Development and Comparative Assessment of Tobacco Waste-Based Composts for Sustainable Agriculture

Abstract

The global demand for compost, produced through the bioconversion of organic waste into nutrient-rich soil amendments, is increasing due to the adverse environmental, health, and economic impacts of synthetic fertilizers. Compost use offers a cost-effective and sustainable alternative, improving soil fertility and long-term productivity. However, the potential of tobacco waste as a composting substrate remains insufficiently investigated. This study aimed to evaluate the feasibility of utilizing tobacco waste as a composting feedstock and to develop an optimized composting method. Tobacco waste (scrap leaves and midrib stems) was composted with cow manure in earthen pots to promote decomposition and nutrient mineralization, and its performance was compared with compost produced from cow manure and vegetable waste (vegetable leaves). Vermicomposting, which involves the addition of earthworms to conventional compost treatments, was also implemented to enhance composting efficiency and nutrient release. The final composts, both conventional and vermicompost, were analyzed for organic carbon (OC), nitrogen (N), phosphorus (P), potassium (K), sulfur (S), and the maturity duration. Among the three conventional compost variants, the mixture of cow manure and tobacco leaves had the highest nitrogen concentration at 1.45% and the cow manure and tobacco stems had 1.23% as the second best. Cow manure and tobacco stem compost had the highest K content of 1.13%, followed by tobacco leaves (0.99%). Sulfur levels were also found to be higher in the tobacco stem compost compared to the other compost types, with the highest value of 0.56%, followed by tobacco leaves (0.23%). All three vermicompost variants outperformed their conventional counterparts in terms of nutrient concentrations and achieved maturity in shorter durations. The cow manure with tobacco stem mixed vermicompost was notable for its elevated potassium (1.35%) and sulfur (0.89%) contents. The results indicate that vermicomposting offers a faster and more nutrient-enriched composting approach, particularly with tobacco waste. Incorporating tobacco waste into this process has the potential to produce high-quality compost, presenting a sustainable strategy for waste valorization and enhancing soil fertility.

1. Introduction

Bangladesh faces a critical issue in its agriculture sector due to the progressive depletion of soil organic matter. Presently, most soils in Bangladesh contain less than 2% organic matter, and about 45% of cultivable land has levels below 1% [1]. This alarming depletion occurred due to intensive farming, overuse of chemical fertilizers, and minimal application of organic amendments, leading to reduced soil fertility and stagnating crop productivity in several regions [2,3]. Moreover, rapid urbanization and industrialization have significantly increased solid waste generation from domestic, commercial, and agro-industrial sectors. This increase in waste, driven by population growth and rising living standards, creates a serious challenge to environmental sustainability [4].

Rice, jute, sugarcane, potato, pulses, wheat, tea, and tobacco are the principal crops of Bangladesh, contributing about 56% of the total agricultural GDP [5]. The tobacco industry remains economically significant, with about 1% of the national GDP allocated to tobacco-related activities [6]. Despite occupying only 0.22% of agricultural land and employing less than 0.5% of the labor force, tobacco remains economically lucrative compared to many staple crops [7]. During the 2020–2021 cropping year, 100,285 acres of land were cultivated with tobacco, yielding 92,327 metric tons [8]. Thus, considering 26–32% waste generation of the total production, the estimated waste stream in Bangladesh could be about 24,000 to 30,000 tons in 2020–2021, although no nationwide survey has confirmed this figure [9]. In most tobacco-growing areas, such waste is used for making low-quality domestic tobacco products, landfilled, or burned for cooking or in brickfields without proper treatment, leading to air, water, and soil pollution.

Globally, tobacco waste was estimated at 1.25 million metric tons in 2005 [10]. Tobacco cultivation and manufacturing generate significant amounts of waste, as approximately 30% of the tobacco crops end up as waste [9], primarily comprising midribs and scraps [11]. The midrib, a central vein, must be removed to prevent manufacturing defects such as holes and altered smoking characteristics [12]. Scrap consists of small, broken leaf pieces unsuitable for further processing [13]. Tobacco has high nicotine and organic carbon content; it is not suitable for direct landfill disposal [14]. Considering the chemical profile, tobacco waste is highly heterogeneous and rich in bioactive compounds, including nicotine, solanesol, chlorogenic acid, and phenolic substances [15]. Tobacco waste is a significant issue in developed countries, including Bangladesh, with economic, environmental, and social implications. The unplanned disposal of tobacco waste has led to various environmental issues, including air and water pollution [16]. Due to these factors, tobacco waste management has garnered considerable attention over the past few years [17].

Studies suggest that tobacco waste has potential uses in organic fertilizer production, briquettes for energy, or as feedstock for reconstituted tobacco [18]. However, most of these prospects pose environmental risks or require costly pretreatment [19]. One of the promising solutions is composting, an aerobic microbial process that transforms organic waste into stable humus and nutrients, thereby improving soil fertility and structure while mitigating environmental risks [20]. Composting usually involves three microbial phases, where bacteria and fungi break down sugars, proteins, and complex compounds into stable organic matter [19]. Nicotine and other alkaloids present in tobacco waste are known to partially degrade during composting through microbial oxidation. However, degradation efficiency depends on temperature, microbial diversity, and duration [21]. Organic fertilizers, such as compost and manure, have long been used to enhance the soil’s physical, chemical, and biological properties [22]. The presence of organic matter in the soil is crucial for maintaining soil fertility and reducing nutrient losses. Thus, composting is a viable option that converts waste into an organic fertilizer, rich in nutrients and organic matter.

However, traditional composting often requires several months to break down organic waste completely, delaying nutrient availability. Again, poorly managed piles can produce unpleasant odors and release methane or nitrous oxide, contributing to greenhouse gas emissions. In contrast, vermicompost exhibited significantly higher nutrient concentrations than conventional compost, and when incorporated into soil, it supported greater microbial abundance and activity, resulting in enhanced ryegrass yields [23]. Earthworms and microbes break down waste more rapidly in vermicomposting, producing compost in 1–3 months. Composting is an aerobic decomposition process mediated by microorganisms, while vermicomposting integrates the synergistic activity of microorganisms and earthworms [24]. Vermicomposting is often considered superior to conventional composting due to its enhanced pathogen suppression [25] and its greater efficacy in improving soil aeration, water-holding capacity, and microbial diversity. Numerous studies have demonstrated that vermicompost can substantially increase crop yield and quality [7].

