Effect of foliar application of biostimulants on growth, yield and quality of onion cv. Akola Safed

Introduction

Among the bulb vegetables of the Alliaceae family, onion (Allium cepa L.) holds a distinct place in Indian agriculture, valued not only as an everyday culinary condiment but also as a crop that supports farmers' incomes and contributes meaningfully to horticultural exports. During 2024-25, the country grew onion on close to 1.97 million hectares, producing 30.77 million tonnes at a productivity of 15.62 t ha⁻¹, with Maharashtra, Madhya Pradesh and Karnataka accounting for the bulk of national output (Government of India, 2025) [6] . Akola Safed, a white-bulbed variety developed at Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola, is prized locally for its bulb quality and its ability to store well after harvest. Even so, field-level productivity of this and other varieties keeps running into trouble because of erratic weather and the usual mix of biotic and abiotic stresses that vegetable growers face problem about. Against this problem, biostimulants have gained popularity as a comparatively sustainable way to lift crop performance, working through improved nutrient-use efficiency and physiological resilience rather than by supplying nutrients straight away. Broadly, these are substances or microorganisms that, once applied, switch on natural physiological pathways in the plant that improve how well it takes up and uses nutrients, cope with abiotic stress, and finish with better quality produce-and they do this irrespective of what nutrients they themselves contain. Each of the biostimulants examined here works somewhat differently: humic and fulvic acids aid nutrient absorption and root proliferation; PDKV Humi-K, a humic-acid formulation enriched with phosphorus and potassium, adds a nutritional component on top of the usual humic-substance effects; amino-acid biostimulants act as ready-made building blocks for protein synthesis and help plants recover metabolically under stress; silicic acid reinforces cell walls and improves stress tolerance; and seaweed extracts, being naturally rich in cytokinins and other bioactive molecules, drive cell division and slow down senescence. Despite this range of known modes of action, there is still little comparative evidence on how these particular biostimulants perform on onion cv. Akola Safed under Vidarbha's agro-climatic conditions. The present study was undertaken to fill that gap and examine the effect of their foliar application on the growth and yield of this variety.

Materials and Methods

This study was conducted at the Instructional Farm, Department of Vegetable Science, Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola (Maharashtra), during rabi 2024-25. Seven treatments were tested in a Randomised Block Design with three replications: T 1 (Humic acid 0.2%), T 2 (PDKV Humi-K 2.5%), T 3 (Fulvic acid 0.1%), T 4 (Amino acid 0.2%), T 5 (Silicic acid 0.5%), T 6 (Seaweed extract 0.2%) and T 7 , an untreated control sprayed with plain water. All treatments were applied as foliar sprays. Seedlings of onion cv. Akola Safed went into the field on 10th January 2025, spaced at 15 × 10 cm, with a gross plot size of 3 × 2 m². Before transplanting, FYM was worked in at 25 t ha⁻¹ along with a basal dose of 50:50:50 kg N:P 2 O 5 :K 2 O ha⁻¹; a further 50 kg N ha⁻¹ was top-dressed 30 days later. Other than these treatments, the crop was managed as per the standard package of practices followed in the region. Growth was tracked through plant height and number of leaves per plant, both recorded at 30, 60 and 90 days after transplanting (DAT), along with the number of days taken to reach harvest maturity. On the yield side, the parameters recorded included average bulb weight, total yield, marketable yield, grading of bulbs into A, B and C categories based on equatorial diameter, and the percentage of splitted bulbs, all following standard procedures for onion. Data were analysed statistically following Panse and Sukhatme (1989) [9] ; standard error of mean (S. Em±) and critical difference (CD) at the 5% level were computed for every character studied.

Results and Discussion

A. Growth parameters Plant height (cm): Treatment differences in plant height (Table 1) had not yet shown up at 30 DAT, but became statistically significant by 60 and 90 DAT. By 60 DAT, plants sprayed with Amino acid 0.2% (T 4 ) had grown tallest, at 58.03 cm, a figure statistically on par with T 3 , Fulvic acid 0.1% (57.33 cm); the control (T 7 ) lagged behind at 50.80 cm. This pattern held at 90 DAT as well-T 4 again led at 65.87 cm, on par with T 3 at 63.63 cm, with T 7 once more the shortest at 56.40 cm. Amino acids applied to the foliage are absorbed quickly and can be used almost directly in protein synthesis, sparing the plant the metabolic cost of assimilating nitrogen from scratch; the energy saved appears to be redirected towards cell division and elongation, which would explain the taller plants under T 4 . Comparable responses have been reported by El-Shabasi et al. (2005) [4] in garlic, Shafeek et al. (2018) [10] in onion, Tejada and Gonzalez (2003) [11] in asparagus, and Zewail (2014) [12] in common bean. [7] and Ahmed et al. (2019) [2] in onion. [8] observed. [8] and El-Shafie et al.

