Interaction effect of different levels of phosphorus and biofertilizers on growth and yield of vegetable cowpea (Vigna unguiculata L. Walp)

Introduction

Cowpea [Vigna unguiculata (L.) Walp.], one of the members of family Fabaceae, with a chromosome number of 2n = 22, is an important annual legume crop grown for manifold uses such as vegetable, pulse, fodder and green manure (Saraviya et al., 2014) [14] . It is commonly defined as lobia, black-eyed pea, crowder pea or southern pea. The crop is believed to have originated in Central Africa and is widely cultivated in tropical and subtropical regions of the world. Compared to other legume crops, cowpea is known for its short duration, which enables crop to evade the impacts of climatic changes and exhibit better adaptability to wide range of abiotic stresses (Herniter et al. 2020) [8] . Cowpea is also recognized as a "poor man's protein" due to its high protein content, ranging from around 23-25 per cent on dry weight basis, along with appreciable amounts of carbohydrates, vitamins and minerals (Aremu et al. 2007) [2] . In India, this crop occupies an area of about 13.3 million hectares with a total production of 8.06 million tonnes and an average productivity of 596 kg ha⁻ ¹ (GOI, 2023) [6] . In Gujarat, it is cultivated over an area of 0.34 lakh hectares with a production of about 3.53 million tonnes (Anon., 2022) [1] . The integrated use of inorganic nutrient sources and organic fertilizers not only enhances nutrient supply and maintains overall soil health, but also increase the crop yield (Kumar and Singh, 2010) [11] . Indian soils are generally low to medium in available phosphorus and plants absorb approximately only 25% of phosphate that is soluble in water, with the remaining becomes converted into insoluble forms. Phosphorus is the second most important macronutrient after nitrogen (Halder and Panda, 2014) [7] and plays a crucial role in the development of roots for better nutrient and water uptake. It also promotes the Rhizobium bacterial activity enhancing biological nitrogen fixation and improving the efficacy of soil restorers and biomass. Biofertilizers are beneficial microbial product that are used to enhance the soil microbial activity in the Rhizosphere and improves the nutrient availability for easy assimilation by plants (Sudhakar and Ranganathan, 2020) [17] . Being ecologically, cost effective and renewable, they have become an important part of integrated nutrient management in order to improve crop productivity (Shroti et al. 2018) [16] . Biofertilizers such as Rhizobium, PSB and VAM act as key factors in improving the availability of nitrogen and phosphorus and increasing their uptake by plants. Inducing effective strains of Rhizobium in legume crops helps to improve soil fertility (Shekawat et al. 2018) [15] and root nodulation, thereby supporting better growth performance under nitrogen deficit soils. Phosphate Solubilizing Bacteria dissolve the inaccessible phosphates by bringing out more amount of unavailable fixed phosphates in soil into soluble forms (Elhaissoufi et al. 2022) [5] through the secretion of organic acids and enzymes. VAM forms a symbiotic interaction between fungus and plant roots, enhances phosphorus transport and uptake in plants. This VAM fungi unlike PSB does not solubilize unavailable phosphorus, but stimulate phosphorus, zinc and other nutrients along with their own need and aids in defending plants against pathogens, salinity and drought stress (Beck-Nielsen and Madsen, 2001) [3] . Despite these benefits, the productivity of cowpea remains constrained due to imbalanced nutrient management, poor soil fertility and limited adoption of improved agronomic practices. The country's existing level of production of pulse crops, especially cowpea remains inadequate to meet the growing demand. There is a considerable potential to enhance the productivity of cowpea through improved nutrient availability and biofertilizers. Therefore, the present study was undertaken with the view of improving crop performance and ensure sustainable cowpea production.

