1 Introduction

Brinjal (Solanum melongena L.), also known as eggplant or aubergine, is an important solanaceous vegetable in South and Southeast Asia. Its fruits provide dietary fiber, vitamins, minerals, phenolic compounds, and anthocyanins that contribute to nutritional and antioxidant value [1, 2]. In Bangladesh, brinjal is an economically important crop for smallholder farmers; however, productivity is frequently constrained by declining soil organic matter, nutrient imbalance, and inefficient fertilizer management.

A major e in brinjal production is the dependence on chemical fertilizers for maintaining yield. Excessive or imbalanced fertilizer use can contribute to nutrient losses, deterioration of soil biological functions, and environmental contamination [3]. Integrated nutrient management combines the rapid nutrient supply of mineral fertilizers with organic and biological inputs that may improve nutrient retention, soil structure, and rhizosphere functioning. Previous studies have reported beneficial effects of integrated nutrient management on brinjal growth, yield, soil fertility, and rhizosphere properties [4,5,6].

Tricho-compost is an organic amendment enriched with Trichoderma spp., commonly including Trichoderma harzianum. In addition to supplying organic matter and nutrients, such products may influence nutrient solubilization, root development, soil enzyme activity, and rhizosphere microbial communities [7,8,9]. In brinjal, Trichoderma-enriched biofertilizers and nutrient-enriched composts have improved growth, fruit yield, nutrient accumulation, and post-harvest soil fertility relative to sole fertilizer or conventional organic amendments [10, 11].

Tricho-leachate, the liquid fraction obtained from Trichoderma-enriched compost, has emerged as a promising plant-growth-promoting input. tricho-compost and tricho-leachate have reduced seedling mortality and soil-borne disease in cabbage nurseries [12]. While other Trichoderma-based liquid or rhizosphere-active formulations have been associated with improved root architecture, plant vigor, and soil suppressiveness [8, 13, 14]. Their combined evaluation is justified because the solid compost can provide organic matter and a sustained rhizosphere substrate, whereas the leachate can deliver soluble compounds and microbial propagules more rapidly. These complementary functions were not measured directly in the present experiment and are therefore treated as mechanistic hypotheses rather than demonstrated processes.

The research gap is not the absence of Trichoderma research in brinjal, but the limited evidence on the combined use of tricho-compost and tricho-leachate across graded fertilizer-reduction levels. Existing brinjal studies have focused mainly on growth and yield, with less simultaneous attention to chlorophyll status, root development, fruit infestation, and biochemical quality [5, 10, 15]. Evidence from tomato and other vegetables suggests that Trichoderma-based bio-organic fertilizers can maintain productivity under reduced mineral fertilization [16,17,18], but the productivity-quality trade-off in brinjal remains insufficiently quantified. The 100%, 75%, 50%, and 0% RDF levels were selected to represent full fertilization, moderate reduction, substantial reduction, and complete omission, respectively. Accordingly, this study tested whether combined tricho-compost and tricho-leachate could sustain growth, yield, physiological performance, and fruit biochemical quality as mineral fertilizer was progressively reduced. The novelty lies in evaluating these response dimensions together and quantifying the practical trade-off between fertilizer saving and crop performance.

2 Materials and methods

2.1 Experimental site and planting material

The study was conducted at the experimental field (23º57´N to 25º 13´N and 90º56´E to 92 º21´E) of the Department of Horticulture, Sylhet Agricultural University, Bangladesh. The location of the experimental field is between 23057´ and 25013´ north latitude and between 90056´ and 92021´ east longitude. The soil of the experimental field was sandy loam texture. The value of pH, electric conductivity and organic carbon were 5.9, 1.02 ds/m and 0.78%, respectively. The available N, P and K were 0.09% 0.13 (meq/100 g soil), 14.98 (µg/g soil) and 27.01 (µg/g soil), respectively. The average temperature and relative humidity were 32.5 °C/21.83 °C (day/night) and 75.5%, respectively.

