Persistence of Subsoil Compaction in a Mollisol

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Abstract
Persistence of subsoil compaction was tested in Nicollet clay loam (a Mollisol) in southwestern Minnesota. Plots were either not packed or packed in 1960 in the bottom of each plow furrow using about 7.5 bars pressure, and were cropped to corn (Zea mays L.) and alfalfa (Medicago sativa L.) 9 years. Halves of plots were irrigated each year just prior to soil freezing. All plots were tilled with normal farm equipment after initial packing.Soil bulk density below the plow layer did not change over the 9‐year period, but there were small trends for increased bulk density on the not‐packed treatment. Neither crop nor overwinter soil water content affected the packed subsoil. The packed layer was easily identified by penetrometer measurements.Alfalfa root samples taken at the close of the experiment showed that packing reduced mean root weights by as much as 36% in the 40‐ to 90‐cm layer compared to 11% or less in the surface 40 cm. Packing affected the distribution of taproots and fibrous roots in the profile.Soil hydraulic conductivity (K), either saturated or unsaturated, was reduced by packing. Decreases in saturated K averaged 65% in 10‐cm soil depths between 21 and 48 cm and 56% between 61 and 88 cm. Unsaturated K measured in situ also showed persistence of the packing treatment in the 18 to 55‐cm soil layer.
Funding Information
  • North Central Regional Cooperative Research (NC-56)

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