Soil organic matter and microbiological development of technosols in the South Wales Coalfield

Degraded land (formerly 'reclaimed') after surface-coal-mining is a serious problem in South Wales. This project uses forestation to foster soil development on opencast coal-mine spoil technosols. It compares records of humification and the soil microbiological system (microcoenosis) using paired data from the same plantings in 1998 and 2018. Statistical analysis finds no significant difference between samples collected under trees planted by the pit-planting versus trench planting method or trees planted using organic or mineral fertilizer. However, there are strong significant differences in both soil organic matter and microflora components and significant correlations with time since tree planting. Most components of the soil organic carbon (TOC) and the microflora increase, often significantly. However, compared to 2018, 1998 samples contain significantly greater maximum levels of Insoluble Carbon while the microflora had significantly more Ammonifying bacteria. Decreases in Insoluble Carbon explain the relatively small increase in TOC between 1998 and 2018. The % extracted with 0.1 N H2SO4 is significantly larger in 2018, suggesting active weathering. Similarly, both the maxima and minima of total Humic and Fulvic acids content, extracted with 0.1 M Na4P2O7 + 0.1 M NaOH, are significantly greater in 2018. Total microflora shows significant positive correlations with time-since-tree-planting as do the proportions of bacilli and actinomycetes but the correlation with ammonifying bacteria is negative. In 1998, the microflora was dominated by non-spore-forming bacteria while, in 2018, bacilli and actinomycetes prevail; both are involved in the transformation of complex organic compounds and humification. This indicates active transformation of more complex organic compounds and advancing humification. In sum, forestation of these degraded, formerly reclaimed, opencast coal-mine spoils has resulted in a massive increase in both the size and functioning of the soil organic system.