Evaluation of bio-stimulants on growth, yield and biochemical parameters in capsicum under shade net conditions

Introduction

Historical records trace the cultivation of capsicum to ancient civilizations in Central and South America, where indigenous peoples recognized both culinary and medicinal properties of these pungent fruits over 6000 years ago. Modern agricultural systems have transformed capsicum into one of the most important vegetable crops globally, with production exceeding 36 million tonnes annually and cultivation spanning diverse agroclimatic zones from temperate to tropical regions [1] . The economic significance of capsicum extends beyond fresh market consumption to include processing industries, pharmaceutical applications, and ornamental uses that collectively generate substantial revenue for producers and supply chains [2] . Protected cultivation structures including shade nets, polyhouses, and greenhouses have emerged as preferred production environments for high-value vegetable crops where environmental modification enables year-round production and enhanced quality [3] .

Shade net cultivation offers particular advantages in regions experiencing high solar radiation and temperature extremes that limit open field productivity during summer months. The reduced light intensity and temperature moderation within shade structures creates favorable microenvironments for crops like capsicum that are sensitive to heat stress during reproductive development [4] . Bio-stimulants represent a diverse category of substances and microorganisms that enhance plant growth and stress tolerance through mechanisms distinct from direct nutrient supply or pest control [5] . Unlike synthetic fertilizers or pesticides, bio-stimulants work by modifying physiological processes including hormone signaling, nutrient uptake efficiency, and stress response pathways. The growing emphasis on sustainable agriculture and consumer preference for residue-free produce has accelerated research and commercial interest in bio-stimulant technologies [6] . Seaweed extracts derived from marine algae contain complex mixtures of plant hormones, polysaccharides, amino acids, and micronutrients that stimulate growth and enhance stress tolerance in treated crops [7] . Commercial seaweed products based primarily on Ascophyllum nodosum and related species have demonstrated beneficial effects across numerous crop species and production systems. The mode of action involves both direct effects of bioactive compounds and indirect effects through improved soil microbial activity and nutrient cycling [8] . Humic substances including humic acid and fulvic acid represent another important category of bio-stimulants derived from decomposed organic matter. These complex polymeric molecules improve soil physical properties, enhance nutrient availability, and stimulate root development through hormone-like activity [9] . Foliar applications of humic acid have shown positive effects on vegetable crops including improved photosynthetic efficiency and enhanced fruit quality parameters [10] . Amino acid-based bio-stimulants provide building blocks for protein synthesis while also serving signaling functions that influence plant development and stress responses [11] . Exogenous amino acid applications can bypass metabolic bottlenecks during periods of high demand or stress, supporting continued growth and reproductive development. Proline, glycine, and glutamic acid have received particular attention for their roles in osmotic adjustment and antioxidant metabolism [12] . Previous research on bio-stimulant applications in capsicum has yielded variable results depending on formulations tested, application methods, and growing conditions [13] . Systematic comparison of different bio-stimulant categories under controlled conditions would provide valuable guidance for growers seeking to integrate these products into production protocols. This research therefore evaluated the comparative efficacy of seaweed extract, humic acid, and amino acid bio-stimulants on growth, yield, and quality parameters in capsicum under shade net cultivation [14] .

Materials and Methods

Materials:

The experiment was conducted under a shade net structure providing 50% light reduction at a vegetable research facility. Capsicum cultivar California Wonder was selected for its wide adaptation and market acceptance. Seeds were procured from a certified source and seedlings raised in pro-trays filled with cocopeat-vermiculite mixture under protected nursery conditions [15] . Bio-stimulant products included commercial seaweed extract containing 0.1% cytokinin equivalent, humic acid with 12% humic substance content, and amino acid mixture containing 18 Lamino acids at 10% total concentration.

