Comparative effects of homemade and commercial organic fertilizers on yield and fruit quality of cherry tomato (Solanum lycopersicum var. cerasiforme) in Northern Vietnam

1 Introduction

Cherry tomato (Solanum lycopersicum var. cerasiforme) is a high-value horticultural crop widely appreciated for its attractive appearance, superior taste, and rich nutritional composition. Compared with large-fruited tomato cultivars, cherry tomatoes generally contain higher concentrations of soluble sugars, vitamins, and antioxidant compounds such as lycopene and phenolics, which contribute to their recognized health benefits (Raiola et al., 2014). In recent years, consumer demand for cherry tomatoes has increased, particularly in urban markets where food quality, safety, and nutritional value are major purchasing considerations.

Conventional tomato production often relies heavily on synthetic fertilizers to maximize yield. However, excessive application of chemical fertilizer use can contribute to soil degradation, nutrient imbalance, and water pollution through nutrient leaching (Alom et al., 2025). In addition, high nitrogen inputs may increase nitrate accumulation in tomato fruits, raising concerns regarding food safety and human health (Santamaria, 2006). These challenges have intensified interest in nutrient management strategies that maintain productivity while reducing environmental impacts.

Organic fertilization has been widely recognized as a sustainable approach to improving soil fertility and crop productivity. Organic amendments such as compost and manure supply nutrients gradually through microbial mineralization and can improve soil structure, microbial activity, and nutrient retention (Agegnehu et al., 2016; Diacono and Montemurro, 2011). In tomato production, organic fertilizers have been associated with improved yield and fruit quality, including higher soluble solids and antioxidant content (Heeb et al., 2006; Toor and Savage, 2006). Recent meta-analyses have confirmed that the application of organic fertilizer significantly enhances tomato yield and quality, although responses vary with fertilizer source and management practices (Fan et al., 2023; Gao et al., 2023; Yang et al., 2023).

Among organic nutrient sources, homemade organic fertilizers prepared from locally available materials such as crop residues, food waste, and animal by-products offer a low-cost option that supports circular resource use and reduces dependence on external inputs (Bernal et al., 2009). Compost-based fertilizers can improve soil structure, nutrient cycling, and biological activity, thereby enhancing plant growth and productivity (Diacono and Montemurro, 2011). Recent studies have shown that compost and other organic amendments can improve tomato yield and fruit quality under a range of production conditions (Wu et al., 2023; Salehi et al., 2025; Liu et al., 2025; Zhang et al., 2024).

In Vietnam, tomato production plays an important role in vegetable farming, particularly in the Red River Delta, where fertile alluvial soils support intensive cultivation (Huong et al., 2013). Increasing concerns of food safety and environmental sustainability have encouraged efforts to reduce chemical fertilizer use and promote more sustainable practices (Ngo et al., 2025). Recent evidence suggests that organic fertilizers can improve tomato yield and quality while maintaining soil fertility under Vietnamese conditions (Loan et al., 2024).

Despite these advances, few studies have evaluated homemade organic fertilizers formulated from locally available materials under field conditions, and evidence is particularly limited for cherry tomato production in Northern Vietnam. Most previous studies have focused on commercial organic products or standardized composts, which may not reflect the resources and constraints faced by smallholder farmers.

Therefore, this study aimed to compare a homemade organic fertilizer with two commercial organic fertilizers and a water-only control to assess their effects on plant growth, development, yield, and fruit quality of cherry tomato under field conditions in Northern Vietnam. The study provides practical evidence on the potential of locally produced organic fertilizers as a nutrient source for smallholder and household-based tomato production systems.

2 Materials and methods

2.1 Plant material

Cherry tomato (Solanum lycopersicum var. cerasiforme) cultivar ‘Nova’ was used in this study. Seeds were obtained from Johnny’s Selected Seeds (USA). The cultivar is characterized by vigorous vegetative growth, orange-colored fruits with firm texture, and an average fruit weight of 20–22 g. It exhibits tolerance to Fusarium wilt and nematodes and reaches first harvest approximately 60 days after transplanting.