Seeds of BARI Brinjal 4 were collected from the Bangladesh Agricultural Research Institute (BARI) and sown in the seed bed (loose, friable texture and good tilth condition) of the Department of Horticulture, Sylhet Agricultural University on 09 February and 25 days old seedlings were transplanted to the treated plots to observe the variations of the treatments. The spacing between plant to plant and row to row was 60 cm and 50 cm.

2.2 Experimental design and treatments

The experiment was carried out through Randomized Complete Block Design (RCBD). The experimental field was divided into fifteen (15) plots of equal size (1.6✕1 m2). Three (3) plots were assigned to each treatment randomly.

There were a total of five (5) treatments, against which, the growth and yield attributes of brinjal (Solanum melogena L.) were tested. The treatments were T1 (Recommeded dose of fertilizer) as control, T2 (10 t/ha Tricho-compost + full dose of chemical fertilizer + 20 ml/l tricho-leachate), T3 (10 t/ha Tricho-compost + Chemical fertilizer 75% + 20 ml/l tricho-leachate), T4 (10 t/ha Tricho-compost + Chemical fertilizer 50% + 20 ml/l tricho-leachate) and T5 (10 t/ha Tricho-compost + Chemical fertilizer 0% + 20 ml/l tricho-leachate). The different fertilizer levels (100%, 75%, 50%, and 0% RDF) were represent full input, moderate reduction, substantial reduction, and complete omission, thereby allowing the productivity-fertilizer trade-off to be quantified. All the treatments were replicated three (3) times. The irrigation was managed using a watering-can and any excess water after rainfall was drained out as required. The initial irrigation took place immediately after transplanting and precautions were taken to prevent from flowing one plot to another.

2.3 Fertilizer and Trichoderma-based input application

Recommended doses of chemical fertilizer (Urea, TSP and MoP were 10 tons, 300 kg, 100 kg, and 200 kg per hectare, respectively) and cowdung (10 tons per hectare) were obtained from the local market. Cowdung and TSP were applied during final land preparation, and Urea and MoP were applied in two halves, fifteen (15) days before transplanting the seedlings and the remaining fertilizer was applied after thirty (30) days of initial application.

tricho-compost and tricho-leachate were obtained from the market in Bogra through Mennonite Central Committee (MCC) Bangladesh. Tricho-compost was applied during the land preparation which was 15 days before transplanting of the plants. Tricho-leachate was applied four times on the standing crop with an interval of 15 days interval at evening.

2.4 Data collection

During data collection, data of plant height (cm), number of leaves plant− 1 and branch number were collected at 30, 45 and 60 DAT. The data of number of flowers were collected at 45 and 60 DAT and all the remaining morphological data were after harvesting. Lastly, the samples for biochemical analysis were taken at 60 DAT.

2.5 Morphological growth measurement

To evaluate plant development, morphological growth parameters were assessed. In a standard measuring scale, the height of the plant was measured from base to tip of the tallest point. The leaves per plant and primary branches count were counted manually, counting all fully developed leaves and branches per every single plant. We assessed flower number at the maximum flowering time, and we counted the number of fruits per plant later during fruiting. Individual fruit weight was measured using a digital balance, and total fruit weight per plant was recorded as the sum of weights of individual fruit. Yield per hectare was calculated by multiplying the total fruit weight per plant with the population density. SPAD value for leaf greenness was measured using SPAD meter, and root length from the root tip to base of plant (cm) was measured after harvesting. Furthermore, the number of infested fruits was assessed with visual inspection for pest or disease damage.

