Impact of plant growth stimulant (amino acid + fulvic acid) on morpho-physiological, yield and yield attributes of soybean (Glycine max L.)

Introduction

Soybean (Glycine max L. Merrill) is an important leguminous oilseed crop belonging to the family Fabaceae, with a diploid chromosome number of 2n = 40. Soybean is one of the most important leguminous oilseed crops in the world owing to its high protein (38-42%) and oil (18-22%) contents, making it an important source of food, feed and industrial raw materials (Liu, 1997; Rongli et al., 2020) [7,12] . Besides its nutritional and economic importance, soybean contributes significantly to sustainable agriculture through biological nitrogen fixation, which improves soil fertility and reduces dependence on synthetic nitrogen fertilisers (Pandey and Singh, 2019; Teixeira et al., 2018) [11,14] . However, soybean productivity is frequently constrained by poor nutrient use efficiency, imbalanced fertilisation, environmental stresses and inadequate crop management practices, resulting in yields considerably below the genetic potential of modern cultivars (Rouphael and Colla, 2020; Vishwanatha et al., 2022) [13,15] . In recent years, plant biostimulants have emerged as an eco-friendly and sustainable approach for improving crop productivity by stimulating natural physiological and biochemical processes without acting solely as nutrient sources (du Jardin, 2015; Calvo et al., 2014; Rouphael and Colla, 2020) [4,3,13] . According to the European Biostimulant Industry Council, plant biostimulants enhance nutrient use efficiency, improve tolerance to abiotic stress and promote crop quality through multiple physiological mechanisms (du Jardin, 2015; Rouphael and Colla, 2020) [4,13] . Among the different categories of biostimulants, amino acid-and fulvic acid-based formulations have received considerable attention because of their ability to improve nutrient uptake, photosynthetic efficiency, chlorophyll synthesis, enzyme activation, and assimilate translocation (Calvo et al., 2014; Teixeira et al., 2018; Baghdadi et al., 2022) [3,14,1] . Amino acids function as precursors of proteins, enzymes, phytohormones and chlorophyll, while fulvic acid enhances membrane permeability, nutrient mobility and metabolic activity, collectively promoting plant growth and development (Rouphael and Several studies have demonstrated that foliar application of amino acid-based biostimulants significantly improves plant height, leaf area, chlorophyll content, photosynthetic efficiency, flowering behaviour, yield attributes and seed quality in field crops (Kocira et al., 2018; Melo et al., 2024; Han et al., 2024) [6,9,5] . Likewise, humic and fulvic substances have been reported to enhance nutrient acquisition, root growth, carbon assimilation and dry matter accumulation, resulting in increased crop productivity and improved seed quality (Teixeira et al., 2018; Baghdadi et al., 2022) [14,1] . Despite the growing use of plant biostimulants, information on the optimum concentration of Plant Growth Stimulant (PGS) for improving morphophysiological traits, yield attributes and seed quality of soybean under the agro-climatic conditions of Chhattisgarh remains limited. Therefore, the present investigation was undertaken to evaluate the effect of different concentrations of foliar-applied Plant Growth Stimulant (PGS) on morphophysiological traits, yield attributes, seed yield and seed quality of soybean.

Material and methods 2.1 Plant material and experimental conditions

The present investigation, entitled "Impact of biostimulant on morpho-physiological Traits, yield and yield attributes of Soybean (Glycine max L.)" was conducted during the kharif season of 2025-26 at the, College of Agriculture, Indira Gandhi Krishi Vishwavidyalaya (IGKV), Raipur, Chhattisgarh, India. The experiment was laid out in a Randomised Block Design (RBD) with three replications comprising six treatments: T₁ (Control), T₂ (PGS @ 2 ppm), T₃ (PGS @ 4 ppm), T₄ (PGS @ 6 ppm), T₅ (PGS @ 8 ppm) and T₆ (PGS @ 10 ppm). The soybean variety RSC-1040 was sown on 08 July 2025, following the recommended package of practices. Plant Growth Stimulant (PGS), an amino acid-and fulvic acid-based biostimulant, was applied as a foliar spray at the pre-flowering and pre-pod formation stages according to the respective treatment concentrations, whereas distilled water was sprayed in the control treatment. All agronomic and plant protection practices were kept uniform for all treatments throughout the experimental period.

Morpho-physiological parameters

Morphological observations, including plant height, number of leaves and number of branches per plant, were recorded at the specified crop growth stages. Physiological parameters comprising SPAD chlorophyll index, chlorophyll fluorescence (Fv/Fm), specific leaf area (SLA) and specific leaf weight (SLW) were measured following standard procedures. Phenological observations, including days to first flowering, days to 50% flowering and days to pod initiation, were also recorded during the crop growth period.

Yield and yield attributes

At physiological maturity, observations on pods per plant, pod length, number of seeds per pod, 100-seed weight, seed yield per plant, biological yield and harvest index were recorded following standard procedures. The recorded observations were used to evaluate the effect of different concentrations of Plant Growth Stimulant on soybean productivity.

