VOA Special English 慢速英语听力材料

Today we finish a two-part series. A listener in Brazil asked about agroecology（农业生态学）. This is a field of ideas about how to farm productively but also protect natural resources.

Last week, we discussed how agroecology is seen in many ways as an answer to the Green Revolution. That movement has given us modern farming methods.

Agroecology and the Green Revolution both want to increase productivity. But they work toward this common goal in different ways. Many agroecologists question how long modern farming methods can continue.

Modern farming uses land intensively. Often the same crop is grown on the same land year after year. Soil breaks down and washes away. Also, fewer kinds of the same plant are grown. This can limit the number of kinds that may have useful genetic qualities.

Another issue is fertilizer. Agroecologists say they would use organic materials and compost in place of chemicals. The Green Revolution has shown that chemical fertilizer（化学肥料）can greatly increase crop productivity. But it can also pollute water supplies.

To water crops, agroecologists say they would use methods that reduce the need for irrigation. Irrigation is an ancient idea. Water is pulled from the ground or brought from another place. Irrigated crops are highly productive. Sixteen percent of all farmland in the world is irrigated. But this sixteen percent of the farmland produces forty-percent of all food.

Yet irrigation systems can use up groundwater（地下水）faster than nature can replace it. And there are costs to taking water from other areas.

To control pests, agroecologists say they would use helpful insects to kill harmful ones. In the last fifty years, however, farmers have increased the use of insecticides. These chemical poisons do destroy harmful insects. But they also kill helpful ones, and can cause pollution and health problems. Also, pests can develop the ability to resist chemicals.

One place to learn more about agroecology is at the Web site agroecology dot o-r-g. This site is operated by the University of California at Santa Cruz. Steven Gliessman is a professor in the Center for Agroecology there. He has written several books on the subject.

This VOA Special English Agriculture Report was written by Mario Ritter. If you have a question for us, write to special@voanews.com. This is Doug Johnson.