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 influencing N-transformation processes within a he terogeneous soil environment. Literature relating tillage to microbial proc esses is assessed critically focusing on (a) degrees of physical disruption and N-processes, (b) interactions between organisms and the soil pore netw ork, and (c) the role of soil structure in mediating oxygen movement to sit es of microbial activity in soil. Spatial heterogeneity is shown to be a ke y characteristic of soil structure and N-transformation processes, impactin g on predator:prey relations, microbial habitable pore space, and the model ling of the soil system with respect to denitrification. 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 profi le scale. (C) 2000 Elsevier Science B.V. All rights reserved.