Although tobacco waste has been investigated for uses such as reconstituted tobacco production [26], briquettes, or the extraction of valuable compounds [27], its application in soil amendment through composting or vermicomposting has received limited attention. To date, we are not aware of any comprehensive studies that have compared the nutrient profiles of compost and vermicompost produced from tobacco waste.

Therefore, this study aims to test whether the integration of tobacco waste with conventional composting and vermicomposting processes can produce a nutrient-rich organic amendment comparable to composts derived from traditional biomass such as vegetable residues. Specifically, the study investigates whether the addition of tobacco residues influences compost nutrient enrichment and maturity when compared across different biomass types.

2. Materials and Methods

2.1. Study Area

The study was conducted in Saptibari, Lalmonirhat District, located in the northern part of Bangladesh. It lies between 25°89 North latitude and 89°39 East longitude. The area experiences tropical weather, receiving approximately 2500 mm of rain each year, primarily during the monsoon season from June to October, with July and August being the rainiest months [28]. The average temperature and precipitation status are described in the appended Figure 1 [29]. Ambient temperature, rainfall, and relative humidity directly influence moisture retention, aeration, and microbial metabolic activity, which collectively determine the rate of organic matter decomposition and compost maturity [30]. Seasonal variations in rainfall and temperature can accelerate or delay the thermophilic and mesophilic phases, thereby affecting nutrient stabilization and humification [23,31].

Figure 1. Average temperature and precipitation of Lalmonirhat, Bangladesh.

2.2. Materials Used for Composting

The study was set on the farmer’s premises at Dologram village, Lalmonirhat, Bangladesh. Study materials such as cow dung, vegetable leaves, tobacco stem, and tobacco leaf were collected from the farmer’s house. The stems were cut into pieces measuring 1 to 2 cm in size to accelerate decomposition. Earthworms (Eisenia fetida), essential for vermicomposting [32], were collected from the local NGO, RDRS (Rangpur Dinajpur Rural Service). Additionally, traditional earthen pots were purchased from a village market and used as composting containers due to their porous nature, which supports microbial activity. These materials were used for the development of both traditional compost and vermicompost in the study.

2.3. Preparation of the Compost

Compost preparation is a critical process, as it directly influences the quality and effectiveness of the final product [33]. In this study, the process was carried out through a series of systematic steps. At first, composting materials were selected based on the study design. For conventional compost, three combinations were prepared: (i) cow manure and vegetable leaves, (ii) cow manure and tobacco leaves, and (iii) cow manure and tobacco stems. Similarly, for vermicompost, three mixtures were used: (i) cow manure, vegetable leaves, and earthworms, (ii) cow manure, tobacco leaves, and earthworms, and (iii) cow manure, tobacco stems, and earthworms. Representative samples of each raw material, ranging from 10 to 20 g, were collected for laboratory analysis before full-scale composting (applicable for conventional compost only). The carbon-to-nitrogen (C:N) ratio of each sample was determined. Based on the test results, the C:N ratios were then adjusted using a rational method, as presented in Table 1, Table 2 and Table 3. Proper adjustment of the C:N ratio ensured optimal decomposition and nutrient balance in the resulting composts, as mentioned in the C/N Ratio-CORNELL Composting [34] experiment. The study was conducted under on-farm conditions to assess realistic farmer-level composting conditions rather than controlled-lab composting, so the initial OC could not be standardized independently. However, it was indirectly controlled through the C:N ratio adjustment using the rationing method.

Table 1. Adjustment of the C:N Ratio by the Rationing Method for Different Feedstock Combinations.

Primary Substrate	Co-Substrate	Average C:N Ratio of Components	Mixing Ratio (by Weight)	Rationing (C:N Contribution)	Adjusted C:N Ratio	Remarks
Cow manure	Vegetable leaves	17.56:1 (Cow manure), 78.67:1 (Vegetable leaves)	4:1	70.24:4 + 78.67:1 = 148.91:5	29.78:1	Ideal (≈30:1), sine qua non of perfect composting
Cow manure	Tobacco leaves	17.56:1 (Cow manure), 70.67:1 (Tobacco leaves)	4:1	70.24:4 + 70.67:1 = 140.91:5	28.18:1	Suitable for composting (within 25–35:1 range)
Cow manure	Tobacco stems	17.56:1 (Cow manure), 98.76:1 (Tobacco stem)	4:1	70.24:4 + 98.76:1 = 169:5	33.80:1	Suitable for composting (within 25–35:1 range)

The C:N ratio of each compost mixture was adjusted using the rationing method, where the carbon and nitrogen contributions of each component were proportionally combined based on their fresh-weight ratios. The target range for effective composting (25:1–35:1) was achieved across all treatments, with the mixture of cow manure and vegetable leaves yielding an adjusted proportion of 29.78:1, often regarded as the sine qua non of optimal composting [31].

The raw materials were proportioned based on predefined mixing ratios. For conventional compost, the ratio of cow manure to vegetable leaves, tobacco leaves, and tobacco stems was maintained at 4:1. For vermicompost, the proportion of cow manure, plant material (vegetable leaves, tobacco leaves, or stems), and earthworms was 4:1:0.25, ensuring a balanced environment for microbial and worm activity.

The composting process followed a stepwise procedure beginning with raw material sourcing from nearby tobacco-growing villages and local vegetable markets. The collected materials were subjected to sample collection and characterization to determine their initial organic carbon and nitrogen contents. Based on these results, the C:N ratio adjustment was performed following the rationing method to achieve an optimal balance of approximately 30:1. The prepared feedstocks were then mixed according to the determined ratios and placed in open-field pits for decomposition under natural conditions. This sequential process ensured appropriate substrate selection, proportioning, and setup to promote effective microbial activity and compost maturation. A net was used to cover the upper portion of the earthen pots to keep insects away. All earthen pots were inspected once every three days.

