Ž . Geoderma 82 1998 1–3 Biogeochemistry of isotopes in soil environments: theory and application L.C. Nordt a, ) , E.F. Kelly b , T.W. Boutton c , O.A. Chadwick d a Department of Geology, Baylor UniÕersity, Waco, TX 76798, USA b Department of Agronomy, Colorado State UniÕersity, Fort Collins, CO 80523, USA c Department of Rangeland Ecology and Management, Texas A&M UniÕersity, College Station, TX 77843, USA d Department of Geography, UniÕersity of California, Santa Barbara, CA 93106, USA Accepted 15 April 1997 Scientific disciplines make significant theoretical advances when new and innovative techniques emerge. For example, pedology has been enhanced by the recognition that soils consist of weathered mineralogical and organic compo- nents supporting plant and animal life, that soils form as a function of indepen- Ž . dent soil-forming factors climate, biota, parent material, topography, time , and that some soil processes can be quantified by mass balance calculations. Further progress in pedology will inevitably come from increased quantification and modeling of soil forming processes. We believe that the use of natural isotopic tracers provides a powerful technique that will fulfil this need and take pedology into the 21st century. Understanding the biogeochemistry of different isotopic systems in soils can increase our ability to unravel complex biotic and abiotic interrelationships by resolving patterns and processes at appropriate spatial and temporal scales. Isotopes can heighten our understanding not only of soils, but of the entire earth–atmosphere–biosphere system. Isotopic ratios in nature integrate and record information regarding processes that form key components of soils, rates of these processes, and the environmental conditions prevailing at the time the components were formed. Hence, isotopic indicators recovered from soils can be used to study topics as diverse as: the origin of soil constituents, including those created by anthropogenic processes; organic matter turnover rates; nutrient ) Corresponding author. Fax: q1 254 710 2673. 0016-7061r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. Ž . PII S0016-7061 97 00094-3