doi:10.1038/nindia.2018.83 Published online 2 July 2018
India is emerging as a ‘global hot spot’ for nitrogen pollution – a looming threat to its environment – owing to increased dependence on nitrogen fertilisers and notoriously low nitrogen uptake by crops resulting in its leakage into the soil.
The alarm bell was sounded recently by experts attending India's first international event around the issue held in New Delhi as part of World Environment Day (4 June 2018).
"Much of India's air pollution is linked to ammonia from agriculture and nitrogen oxides from combustion sources," said Mark Sutton from the Centre for Ecology & Hydrology (CEH), UK and director of International Nitrogen Management System (INMS), a UN-backed global coalition of scientists and institutions fighting nitrogen pollution.
Sutton, who chaired the event, said the enormity of the problem has prompted the first Asian study on nitrogen – the Indian Nitrogen Assessment (INA) – that urges India to champion better management of nitrogen.
Chemical fertilisers account for over 77% of agricultural nitrogen oxide emissions in India and cattle contribute to 80% of the country's ammonia production, says Nandula Raghuram, Dean of Biotechnology at Indraprastha University in New Delhi and President of Indian Nitrogen Group (ING), a voluntary body of over a hundred scientists and stakeholders.
"Since 2002, nitrogen oxides have replaced methane as the second largest greenhouse gas from Indian agriculture," says Raghuram, who co-authored the INA report that identified significant sources of reactive nitrogen and their contribution to regional, national and global nitrogen cycles.
Nitrogen makes up the bulk of the atmosphere and is harmless by itself. However, reactive forms of nitrogen like nitrate, ammonia and nitrous oxide are harmful. Nitrous oxide, like carbon dioxide, is a greenhouse gas. While these compounds react to form fine particulate matter (PM 2.5) closely linked to cardiovascular and respiratory illness, the problem is compounded by their mixing with water bodies, threatening drinking water quality, freshwater ecosystems and coastal zones. They also increase algal blooms, which kill fish by reducing oxygen levels in water, and contribute to greenhouse gas emissions.
ING founder Yash Pal Abrol said the alarming nitrogen pollution level in India needs continued government action and involvement to keep pace with the ever changing scenario.
Experts acknowledged that India has begun taking note of the damage from what Raghuram calls a "potential nitrogen bomb." The government has mandated companies to sell urea fertiliser coated with neem oil. In Andhra Pradesh, farmers are adopting the Japanese concept of natural farming that involves spraying cattle dung-laced bio-inoculants in farms to stimulate microbial growth for soil nitrogen mobilisation.
Sutton however warns that nitrogen pollution in India may get worse considering the 6% annual rate of increase in nitrogen oxides emissions projected in the INA report. However one positive sign, he says is Prime Minister Narendra Modi's announcement last November of plans "to halve fertiliser use by 2022."
But Himanshu Pathak, director of the National Rice Research Institute in Cuttack, Odisha, cautions that the use of nitrogenous fertiliser will have to increase several folds by 2050 to meet the demand of increased food production. "Crop management practices, which lead to increased nitrogen use efficiency while limiting the nitrogen loss, hold the key to mitigating reactive nitrogen emissions," he says.
The UN-backed International Nitrogen Management System is drafting a South Asian nitrogen assessment, led by Indian researchers, and hopes to present a Nitrogen Resolution at the next UN Environment Assembly.