Effect of biofertilizers and biostimulants on growth, flowering and yield attributes of okra (Abelmoschus esculentus L. moench)

Introduction

Okra (Abelmoschus esculentus (L.) Moench) is an important vegetable crop belonging to the family Malvaceae and possessing a chromosome number of 2n = 130. It is predominantly cultivated in tropical and subtropical regions and is believed to have originated in Tropical Africa. The crop is commonly known as bhindi or lady's finger and is valued for its tender, immature fruits, which are widely consumed as a vegetable. In addition to its nutritional importance, okra possesses medicinal and industrial significance, making it an important component of vegetable-based agricultural production systems (Gaikwad et al., 2021) [6] . The productivity of okra is influenced by several interacting factors, including seed quality, nutrient availability, environmental conditions and plant physiological processes. Therefore, sustainable approaches capable of improving nutrientuse efficiency and plant growth are increasingly important for enhancing productivity without excessive dependence on conventional chemical inputs. These limitations have stimulated interest in alternative and complementary nutrient-management strategies that can improve crop productivity while maintaining soil fertility and biological activity (Tyagi et al., 2016). Consequently, the integration of biological inputs and plant biostimulants has emerged as a promising component of sustainable crop production [18] . Biofertilizers contain beneficial microorganisms that, when applied to seed, soil or plants, contribute to nutrient availability and plant growth through various biological processes. Nitrogenfixing microorganisms can contribute biologically available nitrogen, while phosphate-solubilizing microorganisms improve the availability of otherwise less-soluble phosphorus compounds. Potassium-solubilizing microorganisms similarly contribute to the release of potassium from relatively unavailable sources. In addition to nutrient mobilization, beneficial microorganisms may produce growth-promoting substances and vitamins and can contribute to the suppression of certain soil-borne pathogens through antagonistic interactions (Nayak et al., 2019; Sharma et al., 2024). The presence of nitrogen-fixing, phosphate-mobilizing and other beneficial microorganisms can therefore improve the availability and utilization of plant nutrients and strengthen the biological functioning of the soil environment (Singh et al., 2018) [13, 16, 17] . Among the important biofertilizers, Azotobacter, phosphatesolubilizing bacteria (PSB) and potassium-solubilizing bacteria (KSB) perform complementary functions in plant nutrition. Azotobacter is associated with biological nitrogen contribution, whereas PSB and KSB facilitate the mobilization of phosphorus and potassium, respectively. Their combined application may therefore provide a broader nutritional benefit than the use of an individual microbial inoculant. Such integration is particularly relevant in vegetable crops such as okra, where rapid vegetative growth followed by continuous flowering and fruit development creates a substantial demand for nutrients throughout the growing season. The complementary activities of these microorganisms may improve nutrient acquisition and subsequently support plant growth, reproductive development and yield formation. Biostimulants represent another important approach for improving crop performance. They are materials or substances capable of stimulating natural plant processes and improving crop growth, physiological efficiency, quality and productivity. Their beneficial effects may involve improved photosynthetic activity, nutrient acquisition, stress tolerance and translocation of photoassimilates towards developing plant organs. Thus, biostimulants may complement conventional nutrientmanagement practices by improving the efficiency with which plants utilize available resources rather than simply supplying nutrients directly. Among different biostimulant groups, seaweed extracts and humic substances have received considerable attention because of their potential influence on root development, nutrient uptake, physiological activity, flowering and yield. Seaweed extract is a biologically active material containing a range of compounds that can stimulate plant growth and improve crop performance. (2016) highlighted the broader potential of seaweed-based biofertilizers in promoting plant growth and improving nutrient and water uptake [4,9,11,12] . Humic acid is another important biostimulant that can influence plant growth by improving the growing environment and supporting nutrient acquisition and utilization. Humic substances have been associated with improved root and shoot development, nutrient availability, plant growth and yield. [2,5,7,8,15,19] .