2.2 Experimental site and environmental conditions

The experiment was conducted from September 2024 to February 2025 at Green Field Agricultural Technology JSC, Chi Minh Commune, Hung Yen Province, Vietnam (Red River Delta region). The site is characterized by fertile alluvial soil and is managed under organic-oriented production practices. Such agroecological conditions are considered suitable for evaluating organic fertilization strategies in vegetable crops (Loan et al., 2024).

2.3 Experimental inputs, design, and treatments

Five organic fertilizer types were included in the study: (i) Divital-Germany (>52% organic matter; NPK 2:3:2), (ii) Biooptima 1 (60% organic matter; C/N ratio 12), (iii) Biooptima 2 (30% organic matter; C/N ratio 12), (iv) a homemade organic fertilizer prepared from soybean, banana, egg, molasses, and microbial inoculant (Emzeo), and (v) composted cattle manure. Biooptima 1 and composted cattle manure were applied uniformly to all plots as basal fertilizers, whereas Divital-Germany, Biooptima 2, and the homemade organic fertilizer were used as the treatment factors.

A homemade organic fertilizer was prepared using 3 kg of soybean meal, 3 kg of mashed ripe bananas, 15 eggs, 1 L of molasses, 200 g of Emzeo microbial inoculant, and 8 L of clean water. The mixture was fermented in a covered plastic container under shaded conditions and stirred every 3 days. After 3 weeks, the fertilizer reached a well-decomposed state and was applied after dilution. The inclusion of multiple organic nutrient sources follows previous studies highlighting variability in nutrient mineralization and plant response depending on fertilizer origin (Fan et al., 2023; Zhang et al., 2024).

The study was arranged in a randomized complete block design (RCBD) with four treatments and three replicates. Each replicate consisted of 10 plants. All plots received a uniform basal application equivalent to 20 t ha^-¹ of Biooptima 1 and 30 t ha^-¹ of composted cattle manure before transplanting.

The four treatment groups were defined according to the weekly fertigated solution applied after transplanting:

• Control (water): weekly irrigation with water only.
• Treatment 1 (Divital-Germany): weekly application of Divital-Germany solution.
• Treatment 2 (Biooptima 2): weekly application of Biooptima 2 solution.
• Treatment 3 (Homemade organic fertilizer): weekly application of homemade organic fertilizer solution.

The seedling substrate consisted of alluvial soil, rice husk, and a commercial seedling medium (BVB, Netherlands). Biological plant protection agents included neem-based formulations, soapberry extract, and Trichoderma spp., which are commonly used in sustainable horticultural systems (Gao et al., 2023).

2.4 Preparation and application of fertilizer solutions

Divital-Germany and Biooptima 2 were pre-fermented in water (7.5 kg in 20 L) for 3 days before application. The homemade fertilizer was produced through anaerobic fermentation of soybean, banana, egg, molasses, and microbial inoculant for 30 days, followed by dilution at the same ratio. Stock solutions were diluted to stage-specific concentrations according to crop developmental requirements: 700 ppm at the seedling stage, 1000 ppm at flowering, and 1200 ppm during fruit development. These concentration ranges are consistent with previous studies on organic nutrient management in tomato (Fan et al., 2023). Each plant received 250 mL of fertilizer solution per application, applied directly to the root zone once per week.

2.5 Crop establishment and management

Seeds were sown in 84-cell trays containing commercial substrate and covered for 2 days under low-temperature conditions to promote uniform germination. Seedlings were transplanted at the two-true-leaf stage into nursery containers filled with a mixture of alluvial soil, composted manure, and rice husk, and subsequently transplanted to the field at 5–6 true leaves.

Plants were arranged in a staggered double-row system with 0.4 m spacing between plants and 0.8 m between rows, equivalent to a planting density of 31,250 plants ha^-¹. Irrigation was applied daily to maintain optimal soil moisture, and fertilization treatments commenced 2 days after transplanting. Crop management practices included trellising using an A-frame system (1.7–1.8 m height), pruning of lateral shoots, removal of senescent leaves, and periodic plant tying at 2–3 day intervals. Apical pruning was performed when plants exceeded trellis height to promote assimilate allocation to fruit development.

2.6 Measurements and data collection

2.6.1 Growth parameters

Growth observations included days to 50% flowering, days to first harvest, and total crop duration. Plant height (cm) and number of leaves per plant were recorded at 10-day intervals throughout the vegetative growth period.

