Assessment of Sewage Sludge Application with Beneficial Microbial Inoculants on Fenugreek Productivity in Sandy Loam Soil

Technical Summary: Assessment of Sewage Sludge Application with Beneficial Microbial Inoculants on Fenugreek Productivity in Sandy Loam Soil

Problem Statement
Modern agricultural ecosystems require a balanced supply of primary macronutrients—nitrogen (N), phosphorus (P), and potassium (K)—to optimize biomass accumulation and fertilizer use efficiency. Sandy loam soils, common in regions like the Upper Gangetic Plain, are characterized by low organic matter and limited nutrient retention capacity. While synthetic fertilizers address nutrient deficits, there is a need for sustainable strategies that integrate organic amendments and bio-fertilizers to enhance soil fertility without environmental degradation. Fenugreek (Trigonella foenum-graecum L.), a leguminous crop with significant culinary and pharmaceutical value, serves as a model for investigating these integrated nutrient management practices. The study addresses the challenge of maximizing fenugreek productivity in sandy loam soils through the synergistic application of sewage sludge, chemical fertilizers, and microbial inoculants.

Methodology
A field experiment was conducted during the Rabi season of 2023–24 at the Soil Science Research Farm of Sam Higginbottom University of Agriculture, Technology, and Sciences in Prayagraj, Uttar Pradesh. The site features a subtropical climate and sandy loam soil. The study employed a Randomized Block Design (RBD) with three replications.

The experimental design included 18 treatments varying in the application rates of NPK fertilizers (0%, 50%, and 100% of recommended doses), sewage sludge (0, 15, and 30 t ha⁻¹), and microbial inoculants (Rhizobium and Phosphate Solubilizing Bacteria - PSB).

• Inoculation: Rhizobium was applied as a seed treatment at 2 g kg⁻¹ seed, while PSB was applied to the soil at 3 kg ha⁻¹ during sowing.
• Sludge Application: Sewage sludge was broadcast uniformly across the field.
• Measurements: Growth attributes (plant height, number of branches) were recorded at 30 and 50 Days After Sowing (DAS). Yield attributes included pod length, number of pods per plant, number of seeds per pod, test weight (1000-seed weight), and seed yield (q ha⁻¹).

Key Contributions and Results
The study evaluated the impact of integrated nutrient management on fenugreek growth and yield. The results indicated that the co-application of urban sewage sludge with bio-inoculants significantly elevated elemental nutrient availability, particularly bioavailable phosphorus and nitrogen, leading to pronounced improvements in vegetative development and seed quality compared to controls.

• Growth Attributes: The treatment combining 100% NPK, 30 t ha⁻¹ sewage sludge, and Rhizobium (Treatment T18) recorded the maximum plant height (39.1 cm at 30 DAS and 54.1 cm at 50 DAS) and the highest number of branches per plant (4.1 at 30 DAS and 5.2 at 50 DAS). These values were significantly superior to the control (T1: 0% NPK + 0 sludge + 0 inoculants), which recorded 28.2 cm and 47.1 cm height, respectively.
• Yield Attributes: Treatment T18 also yielded the highest values for pod length (12.5 cm), number of pods per plant (27.8), number of seeds per pod (14.9), and test weight (12.47 g).
• Seed Yield: The maximum seed yield of 19.92 q ha⁻¹ was achieved with Treatment T18. This was significantly higher than the minimum yield of 13.27 q ha⁻¹ observed in the control treatment (T1). Treatment T17 (100% NPK + 30 t SS + PSB) followed closely with 19.78 q ha⁻¹.

The data demonstrated a positive trend where increasing levels of NPK, sewage sludge, and bio-fertilizers correlated with improved growth and yield parameters. The synergistic interaction between mineral inputs, organic amendments, and bio-inoculants optimized rhizosphere nutrient availability, chlorophyll synthesis, and photosynthetic capacity.

Significance and Claims
The paper claims that the integrated management of chemical fertilizers, sewage sludge, and beneficial microbial inoculants offers a sustainable pathway for enhancing soil fertility and agricultural productivity in sandy loam soils. Specifically, the study suggests that:

1. Synergistic Effects: The combination of sewage sludge with Rhizobium and PSB induces synergistic effects on organic matter mineralization, insoluble phosphate solubilization, and biological nitrogen fixation.
2. Environmental Sustainability: This management practice can enhance crop yields and soil fertility without posing threats to the environment, potentially reducing dependence on synthetic fertilizers.
3. Optimal Strategy: The application of 100% NPK combined with 30 t ha⁻¹ sewage sludge and Rhizobium inoculation (Treatment T18) represents the most effective strategy for maximizing fenugreek productivity under the studied conditions.

The authors conclude that such integrated nutrient management practices can greatly enhance soil biological functionality and physical structure, fostering ecological resilience while meeting the nutrient demands of leguminous crops like fenugreek.