Statistical analysis

The experimental data were subjected to analysis of variance (ANOVA) appropriate for the Randomised Block Design (RBD). Treatment means were compared using the Critical Difference (CD) test at the 5% level of significance, wherever the F-test indicated significant treatment effects.

Result and Discussion

assimilate availability during the reproductive stage (Baghdadi et al., 2022; Kocira et al., 2018) [1,6] . Overall, the superior performance of PGS @ 6 ppm for most growth, physiological and yield traits indicates that this concentration provided optimum physiological stimulation for improving soybean productivity under the experimental conditions (Rouphael and Colla, 2020; Vishwanatha et al., 2022) [13,15] .

Conclusion

The present investigation demonstrated that foliar application of Plant Growth Stimulant (PGS) containing amino acid and fulvic acid can effectively improve the growth, physiological performance, yield attributes and productivity of soybean under the agro-climatic conditions of Chhattisgarh. Among the evaluated treatments, PGS @ 6 ppm (T₄) showed the most consistent and superior performance, recording higher number of leaves and branches, SPAD chlorophyll index, chlorophyll fluorescence, pods per plant, pod length, seeds per pod, biological yield, seed yield and harvest index. PGS @ 4 ppm performed better for plant height at earlier growth stages and 100-seed weight, while higher concentrations also improved several physiological and yield traits. The findings indicate that an optimum concentration of PGS can enhance photosynthetic efficiency, assimilate production and reproductive development, ultimately contributing to greater soybean productivity. Therefore, foliar application of PGS @ 6 ppm at pre-flowering and pre-pod formation stages may be considered a promising approach for improving soybean growth, yield and physiological performance under similar agro-climatic conditions.

References

1. Baghdadi A, Della Lucia MC, Borella M, Bertoldo G, Ravi S, Zegada-Lizarazu W, Chiodi C, Pagani E, Hermans C, Stevanato P, Nardi S, Monti A, Mangione F. A dual-omics approach for profiling plant responses to biostimulant applications under controlled and field conditions. Front Plant Sci. 2022;13:983772.
2. Bulgari R, Franzoni G, Ferrante A. Biostimulants Application in Horticultural Crops under Abiotic Stress Conditions. Agronomy. 2019;9(6):306.
3. Calvo P, Nelson L, Kloepper JW. Agricultural uses of plant biostimulants. Plant Soil. 2014;383(1-2):3-41.
4. du Jardin P. Plant biostimulants: Definition, concept, main categories and regulation. Sci Hortic. 2015;196:314.
5. Han Ş, Sönmez İ, Qureshi M, Güden B, Gangurde SS, Yol E. The effects of foliar amino acid and Zn applications on agronomic traits and Zn biofortification in soybean (Glycine max L.). Front Plant Sci. 2024;15:1382397.
6. Kocira S, Szparaga A, Kocira A, Czerwińska E, Wójtowicz A, Bronowicka-Mielniczuk U, Koszel M, Findura P. Modeling biometric traits, yield and nutritional and antioxidant properties of seeds of three soybean cultivars through the application of biostimulant containing seaweed and amino acids. Front Plant Sci. 2018;9:388.
7. Liu K. Soybeans: Chemistry, Technology, and Utilization. New York: Chapman & Hall; 1997.
8. Manu SM, Halagalimath SP, Biradar BD, Chandranath HT. Effect of nutrient management on chlorophyll content (SPAD value) and productivity of soybean (Glycine max L.). Int J Chem Stud. 2020;8(1):19791981.
9. Melo SM, Figueiredo CC, Ramos MLG, Rocha OCB, Aguiar ER, Oliveira AD. Effects of foliar application of amino acid-based biostimulants on growth and yield of soybean. Agron J. 2024;116(2):451-462.
10. Moe S, Girdthai T. Relationships of soybean (Glycine max L. Merrill) accessions based on physiological and agro-morphological traits. Int J Chem Environ Biol Sci. 2013;1(2):375-379.
11. Pandey AK, Singh AK. Effect of drought stress on physiological traits of soybean. Legume Res. 2019;42:522-528.
12. Rongli H, Yang Z, Yuan S, Zhou X. Research status of soybean symbiosis nitrogen fixation. Oil Crop Sci. 2020;5(1):6-10.
13. Rouphael Y, Colla G. Biostimulants in agriculture. Front Plant Sci. 2020;11:40.
14. Teixeira WF, Fagan EB, Soares LH, Soares JN, Reichardt K, Dourado Neto D. Seed and foliar application of amino acids improve variables of nitrogen metabolism and productivity in soybean crop. Front Plant Sci. 2018;9:396.
15. Vishwanatha S, Ramarao R, Shwetha BN, Koppalkar BG, Ashoka N, Ananda N, Umesh MR, Vinaykumar M, Naik VS. Response of blackgram (Vigna mungo L.) and soybean (Glycine max L.) to novel biostimulants in North Eastern Dry Zone of Karnataka. Legume Res. 2022;45(9):1130-1136.