Rice is one of the world’s most important foods. In fact, it is a staple crop for about 40% of the world’s population. Unfortunately, growing rice can cause a number of environmental and health problems. In particular, rice requires lots of nitrogen fertilizer, which can lead to a whole host of environmental problems. Nitrogen isn’t inherently bad. All plants need nitrogen to grow, but all plants can only use so much nitrogen at a time. Rice, though, needs more nitrogen than many other plants, and in order to grow as much rice as the world needs, most farmers need a little help from nitrogen fertilizer. Nitrogen only becomes a problem when it escapes from the crops where it is applied. This can happen in a number of ways. Chemical reactions in the soil can produce gasses that carry nitrogen into the air, and water running off of the ground or soaking into it can move nitrogen with it. When this happens, nitrogen ends up in places where more nitrogen isn’t necessarily a good thing. Some loss of nitrogen from crops is inevitable, but there are a number of things that rice farmers can do to reduce how much nitrogen ends up in the environment. Given the importance of rice to feeding the world’s growing population, it is important that rice farmers and local governments take make efforts to use the best practices possible to reduce the harmful side effects of using nitrogen fertilizer.
How Does Nitrogen Fertilizer become Nitrogen Pollution?
Two chemical processes are responsible for most of the air pollution that results from using nitrogen fertilizer on rice crops. These are formally called “ammonia volatilization” and “denitrification.” Both occur as a result of nitrogen fertilizer dissolving in water. Both of these processes produce gasses that contain nitrogen. Nitric oxide, one of these gasses, is a powerful greenhouse gas that has serious global warming potential. Because it is very good at absorbing radiation and stays in the atmosphere for a very long time, nitric oxide is considered to be 300 times as powerful of a greenhouse gas as carbon dioxide. Nitric oxide can also contribute to acid rain. In the case of acid rain, nitrogen may be carried many miles through the atmosphere and deposited on crops and ecosystems far from the source. At this point, the nitrogen is in a different form than when it was originally used as fertilizer, and it is actually quite harmful to plants, including other food crops.
Water pollution from nitrogen happens through simpler processes than air pollution. For instance, nitrogen may be carried into rivers and streams simply by rainfall or excess irrigation water, or it may soak deep into the ground and into groundwater. Especially in places where people rely on groundwater for drinking or irrigation, this can be a serious problem. Nitrogen can make groundwater toxic and can lead to health problems in adults and especially in infants. If applied to crops for irrigation, the nitrogen may accumulate in the plants and when consumed, cause health problems such as liver problems.
What Can We Do About Nitrogen Pollution?
Fortunately, there are a variety of options for reducing the amount of nitrogen lost from using nitrogen fertilizer on rice crops. Ammonia volatilization and denitrification can be reduced by adding other substances to the crop along with the fertilizer that slow down the chemical reactions that produce the harmful gasses. Also, air pollution and nitrogen loss from runoff can be reduced if the fertilizer is injected into the soil instead of just being spread on top. Special crop management practices, such as rotating rice crops with plants that have deeper roots such as maize or indigo can help remove nitrogen from deep in the soil before it gets into groundwater.
By far the most universal solution, though, is simply to use less nitrogen fertilizer. Nitrogen fertilizer is cheap and accessible to farmers across the world, but governments and other organizations could help make alternatives available as well. For instance, farmers can use live microbes that help plants grow, allowing them to use less fertilizer.
When people first began using nitrogen fertilizer to help their crops grow, probably no one thought of all the complicated environmental and health impacts that nitrogen could have once it escaped into the broader environment. Today, though, with knowledge of these problems, we can begin to take steps to solve them and find ways to feed the world without compromising our health and environment.
Choudhury, A. T. M. A., and I. R. Kennedy. “Nitrogen fertilizer losses from rice soils and control of environmental pollution problems.” Communications in Soil Science and Plant Analysis 36, no. 11-12 (2005): 1625-1639.
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