2.4. Maturity Determination

The completion of composting and vermicomposting processes was assessed based on a combination of temperature monitoring and physicochemical analysis, depending on the composting method used. For conventional compost, maturity was primarily determined through daily temperature monitoring using a compost thermometer. Temperature served as a simple and effective indicator of microbial activity and compost stability. Temperature was recorded daily using a digital compost thermometer (accuracy ± 0.5 °C) to produce temperature-time profiles for each treatment. The moisture content of the composting mixture was maintained between 55 and 65% throughout the process by weighing samples every three days and adjusting with distilled water as required. Moisture percentage was calculated gravimetrically by oven-drying subsamples at 105 °C for 24 h.

In the case of vermicomposting, maturity was assessed through detailed analysis of physicochemical properties before and after the composting process. Approximately 25 g of each compost sample was collected, air-dried, ground into fine powder, and stored in airtight plastic packets for laboratory analysis. Key parameters analyzed included pH, electrical conductivity (EC), organic carbon (OC), C:N ratio, nitrogen (N), phosphorus (P), potassium (K), sodium (Na), and calcium (Ca). Vermicompost maturity was confirmed when the pH stabilized within the 6.0 to 8.5 range and EC values remained below 4.0 mS/cm, indicating suitability for agricultural use. Upon achieving maturity, final compost samples from each treatment group were collected and analyzed for major nutrients, i.e., N, P, K, S, and OC, to evaluate compost quality and readiness for field application.

2.5. Sample Analysis

Total Nitrogen content (N): One gram of oven-dry dairy waste samples was taken into a micro-Kjeldahl flask to which 1.1 g catalyst mixture (K₂SO₄:CuSO₄:5H₂O; Se = 100:10:1), 2 mL 30% H₂O₂, and 3 mL H₂SO₄ were added. The flasks were swirled and allowed to stand for about 30 min. Then, heating (380 degrees Celsius) was continued until the digest was clear and colorless. After cooling, the content was taken into a 100 mL volumetric flask, and the volume was made up to the mark with distilled water. A reagent blank was prepared similarly. The digest was used for nitrogen determination.

After digestion was completed, 40% NaOH was added to the digest for distillation. The evolved ammonia was trapped in a 4% H₃BO₃ solution and mixed with 5 drops of a solution containing bromocresol green (C₂₁H₁₄O₅Br₄S) and methyl red. Finally, the distillate was titrated with standard 0.01 NH₂SO₄ until the color changed from green to pink. The final nitrogen percentage is calculated using a formula (Equation 1) that incorporates the volume of acid used in the titration and the initial weight of the sample [35].

$$\%N={\displaystyle \frac{(\mathrm{T}-\mathrm{B})\times \mathrm{n}\times 0.014\times 100}{S}}$$

(1)

where N is the total Nitrogen in percentage, T is the sample titration value (mL) of standard H₂SO₄, B is the blank titration value (mL) of standard H₂SO₄, n is the strength of H₂SO₄, and S is the weight of the dairy waste sample in grams.

Available Phosphorus (P): Available Phosphorus was extracted from the soil by shaking it with 0.5 M NaHCO₃ solutions at pH 8.5, following the composting method. The extracted phosphorus was determined by developing the blue color by SnCl₂ reduction of phosphomolybdate complex, measuring the intensity of color calorimetrically at 660 nm wavelength, and calibrating the reading to the standard P curve [36].

Exchangeable Potassium (K): Exchangeable Potassium was excreted with 1.0 N NH₄ (pH 7) K, which was determined from the extract by a flame photometer and calibrated with a standard K curve [37,38].

Available Sulfur (S): Available Sulphur was extracted with CaCl₂ solution (0.15%). The S content in the extract was estimated turbidimetrically with a spectrophotometer at 420 nm [39].

Organic Carbon (OC): Determining organic carbon in a sample is based on the Walkley-Black chromic acid wet oxidation method [40]. The process works through oxidation, where a strong oxidizing agent, potassium dichromate (K₂Cr₂O₇), reacts with the organic matter in the sample. This reaction is initiated by the heat generated when concentrated sulfuric acid (H₂SO₄) is added. After the reaction is complete, the amount of unreacted potassium dichromate is measured through titration with ferrous sulfate. The amount of organic carbon is then calculated based on the amount of dichromate consumed; therefore, a higher titration value (indicating more leftover dichromate) indicates a lower amount of organic carbon in the original sample [41].

C-N ratio: The C/N ratio was obtained by dividing the C content by the N content of organic material. The C/N ratio is important because microorganisms require approximately 1 part of nitrogen for every 30 parts of carbon for their growth and metabolism. If this ratio exceeds 25:1, the nitrogen will be lacking, and the materials will decompose more slowly, as mentioned in the (C/N Ratio—CORNELL Compost) experiment [34].

2.6. Statistical Analysis

Nutrient data (Organic Carbon, Nitrogen, Phosphorus, Potassium, and Sulfur) were analyzed using one-way ANOVA (Analysis of Variance) and Tukey HSD (Honestly Significant Difference) tests to evaluate differences among treatments. Each compost and vermicompost treatment were represented by one independently managed pile. For each pile, three subsamples were collected from different positions (top, middle, and bottom) and analyzed in triplicate for each nutrient to account for analytical variation. The mean values of these triplicates were used for comparison.

Because true biological replication (i.e., multiple independent piles per treatment) was not available, the results should be interpreted as indicative of directional trends rather than conclusive statistical inference. The analysis was performed to quantify treatment-wise differences and support comparative evaluation between conventional and vermicomposting systems. Statistical computations were conducted using Python (v3.12) and the statsmodels and scipy libraries.

