What could be messing with my soil pH readings when organic matter is high?

[Zachary_G]

I'm trying to analyze some soil samples for a community garden project and my pH readings are all over the place. I calibrated the meter with fresh buffer solutions, but I'm wondering if the high organic matter content is interfering with the electrode.

[Aria_W]

I’ve had something similar. Fresh buffers didn’t stop the readings from wandering once the soil was high in organic matter. The electrode would seem to slow and drift as gunk from the OM built up on the glass. I’d rinse the tip, wipe it, and re-check, but the numbers still moved between samples. I ended up letting the soil slurry sit a bit and measuring the clear liquid on top, which helped reduce some noise but it still wasn’t stable.

[RichardT]

We tried comparing with a soil extract method and even swapped in a clean, new electrode. The first time we did a 1:1 soil to water mix, the results hardened into a fairly tight band around mid 6s after a few minutes, which made us trust the instrument a bit more. But then a different batch of soil behaved completely differently, and we ended up chasing drift again.

[AddisonUM]

Do you think the organic matter is the main issue, or is the problem the sample handling, like not letting the slurry settle long enough?

[Nathan8]

I keep thinking maybe the real problem is just how variable the garden soil is. One plot is sandy, another is clay, and the same meter seems to talk to us differently last week than this week. A small temperature change or moisture level could be messing with readings, and I’m not sure we’re really solving it.