Hydraulic Conductivity and Water Retention of Clay Soils Containing Coarse Fragments

Field observations show that clay soils with medium to high coarse fragment contents are less compacted, have a more favorable structure and provide better physical condition for tree growth than similar soils containing small amounts of coarse fragments. The effect of coarse fragments on soil compaction, hydraulic conductivity, and moisture retention at low suctions was investigated. Increasing coarse fragment content increased resistance to compaction and consequently preserved lower soil bulk density. Larger volumes of large pores were found after compaction of soil with increasing coarse fragment content. In compacted soils of increasing coarse fragment content, hydraulic conductivity was higher. Aerated porosity of soils between fragments increased with increasing fragment content. It was concluded that coarse fragments contribute to improved physical conditions by acting as a “skeleton,” which resists soil compaction.