Carbon Footprint, Energy Dynamics, and Eco-Efficiency of Tomato–Green Gram Cropping System Under Conventional and Alternative Nutrient Regimes

Agriculture is a major contributor to greenhouse gas (GHG) and energy consumption due to the intensive use of synthetic chemicals, posing serious threats to the environment, soil and human well-being. This issue is particularly important in tomato-growing regions of Tamil Nadu, where high-input farming practices are widely adopted. Therefore, identifying a sustainable nutrient management strategy is essential for developing climate-resilient and resource-efficient systems in line with the Sustainable Development Goals (SDG 2, SDG 7, SDG 12 and SDG 13). A field study was conducted in a tomato–green gram cropping system to evaluate four nutrient management (NM) regimes, namely Integrated (INM), Conventional (CNM), Organic (ONM) and Farmers’ Practice (FNM). The results indicated that the ONM system recorded the highest system productivity (26.4 t ha−1), energy output (200,110 MJ ha−1), energy productivity (0.99 kg MJ−1), energy profitability (8.94), non-renewable energy use efficiency (18.8) and benefit–cost ratio (4.28), while INM is associated with relatively higher nitrous oxide (N2O) emissions. The major contributor to total energy was fertilizers (38.7%). The INM and CNM systems had the highest carbon footprint (0.10 kg CO2e per kg) while the ONM system had the lowest. The ONM system had considerably increased eco-efficiency in terms of energy use (INR 20.1 MJ−1 and INR 226 per kg CO2e) over other regimes. Furthermore, ONM improved the carbon efficiency (80%) and carbon sustainability index (94%) compared to INM. Overall, the findings demonstrate that ONM is a viable, eco-efficient and climate-smart practice that enhances productivity and profitability, improves energy efficiency, and reduces the carbon footprint in vegetable–legume systems.