3. Result

3.1. Nutrient Contents in Conventional Composts

The Organic Carbon (OC) content varied across the three conventional compost types. The highest OC concentration was recorded in the compost made from cow manure and vegetable leaves (15.3%). The composts with tobacco leaves and tobacco stems both exhibited the same OC level of 13.0% as shown in Figure 2. This suggests that vegetable leaves contribute more readily to decomposable organic matter than tobacco residues, which may contain more recalcitrant compounds, potentially slowing down the mineralization of organic matter [42]. The OC difference for treatments is substantial, suggesting a better potential for soil organic matter enrichment in the vegetable-based compost [43].

Figure 2. Sunkey diagram on nutrient flow in conventional compost treatments.

Nitrogen content showed a different trend compared to OC. The compost, containing cow manure and tobacco leaves, had the highest nitrogen concentration at 1.45%. The cow manure and tobacco stems had 1.23%, while the cow manure and vegetable leaves compost had the lowest nitrogen content of 0.67% as given in Figure 2. This result suggests that while tobacco-based composts may have a lower OC, they are relatively richer in nitrogen, possibly due to the inherent nitrogenous compounds in tobacco waste [44]. The higher nitrogen concentration in tobacco leaf compost compared to the vegetable leaf compost highlights the potential of tobacco residues as a nitrogen source in composting [45].

The phosphorus level was the highest in the cow manure and vegetable leaves compost, which was 0.42%. The tobacco leaves had 0.32% and the tobacco stems had 0.31% of phosphorus, as shown in Figure 2. Although the differences are not drastic, the vegetable-based compost had more phosphorus than the compost with tobacco stems. This suggests better P availability from vegetable sources, likely due to the higher phosphorus content in leafy greens [46] and improved microbial breakdown during composting.

Potassium content displayed that the cow manure and tobacco stem compost had the highest K content of 1.13%, followed by tobacco leaves (0.99%), and the lowest was observed in vegetable leaf compost (0.70%), as shown in Figure 2. This reveals that tobacco residues, particularly stems, are rich in potassium, which is essential for plant physiological processes such as water regulation and enzyme activation. The tobacco stem compost had more potassium than the vegetable-based compost, suggesting its greater suitability for potassium-deficient soils [47].

Sulfur levels were also found to be higher in the tobacco stem compost compared to the other compost types, with the highest value of 0.56%, followed by tobacco leaves (0.23%), and the lowest in vegetable leaves (0.20%), as shown in Figure 2. The sulfur content in the tobacco stem compost was nearly 2.75 times higher than that in the vegetable-based compost, indicating the potential of tobacco waste, particularly stems, to enhance sulfur availability in soil.

ANOVA (Analysis of Variance) and Tukey’s HSD (Honestly Significant Difference) results for conventional compost quantify the extent to which each nutrient parameter (Organic Carbon, Nitrogen, Phosphorus, Potassium, and Sulfur) varied significantly among treatments.

All nutrient parameters in conventional compost showed statistically significant differences among treatments (p < 0.05), as shown in Table 2. The F-values ranged from 65.03 for OC to 2920.07 for S, all with p-values < 0.05, denoting strong statistical significance. These high F-values indicate that the type of feedstock (vegetable leaves, tobacco leaves, or tobacco stems mixed with cow manure) had a major effect on the nutrient composition of the final composts.

Table 2. One-way ANOVA summary for Conventional Compost.

Source of Variation	DF	Sum of Squares (SS)	Mean Square (MS)	F-Value	p-Value	Significance
OC	2	104.24	52.12	65.03	0.0001	Significant
N	2	2.460	1.230	512.00	0.0000	Significant
P	2	0.022	0.011	209.61	0.0000	Significant
K	2	0.297	0.149	279.20	0.0000	Significant
S	2	0.241	0.121	2920.07	0.0000	Significant
Error	6	(within-group variation)	-	-	-	-
Total	8	-	-	-	-	-

Table 2. One-way ANOVA summary for Conventional Compost.

Source of Variation	DF	Sum of Squares (SS)	Mean Square (MS)	F-Value	p-Value	Significance
OC	2	104.24	52.12	65.03	0.0001	Significant
N	2	2.460	1.230	512.00	0.0000	Significant
P	2	0.022	0.011	209.61	0.0000	Significant
K	2	0.297	0.149	279.20	0.0000	Significant
S	2	0.241	0.121	2920.07	0.0000	Significant
Error	6	(within-group variation)	-	-	-	-
Total	8	-	-	-	-	-

Pairwise comparisons show significant differences (p < 0.05) among most treatments for OC, N, P, K, and S, indicating distinct nutrient dynamics across composting materials as shown in Table 3. All pairwise comparisons (T₁–T₂, T₁–T₃, T₂–T₃) were significant for Nitrogen (N), with tobacco-leaf compost (T₂) having the highest nitrogen concentration due to intrinsic alkaloid nitrogen compounds present in tobacco residues. For Potassium (K) and Sulfur (S), both elements showed highly significant differences across all treatments, with the tobacco stem compost (T₃) emerging as the richest source, reflecting the high mineral content inherent in stem tissues.

Table 3. Tukey HSD post hoc test for Conventional Compost.

Nutrient	Treatment Comparison	Mean Difference	p-Value	Significance
OC	T1 vs. T2	+2.30	0.001	Significant
	T1 vs. T3	+2.30	0.001	Significant
	T2 vs. T3	0.00	0.998	Not Significant
N	T1 vs. T2	−0.78	0.000	Significant
	T1 vs. T3	−0.56	0.001	Significant
	T2 vs. T3	+0.22	0.059	Not Significant
P	T1 vs. T2	+0.10	0.008	Significant
	T1 vs. T3	+0.11	0.007	Significant
	T2 vs. T3	+0.01	0.871	Not Significant
K	T1 vs. T2	−0.29	0.003	Significant
	T1 vs. T3	−0.43	0.001	Significant
	T2 vs. T3	−0.14	0.242	Not Significant
S	T1 vs. T2	−0.03	0.004	Significant
	T1 vs. T3	−0.36	0.000	Significant
	T2 vs. T3	−0.33	0.001	Significant

Table 3. Tukey HSD post hoc test for Conventional Compost.

