Bridging yield gaps to enhance greengram (Vigna radiata L.) productivity in India: insights from crop simulation and water productivity analysis

Greengram ( Vigna radiata L.) plays a crucial role in India’s nutritional security and agroecosystem sustainability, though constrained by climatic variability, moisture stress, and suboptimal crop management. To identify pathways for sustainable intensification, the APSIM model was employed to simulate potential yield (Yp), quantify yield gaps, and assess water productivity across twenty major greengram growing districts of India during 2003–2023. Simulations integrated weather, soil profiles, region-specific management practices, and cultivar-specific genetic coefficients, while physical (PWP), irrigation (IWP), and economic (EWP) water productivity indices were evaluated. Observed yields (162–611 kg ha −1 ) remained lower than simulated potential yields (386–1220 kg ha −1 ), resulting in yield gaps of 27–66% (average ~ 389 kg ha −1 ). Central Zone districts exhibited relatively higher EWP. Model performance was robust during calibration and validation (R 2 and NSE ≈ 0.97–0.99; RMSE ≤ 20%; NMSE < 0.05). Carbon budgeting revealed carbon efficiency ranged from 0.65 to 1.98 and a mean Carbon Sustainability Index (CSI) of 0.32. Principal Component Analysis identified irrigation, soil fertility, and crop geometry as dominant yield drivers, while correlation-density matrix highlighted the dependence of grain yield on irrigation. The results demonstrate that improving irrigation management, optimizing nutrient use, and adopting region-specific agronomic practices can substantially reduce yield gaps and enhance water productivity in greengram.