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.