(2019) [5] reported broadly similar gains with fulvic acid in onion.

Marketable yield

The marketable fraction of the crop showed the same lead for T 3 , Fulvic acid 0.1% (26.74 t/ha), on par with T 2 , PDKV Humi-K 2.5% (25.74), T 1 , Humic acid 0.2% (25.21) and T 6 , Seaweed extract 0.2% (23.66), against a low of 20.71 t/ha in the control. Fulvic acid's low molecular weight and strong chelating ability appear to have driven this jump in marketable output, by improving nutrient absorption and translocation and, in turn, photosynthate accumulation in the bulb-resulting in better-developed bulbs and fewer culls needing to be discarded at grading. The broadly similar performance of PDKV Humi-K (T 2 ) and humic acid (T 1 )

likely stems from a related mechanism: both are known to encourage root proliferation and more efficient nutrient utilisation, which supports better bulb bolding even without fulvic acid's sharper chelating action. The control (T 7 ), receiving no biostimulant, fell short on marketable yield simply because bulb development itself remained insufficient. These trends for onion agree with the findings of Mahmoud et al. (2019) [8] and Alhrout and Hasan (2021) [3] in onion. Grading of onion bulbs: Grading the bulbs into A, B and C categories (Table 5) turned up clear treatment effects across all three grades. T 3 (Fulvic acid 0.1%) put out the largest share of premium A-grade bulbs, 42.35%, clearly ahead of every other treatment, while the control managed only 25.30%. B-grade bulbs peaked under T 6 , Seaweed extract 0.2% (39.56%), on par with T 1 and T 2 , and were lowest under T 3 (31.88%)-which makes sense, since fulvic acid was pushing more of its bulbs up into the A category instead. The control also carried the largest share of small, C-grade bulbs (31.20%), pointing to weaker bulb development where no biostimulant was used, whereas T 3 again had the fewest (20.76%). Taken together, these numbers suggest fulvic acid was not simply widening the spread of bulb sizes but genuinely pushing overall bulb development upward, likely through the same chelation-driven nutrient availability discussed above-a pattern also reported by Mahmoud et al.

(2019) [8] and El-Shafie et al. (2019) [5] . Splitted bulbs: Bulb splitting also differed significantly across treatments (Table 6), with T 6 (Seaweed extract 0.2%) keeping it lowest at 1.18%, on par with T 4 , Amino acid 0.2% (1.25%), against a high of 2.96% in the control. Splitting happens when a bulb ends up with more than one growing point instead of one, usually because the hormonal balance driving growth has shifted and apical dominance has broken down. Seaweed extract's effect here likely traces back to the same cytokinin activity discussed earlier-by helping the primary growing point hold its dominance, it appears to keep secondary growing points from taking off, giving more compact, evenly formed bulbs. Abbas et al. (2020) [1] reported a similar reduction in splitting with seaweed extract.

Economics

Benefit: Cost ratio Working through the cost and returns for each treatment (Table 7), T 3 (Fulvic acid 0.1%) came out well ahead on both counts-a net monetary return of Rs. 2,17,308 ha⁻¹ and a benefit:cost ratio of 2.67-with T 2 (PDKV Humi-K 2.5%) close behind at Rs. 2,02,808 ha⁻¹ and a ratio of 2.52. The control brought up the rear, returning only Rs. 1,48,508 ha⁻¹ at a B:C ratio of 2.15. On the whole, spraying Fulvic acid at 0.1% turned out to be the most profitable option among those tested for onion cv. Akola Safed.

Future Scope

There is still room to work out the ideal concentration, spray frequency and growth stage for applying each of these biostimulants, and to see how they behave when combined or applied in sequence rather than alone. It would also help to test them across other onion cultivars, seasons and agroclimatic zones before drawing broader conclusions, and to look more closely at how economically consistent they are under actual farmers' field conditions-something this singleseason trial cannot fully answer on its own.

Conclusion

Putting these findings together, no single biostimulant swept every parameter, but clear patterns did emerge. Amino acid (0.2%) gave the tallest plants, Seaweed extract (0.2%) produced the most leaves per plant, and Fulvic acid (0.1%) brought bulbs to harvest earliest. On the yield side, Fulvic acid (0.1%) again led for average bulb weight, total yield, marketable yield and the share of premium A-grade bulbs and Seaweed extract (0.2%) kept bulb splitting to a minimum. Weighing yield performance against the economics of each treatment, Fulvic acid (0.1%) stands out overall as the most effective and profitable biostimulant for boosting growth and yield in onion cv. Akola Safed.

Acknowledgement

AcknowledgementI would like to thank Dr. A. P. Wagh, Professor, and Dr. A. M. Sonkamble, Professor and Head, Department of Vegetable Science, Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola, for their guidance and support throughout this work, and the Department of Vegetable Science, Dr. PDKV, Akola, for the facilities that made this investigation possible.

References

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