Oklahoma · Soil test

Oklahoma soil-test fertilizer recommendations

Zone Forge reads your Oklahoma soil test in Oklahoma's own calibrated language — the critical levels and rate logic come straight from Oklahoma — OSU SWFAL (PSS-2225) combined lime + nutrient source, not a national average.

See Oklahoma recommendations → Oklahoma lime guide

Critical soil-test levels

  • P: critical 32.5 ppm (Mehlich-3 STI)
  • K: critical 125 ppm (Mehlich-3 STI)

Per Oklahoma — OSU SWFAL (PSS-2225) combined lime + nutrient source — below the critical level, a yield response to the added nutrient is expected.

Published source: Oklahoma — OSU SWFAL (PSS-2225) combined lime + nutrient source

Frequently asked

What soil-test method does Oklahoma use?

Oklahoma — OSU SWFAL (PSS-2225) combined lime + nutrient source. Zone Forge cites the publication on every recommendation.

Is the Oklahoma soil-test calculator free?

Yes — the Oklahoma soil-test recommendation calculator is free and needs no signup. Enter your lab values for source-cited P, K and lime guidance.

Zone Forge reads every Oklahoma soil test in its own state's language, then builds source-cited fertilizer and lime recommendations and full variable-rate prescriptions. See the science →