Effect of inorganic fertilizers and bio-stimulants on growth, yield and quality of okra (Abelmoschus esculentus L. Moench) cv. Kashi Lalima

Introduction

Vegetables occupy a crucial place in human nutrition due to their rich contents of vitamins minerals antioxidants and crude fibre and their consistent consumption is essential for a balanced diet. India's diverse agroclimatic conditions support year-round vegetable cultivation, among which okra (Abelmoschus esculentus L. Moench) 2n = 130 is one of the most important crops grown across tropical and subtropical regions. Okra is valued for its tender, nutritious pods and adaptability to a wide range of soil and climatic conditions (Khalid et al., 2005) [7] . It is an excellent source of vitamins A, B and C minerals fibre and iodine, contributing significantly to dietary health (Kumar et al., 2009) [8] . India is the world leader in okra production, cultivating 557 thousand hectares with a production of 7305 thousand MT, with major producing states including Gujarat, Madhya Pradesh, West Bengal, Bihar and Odisha (Ministry of Agriculture and Farmers Welfare, 2024) [14] . Okra is often-cross-pollinated, with insect-mediated cross-pollination reaching up to 19% and flowers exhibit anthesis between 8-10 AM, supporting reproductive efficiency and fruit set (Kumar et al., 2009) [8] . Its high average nutritional value (ANV 3.21) makes okra superior to many other vegetable crops. Fresh pods contain high moisture, essential minerals vitamin C and significant mucilage which is highly water-soluble and used in various industrial and food applications. Dried fruits contain up to 24% protein and 22% oil while stems and residual biomass serve as raw materials for fibre and paper industries (Kumar et al., 2009) [8] . Sustainable okra cultivation depends heavily on balanced nutrient supply. Over-dependence on chemical fertilizers has resulted in nutrient imbalance, soil degradation reduced soil organic matter and disturbed microflora (Mal et al., 2013) [10] . To counter these issues, Integrated Nutrient Management (INM) has emerged as a promising approach, combining inorganic fertilizers with organic manures and biofertilizers. Biofertilizers such as Azotobacter, Azospirillum and phosphate-solubilizing bacteria enhance nitrogen fixation, phosphorus solubilization, growth hormone production and soil biological activity (Bahadur and Manohar, 2001; Gayathri and Reddy, 2013) [2,4] . INM not only maintains soil fertility but also improves crop yield, quality and sustainability while reducing environmental pollution (Ipsita Das and Singh, 2014) [5] . Adopting INM in okra helps minimize chemical fertilizer dependency, supports longterm soil health and ensures stable productivity (Adilakshmi et al., 2008) [1] .

Materials and Methods

An experiment was conducted at Horticulture Research Farm, Department of Horticulture, at Babasaheb Bhimrao Ambedkar University, Lucknow during March to June 2024-25. The experiment was laid out in randomized block design with 10 treatments replicated thrice. Total numbers of plots were 30 and the net plot size was (2.16 m 2 ). The row to row and plant to plant distance of the experiment was maintained respectively 45 cm and 30 cm. The treatments involved were T 1 (RDF) 100%, T 2 Azspirillum (100%), T 3 Azotobacter (100%), T 4 PSB (100%), T 5 RDF (50%) + Azspirillum (50%), T 6 RDF (50%) + Azotobacter (50%), T 7 RDF (50%) + PSB (50%), T8 Azspirillum (50%) + Azotobacter (50%), T9 Azotobacter (50%) + PSB (50%), T10 RDF (25%) + Azspirillum (25%) +Azotobacter (25%) + PSB (25%). The cultivar used was Kashi Lalima (VROR-157) which was purchased from the Indian Institute of Vegetable Research, Varanasi, Uttar Pradesh, India. As per the recommendations of Department of Horticulture, at BBA University, Lucknow, India recommended dose of fertilizers is added to all plots equally. Seeds were sown using the dibbling method at a depth of 1 to 2 cm on the ridges in the last week of March 2023. The inorganic manures were applied as basal dose before sowing, for proper decomposition, full dose of phosphorus and potassium and half dose of nitrogen as per treatment were applied just before the sowing. The remaining half dose of nitrogen was applied 30 days after sowing. All cultural practices were followed regularly during crop growth and observations were recorded on vegetative characters i.e. days to germination (50%), days to germination (100%), plant height, stem diameter, number of branches, number of leaves, number of flowers per plant, internodal length, Day to first flowering, fruiting and yield characters i.e. days to first flowering, days to 50% flowering, number of fruits per plant, fruit weight, fruit length, fruit diameter, days to first picking, fruit yield per plant, number of seeds per fruits and bio-chemical parameters i.e. total soluble solids ( 0 Brix), Titrable acidity, Ascorbic acid and Moisture content (%). The data on these parameters were subjected to statistical analysis to draw logical conclusions The seeds were sown directly to the field. Light irrigation was given after sowing. total of eight irrigations was done at 10 to 12 days intervals during the vegetative to reproductive phase. Crop harvesting starts from mid-April to the second fortnight of June at 2-3 days intervals.