2.6.2 Physiological measurements

Leaf chlorophyll content was measured using a SPAD-502 chlorophyll meter at two developmental stages: (i) 6–7 true leaves and (ii) fruit development stage. Measurements were taken from three canopy positions, with three readings per leaf averaged.

2.6.3 Yield components

Yield-related parameters included number of flowers per cluster, number of clusters per plant, fruit set (%), number of fruits per plant, mean fruit weight (g), and yield per plant (kg). Mean fruit weight was determined from a representative sample of 10 fruits per plot. Theoretical yield (t ha^-¹) was calculated by multiplying the average yield per plant (kg plant^-¹) by the planting density (plants ha^-¹) and converting the result to tons per hectare. Actual yield (t ha^-¹) was calculated from the total fresh fruit weight harvested from each experimental plot and expressed on a hectare basis.

2.6.4 Fruit quality assessment

Fruit quality parameters included fruit length and diameter (cm), soluble solids content (°Brix), and nitrate concentration (mg kg^-¹). Fruit flesh thickness (mm) was determined using a digital caliper and expressed as the mean value of randomly selected fruits from each treatment. Nitrate levels were evaluated to ensure compliance with the maximum permissible limit (MPL) of 150 mg kg^-¹ fresh weight for tomato, as specified in Vietnamese regulations (Vietnam Ministry of Agriculture and Rural Development, 2008) and reported in a previous study (Dodocioiu et al., 2025).

2.7 Statistical analysis

All data were subjected to analysis of variance (ANOVA) using Minitab. Before conducting the ANOVA, Levene’s test was conducted to assess the homogeneity of variances, confirming that this assumption was met (p > 0.05 for all variables). Treatment means were compared using the Least Significant Difference (LSD) test at the 5% probability level (p < 0.05). The coefficient of variation (CV, %) was calculated to assess the degree of variability and experimental precision. All graphics were produced using SigmaPlot 10.0.

For each plot, three plants were randomly selected from the 10 plants for the measurement of growth parameters. The average value obtained from the three sampled plants per plot was considered one replicate for statistical analysis. Data were subjected to analysis of variance (ANOVA) independently at each sampling time.

3 Results

3.1 Effects of fertilizer applications on plant growth

3.1.1 Effects of fertilizer applications on plant height

Plant height increased progressively across all treatments from 38 to 129 days after sowing (DAS), indicating continuous vegetative growth throughout the experimental period (Figure 1). At the early growth stages (38–80 DAS), differences among treatments were minimal, with plant height ranging from approximately 15.8 to 170.2 cm, suggesting that fertilizer effects were not yet pronounced.

From 87–129 DAS, treatment effects became more evident and statistically significant at 5% levels. Plants receiving Divital-Germany (Treatment 1), Biooptima 2 (Treatment 2), and homemade organic fertilizer (Treatment 3) exhibited a faster growth rate compared to the control. At 129 DAS, all treatments reached higher heights with a mean of 325.4 cm compared to that of the control (301.1 cm).

The relatively low coefficient of variation (CV = 1.8–3.9%) across measurement periods indicates high experimental precision. Overall, homemade organic fertilizer proved to be a highly effective treatment for improving plant height, especially during the later growth stages.

3.1.2 Effect of fertilizer applications on stem diameter

As shown in Figure 2, stem diameter increased gradually across all treatments from 38 to 129 days after sowing (DAS), reflecting normal vegetative development of the plants. During the early growth stages (38–52 DAS), no noticeable differences were observed among treatments, with stem diameter ranging from 0.5 to 0.9 cm.

From 59 DAS onward, treatment effects became more apparent, but non-significant at 5% level. Plants treated with Biooptima 2 (Treatment 2) and homemade organic fertilizer (Treatment 3) consistently exhibited slightly larger stem diameters compared to the control and Divital treatment. This trend persisted throughout the later growth stages.

At the final observation (129 DAS), Treatments 2 and 3 reached the highest stem diameter (approximately 1.5 cm), which was higher than that of the control and Treatment 1 (around 1.4 cm). However, no significant difference was observed among these groups.

The coefficient of variation (CV = 0–6.4%) indicates acceptable experimental precision. In summary, homemade organic fertilizer improved stem thickening, which may contribute to better plant vigor and structural stability.

