Broadcast: June 24, 2003
This is the VOA Special English Agriculture Report.
Last week, we described some different kinds of fertilizers. This week, we examine some of the issues involved in their use.
Farmers know that nitrogen fertilizer helps plants grow faster and bigger. But, agricultural scientists say crops generally use only thirty to seventy percent of the nitrogen that is added to soil. Extra nitrogen can pollute ground water, rivers and lakes. This can cause water resources to become overgrown with algae. This organism uses up oxygen, killing fish and other water life.
The World Health Organization says safe drinking water should contain no more than fifty milligrams per liter.
Nitrogen in the soil can become a gas, nitrous oxide. This is mostly formed by microscopic organisms in the soil. Nitrous oxide is known as a greenhouse gas. It has been linked by many scientists to climate change. They say nitrous oxide can trap about three-hundred times more heat than carbon dioxide. The United States Environmental Protection Agency -- the E-P-A -- says increased use of fertilizers is one reason for an increase in nitrous oxide in the atmosphere.
Some experts, though, say nitrogen in the form of ammonia has a greater ability to remain in the soil where plants can use it. Ammonia is a common material used to make fertilizers. These experts point out that nitrogen is everywhere. About seventy-eight percent of Earth’s atmosphere is nitrogen.
Studies have shown that another kind of fertilizer, phosphate fertilizer, can add the metal cadmium to soil. The E-P-A has reported that cadmium and other poisonous substances can start to build up in soil over long periods of time. But the report says these substances did not increase beyond limits set by United States health agencies.
Today, developed nations are using less fertilizer while developing nations are using more. Fertilizers can increase crops. And they can help farmers when the soil is not very good. But there are limits.
The E-P-A advises farmers not to use too much fertilizer. The agency notes that in nineteen-eighty-nine, some farmers in the state of Nebraska began to measure the levels of nitrogen in their soil. Farmers who tested their soil used an average of one-third less fertilizer than those who did not. The testing helped the environment. But it also saved the farmers money.
This VOA Special English Agriculture Report was written by Mario Ritter.