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Important steps in developing reliable bioindicators for soil quality are characterising soil biodiversity and determining the response of its components to environmental factors across a range of land uses and soil types. Baseline data from a national survey in Ireland were used to explore relationships between diversity and composition of micro-organisms (bacteria, fungi, mycorrhiza), and micro-, meso- and macro-fauna (nematodes; mites; earthworms, ants) across a general gradient representing dominant land uses (arable, pasture, rough-grazing, forest and bogland). These diversity data were also linked to soil physico-chemical properties. Differences in diversity and composition of meso- and macro-fauna, but not microbes, were clear between agriculturally-managed (arable and pasture) and extensively-managed (rough-grazing and bogland) soils corresponding to a broad division between ‘mineral’ and ‘organic’ soils. The abundance, richness and composition of nematode and earthworm taxa were significantly congruent with a number of the other groups. Further analysis, using significant indicator species from each group, identified potential target taxa and linked them to soil environmental gradients. This study suggests that there is potential surrogacy between the diversity of key soil taxa groups and that different sets of bioindicators may be most effective under agricultural and extensive land use.

To study the effects of earthworm casting on organic matter dynamics, control soil and casts were added as a surface layer (Horizon I) to perspex cylinders containing a ‘base’ soil depleted in organic C (Horizon II). Three treatments with different Horizon I were used; a control containing uningested soil and oak litter (Quercus petraea (Mattuschka) Lieblein), cast derived from the same substrates, and a third (Ew+cast) where cast as well as endogeic (Aporrectodea caliginosa Savigny, Allolobophora chlorotica Savigny) and anecic (Lumbricus terrestris L.) earthworms were included. These were monitored over a 2 1 2 year period. Moisture fluctuations were reduced and higher amounts of organic matter and C were present in Horizon I with the cast treatment after 2 years. In addition, the proportion of clay C (and to a lesser extent light fraction) in Horizon I decreased significantly in the control and cast treatments while there was a corresponding increase in the proportions of silt C. Overall, earthworm activity had a limited effect on C distribution in the particle size fractions studied, though the dynamics of organic matter/particle associations may require more than 2 1 2 years before clear patterns emerge.