Results and Discussion

Growth attributes Plant height (cm) At (30, 45 and 60 DAT) plant height varied noticeably among treatments. The highest growth was observed in T 10 (25% RDF + 25% Azospirillum + 25% Azotobacter + 25% PSB), which recorded (70.73 cm), indicating a strong synergistic effect of the combined biofertilizers. T 5 (50% RDF + 50% Azospirillum) produced the next tallest plants (67.71 cm), while the shortest plants (56.03 cm) were noted under the T 1 treatment receiving only the full recommended dose of fertilizers. This trend is also supported by Singh and Choudhary (2018) [19] and Meena et al. (2019) [12] .

A marked improvement in the number of leaves was evident across all observation stages (30, 45 and 60 DAT). The treatment T 10 recorded the highest leaf count (26.13 cm) leaves per plant, demonstrating the strong influence of combined biofertilizers with reduced RDF on foliage development. This was closely followed by T 5 , which produced (25.20 cm) leaves per plant. In contrast, the lowest leaf number (19.01 cm) was observed in T 1 , indicating that sole application of RDF was less effective in promoting leaf proliferation compared with integrated nutrient approaches.

Significant differences in stem diameter were observed among the treatments across all growth stages (30, 45 and 60 DAT). The maximum stem thickness (85.63mm) was obtained under T 10 , highlighting the positive impact of integrating multiple biofertilizers with reduced RDF on stem robustness. This was followed by T 5 which recorded a stem diameter of (83.78mm). The minimum diameter (72.03mm) was noted in T 1 indicating that plants receiving only the recommended dose of fertilizers exhibited comparatively lower structural growth than those under integrated nutrient treatments a trend further supported by Jat et al. (2015) [6] and Reddy and Raghavendra (2017) [16] . [15] Fruit length also varied significantly among treatments. The longest fruits (12.93 cm) were produced under T 10 , demonstrating the superior impact of combined biofertilizers with reduced RDF. This was closely followed by T 5 , which recorded a fruit length of (12.81 cm). The shortest fruits (8.30 cm) were obtained from T 1 , indicating that exclusive use of RDF was less supportive for optimum fruit development compared to integrated nutrient management. Similar enhancement report under integrated nutrient strategies has been documented by (Chauhan et al. 2021) [3] .

Significant differences were recorded among the treatments with respect to fruit girth and fruit weight. The maximum fruit girth (1.88 cm) was obtained under T 10 (25% RDF + 25% Azospirillum + 25% Azotobacter + 25% PSB), indicating the strong promotive effect of integrating multiple biofertilizers with reduced chemical fertilization. This was followed by T 5 (50% RDF + 50% Azospirillum), which recorded a girth of (1.78 cm), while the minimum girth (0.98 cm) was observed under T 1 (100% RDF).

A similar trend was reflected in fruit weight. The highest fruit weight (9.18 g) was achieved in T 10 , demonstrating the superior influence of the combined nutrient application on pod development and biomass accumulation. The treatment T 5 ranked next with (8.97 g), whereas the lowest fruit weight (7.35 g) was recorded in T 1 , indicating that exclusive reliance on inorganic fertilizers was comparatively less effective in enhancing fruit growth.

Fruit yield per plant (g), Fruit yield per plot (kg) and Fruit yield (q/ha) A significant influence of inorganic fertilizers and biostimulants was observed on fruit yield per plant in okra, Fruit yield showed considerable variation among treatments. The highest yield (188.5 g per plant) was obtained under T 10 , where a balanced combination of (25% RDF + 25% Azospirillum + 25% Azotobacter + 25% PSB), followed by T 5 recorded (169.3 g per plant) respectively. In contrast, the sole application of 100% RDF T 1 produced comparatively lower fruit yield Per plant (116.9 g per plant), indicating the superior effectiveness of integrated nutrient sources over chemical fertilizers alone.

Fruit yield per plot showed significant variation in response to the combined use of biofertilizers and inorganic nutrients.

