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Dairy farmers (landowners) in the Willamette Valley have constructed long term manure storage ponds for containing manure and rainwater volume during the winter period (generally designed for 180 days). These liquid volumes are applied to crop fields primarily from April to November (irrigation season), and on occasion during the remaining months (storage season).

Landowners have asked for some form of irrigation scheduling. They recognize the need to improve water use, reduce surface erosion, and minimize deep leaching of solutes such as nitrate nitrogen. In short, they apply liquid volumes without a clear understanding of how much to apply based on soil moisture conditions.

A series of Weather Stations were established on four dairy farms in the Willamette Valley. Watermark (Irrometer Company, Riverside, Calif.) granular matric sensors were established in crop fields. The Soil Water Characteristic Curve (SWCC) is being derived for these fields. Landowners will soon have a greater knowledge of their crop fields in terms of volumetric water content at a given matric potential. More precise liquid volumes can be applied during the irrigation season and possibly during the typical storage period.

The end result of this work improves water use by landowners, optimizes crop yield, reduces surface runoff and the potential for deep leaching of solutes through the vadose zone, and improves the overall water resources in the Willamette River Watershed [USGS Hydrologic Unit Codes: HUC 1709005 (North Santiam), and HUC 1709007 (Middle Willamette)].