Materials and Methods

The field investigation was conducted during summer season 2024 and 2025 at Vegetable Research Farm, Regional Horticultural Research Station, ASPEE College of Horticulture, Navsari Agricultural University, Navsari under the South Gujarat agro-climate zone. The experiment was laid out in a Factorial Randomized Block Design concept comprising of twelve treatment combinations with four levels of phosphorus viz., P1: 50% RDP, P2: 75% RDP, P3: 100% RDP, P4: 125% RDP and three levels of biofertilizers viz., B0: no biofertilizer application, B1: PSB @ 1%, B2: VAM @ 0.2% replicated thrice. The soil of experimental field was clayey in texture, slightly alkaline in nature (pH 7.8) with low nitrogen, moderate phosphorus and high potassium content. Crop was fertilized as per the recommended dose of nutrients with NPK dose of 20:40:00 kg/ha. FYM (25 t/ha) was applied at the time of land preparation, where half dose of nitrogen in the form of urea and full dose of phosphorus in the form of SSP was applied as per the treatment combinations as a basal dose. The remaining dose of nitrogen was given in split doses at 30 and 45 DAS. Novel organic liquid nutrient at 1.5 % was given as common foliar application to all treatments at 30 DAS and 45 DAS. Seeds of cowpea variety AVCP-1 was sown at 25 kg/ha by maintaining a spacing of 45 x 30 cm with gross plot area of 3.6 x 3 m and net plot area of 2.7 x 2.4 m. Before sowing, seeds were inoculated with strains of Rhizobium and PSB each at 10 ml/kg of seeds. In addition, VAM at 2 g/kg of seeds were also used in seed inoculation. The observations on growth parameters i.e., days to first flowering, plant height (cm), number of branches per plant, number of leaves per plant, flowering node and yield parameters i.e., pod length (cm), pod width (cm), number of seeds per pod, number of pods per plant, number of pods per cluster, harvest index (%) and green pod yield (kg/ha and t/ha) were recorded at different growth stages from randomly tagged five plants. The results were subjected to statistical analysis using standard ANOVA method as suggested by Panse and Sukhatme, 1985 [12] . The application of phosphorus with PSB significantly improved the growth parameters of vegetable cowpea. Higher values were recorded with the treatment, 100% RDP along with 1% PSB. This improvement is attributed to essential role of phosphorus in plant metabolic processes such as energy transfer, cell division and root development.

Adequate phosphorus nutrition also enhances photosynthetic efficiency and carbohydrate metabolism, which contributes to higher vegetative growth and reproductive development.

In addition, phosphate solubilizing bacteria improves the availability of phosphorus in the rhizosphere by converting insoluble forms into available forms through the production of organic acids and phosphatase enzymes. The synergistic effect of phosphorus and PSB enhances nutrient uptake, microbial activity and overall nutrient use efficiency, leading to increased synthesis and translocation of assimilates to plant parts. Consequently, improved nutrient availability and efficient utilization of nutrients resulted in increased plant height, number of branches and leaves with earlier flowering. These findings are in close agreement with Surya Kant et al. (2016) [18] in Urdbean, Kothyari et al.

(2017) in garden pea, Punarbati Heisnam et al. (2017) [13] , Jayshree and Umesha (2021) [9] in cowpea and Danish et al.

Yield parameters

Different levels of phosphorus and biofertilizer combinations influenced the yield contributing parameters viz., pod length, pod width, number of seeds per pod, weight of pod, number of pods per plant, number of pods per cluster and green pod yield as depicted in Table 3.

Pod length recorded at the time of 6 th picking did not differ significantly. However, numerically higher pod length (14.35 cm) was observed under 100% RDP coupled with 1% PSB, while the lowest pod length (11.02 cm) was being observed under the treatment consisting of 50% RDP + no biofertilizer application (T1).

Relative to pod width, significant difference was observed at 6 th picking with maximum pod width (1.12 cm) recorded under the application of 100% RDP + 1% PSB (T8), which remained statistically at par with treatments, T5 (1.00 cm) and T12 (0.89 cm), whereas the minimum pod width (0.54 cm) was exhibited by the application of 50% RDP + no biofertilizer (T1). [13] , Jayshree and Umesha (2021) [9] in cowpea, Danish et al. (2025) [4] and Umeed et al. (2024) [9] in green gram.

Conclusion

From the results of present investigation, it can be concluded that 100% RDP combined with 1% PSB was observed to the best treatment with respect to earliness and in enhancing the growth and yield parameters of vegetable cowpea.

Acknowledgement

AcknowledgementThe authors express their sincere gratitude to the Department of Vegetable Science, Navsari Agricultural University, Navsari, Gujarat for providing essential facilities and guidance to successfully conduct the research work.

References

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