2.6 Biochemical assessment

Total phenolic, flavonoid compounds and total antioxidant contents in brinjal were measured by mixing 1.0 g fresh brinjal fruit samples with 6 ml of chilled 80% ethanol. The mixtures were then centrifuged for 20 min at 4 °C at 12,000 RPM and the consequential supernatant was used for further analysis of phenolic and flavonoid content with 3 analytical replicates. The total phenolic content (TPC) was measured using the Folin-Ciocalteu method. In this method, the extract was mixed with Folin-Ciocalteu reagent and sodium carbonate. The absorbance was measured at 765 nm after incubation, and gallic acid is used as the standard for calibration [19]. Total flavonoid content (TFC) was commonly determined by the aluminum chloride colorimetric method. The extract was mixed with aluminum chloride and the absorbance was measured at 510 nm. Quercetin was used as a standard for the calibration curve [19].

Total Antioxidant activity (DPPH) was measured by the DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging method. The extract was mixed with DPPH solution, and the absorbance was measured at 517 nm. The percentage inhibition was calculated based on the decrease in absorbance [19].

Total anthocyanin content was determined by the pH differential method, where absorbance was measured at 520 nm and 700 nm in buffers of pH 1.0 and 4.5. The absorbance difference was used to calculate the anthocyanin content [20].

2.7 Data analysis

The collected data were analyzed by using SPSS 29 for windows statistical package (SPSS, Chicago, IL, USA). The experiment was analyzed according to a randomized complete block design (RCBD) with five treatments and three replications. Treatment means were separated using Tukey’s honestly significant difference (HSD) test with MSTAT software. The assumptions of normality and homogeneity of variance were checked before performing ANOVA. Differences among treatment means were considered statistically significant at P < 0.01, unless otherwise indicated by the original analysis.

3 Results

3.1 Effect of treatments on morphological parameters of brinjal

3.1.1 Plant height and leaf number of brinjal

Plant height differed among treatments at 30, 45, and 60 DAT (Fig. 1A). T2 consistently produced the tallest plants and reached 55.66 cm at 60 DAT, whereas T5 produced the shortest plants. T1 reached 41.34 cm at 60 DAT, while T3 and T4 were intermediate at approximately 34.27 and 32.47 cm, respectively. Thus, the principal observed response was the superior plant height under T2; T3 and T4 did not exceed T1 for this trait at 60 DAT.

Fig. 1
Fig. 1
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Effects of treatments on A plant height and B leaf number at 30, 45, and 60 days after transplanting (DAT). Values are means ± SE (n = 3). Vertical bars indicate the standard error. Means not sharing a common letter within the graph are significantly different at P < 0.001 according to Tukey’s HSD test

Leaves per plant ranged from 6.67 to 24.67 across treatments and sampling dates (Fig. 1B). T2 produced the highest leaf numbers at 30, 45, and 60 DAT (11.67, 18.67, and 24.67 leaves plant−1, respectively), followed by T3. T5 produced the fewest leaves at each observation. At 60 DAT, T3 and T4 produced 22.67 and 20.67 leaves plant−1, respectively, compared with 19.33 leaves plant−1 in T1. Treatments not sharing a letter differed significantly according to Tukey’s HSD test.

3.1.2 Branch number and flower number of brinjal

Primary branch number differed among treatments at 30, 45, and 60 DAT (Fig. 2A). T2 produced the highest branch numbers at the three observation times (6.00, 8.67, and 9.00 branches plant−1), whereas T5 produced the lowest values (2.33, 4.33, and 4.67 branches plant−1). T3 was generally the second-best treatment, while T1 and T4 showed intermediate responses.

Fig. 2
Fig. 2
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Effect of tricho-compost and tricho-leachate on A number of branches per plant & B number of flowers per plant. Data indicates the mean of three replications. Vertical bars indicate the standard error. Means not sharing a common letter within the graph are significantly different at P < 0.001 according to Tukey’s HSD test

Flower number differed among treatments at 45 and 60 DAT (Fig. 2B). T2 produced the highest values at both sampling times (9.67 and 16.33 flowers plant−1), followed by T3 (7.67 and 14.33 flowers plant−1). T5 produced the fewest flowers (4.33 and 8.67 flowers plant−1). The letter groupings indicate that T2 and T3 were statistically similar at 60 DAT, whereas T2 was superior to the remaining treatments at 45 DAT.

