Subject
- Soils -- Oregon -- Willamette River Valley14
- Water resources development -- Oregon -- Willamette River Valley10
- Soil conservation -- Oregon -- Willamette River Valley8
- Upper Willamette Resource Conservation and Development Project8
- Irrigation -- Oregon -- Willamette River Valley5
- Air -- Pollution -- Oregon -- Willamette River Valley4
- Agriculture -- Oregon -- Willamette River Valley3
- Alfalfa -- Oregon -- Willamette River Valley3
- Burning of land -- Oregon -- Willamette River Valley3
- Cercopidae -- Oregon -- Willamette River Valley3
- Douglas fir -- Oregon -- Willamette River Valley3
- Farm income -- Oregon -- Willamette River Valley3
- Land use -- Oregon -- Willamette River Valley3
- Limnanthes -- Oregon -- Willamette River Valley3
- Oregon oak -- Oregon -- Willamette River Valley3
- Spraying and dusting in agriculture -- Oregon -- Willamette River Valley3
- Agricultural productivity -- Oregon -- Willamette River Valley2
- Agriculture -- Economic aspects -- Oregon -- Willamette River Valley2
- Apples -- Diseases and pests -- Control -- Oregon -- Willamette River Valley2
- Douglas fir -- Economic aspects -- Oregon -- Willamette River Valley2