Effect of potassium mobilizing bacteria on growth and yield of black gram (Vigna mungo L.)

Introduction

Black gram (Vigna mungo L.), also known as Urd bean, is an important short-duration pulse crop belonging to the Fabaceae family, widely cultivated in India because of its high nutritional value, adaptability to diverse agro-climatic conditions and ability to contribute to soil fertility through biological nitrogen fixation making it suitable for sustainable cropping system. This pulse crop is rich in nutrients, containing 20-25% protein, 55-65% carbohydrates, 1.3% fats and 40-47% starch as well as various minerals such as phosphorus, potassium, calcium, iron, magnesium, sodium, zinc, copper and essential vitamins (Vitamin A, Vitamin B 1 , Vitamin B 3 , Vitamin C and trace amounts of thiamine, riboflavin, niacin) (Swaminathan et al, 2020) [12] . Owing to its high nutritional value, black gram forms an important component of the vegetarian diet in India and holds considerable significance in sustainable pulse-based production systems. Despite its importance, the productivity of black gram remains constrained by several factors, including inadequate and imbalanced nutrient supply. Among the major plant nutrients, potassium plays an important role in growth and yield as it is involved in assimilation, transport, and storage tissue development (Nathiya et al, 2015) [7] . Potassium is required in relatively large quantities by plants and has a significant influence on several biochemical and physiological processes. It regulates stomatal movement, maintains cellular osmotic balance, enhances photosynthetic activity and contributes to the efficient translocation of assimilates from source to sink. In black gram, potassium has been known to significantly improve growth, yield and nutrient uptake, demonstrating the importance of potassium management for achieving higher productivity (Athokpam et al., 2009; Karthikeyan et al., 2020) [1,5] . However, the total potassium content in soil does not necessarily reflect its availability in the plants, as a major proportion of soil potassium exists in mineral and nonexchangeable forms that are not readily accessible to the crops. Despite potassium being the seventh most abundant element found in the Earth's crust, only 1 to 2% of this element is available to plants (Sparks and Huang, 1985) [10] . About 90 to 98% of the total potassium present in the soil is found locked within primary minerals in insoluble forms such as feldspar, mica, and illite, which are unavailable to plants (Olaniyan et al., 2022; Meena et al., 2014) [8,6] . K in soil is present in several forms, including mineral K, non-exchangeable K, exchangeable K and solution K. Continuous cropping and intensive cultivation have accelerated the depletion of available potassium from their reserves, thereby resulting in reduced crop productivity and nutrient use efficiency. Consequently, improving the availability of native soil potassium is a necessary component of efficient potassium management. Potassium mobilizing bacteria (KMB) can be used as a promising biological approach for increasing the availability of otherwise inaccessible forms of potassium in soil. These microorganisms are capable of releasing potassium in soluble forms through mechanisms such as production of organic and inorganic acids, chelation, acidolysis, polysaccharides production, complexolysis and exchange reactions (Etesami et al., 2017) [3] . Through these mechanisms, KMB enhance the release of potassium from soil minerals and improves its availability in the rhizosphere. Inoculation with KMB may consequently improve plant nutrient acquisition and create more favourable conditions for plant growth and yield formation. Efficient nutrient management is essential for achieving higher productivity in black gram. Integrated nutrient management provides a sustainable and environmentally sound strategy for improving crop performance while reducing the dependency on chemical fertilizers. In this context, the present study was undertaken to evaluate the influence of potassium mobilizing bacteria (KMB) biofertilizer in combination with varying levels of soil-applied potassium fertilizer on the growth and yield of black gram.