Nutrient	Treatment Comparison	Mean Difference	p-Value	Significance
OC	T1 vs. T2	+2.30	0.001	Significant
	T1 vs. T3	+2.30	0.001	Significant
	T2 vs. T3	0.00	0.998	Not Significant
N	T1 vs. T2	−0.78	0.000	Significant
	T1 vs. T3	−0.56	0.001	Significant
	T2 vs. T3	+0.22	0.059	Not Significant
P	T1 vs. T2	+0.10	0.008	Significant
	T1 vs. T3	+0.11	0.007	Significant
	T2 vs. T3	+0.01	0.871	Not Significant
K	T1 vs. T2	−0.29	0.003	Significant
	T1 vs. T3	−0.43	0.001	Significant
	T2 vs. T3	−0.14	0.242	Not Significant
S	T1 vs. T2	−0.03	0.004	Significant
	T1 vs. T3	−0.36	0.000	Significant
	T2 vs. T3	−0.33	0.001	Significant

Here, T₁: Cow Manure + Vegetable Leaves, T₂: Cow Manure + Tobacco Leaves, T₃: Cow Manure + Tobacco Stems.

3.2. Duration of Composting

The composting duration varied depending on the materials used. Figure 3 shows that the mixture of cow manure and vegetable leaves decomposed the fastest, completing in 70 days, likely due to the soft, easily degradable nature of vegetable residues. Compost with cow manure and tobacco leaves took 81 days, while cow manure and tobacco stems required the longest time at 104 days, likely due to their higher lignin and cellulose content. These findings suggest that composting soft-green biomass can accelerate the process of composting due to its high moisture content, low C:N ratio, and low lignin levels, whereas fibrous, lignin-rich materials such as tobacco stems, maize stalks, sugarcane bagasse, or jute sticks extend the decomposition period [48].

Figure 3. Temperature-Time profile showing thermophilic and maturation phases for different conventional compost treatments.

3.3. Nutrient Contents Available in Vermicomposts

Organic carbon levels were the highest in the vermicompost prepared with cow manure, vegetable leaves, and earthworms, which recorded 45.3% OC, followed by tobacco leaves (40.8%) and tobacco stems (38.7%). Vermicompost exhibited higher organic carbon compared to conventional compost due to the synergistic action of earthworms, which accelerates the fragmentation of organic substrates while reducing carbon loss through CO₂ respiration. Earthworms enhance microbial biomass and enzyme activities, leading to the stabilization of humic substances and partial preservation of organic carbon during decomposition [49].

As shown in Figure 4, vegetable-based vermicompost provides greater organic enrichment. This is due to the high degradability of vegetable residues and the active interaction of microbes and worms, as observed by Di et al. (2022) [50]. Nitrogen content was highest in the cow manure, tobacco stems, and earthworm mixture (2.68%), followed by vegetable leaves (2.50%) and tobacco leaves (2.23%), as given in Figure 4 This indicates that tobacco stems can contribute more nitrogen when processed through vermicomposting, despite their higher lignin content [51]. Phosphorus concentrations were relatively close across all treatments, with vegetable leaf-based vermicompost slightly ahead at 1.28%, compared to 1.22% in tobacco leaf and 1.19% tobacco stem composts, as shown in Figure 4. This marginal difference suggests that all organic inputs have a similar potential for phosphorus mineralization.

Figure 4. Sunkey diagram on nutrient flow in vermicompost treatments.

The highest potassium concentration was found in vermicompost made from cow manure, tobacco stems, and earthworms at 1.35%, followed by tobacco leaves (1.28%) and vegetable waste (1.21%), as mentioned in Figure 4. This suggests that tobacco residues, particularly stems, are rich in potassium and effective in increasing the K content during vermicomposting [22]. The sulfur content was also highest in the tobacco stem-based vermicompost, reaching 0.89%, compared to 0.52% in tobacco leaves and 0.40% in vegetable waste, as shown in Figure 4. These results suggest that tobacco stems, though slower to decompose, are valuable sources of sulfur in vermicompost production [52].

ANOVA and Tukey HSD results for vermicompost quantify the extent to which each nutrient parameter (Organic Carbon, Nitrogen, Phosphorus, Potassium, and Sulfur) varied significantly among treatments.

Under vermicomposting, all nutrients also showed significant variation among treatments, confirming enhanced nutrient mineralization and stabilization. The F-values were lower overall, ranging from 11.70 (P) to 1196.01 (S), but still statistically significant (p < 0.05) as shown in Table 4. This reflects that although nutrient variability persisted, the presence of earthworms and enhanced microbial decomposition tended to stabilize nutrient differences across feedstocks. Still, sulfur and nitrogen maintained the highest variation, reaffirming that biomass composition and worm activity strongly influence nutrient transformation efficiency.

Table 4. One-way ANOVA summary for Vermicompost.

Source of Variation	DF	Sum of Squares (SS)	Mean Square (MS)	F-Value	p-Value	Significance
OC	2	220.15	110.08	47.07	0.0002	Significant
N	2	0.273	0.136	47.27	0.0002	Significant
P	2	0.003	0.0015	11.70	0.0085	Significant
K	2	0.017	0.008	13.26	0.0063	Significant
S	2	0.139	0.069	1196.01	0.0000	Significant
Error	6	(within-group variation)	-	-	-	-
Total	8	-	-	-	-	-

Table 5 shows that the Tukey HSD analysis confirmed that OC, N, P, K, and S varied significantly across treatment pairs, demonstrating that the synergistic activity of earthworms and microbial communities led to selective nutrient transformation and mineralization. All pairwise comparisons (T4–T5, T4–T6, and T5–T6) were significant for Nitrogen (N), with the tobacco-stem vermicompost (T6) showing the highest N concentration. Phosphorus (P) levels also differed significantly among the treatments, with T4 exhibiting higher phosphorus availability than the tobacco-based vermicomposts. For Potassium (K) and Sulfur (S), both nutrients showed highly significant differences among treatments, with the tobacco-stem vermicompost (T6) emerging as the most enriched. The elevated potassium and sulfur contents in T6 indicate enhanced mineral release from tobacco stem tissues during vermicompost decomposition.

