Soil physical conditions on reclaimed colliery spoil heaps

Abstract

SummarySoil physical conditions are inherently poor and lead to summer droughtiness and winter waterlogging on many spoil heaps. The high stone content makes soil physical measurement difficult. The development of appropriate field and laboratory methods, which allow the calculation of sample composition, bulk density, total porosity, air‐ and water‐filled porosities and available water capacity are described.A survey of 12 reclaimed colliery spoil heaps of varying age showed that, apart from an increase in organic matter in the surface layer (0–5 cm) with increasing age of site, there were no consistent trends with age and this is attributed to initial between‐site variability. General trends with depth down the profile to 30 cm were obtained by combining the data from all 12 sites. With increasing depth the bulk density increased and the porosity decreased. A higher porosity in the 0–5 cm layer was associated with (i) lower stone content (>2 mm) due to weathering and (ii) organic matter accumulation. In the subsurface layers (>5 cm) the stone content was essentially constant and the decreasing porosity with depth is explained as being due to settling. Overall there was a strong negative correlation between porosity of samples and stone content, which in turn was determined by the weatherability of the material.