3.1.3 Effect of treatments on yield and yield-contributing traits of brinjal

Yield components followed a consistent overall pattern, with T2 producing the highest fruit number (74.33 plant−1), individual fruit weight (80.40 g), total fruit weight (4.16 kg plant−1), and yield (25.76 t ha−1) (Fig. 3). The T2 yield was 17.5% higher than that of T1 (21.92 t ha−1), indicating that addition of tricho-compost and tricho-leachate to the full RDF increased maximum productivity.

Fig. 3
Fig. 3
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Effect of tricho-compost and tricho-leachate on A Number of fruits per plant, B Individual fruit weight, C Total Fruit weight per plant & D Yield. Data indicates the mean of three replications. fertilizer 50% + 20 ml/l tricho-leachate, T5 = 10 t/ha Tricho-compost + Chemical fertilizer 0% + 20 ml/l tricho-leachate. Vertical bars indicate the standard error. Means not sharing a common letter within the graph are significantly different at P < 0.001 according to Tukey’s HSD test

Individual fruit weight was highest in T2 (80.40 g), followed by T3 (76.48 g), T4 (72.66 g), T1 (72.50 g), and T5 (67.68 g) (Fig. 3B). T2 differed significantly from the other treatments, while T1 and T4 were statistically similar.

Total fruit weight per plant ranged from 3.66 to 4.16 kg (Fig. 3C). T2 produced the highest total fruit weight (4.16 kg plant−1), followed by T3 (4.04 kg plant−1), T4 (3.93 kg plant−1), T1 (3.91 kg plant−1), and T5 (3.66 kg plant−1). T2 was significantly superior, while T1 and T4 were statistically similar.

Brinjal yield differed among treatments (Fig. 3D). T2 produced the maximum yield (25.76 t ha−1), followed by T3 (23.55 t ha−1), T4 (22.14 t ha−1), T1 (21.92 t ha−1), and T5. T3 yielded 7.44% more than T1 while using 25% less chemical fertilizer than T2. According to the letter groupings, T3 was significantly lower than T2 but higher than T1, whereas T1 and T4 were statistically similar.

3.1.4 Effect of treatments on SPAD value, root length, and infested fruits of brinjal

T2 produced the highest SPAD value (66.30), representing a 17.3% increase over T1 (56.53), while T3 and T4 increased SPAD by 10.9% and 5.3%, respectively (Fig. 4A). Root length was also greater in T2 (35.87 cm; +26.0% versus T1), T4 (33.77 cm; +18.6%), and T3 (30.10 cm; +5.7%) than in T1 (28.47 cm) (Fig. 4B).

Fig. 4
Fig. 4
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Effect of tricho-compost and tricho-leachate on A leaf greenness (SPAD), B Root length, & C Number of Infested Fruits by BSFB. Data indicates the mean of three replications. Vertical bars indicate the standard error. Means not sharing a common letter within the graph are significantly different at P < 0.001 according to Tukey’s HSD test

Fruit infestation was lowest in T2 (14.67 fruits), 39.7% below T1 (24.33 fruits). T3 and T4 reduced infestation by 26.0% and 16.4%, respectively, relative to T1 (Fig. 4C). These data document treatment-associated differences in visible infestation but do not identify the biological mechanism responsible.

3.2 Effect of treatments on biochemical quality traits of brinjal fruit

T2 produced the highest total phenolic content, total flavonoid content, DPPH radical-scavenging activity, and anthocyanin content (Fig. 5A). Relative to T1, T2 increased these traits by 48.1%, 38.4%, 37.8%, and 50.0%, respectively.

