The Indian Nitrogen Challenge in a Global Perspective

Human activities have massively altered the global nitrogen (N) cycle, doubling annual production of reactive N (N_r) compounds from atmospheric dinitrogen (N₂). The use of 120 Mt year^-1 fertilizer N, with a global terrestrial/atmospheric N fixation of 285Mtyear^-1, has provided huge benefits for global food production. However, nitrogen use efficiency (NUE) of the world food system is only -15%. The lost N_r creates a cascade of air and water pollution and greenhouse gas emissions, until it is eventually denitrified back to N₂.India clearly illustrates a dual N challenge for food and environment, consuming 17Mt of N fertilizer annually (14% of the global total), which has increased since 1970 at 6% year^-1 approximately. Emissions of nitrogen oxides (NO_x) from combustion sources are also increasing rapidly at 6.5% year^-1 currently. By comparison, population growth rate is lower (2% year^-1), while ammonia (NH₃) emission increase is even less (1%), pertaining to smaller changes in livestock numbers. At current rate, Indian NO_x emissions will exceed NH₃ emissions by 2055. India currently loses N_r worth US$10billionyear^-1 as fertilizer value, while costs of N_r to health, ecosystems, and climate are estimated at US$75 (38-151) billion year^-1.Only a small fraction of the Indian population consumes animal products, hence per capita N_r use and pollution is much less than in many developed countries. However, rates of meat consumption are increasing. While published projections from the UN Food and Agriculture Organization anticipate a doubling of South Asian fertilizer consumption from 2006 to 2050 (equivalent to 1.9% year^-1 increase), these projections lack transparency and require reevaluation. In practice, the future nitrogen cycle for India will depend on scientific advances in agronomy, genetics and environment, and the extent to which government and society grasp the emerging opportunities for optimizing N management.