Materials and Methods:

The materials and the methods adopted during the course of present investigation entitled "Effect of biofertilizers and bio-stimulants on growth flowering and yield attributes of okra (Abelmoschus esculentus L.)" which was carried out during the year2022-23 and 2023-24 under the climatic condition of Gwalior. The experiment was carried out in horticulture research farm of the College of Agriculture, R.V.S.K.V.V. Gwalior, situated in Grid zone at the latitude of 260 13'N and longitude 760 10'E with an altitude of 197 meters from mean sea level (MSL). The soil of the experimental field was alluvial, sandy clay loam in texture and classified as typic us ochrepts at sub group level.Planting of okra variety Pusa Bhindi -5 was done in summer season with spacing of 45 cm row to row and 30 cm plant to plant in 21 plots, which replicated three times in Randomized Block Design. All the biofertilizer applied through foliar spray @ 2ml/lit. of water after 25 days of sowing. Bio-stimulants (Sea weed extract & Humic acid) used through foliar spray @ 2% & 4% after 30 days of sowing. The data on days to first flower appearance, days to 50% flowering, number of flowers per plant, days to first picking were recorded during the crop session. While data of number of fruits per plant, fruit yield per plant (g), number of seed per fruit were recorded at the time of harvesting.

Results and Discussion

Growth Parameters Days to first flower appearance A thorough study of the result presented in table 2 reveals that all the treatment combinations comprising of different biofertilizers and bio-stimulants exerted significant impact in the reduction of days to first flowering. The minimum days to first flowering during first year, second year and pooled data was observed in treatment combination T 21 (Azotobactor+ PSB + KSB + Humic acid 4%) i.e. 32.60, 30.40 and 31.50 (days). It was followed by treatment T 17 (Azotobactor+ PSB + KSB+ Humic acid 2%) in the first year, found at par with treatment T 17 , T 13 and T 9 in the second year and pooled data. While the maximum number days to first flower appearance was recorded in T 1 (control) i.e. 43.37, 41.34 and 42.36 (days) during the first year, second year and pooled data. reported favourable effects of humic acid on growth and flowering-related characteristics in okra [2,3,7,15,19] .

Days to 50% flowering

A critical analysis of the data presented in table 2 shows that all the treatment combinations comprising of different biofertilizers and bio-stimulants exerted prominent effect in the reduction of days to 50% flowering. Thus, the relatively early flowering observed under treatments containing seaweed extract can be viewed within the broader context of enhanced plant physiological performance under biostimulant application [9,12] .

Number of flowers per plant

Through the critical analysis of the data presented in table 3 improvements in plant height, leaf production, branching, leaf area and chlorophyll under humic acid application and suggested that improved soil fertility, nutrient and water availability and nutrient uptake could contribute to enhanced plant growth. These observations support the interpretation that improved reproductive development in the present study was associated with a more favourable plant nutritional and physiological environment [7,15] .

Days to first picking

Through the study of the data presented in [19] , who reported that humic acid application positively influenced fruit diameter, fruit length, fruit weight, number of fruits per plant and early yield in tomato. Their findings provide direct support for the role of humic substances in improving fruit production. Similarly, Abdel et al. (2010) reported enhanced growth and yield responses in watermelon following the application of Ascophyllum nodosum seaweed extract. Koyama et al. (2012) [9] also observed an increase in tomato yield following repeated application of seaweed extract, although fruit characteristics were not altered. These observations indicate that biostimulants may influence productivity through improvement in overall plant performance rather than necessarily altering every individual fruit characteristic. The present results are further supported by Sundharaiya et al. (2016), who recorded significant improvement in plant growth, bulb characteristics and yield of multiplier onion with 2% seaweed extract. Meena et al. (2017) [10] likewise reported significant improvement in fruit number and other yield-related characteristics of cucumber with the application of humic acid and micronutrients. Thus, the present increase in fruit number under T 21 is consistent with the broader evidence that humic substances and seaweed-derived biostimulants can positively influence reproductive performance and yield formation.

