Ecological challenges for soil science

Soil Science integrates specific contributions from physics, chemistry, bio logy, and the human sciences. During the last 2 decades, these approaches, which had primarily developed separately and at different speeds, have been progressively integrated. Ecology has contributed a significant number of integrative concepts and questions, some, such as nutrient cycling and ener gy budgets, that are rather old, and others, such as soil engineering by ma croinvertebrates, the relationship between biodiversity and soil function, and the impact of landscape fractionation, that are more recent. An important issue common to all disciplines in Soil Science is that of sca les. Ecological studies have shown that similar activities, e.g., the build ing of solid structures by invertebrates for their sheltering or gut transi t of soil for digestion, may affect soil function at different scales, affe cting the rates of processes in sometimes opposite directions. The concept of functional domains in soil, derived from soil ecological research, defin es a scale at which physical, chemical, and biological processes can be stu died efficiently in a true multidisciplinary approach. Functional domains a re specific sites in soils defined by a main organic resource (leaf litter or soil organic matter), a major regulator, biotic (i.e., an invertebrate ' engineer' or roots) or abiotic (like freezing/thawing or drying/rewetting a lternates), a set of structures created by the regulator (for example, feca l pellets, galleries, or cracks), and a community of dependent invertebrate s of smaller size and microorganisms that live in these structures. Functio nal domains may be physically identified in soils and specifically studied using the different disciplinary approaches. Specific micromorphologic, iso topic, and other techniques allow us to address issues at this scale adequa tely. Ecological research also provides a theoretical background for manage ment of soils at the larger integrative scales of landscape and regions. Essential issues for the near future should use this interdisciplinary appr oach. Sustainability of cropping systems and maintenance of soil ecosystem services depend more on an integrated approach than do the extreme developm ents in single disciplines in isolation that originated the series of probl ems we now face: large scale soil erosion, nutrient transfers to neighborin g ecosystems, threats of genetically modified organisms, or biodiversity ac cidents.