Human-induced nitrogen emissions have surpassed natural emissions, damaging health and the environment

Nitrogen Overload

For the past 40 years, Ramesh Kumar, a farmer in Murthal village in Haryana’s Sonipat district, has been applying 200 kg of urea in a year on every hectare (ha) of his land. Kumar, who grows rice and wheat, says the yield has been more or less the same every year. But he admits that he cannot think of farming without urea.

“With only organic manure, I will grow nothing,” he says.

Kumar’s use of urea reflects India’s increasing dependence on artificial nitrogen fertilisers. Indian Fertiliser Scenario 2014, an annual publication of the department of fertilisers under the Ministry of Chemicals and Fertilisers, states that the use of urea in the country has increased by more than 50 per cent since 2000—the per hectare consumption of nitrogen is at least 100 kg in eight Indian states, including Bihar, Punjab, Haryana, Uttarakhand, Uttar Pradesh, undivided Andhra Pradesh, Tamil Nadu and Puducherry.

But India is not alone. During the past century, the global consumption of nitrogen has seen a steady increase. In 1980, developed countries accounted for 70 per cent of the world’s total nitrogen consumption. By 2010, it was the developing countries which accounted for 70 per cent of the global nitrogen consumption. India is the second-highest consumer of nitrogen in the world after China. According to the Food and Agriculture Organization, China’s annual consumption of nitrogen is 44.97 million tonnes, while India consumes 16.48 million tonnes—four times more than Brazil’s annual consumption of 4.25 million tonnes.

The increasing rate of nitrogen use by humans has led to an imbalance in the nitrogen content in the environment. According to “Our Nutrient World”, a 2013 report of the United Nations Environment Programme (UNEP), human-induced nitrogen inputs or fertilisers and associated emissions from agriculture, fossil fuel burning, sewage and industrial waste have directly or indirectly far surpassed natural emissions, causing nitrogen pollution that has reached alarming levels. A study published in the journal Environmental Research Letters in June this year shows that the annual economic loss in the US due to energy wastage and damages to the environment and human health from nitrogen pollution is $210 billion. “Our Nutrient World” estimated that the global cost of damage from nitrogen could go up to US $2,000 billion.

Similar studies are not available for India. The threats posed by nitrogen pollution are individually and collectively a huge problem for the global society today, says M A Sutton, lead author of the UNEP report (see ‘We can manage nitrogen...’,).

From nutrient to pollutant

Nitrogen, which is a vital macronutrient for most plants, is the most abundant element in the atmosphere. A little over 78 per cent of dry air on Earth is nitrogen. But atmospheric nitrogen, or dinitrogen, is unreactive and cannot be utilised by plants directly. Until the beginning of the 20th century, farmers depended on a natural process called nitrogen fixation for the conversion of atmospheric nitrogen into reactive nitrogen in the soil: nitrogen-fixing bacteria like rhizobia live symbiotically with leguminous plants, providing nitrogen to the plant and soil in the form of reactive compounds like ammonia and nitrate.

But the natural nitrogen cycle was inadequate to feed the growing population. Scientists Fritz Haber and Carl Bosch solved this problem by producing ammonia by combining atmospheric nitrogen with hydrogen gas at high temperature and pressure—known as the Haber-Bosch process. The Green Revolution, which was instrumental in establishing food security in the developing countries in the 1960s, was driven by artificial nitrogen-fixation. Today, about half of the world’s population depends on this process for its nutrition.

But over 80 per cent of the nitrogen in soil is not utilised by humans (see ‘What goes down comes up’, ). While over four-fifths of the nitrogen is used to feed livestock, only about six per cent reaches humans in case of non-vegetarian diet, as compared to the 20 per cent that reaches the plate of a vegetarian.

Nitrogen becomes a pollutant when it escapes into the environment and reacts with other organic compounds. It is either released into the atmosphere, gets dissolved in water sources such as rivers, lakes or groundwater, or remains in the soil. While it might lead to favourable growth of species that can utilise this nutrient, nitrogen as a pollutant is often detrimental to the environment and health (see ‘Nefarious nitrogen’). According to the World Health Organization, nitrate-contaminated drinking water can cause reduced blood function, cancer and endemic goiters (see ‘Pollutants and effects’,). Surplus inputs of nitrogen compounds have been found to cause soil acidification. The lowering pH, as a result of the acidification, can lead to nutrient disorders and increased toxicity in plants. It may also affect natural soil decomposition. Quite a few studies have been conducted on the efficiency of nitrogen fertiliser and the general conclusion is that its use decreases soil fertility, says Tapan Adhya, professor at the School of Biotechnology in the Kalinga Institute of Industrial Technology, Bhubaneswar, Odisha.

