The effects on topsoil of long-term storage in stockpiles

Summary

During many quarrying, civil engineering and landscaping schemes topsoil is stripped from the site and stored in large heaps. These remainin situ for many years before the soil is reused and it is generally believed that there is a great reduction in the ‘quality’ of the soil during that period.

A study of stockpiles of different size, age and soil type has revealed that biological, chemical and physical changes do occur, mainly as a result of anaerobic conditions within the heaps, but also as a result of mechanized handling during the stripping and stockpiling. Visible changes occur within 0.3 m of the surface of stockpiles of clayey textured soils, but only below about 2 m depth for sandy textures. These visible changes are accompanied by chemical changes, particularly in the forms of nitrogen present but also in the content of available nutrients, pH and organic matter levels. Biological changes include reductions in potential for mycorrhizal infection, soil biomass and especially earthworm population. The soil atmosphere contains high levels of carbon dioxide, methane, ethane and ethylene. Physical changes include reduction in aggregate stability and resistance to compaction, increase in bulk density and changes in pore size distribution and micro-structure, as revealed by scanning electron microscopy.

Limited evidence suggests that many of the adverse effects quickly disappear when the soil is respread.