Impact of the hydrophobicity of Quincy soil on water quality

This project will determine the intensity and extent of the adverse effects of Quincy and associated soils on ground water consumption, groundwater contamination from agricultural nutrients, and surface water quality. Quincy soils have been found to exhibit a behavior called hydrophobic–armoring that leads to preferential flow and enhanced erosion. The project is focused on the Middle Columbia-Wallula Lake Watershed because of the extent of Quincy and associated soils within the watershed (Figure 1), and the documented concerns of local growers and experiment station scientists working in this watershed.

Figure 1 – (Left) Study site location. (Right) Distribution of Quincy (orange), and associated soils (yellow and green) within watershed.

The lower Columbia River Basin of Oregon and Washington has approximately 500,000 acres of irrigated soils. About 20% of this area is Quincy or related soils that developed from sandy-textured fluvial and eolian. Soil Survey describes Quincy as having rapid infiltration, as would be expected of a sandy soil. However, an increasing number of growers farming these soils are experiencing soil wetting problems and restricted infiltration.

Figure 2. (Left) Water infiltration under normal soil conditions. (Right) Water infiltration for hydrophobic-armoring soils

In an agricultural setting, water is shed from tillage ridges and runs into furrows where it ponds and then infiltrates, percolating downward and bypassing the root zone (Figure 4). Consequently, young plants experience drought stress. In response, growers irrigate more frequently and apply more water to keep high value crops from wilting and going into water stress. In one 5000-acre field surveyed, water is applied continuously through center pivots at 0.3 inches of water per 18-hour cycle. Grower estimates that he applies ~30% more water than needed by the crop, corresponding to ~ 10-12” of additional water at a cost of $65-78/acre).

Excessive irrigation also impacts ground and surface water quality. Nitrate applied with the irrigation water will also bypass the root zone and percolate to the groundwater. Nitrate levels in wells have been increasing and in 1994 the Oregon Department of Environmental Quality designated the region a groundwater management area. Growers typically apply 250-300 lb N/acre on potato crops. Although the actual amount of nitrogen leaching below the root zone is not yet known, there is an obvious environmental risk. Uneven infiltration also leads to runoff from these fields and associated soil erosion.

Water droplet on hydrophobic soil

This project intends to develop an understanding of the physical properties of Quincy soil, determine the impact these have on water quality and identify amelioration techniques that will enhance agriculture and reduce environmental stress. (supported by a grant form the Agricultural Research Foundation).