Effect of fertility levels and liquid bio-fertilizers on growth dynamics of Black gram (Vigna mungo L. Hepper)

Introduction

Black gram (Vigna mungoL. Hepper) commonly known as "Urd" belongs to family leguminosae is one of the important kharif pulse crops. It is commonly grown in summer and rainy seasons in Northern India. Black gram is highly nutritious, contain 24 per cent protein, 1.3 per cent fat, 0.9 per cent fiber,60 per cent carbohydrates, several vitamins and essential amino acids. Black gram is adaptable to various soil types, including those with low and high pH, acidic and alkaline or sodic soil (Yadav et al., 2024) [21] . Black gram is consumed in the form of 'dal' (whole or split, husked and un-husked) or perched. It differs from other pulses in its peculiarity of attaining mucilaginous pasty character when soaked in water. In the South, it is consumed in variety of ways across the form North to South in preparation of different regular and popular dishes like vada, idli, dosa, halwa, imarti in combination with other food seeds and also used as a nutritive fodder for milch cattle. It helps to controls soil erosions and competes with weeds effectively due to its deep root system and foliage dense cover. Additionally it fixes atmospheric nitrogen into the soil, thereby improving the soil fertility. Pulse plays a vital role in the Indian agriculture after cereals and oilseed crops because it is the second important constituent of diet after cereals. Pulses are essential with regards to its contribution to human nutrition and also in respect of their contribution to farmer's income. They also contribute significantly through enriching the soil with nitrogen fixation. India is the largest grower and consumer of pulses in the world. India is the world's largest producer as well as consumer of black gram. In India, during the year 2022-23, black gram occupied on 4.4 million ha area with production of 1.84 million tonnes and the average productivity was 598 kg ha -1 (Directorate of Economics and Statistics, 2022-23) [5] . Among the states, Rajasthan, Madhya Pradesh, Maharashtra, Andhra Pradesh, Uttar Pradesh, Tamil Nadu and Gujarat are the major black gram producing states. In Rajasthan, black gram is predominantly grown in kharif season under rainfed conditions. In the Rajasthan state, black gram occupies 3.21 lakh ha area with production of 1.35 lakh tonnes and the average productivity was 420 kg ha -1 (Department of Agriculture, Government of Rajasthan, 2022-23) [3] . In Rajasthan, it is mainly cultivated in Chittorgarh, Udaipur, Ajmer, Jhalawar, Kota, Bundi and Baran districts. In the recent years, continuous and imbalance application of chemical fertilizers with little or no use of organic manure is leading to poor nutrient use efficiency, low yield of crop, poor physical and biological property of soil. At the same time increasing cost of production due to more and more use of costly nutrient sources is becoming unaffordable to the most of farmers. Hence, it has become imperative to search for other complementary and alternative sources of nutrients, among which use of bio-fertilizers of biological origin in black gram is an important avenue. In this approach, microbial fertilization with Rhizobium well as NPK consortium has been found promising to improve soil health and crop production there has been understandable concern about decline in the per capita availability of pulses. Nitrogen plays important role in synthesis of chlorophyll, amino acids and other organic compounds of physiological significance in plant system. Nitrogen is the most frequently deficient nutrient in crop production, and most nonlegume systems require nitrogen inputs. Phosphorus is second important nutrient for crop after nitrogen. Phosphorus is referred to as the "kingpin" in Indian agriculture and also as the "energy currency" of plants (Dey et al., 2017) [4] . Its role in root development, nodule formation and plays important role in energy transfer in the living cells by means of high energy phosphate bond of ATP. Phosphorus is an important for formation and translocation of carbohydrate, fatty acids, glyceroides and other essential intermediate compounds.

Rhizobium plays an important role in increasing the availability of nitrogen to the plants and helps in boosting the production through nitrogen fixation. Bio-fertilizers are compounds that contribute nutrients the natural process of fix atmospheric nitrogen, solubilizing phosphorous and aid for plant development through the manufacture of growth encouraging material (Suhag et al., 2016) [19] . Economic success of these legumes depends upon symbiotic nitrogen fixation, so seed inoculation with appropriate strains of Rhizobium is important to improve symbiotic nitrogen fixationwhichrequiressurvivalandestablishmentofinoculatedrhizo biainthesoil environment (Da and Deng, 2003) [2] . However,manybioticandabioticfactorsaffectthe persistenceofsymbioticallyeffectiveintroduced rhizobial strainin soil(Sessitschet al., 2002; Lebrazi and Benbrahim 2014) [16,11] . It has been observed that the properly screened local strains are more effective for a particular agro-climatic region than the strains imported from other places in general (Gupta et al., 2000) [7] .