Fig. 5
Fig. 5
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Effect of tricho-compost and tricho-leachate on A Total phenolic content, B Total flavonoid content, C Total antioxidant in percentage, & D Total anthocyanin content of brinjal fruit. Vertical bars indicate the standard error. Means not sharing a common letter within the graph are significantly different at P < 0.001 according to Tukey’s HSD test

Total flavonoid content was highest in T2 (6.67 µg GAE mg−1 DW), followed by T3 (5.71 µg GAE mg−1 DW), T1 (4.82 µg GAE mg−1 DW), T4 (4.73 µg GAE mg−1 DW), and T5 (3.67 µg GAE mg−1 DW) (Fig. 5B). T2 and T3 were statistically similar, while T1 and T4 shared the same letter group.

DPPH radical-scavenging activity was highest in T2 (27.93%), followed by T3 (22.91%), T4 (20.37%), T1 (20.27%), and T5 (16.56%) (Fig. 5C). T2 was significantly superior to the other treatments, whereas T1 and T4 were statistically similar.

Total anthocyanin content was highest in T2 (0.06 mg g−1 DW) and T3 (0.05 mg g−1 DW), which were statistically similar (Fig. 5D). T1 and T4 each recorded 0.04 mg g−1 DW and shared the same statistical group, while T5 produced the lowest value (0.03 mg g−1 DW).

3.3 Pearson’s correlation and principal component analysis (PCA)

The correlation analysis revealed significant relationship among the majority of the evaluated yield and qualitative traits (Fig. 5). Strongly positive significant correlation was found on the yield parameters and fruit quality attributes of brinjal. Fruit yield showed positive correlation with the number of fruit per plant (r = 0.98, p < 0.01), individual fruit weight (r = 0.99, p < 0.01) and fruit weight per plant (r = 1.00, p < 0.01). In addition, anthocyanin, total phenolic content (TPC), total flavonoid content (TFC) and antioxidant activity exhibit a strong and mutual positive association with correlation coefficient ranging from r = 0.94 to r = 1.00. Therefore, the correlation analysis provides valuable insights into trait relationships and can assist in selecting superior tricho-compost and tricho-leachate treatment with improved fruit quality, nutritional value, and commercial potential.

In the PCA (Principal Component Analysis) biplot along with PC1 (37.1%) and PC2 (19.9%), respectively were performed to evaluate spatial distribution and relationship among yield and fruit quality traits of brinjal through tricho-compost and tricho-leachate application (Fig. 5). PCA showed that the positive relationship among parameters of fruit yield and quality attributes including number of fruit per plant, individual fruit weight, fruit weight per plant with tricho-compost and tricho-leachate application (Fig. 6).

Fig. 6
Fig. 6
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Correlation and principal component analysis (PCA) of tricho-compost and tricho-leachate on the yield and qualitative traits of brinjal

4 Discussions

The present findings show that tricho-compost and tricho-leachate performed best when they were combined with an adequate supply of mineral fertilizer rather than used as complete substitutes. T2 produced the strongest overall responses in growth, yield, SPAD value, root length, and biochemical quality, whereas T5 generally showed the poorest performance. T3 maintained relatively high productivity and fruit quality while using 25% less chemical fertilizer, whereas T4 reduced chemical fertilizer use by 50% but produced a smaller productivity response. These differences among the treatments were directly observed in the experiment. However, microbial activity, nutrient mineralization, nutrient uptake, nutrient-use efficiency, chlorophyll retention, and stress mitigation were not directly measured. Therefore, these processes should be considered plausible explanations supported by previous studies rather than mechanisms confirmed by the present experiment. Earlier research has shown that Trichoderma-active compost systems and other organic amendments can influence soil enzyme activity, fungal communities, nutrient cycling, and plant development [7, 9, 21, 22].