Table 5. Tukey HSD post hoc test for Vermicompost.

Nutrient	Treatment Comparison	Mean Difference	p-Value	Significance
OC	T4 vs. T5	+4.55	0.004	Significant
	T4 vs. T6	+6.64	0.001	Significant
	T5 vs. T6	+2.09	0.048	Significant
N	T4 vs. T5	+0.27	0.038	Significant
	T4 vs. T6	−0.18	0.067	Not Significantns
	T5 vs. T6	−0.45	0.002	Significant
P	T4 vs. T5	+0.07	0.021	Significant
	T4 vs. T6	+0.09	0.014	Significant
	T5 vs. T6	+0.02	0.625	Not Significant
K	T4 vs. T5	−0.07	0.081	Not Significant
	T4 vs. T6	−0.14	0.009	Significant
	T5 vs. T6	−0.07	0.072	Not Significant
S	T4 vs. T5	−0.12	0.018	Significant
	T4 vs. T6	−0.49	0.000	Significant
	T5 vs. T6	−0.37	0.001	Significant

Here, T₄: Cow Manure + Vegetable Leaves + Earthworms, T₅: Cow Manure + Tobacco Leaves + Earthworms, and T₆: Cow Manure + Tobacco Stems + Earthworms represent the vermicompost treatments. The ANOVA and Tukey HSD analyses revealed significant numerical differences (p < 0.05) among treatments for all nutrient parameters for conventional and vermicompost treatments. However, since each treatment was represented by a single composite composting pile, the significance values should be interpreted cautiously, as they primarily reflect analytical rather than biological variability. The trends nevertheless demonstrate clear and consistent differences between composting materials and processes, supporting the comparative conclusions drawn.

3.4. Duration of Vermicomposting

The decomposition period varied significantly among the three vermicompost treatments, as shown in Figure 5. The mixture of cow manure, vegetable leaves, and earthworms decomposed the fastest, completing in just 40 days, indicating the high degradability and soft texture of vegetable residues, which promote rapid earthworm activity and microbial action. In contrast, the mixture of cow manure, tobacco leaves, and earthworms required 52 days, while the combination of cow manure, tobacco stems, and earthworms took the longest, 79 days. The extended duration for tobacco stems is likely due to their higher lignin and cellulose content, which slows down the decomposition process even in the presence of earthworms. These findings suggest that while vermicomposting significantly shortens the overall composting time, the choice of organic material still plays a crucial role in determining the maturity period [48].

Figure 5. Temperature-Time profile showing thermophilic and maturation phases for different vermicompost treatments.

3.5. Comparison Between Conventional and Vermicomposts

Vermicomposts consistently demonstrated significantly higher organic carbon content than conventional composts. The OC concentration reached 45.3% in the vermicompost with vegetable leaves, followed by 40.8% (vegetable leaves and cow manure) and 38.7% (vegetable stems and cow manure). In contrast, conventional composts had notably lower OC: 15.3% (vegetable leaves and cow manure), 13.0% (tobacco leaves and cow manure), and 13.0% (tobacco stems and cow manure). Nitrogen content was also higher across all vermicompost types. The highest N level was observed in the tobacco stem vermicompost (2.68%), followed by vegetable leaves (2.50%) and tobacco leaves (2.23%). In comparison, conventional composts had much lower N values: 0.67% (vegetable leaves and cow manure), 1.45% (tobacco leaves and cow manure), and 1.23% (tobacco stems and cow manure). Phosphorus concentrations were markedly higher in vermicomposts, particularly in the mixture with vegetable leaves (1.28%), followed by tobacco leaves (1.22%) and tobacco stems (1.19%). The corresponding values for conventional composts were significantly lower: 0.42%, 0.32%, and 0.31%, respectively. Vermicomposts again showed superior potassium content, ranging from 1.21% (vegetable leaves) to 1.35% (tobacco stems), while conventional composts recorded 0.70%, 0.99%, and 1.13%, respectively. Sulfur levels followed a similar trend. Vermicomposts showed 0.89% (tobacco stems and cow manure), 0.52% (tobacco leaves and cow manure), and 0.40% (vegetable leaves and cow manure), while conventional composts ranged much lower at 0.56%, 0.23%, and 0.20%, respectively.

Figure 6 shows that there are significant numerical differences (p < 0.05) among treatments for all nutrient parameters for conventional and vermicompost treatments.

Figure 6. Comparative nutrient composition (OC, N, P, K, and S) between conventional compost and vermicompost prepared using vegetable leaves, tobacco leaves, and tobacco stems. The letters above bars (a, b, c) indicate significant differences among treatments based on Tukey’s HSD test at p < 0.05.

A similar result was found by Degefa et al. (2022) [53] when comparing composted and vermicomposted kitchen waste. It is found that the pH (7.4), Organic Carbon (3.71%), Available Phosphorus (12.3 ppm), Total Nitrogen (0.60%), and Carbon-to-Nitrogen Ratio (20.58) are present in the compost. On the other hand, pH (7.23), Organic Carbon (8.50%), Available Phosphorus (20.1 ppm), Total Nitrogen (1.70%), and Carbon Nitrogen Ratio (11.5) are present in vermicompost kitchen waste. The results demonstrated that Vermicomposting had higher Organic Carbon, Available Phosphorus, and Total Nitrogen, while higher pH and C/N ratios were found in conventional composting.

All nutrients exhibited significant treatment effects, confirming that organic matter source (vegetable vs. tobacco residues) strongly influences compost nutrient dynamics. Organic carbon and phosphorus were higher in vegetable-based composts, while nitrogen, potassium, and sulfur were enriched in tobacco-residue-based treatments.