3.1.3 Effect of fertilizer applications on leaf number

The number of leaves per plant increased steadily across all treatments from 38 to 129 days after sowing (DAS), indicating continuous vegetative development (Figure 3). During the early stages (38–73 DAS), differences among treatments were minimal and non-significant at 5% level, with leaf numbers ranging from approximately 6.0 to 23.8 leaves per plant.

From 80 DAS onward, treatment effects became more evident. Plants receiving organic fertilizers, particularly Divital-Germany (Treatment 1), Biooptima 2 (Treatment 2), and homemade organic fertilizer (Treatment 3), tended to produce more leaves compared to the control. Those differences between treatments and control were statistically significant at 5% level, but non-significant among the treatments themselves. At the final observation (129 DAS), three treatments had an average leaf number of 40.8 leaves, while the control treatment had the value of 39.9 leaves. The coefficient of variation (CV = 0.7–2.7%) indicates high experimental precision.

3.1.4 Effect of fertilizer applications on SPAD index

The SPAD index, representing leaf chlorophyll content, showed relatively small variation among treatments at both observation times (48 and 104 days after sowing), as shown in Table 1. At 48 DAS, SPAD values ranged from 49.0 to 52.2, with the control and Biooptima 2 treatments recording the highest values (52.2), while Divital and homemade organic fertilizer showed slightly lower values (49.0). However, these differences were not statistically significant at the 5% level.

Table 1. Effect of fertilizer applications on SPAD index.

Values followed by different letters are significantly different, whereas those sharing the same letter are not significantly different, according to the LSD test (p < 0.05). DAS (Days after sowing).

A similar pattern was observed at 104 DAS. The control and Biooptima 2 treatments maintained higher SPAD values (52.4), whereas Divital and homemade organic fertilizer treatments recorded lower values (46.1). Despite this numerical variation, statistical analysis indicated no significant differences among treatments. The coefficient of variation (CV = 7.1–7.8%) suggests moderate variability in the data.

3.1.5 Effect of fertilizer applications on yield components

Table 2 shows that the yield components of cherry tomato were only slightly influenced by fertilizer treatments. The number of flowers per cluster ranged from 19.2 to 20.4, with no significant differences observed among treatments. Similarly, the number of fruits set per cluster (17.2–18.1) and the total number of clusters per plant (10.2–10.6) did not differ significantly, indicating that fertilizer type had a limited impact on these parameters.

Table 2. Effect of fertilizer applications on yield components.

Values followed by different letters are significantly different, whereas those sharing the same letter are not significantly different, according to the LSD test (p < 0.05).

In contrast, fruit set percentage showed a clear response to fertilizer application. The control treatment recorded the lowest fruit set (84.0%), which was significantly lower than all fertilized treatments. Among the fertilized treatments, fruit set ranged from 89.4% to 92.1%, with homemade organic fertilizer (Treatment 3) achieving the highest value, although no significant differences were observed among the fertilizer treatments themselves. The relatively low coefficients of variation (CV = 2.2–7.8%) indicate good experimental precision. While fertilizer application did not significantly affect most yield components, it significantly improved fruit set percentage, with homemade organic fertilizer showing the highest numerical performance.

3.2 Effect of fertilizer applications on yield

Fertilizer application had a clear influence on the yield performance of cherry tomato, as illustrated in Table 3. The number of fruits per plant ranged from 175.9 to 187.1, with no significant differences among treatments. Similarly, average fruit weight showed a slight increase under fertilized treatments (23–24 g) compared to the control (21 g), although the variation was not statistically significant.

Table 3. Effect of fertilizer applications on the yield of cherry tomato.

Values followed by different letters are significantly different, whereas those sharing the same letter are not significantly different, according to the LSD test (p < 0.05).

In contrast, yield per plant was significantly affected by fertilizer treatments. The control treatment recorded the lowest yield (1.2 kg plant^-¹), while all fertilized treatments showed significantly higher yields, ranging from 1.6 to 1.8 kg plant^-¹. Among them, Biooptima 2 (Treatment 2) and homemade organic fertilizer (Treatment 3) achieved the highest yields (1.8 kg plant^-¹), although no significant difference was observed between these treatments.

