Tillage, habitat space and function of soil microbes

This review examines the effect of tillage on microbial habitat space, and the roles of microbes in in ̄uencing Ntransformation processes within a heterogeneous soil environment. Literature relating tillage to microbial processes is assessed critically focusing on (a) degrees of physical disruption and N-processes, (b) interactions between organisms and the soil pore network, and (c) the role of soil structure in mediating oxygen movement to sites of microbial activity in soil. Spatial heterogeneity is shown to be a key characteristic of soil structure and N-transformation processes, impacting on predator:prey relations, microbial habitable pore space, and the modelling of the soil system with respect to denitri®cation. The latter area is discussed with respect to the notion of how a functional appraisal of soil structure may be approached theoretically, at the aggregate and soil pro®le scale. # 2000 Elsevier Science B.V. All rights reserved.