Extension Search / Soil Labs / Oregon
Soil Testing in Oregon
Oregon’s land-grant university doesn’t run a soil lab for the public, so samples go to a private lab. Extension says which tests to ask for, so your numbers match the state’s fertilizer guidelines.
Test Methods
Ask the lab for:
- Phosphorus: Olsen or Bray P1, depending on the soil. Sodium bicarbonate. Made for alkaline, high-lime soils like most of the West. Made for acid to neutral soils. It reads low on high-lime soils.
- Potassium: Ammonium acetate. The long-standing potassium test. Reads close to Mehlich-3 for potassium.
- Micronutrients: DTPA. The standard micronutrient test for zinc, iron, manganese and copper, made for alkaline soils.
Using different tests for different nutrients is normal. The soil test calculator lets you pick the test for each one.
Labs pull nutrients out of soil with different chemicals, and each one gives a different number for the same soil. 20 ppm on one test and 20 ppm on another don’t mean the same thing, so check which test your report used before you compare it to a chart.
Tests
- Basic test. pH, phosphorus and potassium, usually with calcium and magnesium. Enough for most gardens and lawns.
- Organic matter. How much organic matter the soil holds, which sets how much nitrogen it releases.
- Oregon State doesn't name a public soil lab. Extension says to use a soil testing lab and call first for fees.
- Ask for Olsen phosphorus on alkaline soils, mostly east of the Cascades, and Bray P1 on acid soils, mostly west.
- Ask for ammonium acetate potassium and DTPA micronutrients, the methods OSU's guides are built on.
- Master Gardener offices offer basic pH tests.
Sources: [1] [2]
Sample Tips
- Take 10 or more small cores across the area and mix them in a clean bucket. One spot tells you about one spot.
- Sample gardens and lawns about 6 inches deep, below any mulch or thatch.
- Keep beds that are grown differently, like a lawn and a vegetable garden, as separate samples.
- Wait a couple of months after fertilizing or liming, so the test reads the soil and not the last bag.
- Use the same lab and the same tests each time, so the numbers compare from year to year.
Your county Oregon Extension office can help you take the sample and read the report.
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