A similar trend was observed for both theoretical and actual yields. The control treatment produced the lowest values (24.3 and 23.9 t ha^-¹, respectively), whereas fertilized treatments significantly increased yield, reaching up to 35.3 t ha^-¹ (theoretical) and 30.1 t ha^-¹ (actual). The highest actual yield was recorded under homemade organic fertilizer, followed closely by Biooptima 2.

The coefficients of variation (CV = 5.0–9.0%) indicate acceptable experimental reliability. Overall, while fertilizer treatments did not significantly affect fruit number or weight, they substantially improved yield, with homemade organic fertilizer and Biooptima 2 showing the best performance.

3.3 Effect of fertilizer applications on quality parameters

As shown in Table 4, fertilizer treatments had varying effects on the quality parameters of cherry tomato across the two harvest stages (115 and 128 DAS). Fruit size traits, including fruit length and diameter, showed only slight variation among treatments. Fruit length ranged from 3.7 to 4.0 cm, with no significant differences observed at either harvest stage. In contrast, fruit diameter showed some treatment effects at the first harvest, with Biooptima 2 (Treatment 2) and homemade organic fertilizer (Treatment 3) producing significantly larger fruits than the control. However, these differences were not significant at the second harvest. The images of ripe fruits from the experimental treatments are illustrated in Figure 4.

Table 4. Effect of fertilizer applications on quality parameters of cherry tomato.

Values followed by different letters are significantly different, whereas those sharing the same letter are not significantly different, according to the LSD test (p < 0.05). DAS (days after sowing).

Flesh thickness remained relatively stable across treatments (3.0 – 4.0 mm) and did not show significant differences, indicating that fertilizer type had a limited influence on this parameter. In terms of soluble solids content (°Brix), fertilized treatments generally recorded higher values than the control. At the first harvest, Biooptima 2 and homemade organic fertilizer treatments achieved significantly higher °Brix values (9.6–9.8) compared to the control (7.8). A similar trend was observed at the second harvest, although variation among fertilized treatments was not statistically significant.

Nitrate (NO₃^-) content was significantly affected by fertilizer application. The control treatment consistently showed the lowest nitrate levels (107.5–108.8 mg kg^-¹), while fertilized treatments exhibited higher values. Among the treatments, Biooptima 2 produced the highest nitrate concentration (138.5 mg kg^-¹). In contrast, the homemade organic fertilizer resulted in a significantly lower nitrate concentration than Biooptima 2 (P < 0.05) and did not differ significantly from the control. Nevertheless, nitrate concentrations in all treatments remained below established food safety limits.

The low coefficients of variation (CV = 2.6–3.6%) indicate high experimental precision. Overall, fertilizer application was associated with improvements in certain fruit quality attributes, particularly soluble solids content and fruit diameter. Among the treatments, handmade compost resulted in comparable fruit quality parameters together with relatively moderate fruit nitrate content.

4 Discussion

The present study demonstrates that organic fertilization, particularly the application of homemade organic fertilizer, significantly influenced the growth, yield, and quality of cherry tomato under field conditions in Northern Vietnam. Relative to the water-only control, the homemade organic fertilizer increased final plant height from 301.1 to 327.9 cm (8.9%), stem diameter from 1.4 to 1.5 cm (7.1%), leaf number from 39.9 to 40.8 leaves plant^-¹ (2.0%), fruit set from 84.0% to 92.1% (9.6%), and actual yield from 23.9 to 30.1 t ha^-¹ (26.0%). It also increased soluble solids from 7.8 to 9.6°Brix at the first harvest (23.1%) while maintaining nitrate concentrations below the commonly referenced threshold of 150 mg kg^-¹ for tomato (Santamaria, 2006). The observed improvements in vegetative growth, yield performance, and selected quality parameters highlight the potential of locally produced organic inputs as promising options to commercial organic fertilizer sources.

4.1 Effects on cherry tomato growth and development

4.1.1 Effects on plant growth parameters

Plant height, stem diameter, and leaf number increased progressively throughout the growing period, with treatment differences becoming more apparent after 80 days after sowing. At the final assessment, the homemade organic fertilizer and Biooptima 2 produced the tallest plants (327.9 and 328.1 cm, respectively), which were significantly higher than the control (301.1 cm). Similar trends were observed for stem diameter and leaf number. These responses suggest that the organic fertilizers enhanced nutrient availability during the period of rapid vegetative growth.

