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13 May 2002, 14:14 UTC

This is the VOA Special English AGRICULTURE REPORT.

American scientists are developing ways to limit pollution from agricultural fertilizers in rivers and other waterways. The scientists say they found one method that provides a natural line of defense. Their method involves small pieces of wood called wood chips.

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The scientists buried a large amount of wood chips near crops treated with nitrate fertilizer. They found that the areas filled with wood chips reduced the nitrate in the water by as much as seventy percent.

Dan Jaynes of the United States Agricultural Research Service is leading the study. He works at the Soil and Water Quality office in Ames, Iowa.

In the United States, devices called drainage tiles can speed the removal of extra water from cropland. Farmers build drainage tiles near their fields. The devices help direct unneeded water to nearby waterways. Mister Jaynes notes that farmers use drainage tiles on thirty percent of all cropland in the central United States.

However, when water is removed from fertilized crops, nitrate may not reach deep into the soil. As a result, the fertilizer cannot help plant roots. Often the nitrate fertilizer is washed into rivers and other waterways. It feeds the growth of underwater plants. As the plants die and break down, they use up all the oxygen in the water. This causes a condition known as hypoxia. Plants and animal life cannot live in the water if it does not contain enough oxygen. High levels of nitrate have also caused problems for communities that use rivers for drinking water.

The American scientists carried out their experiment on land with corn and soybean crops. They dug large holes around the fields. These trenches are two meters deep and about two-thirds of a meter wide. They extend in the same direction as the drainage tiles.

The scientists filled the trenches with wood chips up to about one-third of a meter below the surface. Then they covered the chips with soil.

The wood chips create a natural barrier that helps change nitrate into nitrogen gas, which is common in the atmosphere. Mister Jaynes says the method works equally well for small and large farms. He said farmers do not need to supervise the system.

The scientists now will study how long the wood chips are effective before they break down.

This VOA Special English AGRICULTURE REPORT was written by George Grow.