Materials and Methods

A field experiment was conducted at block F 2 , Dryland Farming Research Station, Arjia, Bhilwara (Rajasthan) during kharif, 2025. The experimental soil was clay-loam in texture, slightly alkaline in reaction (pH 7.32), low in organic carbon and available nitrogen, medium in available phosphorus and high in available potassium. The experiment was laid out in a factorial randomized block design with three replications, comprising four fertility levels viz. control, 50% RDF, 75% RDF and 100% RDF and four liquid bio-fertilizers viz. control, Rhizobium @ 5ml kg -1 , NPK consortium @ 5 ml kg -1 and Rhizobium + NPK consortium. The test crop was black gram variety KU-4, sown at a spacing of 30 cm × 10 cm with a seed rate of 15 kg ha -1 . The recommended dose of fertilizer was 20:40 NP kg ha -1 and half nitrogen and full dose of phosphorus were applied at sowing through urea and DAP. The crop was managed through gap filling, pre-emergence atrazine, post-emergence metsulfuronmethyl and hand weeding at critical stages. Observations were recorded on plant height and dry matter accumulation using standard procedures and the data were analyzed by ANOVA as per factorial randomized block design (Panse and Sukhantme, 1985) [12] .

Results and Discussion

Fertility levels: During kharif 2025, fertility levels had a significant effect on all growth parameters of black gram including plant height and dry matter accumulation. Plant height remained non-significant at 30 DAS, possibly because seedlings mainly depend upon seed reserves during the early growth stages. Application of 100% RDF recorded the tallest plants at 60 DASand at harvest with 45.86 and 53.33 cm, respectively which was statistically at par with 75% RDF (45.02 and 53.30 cm) but higher than 50% RDF and control. However, significant improvement at later stages might be due to improved nutritional status of the plant, which enhanced the synthesis of amino acids, proteins and growth-promoting substances, there by stimulating meristematic activity, cell division and cell elongation. Similar findings were reported by Singh et al. (2014) [17] , Jaiswal et al. (2019) [8] , Sarkeret al. (2020) [14] .A similar trend was observed for dry matter accumulation, where 100% RDF recorded the highest values of 2.13, 13.40 and 18.60 g plant -1 at 30, 60 DAS and at harvest, respectively followed by 75% RDF with 17.98, 13.16 and 2.08 g plant -1 . This enhancement might be attributed to improved morphological growth of plants, which facilitated greater interception and efficient utilization of solar radiation, there by promoting higher photosynthetic activity. Adequate fertilizer supply also enhanced the plantsability to utilize favourable environmental conditions for increased synthesis and accumulation of photosynthates, ultimately resulting in higher biomass production. Singh et al. (2020) [18] and Parashar and Tripathi (2020) [13] .

Liquid Bio-fertilizers Among the liquid bio-fertilizers, Rhizobium + NPK consortium recorded the best growth performance as it produced the highest plant height at 60 DAS and at harvest with 46.34 and 53.80 cm, respectively and these values were statistically at par with NPK consortia @ 5ml kg -1 but superior to Rhizobium and control. Rhizobium + NPK consortium also recorded the highest dry matter accumulation of 2.14, 13.50 and 18.52 g plant -1 at 30, 60 DAS and at harvest, respectively. The superior growth performance under Rhizobium + NPK consortium might be attributed to enhanced symbiotic nitrogen fixation, solubilization of insoluble phosphorus and potassium, production of organic acids, chelating compounds in the rhizosphere, and synthesis of plant growth-promoting substances. Similar findings were reported by Selvakumaret al. (2012) [15] , Bhutadiyaet al. (2019) [1] , Gohil et al. (2021) [6] and Verma et al. (2025) [20] . NPK consortia remained statistically at par with Rhizobium + NPK consortium for most growth parameters, likely due to enhanced nutrient availability through nitrogen fixation, phosphorus solubilization and potassium mobilization by beneficial microorganisms, as also reported by Jangir et al. (2016) [9] and Kant et al. (2016) [10] .

Conclusion

Based on findings, it is proposed that application of 100% RDF recorded the best growth performance in black gram, with the highest plant height and dry matter accumulation. Among the liquid bio-fertilizers, Rhizobium + NPK consortium performed best and was better than NPK consortia, Rhizobium and control. Overall, the combined use of 100% RDF and Rhizobium + NPK consortium was most effective for improving growth of black gram.

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