News

doi:10.1038/nindia.2017.145 Published online 24 November 2017

Fertilisers leaking huge amount of nitrogen into soil, water

K. S. Jayaraman




A mammoth exercise in quantifying 'reactive nitrogen' in the environment has found that 65% of the nitrogen used in India as fertilisers may be getting leaked into soil, water and other natural resources, thereby significantly contributing to the country's greenhouse gas burden.

Results of this decade-long assessment of all major sources of nitrogen and quantification of reactive nitrogen (or Nr) have recently been published in a book1 by the Indian Nitrogen Group (ING), a voluntary body of over a hundred scientists and other stakeholders.

"Our environment is accumulating reactive nitrogen at alarming rates," says Nandula Raghuram, a professor at the Indraprasta University in New Delhi and co-editor of the book. This is due to rising dependence on Nitrogen fertilisers coupled with the notoriously low efficiency of nitrogen uptake by crops. 

As much as 65% of applied nitrogen leaks into the environment as Nr that ends up in streams, rivers and lakes leading to eutrophication and algae blooms. The scenario is further complicated by the livestock sector, where cattle and buffaloes are the largest contributors of ammonia.The poultry industry added 0.415 million tons of ammonia to the atmosphere in 2016 and is anticipated to produce 1.089 million tons by 2030. 

In the states of Punjab, Haryana, Delhi, Maharashtra, Andhra Pradesh, and Karnataka with extensive economic and agricultural activities, nitrate concentrations are increasing in surface and groundwater.

By itself nitrogen, that makes up 78% of the atmosphere, is harmless. But reactive nitrogen  —nitrate, ammonia, nitrous oxide and other reactive forms of nitrogen — accumulate in soil, water, atmosphere and coastal oceanic waters, leading to environmental concerns. They contribute to smog, haze, acid rain, and coastal "dead zones". Nitrous oxide, like carbon dioxide, is a greenhouse gas.

Raghuram says the book aims to bring to fore all significant sources of Nr and their contribution to regional, national and global nitrogen cycles. This would help policymakers take informed decisions on sustainable nitrogen management.

The scenario is "quite alarming" but there is a way out, the book says. India, it says, will be able to cut fertiliser consumption by 30% and Nr emissions by 50% by 2050 if new fertilisers are formulated, their uptake by plants and animals optimised, nitrogen is recovered and reused from manure and sewage, and emissions from fossil fuel combustion are reduced.

"The study is timely," says M. S. Swaminathan, hailed as father of India's green revolution. "It will contribute to better understanding of the regional and global nitrogen cycle."


References

1. The Indian Nitrogen Assessment. Eds Abrol, Y. P. et al. (2017) Link