An investigation of the interrelationship between the microbial community and soil structure in soils disturbed by opencast mining

The study aimed to determine the interrelationship between aggregate stability and
microbial biomass in restored soils, and to investigate if the development of the two
parameters in soils disturbed by opencast mining could be influenced by the
application of slow release organic amendments. These objectives were tested using
two microbiological methods; determination of adenosine triphosphate and
dehydrogenase activity, and three structural measurements; determination of
aggregate stability by wet-sieving, shear vane and bulk density. Soil carbon and
nitrogen were also determined.
The first part of the study involved a survey of 16 field areas located in Britain, 12
disturbed and four not disturbed by opencast coal mining. The areas were all
grasslands which varied in the time since restoration, which was between 0-16 years.
A log linear relationship between the soil biomass and stable aggregates > 2 mm was
found for all field areas (y = 38 In x - 69, r = 0.51). The variation in both properties
was also affected by the restoration practices at the individual sites. A cluster
analysis of the measured soil properties separated the restored areas into "good"
restorations, involving progressive restoration, topsoil replacement and early
underdrainage, and "poor" restorations, restored without topsoil or with soil forming
material.
The second part of the study reported on the first 16 months of a field trial set up on a
recently restored opencast coal site situated near Denby in Derbyshire in 1991. A 3 x
4 factorial design involved two organic amendments (straw and wood), and four
vegetation covers. The treatment effects were obscured by natural fluctuations in the
soil properties over the period studied. However, the presence of the organic
amendments alleviated some of the physical problems of the soil, such as
waterlogging and frost damage, which drastically affected the results in 1992. The
soil properties generally improved in the order straw>wood>no amendment for the
majority of soil parameters (structure, C and N), the notable exception being the soil
microbiological parameters which varied substantially throughout the experiment.
Differences between the vegetation covers (a MAFF, a ruderal and a species rich
seed mixture) were small.

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