Toward an Integrated Nitrogen Budget for India: Multi-Sectoral Flows, Circularity, and Environmental Losses.

This study presents the first comprehensive, multisectoral assessment of India's nitrogen (N) budget, quantifying N inputs, flows, circularity, and losses across ten economic sectors. We present a scalable Environmentally Extended Input-Output (EEIO) framework, trace 198 N flows to estimate the conversion potential of input N to reactive nitrogen (Nr) losses, and estimate sectoral N use efficiency (NUE). The total N-input in India is estimated at ∼50 Tg-N yr-1 in 2020, dominated by Haber-Bosch fixation (38%), imports (33%), biological N fixation (27%), and fossil fuel combustion (18%). Cropland and industry together receive ∼90% of total N inputs; however, industry exhibits higher NUE (62%) than cropland (56%), given tighter regulations, whereas agriculture operates as a semiclosed loop with substantial losses. Shifts in dietary patterns toward animal protein and processed foods exacerbate feed-food competition and amplify Nr emissions. Overall, 52% of N inputs are converted to inert N2, 37% are emitted as Nr, and 10% of Nr accumulate within sectors. Atmospheric Nr losses (∼9 Tg-N) are primarily as NH3 (63%), NOx (32%), and N2O (5%), while hydrosphere losses (∼9 Tg-N) occur via runoff (67%) and leaching (33%). Key Nr processes include biomass burning (13 Tg-N), runoff (11 Tg-N), and combustion (8 Tg-N). These findings highlight critical intervention points for reducing N inefficiencies and mitigating environmental Nr load in India's evolving N economy.