Through the analysis of the data presented in table 4 it was observed that maximum average fruit weight was recorded in treatment combination T 21 (Azotobactor+ PSB + KSB + Humic acid 4%) i.e. 16.97, 15.93 and 16.45 (g). It was followed by treatment T 17 . While the minimum average fruit weight was reported in T 1 (control) i.e. 9.01, 8.05 and 8.53 (g) during the first year, second year and pooled data. The increase in average fruit weight under T 21 may be associated with improved nutrient acquisition and utilization resulting from the combined activity of the biofertilizers. PSB and KSB may have contributed to improved phosphorus and potassium availability, respectively, while Azotobacter may have contributed to biological nitrogen enrichment. Humic acid may additionally have enhanced the efficiency of nutrient availability and utilization. The combined influence of these factors could have promoted greater assimilate production and translocation towards developing fruits, thereby increasing fruit weight. The present findings are corroborated by Yildirim et al. (2007) [19] , who reported positive effects of humic acid application on fruit weight and other fruit characteristics in tomato. Meena et al.

(2017) also reported significant improvement in fruit weight along with other fruit characteristics in cucumber following the application of humic acid and micronutrients. These findings are consistent with the present observation that humic acidcontaining treatments, particularly the complete microbial consortium combined with 4% humic acid, produced heavier fruits. The beneficial role of humic substances is also supported by Kirn et al. (2010), who reported a significant increase in yield following the application of potassium humate along with recommended fertilizers. Dursun et al. (2013) observed enhanced leaf, stem and root growth in tomato and eggplant seedlings at the tested humic acid concentrations, while Gad et al. (2015) reported significant effects of humic acid on growth and yield of okra, with 10% producing the highest response among the tested concentrations. Aboohanah (2016) similarly observed significant improvement in growth and root parameters of okra following humic acid application. Collectively, these studies indicate that the beneficial response observed under T 21 may be related to the capacity of humic substances to improve the growing environment and support plant development [2,3,5,8,10] .

Number of seeds per fruit

A keen observation of the data presented in table 5 reveals that the application of biofertilizers and bio-stimulants have significant effect on the number of seeds per fruit. Maximum number of seeds per fruit was observed in treatment combination T 21 (Azotobactor+ PSB + KSB + Humic acid 4%) i.e. 42.12, 41.23 and 41.68. It was followed by treatment T 17 . While the minimum number of seeds per fruit was reported in T 1 (control) i.e. 28.75, 27.86 and 28.30 during the first year, second year and pooled data. The higher seed number under T 21 may indicate improved reproductive development and more favourable conditions during flowering, fertilization and subsequent fruit development. The availability of essential nutrients, particularly nitrogen, phosphorus and potassium, is closely associated with plant growth and reproductive processes. In the present treatment combination, these nutrient-related effects may have been complemented by the biostimulatory influence of humic acid. Nevertheless, because physiological processes such as pollen viability, fertilization success and embryo development were not directly measured in the present experiment, the proposed mechanism should be considered a plausible interpretation of the observed response. The broader findings of Yildirim et al. (2007) support the positive influence of humic acid on fruit-related characteristics, while Abdel et al. (2010) demonstrated improved growth and yield responses following seaweed extract application in watermelon. Meena et al. (2017) [10] also reported improvement in several fruit and yield attributes of cucumber with humic acid and micronutrient application. Although these studies do not establish a direct one-to-one relationship with seed number in the present crop, their findings provide supporting evidence for the beneficial influence of biostimulant-based nutrient management on reproductive and yield-related performance [19] .

