Effect of Azotobacter and Phosphate Solubilizing Bacteria (PSB) on Growth and Yield of Spinach (Spinacia oleracea L.)

Abstract

Spinach (Spinacia oleracea L.) is an important leafy vegetable whose growth and productivity depend on adequate nutrient availability. The use of beneficial microorganisms, particularly Azotobacter and phosphate-solubilising bacteria (PSB), offers a potential approach to improving nutrient availability and reducing dependence on chemical fertilisers. However, the effectiveness of native bacterial isolates under reduced nitrogen and phosphorus fertiliser application requires further field evaluation. The present investigation was undertaken to isolate, characterise and select efficient native Azotobacter and phosphate-solubilising bacteria (PSB) from the rhizosphere of spinach and to evaluate their individual and combined effects with different fertiliser levels on the growth, yield and quality of spinach (Spinacia oleracea L.). Six Azotobacter and four PSB isolates were obtained from sixteen rhizospheric soil samples collected from Kolhapur district. Based on nitrogen-fixing ability and phosphate-solubilising efficiency, Azotobacter isolate-III (11.35 mg N ml⁻¹) and PSB-I (solubilization index 4.0) were selected for field evaluation. The field experiment was conducted during rabi 2025–26 at the Instructional-cum-Research Farm, RCSM Government College of Agriculture, Kolhapur. Among the treatments, T7 (Azotobacter + PSB + 75% N and P₂O₅ + recommended dose of K₂O) recorded superior performance. The minimum number of days to germination (4.0 days) and the maximum germination percentage (91.33%) were recorded under treatment T7. Plant heights under T7 were 31.43, 25.93 and 22.13 cm, leaf areas were 132.00, 105.33 and 103.33 cm², total number of leaves was 43.33, fresh weights were 36.00, 33.56 and 26.28 g plant⁻¹ and dry weights were 18.93, 18.41 and 15.77 g per 100 g fresh weight during the first, second and third cuttings, respectively. T7 also recorded the highest total yield of 18.96 t ha⁻¹, ascorbic acid content of 62.83 mg 100 g⁻¹ and chlorophyll content of 2.27 mg g⁻¹. Root length reached 28.33 cm under T7. The findings demonstrated that combined application of native Azotobacter and PSB with 75% N and P₂O₅ and recommended K₂O improved growth, biomass, yield and quality of spinach and showed potential for efficient nutrient management with reduced N and P fertiliser use.