Earthworm activity affecting organic matter, aggregation and microbial activity in soils restored after opencast mining for coal

Earthworms were introduced into physically degraded soils restored after op encast coal mining. Their effects on soil organic matter and associated soi l aggregation were then measured after a period of 9 yr. Earthworm inputs i ncreased stable aggregation and resulted in a higher proportion of the soil organic matter as carbohydrates. Although the total amount of organic matt er in the top 15 cm was unaffected by the presence of earthworms, there was some redistribution to depth. Earthworms also caused an increase in the ca rbon content of the clay-sized fraction. Aggregation was closely correlated with organic indices, particularly total carbohydrates. There was also evi dence of organic matter having greater efficiency in stabilising aggregates where earthworms were abundant. Earthworm activity increased soil microbia l biomass near the surface but caused a decrease at depth. Metabolic quotie nt was lower near the surface but higher at depth in soils with earthworms; mineralisation constants were lower in soils with earthworms at both sampl ing depths. Overall, the results emphasise the important influence of earth worm activity on aggregate and organic matter stabilisation, processes whic h are closely linked. (C) 2000 Elsevier Science Ltd. All rights reserved.