Soil Compaction Across the Old Rotation.

Evaluating soil compaction levels across the Old Rotation, the world’s oldest continuous cotton (Gossypium hirsutum L.) experiment, has not been conducted since the experiment transitioned to conservation tillage and high residue cover crops with and without irrigation.  Our objective was to characterize soil strength measurements across the experiment using a new approach to complement traditional soil strength analyses collected with a multi-probe cone penetrometer.  Soil strength measurements were collected across all thirteen plots with and without irrigation in Dec. 2014 and average cone index values were calculated across five row positions.  The cone index values were plotted, and the area under each line was calculated.  The calculated area corresponds to a relative compaction value.  This value was used to compare soil strength measurements across irrigated and non-irrigated areas of the six rotations represented.  Results indicate a trend of lower soil strength with more variability across the 3-year rotation compared to the other rotations.  Lower soil strength values for the 3-year rotation appear to correspond to previously documented soil organic carbon increases.  Soil strength measurements analyzed with the new method allowed treatment effects to be easily quantified to facilitate simple comparisons to aid interpretation of treatment effects.