Methods:

The experiment followed randomized complete block design with seven treatments and four replications. Treatments comprised T1-Control (water spray), T2-Seaweed extract 2 ml/L, T3-Seaweed extract 4 ml/L, T4-Humic acid 2 ml/L, T5-Humic acid 4 ml/L, T6-Amino acids 2 ml/L, and T7-Amino acids 4 ml/L. Each plot contained 20 plants at 60 × 45 cm spacing with observations from 10 central plants. Foliar applications commenced one week after transplanting and continued at 15-day intervals until final harvest [16] . Spray solutions were applied during morning hours using knapsack sprayer with sticker at 0.1% concentration. Growth parameters recorded included plant height at fortnightly intervals, branch number, and leaf area index at 60 days after transplanting. Flowering observations comprised days to first flowering and total flower number per plant. Yield parameters included fruits per plant, average fruit weight, and total yield per plant across all harvests. Biochemical analyses performed on marketable fruits included chlorophyll by acetone extraction, ascorbic acid by titration, capsaicin by HPLC, and protein by Kjeldahl method [17] . Data were subjected to analysis of variance and means separated using Duncan's multiple range test at 5% probability level.

Environmental Conditions

The shade net structure maintained temperatures between 22.4°C and 34.8°C compared to 26.8°C to 42.6°C in adjacent open field during the cropping period. Relative humidity ranged from 48% to 82% under the shade net. Light intensity at noon averaged 42,000 lux compared to 86,000 lux outside, confirming approximately 50% light reduction. These environmental modifications created favorable growing conditions for capsicum, particularly during the flowering and fruit development phases when heat stress most severely impacts productivity [18] .

Results

Table 1: Effect of bio-stimulants on vegetative growth parameters in capsicum

Comprehensive Interpretation

The yield response to bio-stimulant treatments demonstrated clear differentiation among product categories. Seaweed extract at higher concentration achieved 74.4% yield improvement over control, followed by humic acid at 38.5%

and amino acids at 23.1% improvement. The cumulative yield curves in Figure 2 illustrate that yield advantage developed progressively across harvest cycles, suggesting sustained enhancement of reproductive capacity rather than simple early growth stimulation.

Discussion

The superior performance of seaweed extract can be attributed to its complex composition including cytokinins, auxins, betaines, and polysaccharides that collectively enhance multiple physiological processes [7] . Cytokinin activity promotes cell division and delays senescence, extending the functional life of photosynthetic tissues. The polysaccharide components including alginates and carrageenans stimulate plant defense responses and may contribute to improved stress tolerance under shade net conditions [8] . Enhanced chlorophyll content in seaweed-treated plants supports the hypothesis that bio-stimulant applications improve photosynthetic capacity. Higher chlorophyll concentrations enable greater light capture efficiency, partially compensating for reduced light intensity within the shade structure [9] . The elevated ascorbic acid and capsaicin levels indicate that seaweed extract influences secondary metabolite biosynthesis, potentially through upregulation of relevant enzymatic pathways. Humic acid treatments showed particular benefits for rootassociated parameters that were reflected in improved nutrient uptake efficiency rather than direct measurement of root mass [10] . The chelating properties of humic substances enhance micronutrient availability in the rhizosphere, supporting enzymatic functions essential for photosynthesis and reproductive development. The intermediate yield response suggests that humic acid applications complement but do not substitute for direct growth-promoting effects of seaweed components. Amino acid applications benefited protein accumulation but showed lesser impact on overall growth and yield parameters. This pattern suggests that under the adequate fertility regime employed in this research, amino acid supply was not a primary limiting factor for vegetative growth. Benefits of amino acid applications may become more pronounced under stress conditions or in systems with suboptimal nitrogen management [11] .

Limitations

This research tested specific commercial formulations that may differ from products available in other markets. The single cultivar and environment combination limits generalization to other genetic backgrounds and growing conditions. Cost-benefit analysis did not account for price variability in bio-stimulant products and market fluctuations in capsicum prices. Root development parameters were not directly measured, limiting understanding of below-ground treatment effects.

Conclusion

This research demonstrates that bio-stimulant applications can substantially enhance capsicum productivity and quality under shade net cultivation conditions. Seaweed extract at 4 ml/L concentration emerged as the most effective treatment, achieving 74.4% yield improvement along with significant enhancements in biochemical quality parameters including chlorophyll, ascorbic acid, and capsaicin content. These findings support the integration of seaweed-based biostimulants into protected capsicum production protocols.

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