Effect of native zinc solubilizing bacteria and zinc levels on growth, yield and economics of maize

Introduction

Maize (Zea mays L.), commonly referred to as the "queen of cereals," is the third most significant cereal crop globally following rice and wheat. It belongs to the poaceae family and is a versatile staple crop that thrives across various environmental conditions. Nutritionally, maize grain contains approximately 6.38% crude protein, 2.81% crude fat, 53.12% TDN, 22.5% hemicellulose and 32.9% cellulose (Noersidiq et al., 2024) [10] , though its primary protein zein lacks essential amino acids such as tryptophan and lysine. The crop is predominantly grown under rainfed conditions, typically requiring 300-500 mm of rainfall (Sah et al., 2020) [12] . Globally, the United States continues to dominate maize production, with an estimated output of 432.34 million metric tonnes for 2025-26 (USDA). In the agricultural year 2025-26, India ranks as the sixth-largest maize producer globally, with approximately 144.08 lakh hectares under cultivation with a production of 550.93 lakh tonnes and an average productivity of 3824 kg/ha (Anon., 2025a). Madhya Pradesh leads in both area and production, followed by Karnataka, Maharashtra, Bihar and Andhra Pradesh. In Gujarat during 2025-26, maize occupied 414.72 thousand hectares with production of 949.85 thousand tonnes and an average productivity of 2290.75 kg/ha. Widespread zinc deficiency in soils not only limits crop yields but also adversely affects the nutritional quality of food. Zinc plays a key role in various enzymatic, metabolic and redox reactions within plants. A deficiency in Zn disrupts the synthesis of carbohydrates, chlorophyll, auxins, cytochromes and nucleotides and compromises membrane stability (Das et al., 2018) [5] . Studies suggest that 96-99% of applied Zn becomes unavailable in soil due to its transformation into insoluble forms, posing a significant challenge especially in calcareous soils. Zinc solubilizing bacteria (ZSB) residing in the rhizosphere convert insoluble Zn fractions into bioavailable forms through secretion of organic acids that lower soil pH (Dinesh et al., 2018) [6] . Important ZSB genera include Pseudomonas, Bacillus, Gluconacetobacter, Enterobacter and Azotobacter. Besides Zn solubilization, ZSB possess multiple plant growth-promoting (PGP) traits including phosphorus and potassium solubilization, nitrogen fixation and production of IAA, gibberellic acid, siderophores and ACC deaminase (Senthil et al., 2018) [14] . Maize is particularly sensitive to Zn deficiency, especially in calcareous soils, where deficiency can severely impact grain yield and quality (Behera et al., 2015) [4] .

Materials and Methods

A field experiment was conducted during the summer season of 2024-25 at College Farm, N. M. College of Agriculture, Navsari Agricultural University, Navsari, Gujarat. Navsari falls under the South Gujarat Heavy Rainfall Zone-1 (Agro Ecological Situation III). The experimental soil was deep black clayey in texture and slightly alkaline in reaction. The experiment was laid out in a Randomized Block Design (RBD) with six treatments replicated four times (24 plots total). Maize variety GM-6 was sown at 20 kg/ha seed rate with 60 × 20 cm spacing on 24 February 2025. The recommended dose of fertilizer (RDF) was 120:60:00 N:P 2 O 5 :K 2 O kg/ha. The six treatments evaluated were: T 1 -Control; T 2 -Zinc solubilizing bacteria; T 3 -Zn at 5 kg/ha; T 4 -Zn at 10 kg/ha; T 5 -Zn solubilizing bacteria + Zn at 5 kg/ha; and T 6 -Zn solubilizing bacteria + Zn at 10 kg/ha. Maize seeds were treated by spraying 5 ml of ZSB culture (Microbacterium paraoxydans) per kg of seed, followed by shade-drying for 3 hours before sowing. Basal fertilizer comprised the full dose of phosphorus (via SSP) and 33% of recommended nitrogen (via Urea); remaining N was applied in two equal splits at knee-high and pre-tasseling stages. Zinc sulphate was applied as a basal dose at recommended rates as per treatments. Atrazine 50% WP was applied as a pre-emergence herbicide. Irrigation was given as per crop requirement. Harvesting was carried out at physiological maturity (98 DAS), followed by threshing and cleaning. In each net plot, five plants were randomly chosen and tagged for recording growth, yield attributes.

Statistical analysis

Data were statistically analysed using Randomized Block Design methodology; significance of variance was tested by 'F' test and Critical Difference (CD) at 5% level of significance was computed (Panse and Sukhatme, 1985) [11] .

Results and Discussion

Growth attributes

Dry matter accumulation at harvest was significantly influenced by different treatments. T 6 (ZSB + Zn at 10 kg/ha) recorded significantly higher dry matter accumulation of 137.88 g/plant, which was statistically at par with T 5 and T 4 . Plant height and number of leaves per plant at harvest was not significantly influenced by the treatments, numerically higher plant height (177.84 cm) and number of leaves per plant (11.81) was recorded under T 6 . The progressive enhancement in dry matter accumulation under combined ZSB and zinc treatments can be attributed to the dual action of potassium nutrients directly inorganic zinc supplementation and microbial solubilization of native soil zinc fractions through production of organic acids by ZSB, which maintain a continuous supply of plant available zinc in the rhizosphere while simultaneously enhancing uptake of nitrogen and potassium nutrients directly governing photosynthesis, assimilate synthesis and overall biomass production. Similar findings were also reported by Goteti et al. (2013) [7] , Verma et al. (2023) [17] and Khongchiu et al. (2025) [8] .

Yield attributes and yield

Application of T 6 (Zn solubilizing bacteria + Zn at 10 kg/ha) recorded the significantly highest number of grains per cob (263.0), grain weight per cob (50.16 g), cob weight (83.68 g), grain yield (3106 kg/ha) and stover yield (6314 kg/ha) over control, however these values are statistically at par with T 5 and T 4 . In contrast, different treatments were failed to exert significant effect on number of cobs per plant, cob length, cob girth and seed index. [9] , Bashir et al. (2021) [3] , Sasank and Dawson (2022) [13] and Verma et al. (2023) [17] .

Economics

Among different treatments, the highest gross return (₹99,999/ha), net return (₹57,215/ha) was realized with T 6 (Zn solubilizing bacteria + Zn at 10 kg/ha) followed by T 5 and T 4 whereas in case of benefit cost ratio, the highest BCR value of 2.38 was obtained with T 5 (Zn solubilizing bacteria + Zn at 5 kg/ha) followed by T 6 , T 4 , T 2 , T 3 and T 1 . Similar findings were reported by Sasank and Dawson (2022) [13] and Sukhwal et al.

Conclusion

The combined application of RDF with Zn at 10 kg/ha with ZSB treated seeds (T₆) was the most effective treatment, recording the highest growth attributes, yield attributes and yield of maize, followed closely by T₅ and T₄. However, T₅ (ZSB + Zn at 5 kg/ha) proved to be more profitable, giving the highest benefit:cost ratio, even though T₆ recorded the highest gross and net returns.

References

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