This clearly demonstrates that vermicomposting enhances organic carbon levels, accelerates nitrogen levels, and enriches the content of potassium, phosphorus, and sulfur more effectively than conventional compost, due to improved microbial activity and the role of earthworms [54].

The composting time was significantly reduced in vermicomposting compared to conventional composting across all material combinations. For cow manure and vegetable leaves, the compost matured in 70 days under conventional methods, but required only 40 days with vermicomposting, resulting in a 30-day reduction (43%). Similarly, composting cow manure with tobacco leaves took 81 days conventionally but just 52 days with earthworms, saving 29 days (36.0%). The most prolonged composting was observed with cow manure and tobacco stems, which took 104 days conventionally, whereas vermicomposting shortened the process to 79 days, reducing the duration by 25 days (24.0%). These results confirm that vermicomposting significantly accelerates the decomposition process, regardless of the organic material used [55].

4. Discussion

4.1. Tobacco Waste-Based Compost Performance

There are no previous findings on the performance assessment and comparison of tobacco waste-based vermicompost with conventional compost. This study finds that the conventional composting with cow manure and tobacco leaves has the highest amount of Nitrogen content, 1.45%. Again, the compost with cow manure and tobacco stems showed the highest amount of Potassium content, 1.13%, and Sulfur content, 0.56%. The superior nutrient release in vegetable-leaf vermicompost is attributed to the low lignin and cellulose content, which promotes faster microbial mineralization, whereas tobacco stems, with higher lignocellulosic fractions, decompose more slowly but retain higher potassium and sulfur concentrations. The interaction between earthworms and microbial communities enhanced enzymatic degradation and nutrient mobilization, explaining the higher OC and N in vermicomposted materials [48]. An experiment was performed by Adediran et al. (2004), where the tobacco waste-based compost reduced the nicotine content of tobacco waste and stimulated microbial activity and nitrogen availability, which led to better growth and yield of Lettuce [44]. Another study conducted by Chaturvedi et al. (2009) showed that the leaf length, number of leaves, fresh and dry weight of bulb, and yield for Garlic (Allium sativum L.) increased by around 30% to control conditions due to the high macro-nutrient content of tobacco waste-based compost [56]. We found another study conducted by Adediran et al. (2005), where the 40% mixing of tobacco waste with 6 types of animal manure significantly increased the germination, growth, and yield of Tomato and Lettuce, proving the feasibility of field application of tobacco-based waste mixed with animal manure [57]. So, compared with the existing study findings, tobacco waste shows significant potential as a composting feedstock.

The findings of this study suggest that tobacco wastes, particularly stems and leaves, hold considerable potential as composting materials when subjected to appropriate processing through vermicomposting. Vermicompost produced from tobacco residues showed enhanced nutrient content, with notably high levels of potassium (up to 1.352%) and sulfur (up to 0.896%). Research with different substrates (kitchen waste, agro-residues, institutional and industrial wastes, including textile industry sludge and fibers) for vermicomposting was performed by [58], who found an increase in nitrogen content for different feed substrates in the order: textile sludge > textile fiber = institutional waste > agro-residues > kitchen waste. His findings reveal that vermicomposting is a suitable technology for the decomposition of different types of organic wastes (domestic as well as industrial) into value-added material. An experiment conducted by Kauser and Khwairakpam (2022) in comparison of vermicompost and conventional compost and vermicompost was found as the most nutrient-efficient composting method, effectively used as a nitrogen recovery method [55]. Another study by Degefa et al. (2022) compared conventional composted and vermicomposted kitchen waste and found that kitchen waste-based vermicompost contains more organic carbon and macro-nutrients than kitchen waste-based conventional compost [53]. So, for vermicompost, the presence of earthworms significantly accelerated the breakdown of organic matter, enhancing microbial activity and improving nutrient bioavailability. This aligns with previous findings indicating that vermicomposting with different feed substrates improves humus formation, soil structure, and nutrient enrichment [59], which play essential roles in plant health, including disease resistance and protein synthesis [60].

There are a number of studies conducted globally on tobacco waste composting, as shown in Table 6.

Table 6. A horizontal comparison of international studies on tobacco waste composting and vermicomposting, focusing on feedstocks, processes, duration, temperature patterns, nutrient outcomes, safety assessments, and agronomic implications. It contextualizes the present study within the global literature.

Region	Feedstocks	Maturity	Nutrient Outcomes	Safety Measurements	Agronomic Outcome	Distinct
Bangladesh (This Study)	Cow manure with (i) tobacco leaves, (ii) tobacco stems, (iii) vegetable leaves, and (iv) earthworms	Compost: 70–104 days; Vermicompost: 40–79 days	Vermicompost has a higher nutrient content than conventional compost. Tobacco stems have higher N, K, and S content compared to vegetable leaves.	Nicotine/phytotoxicity not measured	No crop yield test	Smallholder demonstration study
China—Di et al., 2022 [50]	Fresh tobacco leaves and soil	Co-composting lasted for nearly 10 months	Nitrogen and available potassium increased by roughly 157% and 132%. Pseudomonas, Azotobacter, and Coprinus increased by roughly 244%, 323%, and 675%	Nicotine content decreased dramatically	Stimulate the growth of tobacco plants	Demonstrates the feasibility of tobacco leaf composting.
South Africa—Adediran et al., 2004 [44]	Tobacco waste, sawdust/wood shavings, cow dung, pig dung, poultry manure, or cabbage waste	Compost maturity was achieved after 45–59 days	Improved NPK content and compost quality	Reduced the nicotine content of tobacco wastes from 12,180 mg kg−1 to 4872 mg kg−1 by dilution, while composting reduced it further to <160 mg kg−1 in the final composts.	Lettuce and spinach showed a positive growth response	Early agronomic evidence for tobacco-waste compost
China—Wang et al., 2020 [52]	Chicken manure, tobacco powder, and mushroom substrate	After day 28, the composting entered the end of the active phase	Enhanced nutrient profile and stability	Phytotoxicity tracked; detoxification confirmed by the Chinese national standard	No yield trial	Highlights the detoxification
Vietnam—Nguyen et al., 2022 [45]	Tobacco waste with chicken manure	After 30 days of composting, the heaps were mixed, sampled, and analyzed	Nitrate concentration decreased concomitantly from ∼67 to ∼42 mg NO3–N kg−1 fresh weight	Composting decreased the alkaloid content from ∼6000 to ∼200 mg kg−1	The yield increased from ∼17 to ∼29 t ha−1 for leaf mustard (Brassica integrifolia)	Demonstrates the agronomic benefits of tobacco compost