The stronger vegetative performance of T2, particularly in plant height, leaf number, branch number, and flower production, suggests that the combined treatment created a more favorable nutritional and rhizosphere environment during both vegetative and reproductive development. A larger leaf canopy and a stronger branching structure may have improved light interception and assimilate production. Similarly, the higher SPAD values recorded under T2 and T3 are consistent with better chlorophyll retention and leaf nitrogen status. However, SPAD was used only as an indirect indicator, as neither photosynthetic rate nor tissue nitrogen concentration was measured. The observed response is consistent with evidence showing that integrated organic–mineral fertilization can improve soil properties, crop morphology, biomass accumulation, water retention, and reproductive development in tomato, wheat, arrowroot, lettuce, saffron, and sweet pepper systems [23,24,25,26,27,28,29]. Rather than suggesting that each input acted independently, the present pattern more likely reflects a complementary relationship between the rapid nutrient supply provided by chemical fertilizer and the slower nutrient-release and soil-conditioning functions of tricho-compost and tricho-leachate.

The yield results provide the clearest evidence of the trade-off between maximum productivity and reduced fertilizer use. T2 produced 25.76 t ha − 1, which was 17.52% higher than T1 at 21.92 t ha − 1. T3 produced 23.55 t ha − 1, retaining 91.42% of the yield obtained with T2 and exceeding T1 by 7.44%, despite receiving 25% less than the recommended chemical fertilizer dose. T4 produced 22.14 t ha − 1, retaining 85.95% of the T2 yield and exceeding T1 by only 1.00%. The reported statistical analysis also showed that T1, T3, and T4 were statistically similar for total yield. Therefore, T2 can be regarded as the maximum-productivity treatment, T3 as the strongest compromise between productivity and fertilizer saving, and T4 as a more substantial fertilizer-reduction strategy associated with a greater yield penalty. The weak performance of T5 further suggests that the organic inputs alone could not fully meet the mineral nutrient requirements of brinjal under the conditions of this experiment. This interpretation agrees with previous studies reporting complementary effects of organic amendments, composts, biofertilizers, and mineral fertilizers on fruit number, fruit weight, biomass production, soil fertility, and crop yield [12, 23, 30,31,32,33,34,35]. Nahar et al. [12] further showed that tricho-compost and tricho-leachate can support seedling establishment and fruit production in other crops. Nevertheless, fertilizer-use efficiency was not directly determined in the present study because plant nutrient recovery, nutrient losses, and tissue nutrient concentrations were not measured.

The root-length and SPAD responses provide a reasonable physiological explanation for the observed treatment pattern, although this interpretation remains inferential. The longer roots recorded under T2, together with the relatively strong root responses under T3 and T4, may have increased the volume of soil explored for water and nutrients. At the same time, higher SPAD values may indicate improved chlorophyll retention, which could have helped sustain canopy activity during flowering and fruit development. Recent research supports the possibility that organic amendments and Trichoderma-associated rhizosphere processes can promote root development, mineral solubilization, soil biological activity, and plant vigor [9, 13, 21, 22, 36] reported increases in wheat growth, nutrient concentrations, and soil enzyme activities following vermicompost application, whereas Ramazanoglu [21] found that farmyard manure influenced soil biological activity, SPAD values, nutrient status, and cotton yield. That study also emphasized that the slow mineralization of organic manure may make it insufficient as the sole nutrient source for high-yielding crops. These findings are compatible with the strong performance of the integrated treatments and the comparatively weak response of T5. Earlier studies have also linked combined organic and mineral nutrient inputs with chlorophyll status, microbial biomass, soil biological activity, and overall crop vigor [37,38,39,40]. However, the present experiment measured only maximum root length and SPAD value. Complete root architecture, microbial abundance, enzyme activity, plant nutrient uptake, photosynthetic performance, and stress-related biomarkers were not assessed.

The lower number of visibly infested fruits under T2 and T3 should be interpreted with caution. Although this was an observed treatment effect, the experiment did not identify the causal insect or pathogen, quantify disease pressure, or assess induced resistance. In other cropping systems, Trichoderma species have been reported to suppress certain fungal pathogens through competition, mycoparasitism, antibiosis, volatile compounds, modification of the rhizomicrobiome, and the activation of plant defense responses [8, 14], and tricho-compost and tricho-leachate have also reduced seedling mortality caused by soil-borne pathogens in cabbage [12]. In the present study, the reduction in fruit infestation may therefore have resulted from improved plant vigor, changes in plant nutrition, direct biological suppression, or interactions among these processes. Because these mechanisms were not directly examined, the lower number of infested fruits should not be attributed solely to Trichoderma-mediated disease suppression.