The highest yield per plot (3.03kg) was recorded under T 10 (25% RDF + 25% Azospirillum + 25% Azotobacter + 25% PSB), confirming the strong synergistic influence of integrated nutrient management on yield enhancement. This was followed by (2.72kg) T 5 (50% RDF + 50% Azospirillum), while the lowest plot yield (1.89kg) was obtained under T 1 (100% RDF), indicating the limited effectiveness of sole chemical fertilization. A similar pattern was observed when yield was expressed on a per-hectare basis. Treatment T 10 registered the maximum yield (139.6q/ha), followed by T 5 with (125.3q/ha) respectively. In contrast, T 1 produced the lowest yield (87.15 q/ha), further demonstrating that integrated use of biofertilizers with reduced RDF is more effective in increasing okra productivity than the exclusive application of inorganic fertilizers.

Titratable acidity differed markedly among the treatments. The lowest acidity content (0.20%) was recorded in T 10 (25% RDF + 25% Azospirillum + 25% Azotobacter + 25% PSB), indicating better biochemical quality under integrated nutrient application. This was followed by T 5 (50% RDF + 50% Azospirillum) with 0.31%, while T 2 (100% Azospirillum) and T 8 (50% Azospirillum + 50% Azotobacter) recorded 0.38% and 0.43%, respectively. In contrast, the highest acidity (0.75%) was observed in T 1 (100% RDF), suggesting that exclusive use of chemical fertilizers resulted in comparatively poorer fruit quality. which aligns with findings reported by (Singh and Devi 2020) [20] .

TSS ( 0 Brix)

The observations revealed that the treatments exerted a nonsignificant influence on TSS content; however, numerical differences were evident among the nutrient combinations.

The highest TSS value (3.06 °Brix) was obtained under T 10 (25% RDF + 25% Azospirillum + 25% Azotobacter + 25% PSB), indicating a slight improvement in soluble solids with integrated nutrient application. This was followed by T 8 (50% Azospirillum + 50% Azotobacter) and T 5 (50% RDF + 50% Azospirillum), which recorded 2.67 °Brix and 2.54 °Brix, respectively. In contrast, the lowest TSS (1.11 °Brix) was observed in T 1 (100% RDF), reflecting comparatively poorer fruit quality under sole inorganic fertilization. similar to trends noted by (Meena and Khatik 2018) [13] .

Ascorbic acid (mg/100 g) Ascorbic acid content varied significantly across the treatments, indicating a clear influence of inorganic fertilizers and biofertilizers on the vitamin C concentration of okra. The maximum ascorbic acid content (17.14 mg/100 g) was recorded under T 10 (25% RDF + 25% Azospirillum + 25% Azotobacter + 25% PSB), highlighting the positive impact of integrated nutrient management on enhancing nutritional quality. This was followed by T 5 (50% RDF + 50% Azospirillum) which recorded (16.60mg/100 g) respectively. The treatment T 8 (50% Azospirillum + 50% Azotobacter) also showed a moderate vitamin C level (13.62 mg/100 g). In contrast, the lowest ascorbic acid content (10.62 mg/100 g) was observed in T 1 (100% RDF), indicating comparatively reduced nutritional quality under sole inorganic fertilization. as supported by (Kumar and Thakur 2018) [9] .

Moisture content in okra fruits showed noticeable variation among the different nutrient treatments. The highest moisture percentage (87.63%) was recorded under T 10 (25% RDF + 25% Azospirillum + 25% Azotobacter + 25% PSB), indicating improved water retention and enhanced physiological activity due to integrated nutrient application. This was followed by T 5 (50% RDF + 50% Azospirillum) with (83.52%), recorded respectively. The lowest moisture content (82.50%) was observed in T 1 (100% RDF), suggesting comparatively reduced hydration levels under exclusive chemical fertilization. similar to trends noted by (Sharma and Verma 2019) [18] .

Conclusion

The present study demonstrates that the combined application of inorganic fertilizers and bio-stimulants significantly improved the growth, yield and quality of okra cv. Kashi Lalima. Among the treatments, T 10 (25% RDF + 25% Azospirillum + 25% Azotobacter + 25% PSB) consistently produced the highest plant height, number of leaves, stem diameter, number of flowers, early fruiting, fruit size, fruit girth, fruit weight, number of fruits per plot, yield per hectare and quality parameters including ascorbic acid, moisture content and lower titratable acidity. Treatments T 5 (50% RDF + 50% Azospirillum) and T 8 (50% Azospirillum + 50% Azotobacter) also showed positive effects but were comparatively less effective than T 10 . Sole application of inorganic fertilizers T 1 (100% RDF) was consistently the least effective in enhancing growth, yield and quality. The findings highlight that integrated nutrient management, combining reduced doses of chemical fertilizers with suitable bio-stimulants is a sustainable and efficient strategy to maximize okra productivity and improve fruit quality.

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