Soil Compaction Assessment Calculator

A penetrometer measures cone index — the resistance soil offers to a probe pushed in at a steady rate — and this calculator turns readings taken at 6, 12, 18, and 24 inches into a practical compaction diagnosis. Because sandy, loam, and clay soils resist root growth differently at the same physical density, the root-limiting threshold shifts by texture class (300 PSI for sandy soils, 350 for loam, 400 for clay), and the calculator scans all four depths to find both the peak cone index and where it occurs. From that peak reading it estimates bulk density using a texture-specific linear relationship in the style of the cone-index-to-bulk-density regressions Busscher (1990) published for flat-tipped penetrometer readings on medium-textured soils, and it estimates effective rooting depth as the shallowest point where cone index first exceeds the texture's threshold, minus a 3-inch buffer for the transition zone roots typically won't push through.

Lost rooting depth is then translated into an estimated yield penalty at roughly 3% per inch, capped at 50%, and an overall 0-100 compaction score is derived from the average cone index across all four depths. The diagnosis text calls out a hardpan requiring deep ripping above 500 PSI, moderate compaction warranting biological remediation or targeted tillage above the texture threshold, and mild compaction worth monitoring above 200 PSI. Keep in mind cone index readings are highly moisture-dependent — the same compacted layer reads much higher when the soil is dry — so take all readings at a similar, ideally field-capacity, moisture level for the comparison across depths to mean anything, and treat bulk density and yield-impact figures as planning estimates rather than calibrated lab values.