Extent and Persistence of Subsoil Compaction Caused by Heavy Axle Loads

Abstract

AbstractWheel traffic of heavy farm machinery is causing increased concerns about soil compaction. To offset the increasing weight of large equipment, tires have increased in both size and numbers in an effort to keep constant the contact pressure on the soil surface. Recent research has indicated, however, that increasing axle load can cause increasing and deeper compaction irrespective of surface contact pressure. Axle loads of 9 and 18 Mg were applied in replicated field experiments initiated in 1981 and 1982 in Minnesota as part of an international cooperative study on the effects of high axle loads on deep soil compaction and plant response. Such axle loads are typical of modern harvest and transport equipment. These heavy axle loads were applied only at the beginning of the experiment, and are compared with check treatments where axle loads are limited to ≤4.5 Mg. Various soil parameters were measured to assess the extent and persistence of subsoil compaction. When the subsoil was relatively dry, axle loads of 9 and 18 Mg did not cause significant changes in bulk density, penetrometer resistance, or hydraulic conductivity deeper than about 20 to 30 cm, the normal depth of tillage. However, when the subsoil was relatively wet, bulk density increased about 0.08 Mg m−3 from about the 30‐ to 50‐cm depth. Saturated hydraulic conductivity decreased from 2 to 0.2 cm h−1 due to 18‐Mg axle load on a Webster clay loam (Typic Haplaquolls). A similar relative decrease was measured on a Nicollet clay loam (Aquic Hapludolls). Evidence of subsoil compaction persistence was measured 4 yr after initial heavy axle loading in spite of annual winter soil freezing to depths up to 90 cm.