Impacts of intensive agriculture on soil fauna and ecosystem function: trading function for dependence?

Soils form the basis of agroecosystems, generating the fuel, food and fodder needed to sustain human life. Soil biological communities contribute to almost all ecosystem processes, yet our understanding of how intensive agriculture impacts on these communities, and on fauna-function relationships, lags far behind that of above-ground systems. This thesis investigates the impacts of intensive agriculture, and in particular fertiliser use, on relationships between soil invertebrate abundance, community structure and ecosystem function both above-ground and below-ground. The impacts of fertilisation, including organic and inorganic fertiliser regimes applied at different rates, and irrigation were quantified using realistic experimental field plots in temperate arable and plantation systems. Furthermore, the effects of a gradient of arable management intensity and the value of non-crop habitats in providing refugia for soil fauna were investigated using woodland-to-field transects. Impacts on soil invertebrates, including soil mites, springtails and nematodes, were quantified in terms of changes in abundance and shifts in community structure. Measures of ecosystem function included above-ground productivity, plant nutrient bioavailability and organic matter decomposition. Impacts of fertilisers were complex and varied between systems and faunal groups. Notably, we observed that inorganic fertiliser application reduced soil mite and nematode abundance when applied with irrigation in water-limited, sandy soils. In general, astigmatid mites responded less negatively, or even positively, to intensive management. We observed strong evidence of non-crop habitats providing refugia for soil fauna, and in particular poor dispersers, in intensive arable landscapes. This thesis advances our understanding of soil invertebrate ecology in intensively-managed agricultural systems. We discuss our findings in the context of the sustainable management of soils under a growing population and suggest directions for future research.