Given that Bangladesh is a significant producer of tobacco, large quantities of post-harvest tobacco residues often remain unused or are disposed of in environmentally harmful ways. Composting these wastes could provide a sustainable waste management solution, producing organic fertilizers that help restore declining soil fertility [56]. This practice aligns with the principles of circular economy and climate-smart agriculture, and can benefit smallholder farmers by reducing their dependency on expensive chemical fertilizers [61]. Moreover, vermicomposting notably reduced composting time by up to 43.0% compared to conventional methods, making it a time-efficient option for nutrient recycling [62].

This study conducted a unique conceptual analysis aimed at sustainable tobacco waste management, eradicating environmental pollution from tobacco landfills, and reducing the production of low-quality tobacco products for lower-income consumers in Bangladesh. Tobacco waste is also recycled for the production of low-quality tobacco products, such as Bidi, Jorda, and Gul, in Bangladesh. People with low income are the primary consumers of these low-quality tobacco products. These low-quality tobacco products create dangerous health issues for people in Bangladesh. This study has demonstrated the alternative use of tobacco waste, which provides dual benefits by acting as both a compost and a means of protecting the environment and human health. With the findings of this study, tobacco producers will have a new source of income from tobacco waste while reducing their costs of chemical fertilizers.

4.2. Tobacco Waste Composting Limitations

Despite these advantages, certain limitations must be acknowledged. The decomposition of tobacco stems is relatively slow due to their lignocellulosic nature, which may delay compost maturity unless mechanical shredding and moisture optimization are applied [63]. To overcome the slow decomposition of tobacco stems, pre-shredding to reduce particle size and moisture optimization (55–65%) are recommended. Tobacco residues contain potential toxic compounds such as nicotine, solanesol, and polyphenols that can persist through aerobic composting if the thermophilic phase is short or uneven. In farmer-managed settings, precise control of moisture and C:N ratio may not be feasible, causing process variability. This may pose risks to soil microbiota, plant health, and food safety if not fully degraded during composting [23]. Residual nicotine may cause phytotoxicity or inhibit microbial succession [52] (Li et al., 2021). Potential leachate enriched with nicotine and ammonia can contaminate soil or water nearby. Volatile compounds can also cause odor emission during decomposition, especially in humid tropical climates. To minimize the potential risks associated with tobacco-waste composting, several technical and management improvements are recommended. Maintaining an optimal thermophilic phase above 45 °C for at least 3–4 weeks is essential to promote the microbial degradation of nicotine, solanesol, and polyphenols [23]. Maintaining moisture content between 55 and 65% through regular turning and monitoring [48]. Installing aeration channels or perforated pipes can help minimize anaerobic zones and reduce odor generation, while leachate collection systems prevent the contamination of surrounding soil and water [22]. Before agricultural use, the final compost should be tested for residual nicotine, phytotoxicity (e.g., germination index), and heavy-metal concentrations to ensure environmental and crop safety [63].

To fully realize the potential of tobacco waste composting in Bangladesh, several future steps are necessary. Pretreatment strategies, including particle size reduction and moisture management, should be adopted to enhance decomposition. The use of microbial inoculants may further improve nutrient mineralization and detoxify harmful substances [64]. Since this study did not directly quantify nicotine residues, further analysis of residual bioactive compounds is required to confirm compost safety for food crops. The study did not monitor how continuous application of tobacco-based compost affects soil health, microbial diversity, or heavy-metal accumulation over multiple seasons. While the results clearly highlight treatment-dependent differences in nutrient dynamics between conventional and vermicompost systems, it should be noted that each treatment was represented by a single composting unit. Hence, the ANOVA and Tukey HSD results primarily reflect analytical variability. Further studies incorporating replicated piles under controlled conditions are necessary to confirm these findings with full statistical confidence. Training and awareness programs are also crucial in promoting the adoption of vermicomposting practices among farmers, particularly in rural tobacco-producing regions.

5. Conclusions

This study demonstrated the effectiveness of composting and vermicomposting as sustainable strategies for managing organic waste, particularly underutilized tobacco wastes, in Bangladesh. The results clearly showed that vermicomposts significantly outperformed conventional composts in terms of nutrient enrichment, particularly organic carbon, nitrogen, potassium, and sulfur, while also reducing composting duration by up to 43.0%. Among all treatments, vermicompost made from cow manure and vegetable leaves yielded the highest organic carbon and nitrogen content, whereas tobacco stem-based vermicompost excelled in potassium and sulfur content.

These findings underscore the dual benefits of using agricultural residues, such as vegetable waste and tobacco waste, not only to restore soil fertility but also to mitigate environmental pollution and reduce landfill pressure. By transforming agricultural waste into high-quality organic fertilizer, this approach supports the principles of the circular economy. It offers a practical, low-cost solution for smallholder farmers, particularly in tobacco-producing regions.

Integrating tobacco industry residues into composting practices not only diverts a significant volume of biomass from the waste stream but also promotes eco-friendly soil management. This aligns with global sustainability goals and provides a replicable model for sustainable agricultural intensification and the recycling of organic waste. However, this study demonstrates the nutrient potential of tobacco-waste-based composts; the possible persistence of nicotine or other alkaloids was not analyzed. Hence, before recommending its use in edible crop systems, further assessment of residual nicotine, heavy metals, and phytotoxicity is essential.