Over the last four decades soil ecologists have made tremendous progress in describing, understanding and quantifying the overwhelming complexity of biological, biophysical and biochemical interactions in soil. These interactions shape the soil as a habitat for the soil food web and the vegetation and, thereby, as a regulator of the two main life-supporting processes on Planet Earth: production and decomposition. Changes in decomposition and production processes are governed by (human-induced) changes in the amounts and quality of organic residues and fertilizers entering the soil, changes in the physical environment and, indeed, changes in the soil biota. Hence, decomposition and production processes cannot be manipulated without explicitly addressing the composition and activity of the soil food web.

Using a conceptual model, we argue that quantitative understanding of biophysical interactions, in particular those between soil macrofauna and soil structure, are paramount to understanding biological and biochemical interactions in soil and the transmission of water and nutrients to plants. The need to increase the efficiency of crop production worldwide, and to reverse soil degradation, will set the agenda for soil ecologists in the near future.

Key words: soil structure, soil fauna, food web, ecosystem engineer, carbon, water use efficiency, nutrient use efficiency