“Nitrogen is central to India’s food production, but its use in our agriculture system has put us in a Catch-22 situation. We cannot produce enough food to feed the nation without nitrogen, but at the same time we cannot keep introducing higher quantities of nitrogen because of its polluting effects,” says N Raghuram, director of the South Asian Centre of International Nitrogen Initiative, a group of scientists and researchers working to improve nitrogen efficiency.

Management is the key

The challenge for the current century is to optimise the uses of nutrition while minimising the negative impacts, notes James Galloway, a professor at the University of Virginia, the US, who is researching on the effects of reactive nitrogen. As the problem of nitrogen pollution starts to gain global attention, there have been innovations aimed at improving its efficiency by optimising usage. Eight corn farms in Maryland, the US, have been experimenting with sensor technology, which collects, in real time, data about the quantity of nitrogen plants need.

A simpler method of reducing nitrogen application is precision farming where small quantities of nitrogen are administered routinely instead of large doses applied uniformly over the field. Similarly, tablets and coated forms of nitrogen, when applied at the root level, release nutrients slowly. “Bangladesh has managed to increase the efficiency of nutrition uptake by plants by applying fertilisers through tablets. A similar attempt is being made with neem-coated urea in India,” Adhya says (see ‘Neem-coated growth’, Down To Earth, July 1-15, 2015). Supplemented with organic fertilisers and combined with optimal timing of application, sowing and watering, these methods have shown marked improvement over traditional efficiencies of nitrogen. Europe, which has used such methods in its agriculture, has attained the highest nitrogen use efficiency in the world, according to the Organization for Economic Cooperation and Development (OECD).

Raghuram says nitrogen pollution is an issue of improper management rather than inability. “The costs of abating nitrogen pollution would be much less than the benefits to health and environment. A 20 per cent increase in the rate of efficiency would save an estimated 20 million tonnes of reactive nitrogen by 2020, which equates to an improvement in human health, biodiversity and climate worth US $170 billion,” Sutton explains.

Developed regions such as the US and Europe have published detailed reports about nitrogen usage and pollution. But India is nowhere close to aggregating something similar of its own, says Y P Abrol, founder of the non-profit Indian Nitrogen Group. “For over a decade we have been trying to convince various ministries dealing with nitrogen to take up data collection and a detailed plan of action. But there has been no concerted policy or regulation,” he adds.

Nefarious Nitrogen

Nefarious nitrogen

While Nitrogen compounds potentially pollute every element of our ecosystem, air is the most critical medium in terms of damage through nitrogen pollution. Agriculture, transport, energy production and combustion in industry contribute to emissions of nitrogen pollutants into the air.

The release of ammonia and nitrogen oxides into the lower atmosphere has significant health impacts. Nitrogen oxides are formed through a combination of nitric oxide and nitrogen dioxide. These two nitrogen compounds form fine particulate matter (PM) that has been noted to be a significant contributor towards lung damage, respiratory ailments and reduction of life expectancy. Nitrogen oxides also cause photochemical smog in which high level of tropospheric ozone is produced. This ozone, which is closer to the Earth's surface, is harmful for both humans and the environment. It has been found to cause adverse short-term and chronic impacts on respiratory functions. It is detrimental to agriculture and causes damage to crop production of up to five per cent every year globally.

Nitrous oxide (N2O), another oxide of nitrogen, is a greenhouse gas that is 300 times more reactive than carbon dioxide and has a lifespan of 120 years in the atmosphere. An American study in 2012 found that over a period of 100 years, the heating effects of N2O far outweighed any short-term cooling impact that reactive nitrogen might have. Further, N2O has a potential of ozone depletion in the stratosphere—this ozone protects us from the harmful ultraviolet rays of the sun—that is comparable to the potential of hydrochloroflourocarbons which were phased out in the 1990s as a highly ozone-depleting substance.

Nitrogen can be blamed to a large extent for India's poor air quality. According to media reports, 13 of the 17 most polluted cities in the world are in India. Delhi and Kolkata far exceed the World Health Organization's (WHO's) standard of 40 micrograms per cubic metre for N2O. Chennai and Bengaluru are the only metro cities that are safely within prescribed limits. Twenty-seven Indian states, for which data is available, exceed the WHO limit of 20 micrograms per cubic metre for annual mean PM.

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