These findings are consistent with previous studies reporting that organic fertilizers improve vegetative growth by enhancing soil structure, microbial activity, and nutrient cycling (Agegnehu et al., 2016; Diacono and Montemurro, 2011). The gradual release of nutrients from organic sources may provide a more sustained nutrient supply, thereby supporting continuous plant growth throughout the cropping cycle (Rostaei et al., 2024). In addition, organic fertilizers have been shown to increase root development and nutrient absorption capacity, further contributing to improved plant vigor (Donn et al., 2014; Fauzan et al., 2025). Notably, homemade organic fertilizer performed comparably to commercial organic fertilizers, suggesting its effectiveness as a nutrient source. This may be attributed to its diverse composition, including plant-based materials and animal-derived inputs, which can provide both macro- and micronutrients and beneficial microorganisms.

4.1.2 Effects on chlorophyll content (SPAD index)

In contrast to growth parameters, the SPAD index did not differ significantly among treatments at both observation stages. SPAD values remained within a relatively narrow range (46.1–52.4). Although Biooptima 2 and the control showed slightly higher SPAD values, the differences were not statistically significant. This suggests that all treatments provided sufficient nitrogen to maintain chlorophyll synthesis. Previous studies have reported higher chlorophyll content associated with organic fertilizer than with inorganic counterparts (Gao et al., 2023; Gülüt and Şentürk, 2024). In this study, all treatments involved organic fertilizers, which may explain the absence of significant differences in SPAD index among treatments due to relatively similar nitrogen availability. Notably, the control treatment (water) exhibited slightly higher SPAD values compared to fertilized treatments (treatment 1 – Divital, treatment 3 – Homemade organic fertilizer). This observation may be attributed to differences in nitrogen allocation. Plants receiving fertilization may direct more nitrogen toward reproductive growth, including flower and fruit development, rather than maintaining leaf chlorophyll concentration. Such a trade-off between vegetative and reproductive sinks has been reported in tomato and other horticultural crops (Heeb et al., 2006; Toor et al., 2006). Moreover, organic fertilization often promotes yield formation without necessarily increasing chlorophyll content when baseline nutrient levels are sufficient (Carillo et al., 2025).

4.1.3 Effects on yield components

Yield components such as the number of flowers per cluster, number of fruits set, and number of clusters per plant were not significantly affected by fertilizer treatments. However, fruit set increased from 84.0% in the control to 92.1% under the homemade organic fertilizer, representing a 9.6% improvement. The improvement in fruit set may be associated with better nutrient availability during the reproductive stage, particularly phosphorus and potassium. This plays critical roles in flower development and fruit formation (Fan et al., 2023). Organic fertilizers are also known to improve soil moisture retention and microbial activity, which can enhance pollination efficiency and reduce flower abortion (Zhang et al., 2024).

4.2 Effects on yield performance

Despite the limited effect on yield components, significant differences were observed in yield per plant and overall productivity. Yield per plant increased from 1.2 kg in the control to 1.8 kg under the homemade organic fertilizer, while actual yield increased from 23.9 to 30.1 t ha^-¹. This corresponds to a 26.0% increase over the control and was statistically equivalent to the yields obtained with Biooptima 2 (29.9 t ha^-¹) and Divital-Germany (28.2 t ha^-¹). The increase in yield was primarily associated with improved fruit weight and overall plant performance rather than an increase in fruit number. These results align with previous findings that organic fertilization can enhance tomato yield by improving nutrient availability and soil fertility (Fan et al., 2023; Yang et al., 2023). The comparable performance of homemade organic fertilizer to commercial fertilizers highlights its potential as a cost-effective alternative, particularly for smallholder farmers. Furthermore, the relatively high actual yield obtained under homemade organic fertilizer suggests that locally produced organic inputs can effectively support commercial tomato production.

4.3 Effects on fruit quality

Fruit quality parameters responded differently to fertilizer treatments. While fruit size traits (length and flesh thickness) were not significantly affected, fruit diameter was slightly improved under Biooptima 2 and homemade organic fertilizer treatments. Fruit diameter at the first harvest increased from 3.2 cm in the control to 3.7 cm under the homemade fertilizer, and soluble solids increased from 7.8 to 9.6°Brix. The increase in soluble solids content under organic fertilization has been widely reported and is often attributed to improved carbohydrate metabolism and nutrient balance (Toor et al., 2006). Higher °Brix values are desirable as they enhance fruit taste and market value. In this study, homemade organic fertilizer achieved high °Brix values comparable to Biooptima 2, suggesting its effectiveness in improving fruit quality.

