We all know that you can have too much of a good thing and the same is true for nitrogen. With the Green Revolution, the world thought the solution to world hunger was found in the form of nitrogen rich fertilizers (as well as new technologies, etc.) that dramatically increased yields and drastically reduced food prices. Yet hunger persists and now we have a new problem on our hands. Human use of nitrogen has grown to great excess and human alteration of the nitrogen cycle is having detrimental effects. One article stated that “human activity now fixes more atmospheric N2 into reactive forms than all terrestrial natural processes combined,” Townsend et. al. 2003). We have had too much of a good thing. This situation can be seen playing out in India where the use of nitrogen is no longer beneficial to human health and is in fact causing humans harm. Townsend et. al put it this way, “ the greatest net benefits are found at low to moderate levels of N use, and continued environmental N enrichment will greatly amplify the health costs,” (Townsend et. al. 2003).
Nitrogen use has seen a rapid increase in India since 1950 as it did in many other countries going through their own “green revolutions.” In 1950-51, nitrogen use in India sat at 55,000 tons. This skyrocketed to 11.31 million tons by 2001-02. This was reflected in an increase in food production as well from 50.83 to 222 million tons (Gupta 2005). Nitrogen consumption varies by region in India with the highest consumption being in the north followed by the south, west and east. The increase in consumption in the north is much greater than in the other areas due to the increased cereal production, a high N demanding crop. In states like Punjab and Haryana, much food production has moved to rice-wheat production to keep up with population increase. Rice-wheat is a more nitrogen responsive crop, thus also increasing N fertilizer use (Gupta 2005).
Furthermore, the nutrient use efficiency of N is very low. The use efficiency or how much of the nitrogen is removed by plants above ground varies between 30 and 50 percent depending on types of crops and management (Gupta 2005). This low use efficiency has environmental implications. Past observations report that about half of fertilizer applied to fields is either lost to leaching into ground waters as NO3 or lost in the atmosphere as NH3 and NO (Gupta 2005). Nitrogen lost this way is lost as pollution. Excess nitrogen in rivers and oceans cause eutrophication while excess nitrogen in the air can have serious health risks.
Excess nitrogen in the natural system has serious health risks, not only in India, but also in all parts of the world where excess nitrogen is a problem. Health risks include respiratory complications, cardiac disease and several cancers (Townsend et. al. 2003). For example, high NO levels in the air leads to production of tropospheric ozone, which in turn aggravates coughs, asthma, etc. High levels of nitrate in drinking water (defined by the World Health Organization as more than 10 ppm) can lead to reproductive health problems, methemoglobinemia (especially in infants) and cancer (Townsend et. al. 2003). These health risks are amplified as more and more reactive nitrogen is added to the system.
India, as a developing country, also has a more unique source of excess nitrogen. Field burning of crop residue or FBCR is a practice commonly seen in developing country and a growing problem because of the release of carbon and nitrogen emissions. About 76 percent of this biomass that is burned is from rice and wheat crops, which as already mentioned are major crops in India. Burning this biomass is estimated to emit, in 2010, 0.35 Tg of nitrogen and 140.6 Gg of NOx. Indian states such as U.P, Punjab, Haryana, M.P, Maharashtra, T.N, Karnataka, Andhra Pradesh, Bihar and W.B have been found to contribute maximum to the Indian FBCR emissions,” (Sahai et. al., 2010). As we have already seen excess NOx emissions have serious health risks.
FBCR is also a concern because it leads to loss of soil carbon and nitrogen, nutrients needed for subsequent growing seasons. Is it possible that FBCR is linked to increased nitrogen fertilizer use? Perhaps stopping FBCR could have an effect on the amount of fertilizer being used in India, but more research needs to be done before correlation can be suggested.
Human alteration of the nitrogen cycle is increasingly becoming a problem globally. Whether it is the worldwide case of the Green Revolution and nitrogen fertilizer or the more specialized case of FBCR in India, too much nitrogen is a classic case of too much of a good thing. The health benefits (i.e. increased food production) have peaked and now the increasing use of nitrogen is only amplifying health risks. As for what can be done to combat this, there is still much to be learned. In places like the northern region of India where cereal crops demand nitrogen to produce and food production has to keep pace with a growing population, you can’t quit N cold turkey. Instead more efficient methods need to be developed and farmers need more education as to why FBCR is detrimental. But this brings up a whole new set of issues in India. For now I leave you with this small snippet on nitrogen and India
Sources:
Gupta, A.P. “Nitrogen use scenario in India” Science in China. 2005. <http://www.springerlink.com.libproxy.furman.edu/content/a0122v881617764r/fulltext.pdf>
Sahai, S. et. al. “Assessment of trace gases, carbon and nitrogen emissions
from field burning of agricultural residues in India” Nutr Cycl Agroecosyst. 2010. <http://www.springerlink.com.libproxy.furman.edu/content/8h76543580550904/fulltext.pdf>
Townsend, A.R., et. al. “Human health effects of changing global nitrogen cycle” The Ecological Society of America. 2003.
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