by 14.29%, 12.05%, and 24.42%, respectively ( Table 6 ). On the middle leaves, compared with S0, the K content of S100 and S200 were significantly increased by 21.60% and 24.40%, respectively; the nicotine of S50 was significantly increased by 18.56%, the chlorine content of S100 was significantly decreased by 11.79%; the total sugar, chlorine content and the ratio of K content to chlorine content of S200 were significantly increased by 15.50%, 26.72%, and 38.35%, respectively ( Table 6 ). On the lower leaves, compared with S0, the K content of S100 was significant increased by 8.86%; the chlorine content of S50, S100 and S200 were significantly reduced by 22.25%, 18.57%, and 20.44%, respectively; the ratio of K content to chlorine content of S50, S100 and S200 were increased by 30.56%, 33.29% and 33.15% respectively; the reducing sugar content and the ratio of reducing sugar to total sugar of S50 were significantly increased by 23.96% and 15.05%, respectively; while the starch content of S50 was significantly decreased by 18.98%; the ratio of total sugar to nicotine of S100 was decreased by 7.52%; the N content of S200 was significantly decreased by 15.26%, while the starch content of S200 was significantly increased by 15.14% ( Table 6 ).

Chlorophyll, as an essential pigment for photosynthesis, directly affects leaf photosynthetic capacity and organic matter accumulation (Zhang et al., 2018). Studies indicated that SPAD values were positively correlated with chlorophyll content and dry matter accumulation (Condorelli et al., 2018). Marxen et al. (2016) demonstrated that Si enhanced light interaction in plants. Researchers showed that Si application in rice and maize increased the maximum leaf area, aboveground dry matter weight and yields (Pati et al., 2016; Biswal et al., 2024.). In this study, the plant height and maximum leaf area of tobacco were increased under silicon treatment ( Table 2 ).

This study confirmed that Si fertilizer treatment significantly increased the SPAD values and biomass of tobacco ( Figure 3 ; Table 3 ). At the flower bud stage, the S100 exhibited significantly higher SPAD values than other treatments, although no significant differences were observed among the remaining treatments, their SPAD values remained numerically higher than S0 ( Figure 3 ). That indicated that moderate Si supplementation improved photosynthetic capacity by elevating chlorophyll content, improved tobacco growth, the plants height and leaf area were significantly increased (Huang et al., 2024). This effect may be attributed to silicon’s ability to optimize light utilization through increased leaf conductivity (Verma et al., 2020b). Besides, moderate Si application promoted systemic growth by stimulating root development and nutrient absorption (Parecido et al., 2025). The whole plant biomass in S50, S100 and S200 were significantly increased by 26.53%, 19.95%, and 19.50%, respectively ( Table 3 ). However, at the button stage of tobacco, there was no significant differences in SPAD values, which likely due to natural leaf senescence during later growth stages, which reduced silicon’s chlorophyll synthesis benefits (Luyckx et al., 2017). In addition, excessive application of Si fertilizer may lead to thicker leaves, decreased stomatal conductance, affected CO₂ absorption and photosynthetic efficiency, decreased SPAD values, poor root development and stunted plants (Huang et al., 2024). But this phenomenon was not found in this study ( Figure 3 ).

A large number of researchers found that the application of Si increased the yields of corn, cotton, rice and sugarcane (Yan et al., 2021; Li et al., 2018; Sakurai et al., 2015; Verma et al., 2020a). In this study, the application of Si increased the yields of tobacco as well, which mainly due to Si promoted the growth of tobacco and increased its biomass ( Table 4 ). Additionally, moderate Si improved the physical properties and chemical balance of tobacco leaves, thus enhanced industrial usability, and the proportion of medium to high-quality tobacco was increased, besides, the proportion of medium to high-quality tobacco in the S50 treatment reached 94.75%, which increased the average price of tobacco leaves ( Table 4 ). The increase of production and average price which together lead to an increase in output value, which is beneficial for the income of tobacco farmers and the development of the industry. However, excessive investment in Si may weaken this benefit.