Nitrate content in fruits was significantly influenced by fertilizer treatments, with higher values observed in organic fertilized plots compared to the control. However, all measured values remained below the permissible limit of 150 mg kg^-¹, indicating that the fruits were within the acceptable range for consumption. Among the treatments, homemade organic fertilizer showed relatively moderate nitrate content compared to Biooptima 2. Previous studies have reported that nitrate accumulation in vegetables may vary depending on the nitrogen composition and mineralization characteristics of organic fertilizers (Santamaria, 2006; Yang et al., 2023). Therefore, the differences observed among treatments in the present study may be associated with differences in nutrient release characteristics of the fertilizer sources, although fertilizer composition and nutrient dynamics were not analyzed.

The overall results suggest a linkage among vegetative growth, reproductive performance, and fruit quality. Greater plant height, stem diameter, and leaf development may have contributed to improved photosynthetic activity and assimilate production. The comparable fruit set and fruit quality observed among treatments could be associated with sufficient nutrient supply from the organic fertilizers during plant development. In addition, the relatively moderate nitrate accumulation in fruits may be related to the gradual nutrient release commonly associated with organic fertilizer sources. However, these interpretations should be considered cautiously because the physicochemical properties and nutrient composition of the homemade organic fertilizer were not analyzed. Similar agronomic outcomes may reflect comparable nutrient supply, nutrient release dynamics, or beneficial effects on soil physicochemical and biological properties, but these possibilities remain speculative without chemical analysis. Nevertheless, the homemade organic fertilizer produced yield and fruit quality outcomes comparable to those of commercial organic fertilizers under the conditions of this study.

4.4 Limitations of this study and future research directions

This study was conducted at a single site during one growing season, which may limit the generalizability of the findings under different environmental conditions. Seasonal variability can influence nutrient mineralization and plant responses to organic fertilization (Agegnehu et al., 2016). In addition, the study focused on short-term crop performance and did not assess the long-term impacts of repeated organic fertilizer application on soil health and microbial activity, which are known to develop cumulatively over time (Diacono and Montemurro, 2011).

The nutrient composition and release dynamics of the homemade organic fertilizer were not fully characterized, which may affect reproducibility due to variability in raw materials and composting processes, as widely reported in composting studies (Agegnehu et al., 2016; Bernal et al., 2009). Such variability has also been shown to influence tomato growth and yield responses under organic fertilization systems (Yang et al., 2023). Furthermore, the absence of a mineral fertilizer control limits direct comparison with conventional production systems, and the use of a single cultivar restricts broader applicability across different genotypes (Coyago-Cruz et al., 2017; Yang et al., 2023).

Future research should therefore include multi-location and multi-season trials, detailed characterization of homemade organic fertilizer properties, and comparisons with conventional fertilization regimes. Expanding the study to multiple cultivars and incorporating long-term soil health assessments would provide a more comprehensive evaluation of the role of homemade organic fertilizer in sustainable tomato production systems.

5 Conclusion

This study demonstrated that organic fertilization plays a significant role in improving the growth, yield, and quality of cherry tomato under field conditions in Northern Vietnam compared with the water-only control. The homemade organic fertilizer produced results comparable to the two commercial organic fertilizers tested. It increased fruit set to 92.1%, actual yield to 30.1 t ha^-¹, and soluble solids to 9.6°Brix at the first harvest, while nitrate concentration remained below 150 mg kg^-¹.

The results suggest that homemade organic fertilizer, derived from locally available materials, can serve as a promising option to commercial organic fertilizers. Within the scope of this study, its agronomic performance was similar to that of the commercial organic fertilizers evaluated. Further research should assess its economic feasibility, optimize application rates, and examine long-term effects on soil properties and crop productivity.

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Footnotes

Edited by: Giulia Conversa, University of Foggia, Italy

Reviewed by: Jazbia Shirin, Peking University, China

Benjapon Kunlanit, Mahasarakham University, Thailand