Malheur County Groundwater Management Area

Northeastern Malheur County was declared Oregon's First "Groundwater Management Area" due to elevated nitrate - N and concerns about diacid breakdown product from Dacthal.

A number of different affected groups and various agencies cooperated to develop the NE Malheur County Groundwater Management Plan. The plan embraced environmental goals and the value of producers while relying upon a cooperative voluntary approach for implementation.

Since chemical fertilizers and other N forms convert to nitrate and nitrate can be leached, applied fertilizers can lead to nitrate loading of the groundwater. Similarly, dacthal oxidizes to diacid which is both stable and leaches.

In Malheur County crops have traditionally been furrow irrigated. The large water applications necessary in furrow irrigation both promote nitrate leaching and necessitate more N fertilizer.

Progress in reducing the nitrate and dacthal levels has come about through research, extension, and voluntary implementation.

Research has been conducted on N on potatoes, onions, sugarbeets, and wheat; irrigation management of potatoes and onions; sugar beets and onions as sop up crops; comparison of irrigation systems; and dacthal banding.

Irrigation management has included the determination of critical levels, irrigation scheduling, drip irrigation, sedimentation reduction and evapotranspiration postings.

N fertilizer management for reduced leaching has included determination of N timing, placement and rate; soil and foliar testing; sop up crops, and irrigation scheduling.

Following cooperative efforts the results of research were disseminated through extension and demonstration and have led to widespread implementation of modified practices in:

  • N on potatoes, onions, sugarbeets, wheat
  • Irrigation management of potatoes and onions
  • Sugar beets and onions as sop up crops
  • Comparison of irrigation systems
  • Dacthal banding
  • Alternatives for grass weed control in onions

The groundwater quality of Malheur County is improving.