Materials and Methods

The field experiment was conducted during Kharif 2025 at the Research Farm of the Department of Soil Science, College of Agriculture, Latur. Black gram (Vigna mungo L.) variety NUL-7 (Vishwas) was used for the study. The experimental field was uniform and levelled. The soil of the research farm was dark grey to brown in colour, clayey in texture and dominated by 2:1 type smectite clay minerals. The site falls under hyperthermic temperature regimes, and is characterized by very gentle slopes with moderate erosion. The experiment was laid out in a Randomized Block Design (RBD) comprising eight treatments, each replicated three times. The treatments were T 1 -Control, T 2 -100% RDF, T 3 -100% RDNP + 75% RDK + KMB Seed treatment, T 4 -100% RDNP + 50% RDK + KMB Seed treatment, T 5 -100% RDNP + 75% RDK + KMB Seed treatment + Drenching of KMB at 20 DAS, T 6 -100% RDNP + 50% RDK + KMB Seed treatment + Drenching of KMB at 20 DAS, T 7 -100% RDNP + 75% RDK + KMB Seed treatment + Drenching of KMB at 20 and 40 DAS and T 8 -100% RDNP + 50% RDK + KMB Seed treatment + Drenching of KMB at 20 and 40 DAS. The gross plot size was 3.9 m x 4.0 m. Black gram was sown at a spacing of 30 cm between rows and 10 cm between plants. Nitrogen, phosphorus, and potassium were supplied through urea, single superphosphate (SSP), and muriate of potash (MOP), respectively. The biochemical analysis involved assessing parameters such as plant height, leaf area, seed yield, and straw yield. The recorded data were subjected to appropriate statistical analysis for an RBD, and the treatment means were compared using the critical difference (CD) test at the 5% level of significance.

Results and Discussion

Growth parameters

The date presented in Table 1 indicated that the numerically higher growth parameters, namely plant height (cm) and leaf area (cm 2 plant -1 ) were recorded with T 7 (100% RDNP + 75% RDK + KMB Seed treatment + Drenching of KMB at 20 and 40 DAS). The highest plant height of 16.81 cm, 28.89 cm and 38.98 cm at 30, 45 and 60 DAS, respectively, and leaf area of 482.62 and 515.77 cm 2 plant -1 at 30 and 45 DAS, respectively were recorded under T 7 and it was found to be statistically at par with, T 5 (100% RDNP + 75% RDK + KMB Seed treatment + Drenching of KMB at 20 DAS) and T 8 (100% RDNP + 50% RDK + KMB Seed treatment + Drenching of KMB at 20 and 40 DAS). The lowest value was recorded under T 1 (control). The superior growth performance observed under T 7 may be attributed to the combined effect of potassium fertilization and KMB application. Potassium mobilizing bacteria (KMB) can enhance the availability of potassium in the soil through the production of organic acids and other biochemical processes that facilitate the dissolution and mobilization of potassium from their fixed forms into plant accessible forms. Improved potassium availability may have promoted photosynthetic activity, enzyme activation, cell growth and efficient translocation of assimilated nutrients, thereby supporting plant growth. Furthermore, the nutrients made available through KMB application may have enhanced metabolic activities, cell division and cell elongation, resulting in better plant development. Thus, all of these combined may have created a favourable condition for vegetative growth and development of black gram. The result was in accordance with the findings of Sree et al. (2026) [11] , Thuvaraka et al. (2023) [13] , Bhat et al. (2022) [2] and Ghetiya et al. (2018) [4] .

Yield

The data presented on Table 2 revealed that the application of KMB in combination with different levels of potassium significantly improved seed yield and straw yield of black gram. Among the treatments, T 7 recorded the highest seed yield (11.16 q ha -1 ) and straw yield (17.78 q ha -1 ). The performance of T 7 was statistically at par with that of T 5 and T 8 , whereas the lowest values for seed yield (7.50 q ha -1 ) and straw yield (11.75 q ha -1 ) were recorded under T 1 (control). The superior performance under T 7 may be attributed to the synergistic effect of KMB application and potassium fertilization, which improved the availability and utilization of potassium and other nutrients. Improved nutrient uptake and translocation may have promoted reproductive development, carbohydrate synthesis and assimilate partitioning, resulting in a greater higher seed yield. Enhanced vegetative growth and dry matter accumulation due to continuous nutrient supply during critical growth stages may have further contributed to the higher straw yield recorded under T 7 . These findings are in agreement with the findings of Sree et al. (2026) [11] and Rohan et al. (2022) [9] . Effect of potassium mobilizing bacteria on seed yield (q ha -1 ) and straw yield (q ha -1 ) after harvest of black gram.

Conclusion

Based on the above results, it can be concluded that the growth parameters such as plant height, leaf area and yield (seed yield and straw yield) of black gram increased with the combined application of 100% RDNP + 75% RDK + KMB Seed treatment + Drenching of KMB at 20 and 40 DAS as compared to the control and other treatments.

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