Role of Pulses in Sustainable Agriculture

Introduction

Pulses constitute a foundational pillar of sustainable and climate-resilient agriculture owing to their low carbon and water footprints. As India accounts for a major share of global output with approximately 27.4 MT produced in 2025-26, pulses play an indispensable role in ecological restoration and the national target under the Mission for Aatmanirbharta in Pulses to attain self-sufficiency by 2027.

1. Biological Nitrogen Fixation (BNF)

With the exception of common bean (Rajma), most pulse crops establish a symbiotic mutualism with Rhizobium bacteria to convert inert atmospheric dinitrogen into plant-usable ammonia.

• Molecular Signaling and Infection: Host legume roots exude flavonoids that activate bacterial NodD regulatory genes. This triggers the synthesis of lipochitooligosaccharide Nod factors, inducing root hair curling, the formation of an infection thread, and the subsequent differentiation of bacteria into endosymbiotic bacteroids within nodular symbiosomes.
• Role of Leghaemoglobin: Because the nitrogenase enzyme complex is irreversibly inactivated by free oxygen, leghaemoglobin functions as an oxygen carrier and scavenger. It maintains a microaerophilic niche, providing sufficient dissolved oxygen for bacteroid ATP generation while shielding nitrogenase.
• Stoichiometry of Nitrogen Reduction: The biochemical reaction requires substantial cellular energy:
  N₂ + 8H⁺ + 8e^- + 16 ATP → 2NH₃ + H₂ + 16 ADP + 16 P_i

2. Improvement of Soil Fertility

Pulses enhance both the physico-chemical and biological properties of soil through organic and microbial pathways:

• Soil Organic Carbon (SOC) Dynamics: Pulse crop residues possess a narrow carbon-to-nitrogen ratio (C:N < 30:1), facilitating rapid microbial decomposition and mineralization, which replenishes the labile SOC pool.
• Phosphorus Solubilization and Aggregation: Deep taproots secrete low-molecular-weight organic acids (such as citric and malic acids) that solubilize fixed and recalcitrant native soil phosphorus. Concurrently, symbiotic Arbuscular Mycorrhizal Fungi (AMF) produce the hydrophobic glycoprotein glomalin, which binds micro-aggregates into macro-aggregates, improving soil porosity and water-holding capacity.
• Residual Nitrogen Economy: Effective pulse cropping leaves a positive residual balance of 50 to 100 kg N/ha, substantially offsetting synthetic fertilizer requirements for subsequent feeder crops.

3. Importance in Diversified Cropping Systems

Incorporating legumes into intensive cereal-dominated rotations mitigates ecological degradation and stabilizes farm income:

• Resource Partitioning: Intercropping morphologically dissimilar species (e.g., shallow-fibrous rooted maize with deep-taprooted pigeon pea) minimizes niche overlap, optimizing light, moisture, and root-zone nutrient uptake.
• Catch Cropping: Short-duration varieties, such as summer/zaid mungbean, utilize post-wheat residual soil moisture between Rabi and Kharif seasons, avoiding bare fallow and reducing evaporative loss.
• Trap and Barrier Cropping: Planting pigeon pea along the borders of Kharif cotton acts as a biological trap for bollworms (Helicoverpa armigera), curtailing pesticide dependency through integrated pest management.

Conclusion

Integrating pulses into intensive agricultural rotations serves as a natural buffer against land degradation and declining fertilizer-use efficiency. Sustained institutional support and remunerative procurement through mechanisms like PM-AASHA will incentivize pulse cultivation, aligning agricultural output with dual goals of nutritional security and environmental sustainability.