Special assessment of farmland
Where can I find help with "Farm deferral status" in Multnomah county?
Multnomah County Oregon small farm issues
This publication explains the way farm deferrals are dealt with generally: https://catalog.extension.oregonstate.edu/ec1529. It also helps you evaluate your farm resources and choose an enterprise.
The County Tax Assessor's office deals specifically with deferrals in Multnomah county: https://multco.us/assessment-taxation.