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Keeping topsoil down on the farm.

Keeping topsoil down on the farm

Amid the steeply rolling hills of the Palouse region near Spokane, Wash., lies the ideal "laboratory' for testing the effects of different farming techniques on soil. In that area, one farm has relied on crop rotations and native soil fertility for plant nutrients ever since it was first plowed in 1909. Next to it, another farm, first cultivated in 1908, has been receiving recommended doses of inorganic fertilizers and pesticides since 1948. By examining the soil in two adjacent fields, one belonging to each farm, researchers have now been able to ascertain that an organic farming system is significantly more effective in reducing soil erosion than a system based on the use of manufactured fertilizers.

"The differences are dramatic,' says John P. Reganold of Washington State University in Pullman. "People say there should be differences, but until now, no one had clear evidence.' Reganold and his colleagues report their findings in the Nov. 26 NATURE.

The organic farm used in the study operates on a three-year cycle. It produces winter wheat the first year, then a crop of spring pea the following year. Both crops are harvested. In the third year, Austrian winter pea is planted. The mature plants are plowed under to provide "green manure' for the fields. In contrast, the conventional farm alternates between crops of winter wheat and spring pea. Although the crop yields are similar for both farming systems, the organic farm produces a cash crop on a given field in only two out of three years of the cycle.

It took a long time to find the right sites for a comparison of soil properties, says Reganold. "We picked a spot where the farms touch each other.' Even the slopes and the direction in which the slopes face were identical for both sets of test sites. "In that small area, all environmental conditions were the same except for management,' he says.

Earlier studies had already shown that the organically farmed soil had higher levels of organic matter and a larger mass of microorganisms and soil enzymes. The most dramatic difference revealed by the new study was that the organic farm's topsoil was on the average 6 inches thicker than its neighbor's. In addition, the organically farmed soil held more moisture and had a softer surface crust. Says Reganold, "All that change has taken place since 1948.'

The greater erosion rate shown for conventionally farmed soil indicates that a typical farm with similar soil and slopes could lose all of its topsoil within 50 years, exposing a denser, less fertile, clay subsoil. Wheat yields go down substantially in this harder soil.

If conventional farming systems are not modified, the loss of valuable topsoil will continue, and in the long term, productivity will decline, says Reganold. Unfortunately, many farmers can't afford to put in a legume-based, green-manure crop and periodically leave fields out of production.
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Title Annotation:research compares effects of organic and conventional farming on soil
Author:Peterson, Ivars
Publication:Science News
Date:Dec 5, 1987
Words:484
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