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Testing water from sampling well for herbicides and nitrate.

Iowa Study Examines How to Sustain Watersheds

By Dawn Johnson
November 18, 1997

A six-year study of highly erodible soils on four southwest Iowa watersheds may give scientists new clues on how sustainable farming methods affect soil and water quality.

A watershed is the land from which the rainfall runoff flows to a common drainage point. Watershed size can range from a few to many thousands of acres.

Traditional farming methods include deep moldboard plowing, cultivating and other techniques that disturb the soil and can increase erosion and the amount of sediment reaching rivers. But Agricultural Research Service scientists want to find farming practices that will protect and improve water and soil quality over time, as well as allow farmers to make a profit.

Sustainable practices include tilling the land less--or not at all--or using less invasive tillage, such as chisel plowing, that disturbs only a strip of soil to help guard against erosion.

The study, which began in 1996, could lead to new management tools for small farms because the watershed, not the farm’s property boundaries, will be the geographic context for farming decisions. The watershed approach is a departure from tradition. Farmers typically manage soil and water resources based on property boundaries described in the deed.

Soil in all four study watersheds is highly erodible and has been farmed with traditional methods for many years. The scientists, at ARS’ National Soil Tilth Laboratory in Ames, Iowa, will study sustainable systems on three of the four watersheds. The fourth will continue to be farmed conventionally.

Scientists will measure how a switch to sustainable practices affects weed populations, water infiltration and absorption, soil structure and productivity, crop yields, insect and disease patterns, and movement of herbicides and nitrates through the soil.

An article about the watershed study appears in the November 1997 issue of Agricultural Research, ARS’ monthly magazine. The report also is on the World Wide Web at:


Scientific contact: Tom Moorman, USDA-ARS Agricultural Land Management Research unit, National Soil Tilth Laboratory, 2150 Pammel Drive, Ames, Iowa, (515) 294-2308, fax (515) 294- 8125,