Water, energy, food, and environment are strongly interconnected in agricultural systems, and understanding these linkages is essential for sustainable crop production. This study evaluated the inter-linkage among water-energy-food-greenhouse gas (WEFG) dimensions in Indian mustard under varying irrigation, nitrogen (N) rates and bio-regulator (BR) application using WEFG framework to identify resource-efficient and environmentally-sound management practices. A three-year field experiment was conducted in arid region of India with three irrigation levels [full (FI, 100 % ETc), moderate deficit (MDI, 70 % ETc), severe deficit (SDI, 40 % ETc)], three N rates (40, 80, 120 kg N ha(-1)), and three BR treatments [without BR, thiourea (500 ppm), salicylic acid (0.5 mM)]. Water and energy use, yield, profitability, resource-use efficiency and CO2-eq emissions were quantified and integrated through WEFG Nexus Index (WEFGNI). Irrigation accounted for 95 % of water and 37-66 % of energy use. FI produced highest yield but substantially increased water/energy use and emissions, while SDI reduced resource consumption and emissions but caused substantial yield/profit losses. MDI reduced water (similar to 25 %) and energy (20-40 %) consumption with negligible yield loss (<= 4 %), achieving higher resource use efficiencies. Higher N rates under FI and MDI enhanced yield/profitability but also enhanced emissions, while BR application enhanced productivity, profitability and efficiency particularly under MDI and SDI. The combination of MDI, 120 kg N ha(-1), and BR application achieved highest WEFGNI, indicating optimal balance among productivity, efficiency and environmental performance. The WEFG framework effectively capture trade-offs and synergies across nexus dimensions, offering a tool to guide sustainable crop management strategies aligned with the SDGs.