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A fertilizer is any substance applied to land to increase plant growth and produce higher crop yield. Fertilizers may be made from organic material, such as animal manure or compost, or it may be chemically manufactured. Manufactured fertilizers contain varying amounts of inorganic nitrogen, phosphorus, and potassium, all of which are nutrients that plants need to grow.

Since the 1950s crop production worldwide has increased dramatically because of the use of fertilizers. In combination with the use of pesticides and improved varieties of crops, fertilizers have greatly increased the quality and yield of such important foods as corn, rice, and wheat, as well as fiber crops such as cotton. However excessive and improper use of fertilizers have also damaged the environment and affected the health of humans.

It has been estimated that as much as 25% of applied agricultural fertilizer in the United States is carried away as runoff. Fertilizer runoff has contaminated groundwater and polluted bodies of water in agricultural areas. Ammonia, released from the decay of nitrogen fertilizer, causes minor irritation to the respiratory system. High concentrations of nitrate in drinking water are more serious, especially for infants, because of interference with the ability of the blood to transport oxygen. High and unsafe nitrate concentrations in drinking water have been reported in all countries that practice intense agriculture, including the United States. The accumulation of nitrogen and phosphorus from chemical fertilizers in waterways has also contributed to the eutrophication of lakes and ponds.

Few people would advocate the complete elimination of the use of chemical fertilizers. However, most environmentalists and scientists urge that more efficient ways be found of using fertilizers. For example, some farmers apply up to 40% more fertilizer than they need for specific crops. Frugal applications, occurring at small rates and on an as-needed basis for specific crops, helps to reduce the waste of fertilizer and the pollution of runoff and the environment. The use of organic fertilizers, including animal waste, crop residues, grass clippings, and composted food waste, is also encouraged as an alternative to the use of chemical fertilizers.

See also Composting.

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