This is the VOA Special English Agriculture Report.
Last week, we described somedifferent kinds of fertilizers. This week, we examine some of theissues involved in their use.
Farmers know that nitrogen fertilizer helps plants grow fasterand bigger. But, agricultural scientists say crops generally useonly thirty to seventy percent of the nitrogen that is added tosoil. Extra nitrogen can pollute ground water, rivers and lakes.This can cause water resources to become overgrown with algae. Thisorganism uses up oxygen, killing fish and other water life.
The World Health Organization says safe drinking water shouldcontain no more than fifty milligrams per liter.
Nitrogen in the soil can become a gas, nitrous oxide. This ismostly formed by microscopic organisms in the soil. Nitrous oxide isknown as a greenhouse gas. It has been linked by many scientists toclimate change. They say nitrous oxide can trap about three-hundredtimes more heat than carbon dioxide. The United States EnvironmentalProtection Agency — the E-P-A — says increased use of fertilizersis one reason for an increase in nitrous oxide in the atmosphere.
Some experts, though, say nitrogen in the form of ammonia has agreater ability to remain in the soil where plants can use it.Ammonia is a common material used to make fertilizers. These expertspoint out that nitrogen is everywhere. About seventy-eight percentof Earth’s atmosphere is nitrogen.
Studies have shown that another kind of fertilizer, phosphatefertilizer, can add the metal cadmium to soil. The E-P-A hasreported that cadmium and other poisonous substances can start tobuild up in soil over long periods of time. But the report saysthese substances did not increase beyond limits set by United Stateshealth agencies.
Today, developed nations are using less fertilizer whiledeveloping nations are using more. Fertilizers can increase crops.And they can help farmers when the soil is not very good. But thereare limits.
The E-P-A advises farmers not to use too much fertilizer. Theagency notes that in nineteen-eighty-nine, some farmers in the stateof Nebraska began to measure the levels of nitrogen in their soil.Farmers who tested their soil used an average of one-third lessfertilizer than those who did not. The testing helped theenvironment. But it also saved the farmers money.
This VOA Special English Agriculture Report was written by MarioRitter.