Fruit yield per plant

Through the analysis of the data presented in table 5 it was observed that maximum fruit yield per plant was recorded in treatment combination T 21 (Azotobactor+ PSB + KSB + Humic acid 4%) i.e. 396.97, 392.91 and 394.94 (g). It was followed by treatment T 17 . While the minimum fruit yield per plant was reported in T 1 (control) i.e. 291.07, 287.01 and 289.04 (g) during the first year, second year and pooled data. The higher fruit yield under T 21 can be interpreted as the cumulative result of its superior performance for the individual yield components. The treatment produced the highest number of fruits per plant, the highest average fruit weight and the highest number of seeds per fruit. Thus, the enhancement in fruit yield was not attributable to improvement in a single component but appeared to be associated with simultaneous improvement in several yield-determining attributes. This integrated response is particularly important when evaluating combined biofertilizer and biostimulant treatments. The present findings are in accordance with Yildirim et al. (2007) [19] , who observed improvement in fruit yield and fruit characteristics with humic acid application in tomato. Abdel et al. (2010) reported enhanced growth and yield responses in watermelon following seaweed extract application. Koyama et al. (2012) [9] also recorded increased tomato yield with seaweed extract application, even though fruit characteristics remained unchanged. These observations support the possibility that biostimulants can enhance crop productivity through their influence on overall plant performance and yield formation. The results are further supported by Sundharaiya et al. (2016), who reported significant improvement in yield and yield-related bulb attributes of multiplier onion with seaweed extract. Murtic et al. (2018) [11] found that 2% seaweed extract improved adaptability, yield and quality of cherry tomato under both regular and drought-stress conditions. Such findings are relevant because they demonstrate that biostimulant applications can contribute to productivity across differing growing conditions.

The superiority of the integrated treatment containing all three biofertilizers is also important in interpreting the treatment response. The performance of T 5 , consisting of Azotobacter + PSB + KSB without an additional biostimulant, was better than several two-component biofertilizer combinations, indicating the potential advantage of combining complementary microbial functions. However, further improvement was evident when the complete microbial combination was supplemented with seaweed extract or humic acid. Among these, T 21 consistently produced the strongest response. This pattern suggests that the biostimulant component may have complemented the nutrient-mobilizing functions of the microbial inoculants rather than acting independently. Such an interpretation is consistent with the concept of integrated nutrient and biostimulant management, in which improved nutrient availability and plant physiological efficiency operate simultaneously. The response to humic acid concentration also provides an important observation. T 17 , containing Azotobacter + PSB + KSB + humic acid 2%, generally ranked immediately after T 21 , whereas T 21 contained humic acid at 4%. The better overall performance of T 21 within the tested range indicates a favourable response to the higher humic acid concentration when combined with the complete biofertilizer consortium. However, the present data should be interpreted as a treatment response within the concentrations evaluated and should not be taken as evidence that increasing humic acid concentration indefinitely would continue to improve crop performance Murtic et al. (2018), who reported beneficial effects of seaweed-derived biostimulants on crop growth, yield and plant adaptability. The findings of Nabti et al. (2016) further support the broader role of seaweed-based biofertilizers in improving plant growth and nutrient and water uptake [4,5,7,8,9,10,11,12,15,19] .

Conclusion

The present investigation demonstrated that integrated application of biofertilizers and biostimulants significantly improved the growth, flowering, yield attributes and yield of the crop compared with the control and simpler treatment combinations. Among the evaluated treatments, T 21 (Azotobacter + PSB + KSB + humic acid 4%) emerged as the most effective treatment across the two years and pooled analysis. It recorded earlier flowering (31.50 days), earlier 50% flowering (34.31 days), higher number of flowers per plant (13.64), more fruits per plant (18.58), greater average fruit weight (16.45 g), higher seeds per fruit (41.68), and maximum fruit yield per plant (394.94 g). Treatment T 17 (Azotobacter + PSB + KSB + humic acid 2%) generally ranked second. The superior performance of T 21 indicates the potential advantage of combining complementary biofertilizers with humic acid at the higher tested concentration. Overall, integrated biofertilizer-biostimulant management offers a promising approach for enhancing crop productivity and improving nutrient-use efficiency.

Acknowledgement

AcknowledgmentWe wish to thank the Department of Horticulture, College of Agriculture, R.V.S.K.V.V., Gwalior, M.P. for kind support during the research work.

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