The biochemical findings strengthen the agronomic importance of the integrated treatments beyond yield alone. T2 produced the highest total phenolic content, total flavonoid content, DPPH radical-scavenging activity, and anthocyanin content. Importantly, T3 maintained substantial fruit-quality benefits while using 25% less chemical fertilizer. Compared with T1, T3 increased total phenolics by 19.67%, total flavonoids by 18.46%, antioxidant activity by 13.02%, and anthocyanin content by 25.00%. Phenolics, flavonoids, and anthocyanins contribute to the nutritional and antioxidant quality of brinjal fruit, while stronger in-vitro radical-scavenging activity indicates greater antioxidant potential. Maintaining these traits while reducing chemical fertilizer input could therefore improve the nutritional-quality profile of the crop and may create opportunities for market differentiation based on more resource-efficient nutrient management. However, market value, consumer acceptance, sensory characteristics, shelf life, bioavailability, and health outcomes were not evaluated. Therefore, a definite price premium or direct health benefit cannot be claimed. Comparable changes in fruit quality, leaf mineral status, metabolite profiles, phenolic accumulation, flavonoid content, and antioxidant capacity have been reported under combined organic, biological, and mineral nutrient-management systems [41,42,43,44,45,46]. These studies support the hypothesis that improved nutrient availability and plant physiological status may influence secondary-metabolite accumulation, although the specific metabolic pathways responsible for the present findings were not directly investigated.

Overall, the most suitable treatment will depend on the farmer’s production goal. T2 would be the preferred option when achieving the highest possible yield and fruit biochemical quality is the main priority. However, T3 offered a more practical balance, as it maintained a high yield and improved fruit quality while reducing the recommended chemical fertilizer dose by 25%. Although T4 reduced chemical fertilizer use by 50%, its yield was only slightly higher than and statistically similar to that of T1, suggesting that the larger fertilizer saving came with a greater productivity trade-off. The comparatively poor performance of T5 also shows that tricho-compost and tricho-leachate alone could not fully meet the nutrient requirements of brinjal under the conditions of this study. Further research should therefore examine the processes behind these responses by measuring soil microbial communities, Trichoderma colonization, soil enzyme activity, nutrient mineralization, plant nutrient uptake, fertilizer-recovery efficiency, complete root development, photosynthetic activity, chlorophyll concentration, stress indicators, and the organisms responsible for fruit infestation. Trials conducted across different seasons and locations, together with economic, postharvest, and consumer assessments, will also be necessary before any fertilizer-reduction strategy can be recommended for wider commercial use.

5 Conclusion

The combined application of tricho-compost and tricho-leachate with chemical fertilizer improved brinjal growth, yield, SPAD value, root length, biochemical fruit quality, and the number of visibly infested fruits relative to chemical fertilizer alone or Trichoderma-based inputs without mineral fertilizer. T2 (10 t ha−1 Tricho-compost + 20 mL L−1 Tricho-leachate + 100% RDF) produced the maximum overall response, including the highest yield of 25.76 t ha−1. However, the findings do not support complete replacement of chemical fertilizer: T5 performed poorly, whereas T3 (the same tricho-compost and tricho-leachate rates with 75% RDF) maintained a high yield of 23.55 t ha−1 and strong quality performance. Therefore, 75% RDF combined with tricho-compost and tricho-leachate appears to provide the best practical balance between productivity and a 25% reduction in chemical fertilizer under the conditions of this study. Because the experiment was conducted at one location during one season with three replications, multi-location and multi-season trials, together with economic analysis and direct measurements of soil and plant nutrient dynamics, are required before large-scale recommendation.