Agricultural soils are subjected to many applied mechanical stresses that influence their behavior. Stresses arise from tillage machines, seeders and chemicals applicators, tractors, and equipment for harvest and transport. Applied stresses may compact or loosen the bulk soil. Micro sections of soil (aggregates or clods) may be compacted during tillage while the bulk soil is loosened. Because most granular soils are combined into structural units of varying sizes with different strengths and properties, prediction of the effect of stresses on the behavior of bulk soils is difficult. The basic strength properties of soil are determined by many fac tors: the size distribution of particles, chemical and mineralogical properties of inorganic clay fraction, the organic matter content and composition, the water content and the stress history. These factors combine and interact to produce many possible behavior patterns. Changes in structure of the soil from applied stresses and biologi cal reactions may profoundly influence storage and transmission of water, heat, and air, and the mechanical resistance to penetration by plant roots. They may also affect the traction of vehicles. Manipulation of structural properties of soils by tillage implements is a major cost under most crop production systems. Reduced energy use is also a significant conservation objective. Improved management systems are very dependent upon a better understanding of soils' response to applied stresses. The content of this book resulted from a NATO Advanced Research Workshop held in St. Paul, Minnesota, U.S.A. September 13-16, 1988.

This book provides a global review of the mechanisms, incidence and control measures related to the problems of soil compaction in agriculture, forestry and other cropping systems. Among the disciplines which relate to this subject are soil physics, soil mechanics, vehicle mechanics, agricultural engineering, plant physiology, agronomy, pedology, climatology and economics.The volume will be of great value to soil scientists, agricultural engineers, and all those involved with irrigation, drainage and tillage. It will help to facilitate the exchange of information on current work throughout the world, as well as to promote scientific understanding and stimulate the development, evaluation and adoption of practical solutions to these widespread and urgent problems.

Soil Structure offers a multidisciplinary approach to the study of soil structure and its relevance to wide ranging investigations in environmental sciences. Topics covered in Soil Structure include soil structure determination, soil fabric genesis and functions, strength and stress distribution, fabric changes in plastic clays, the effects of organic matter and earthworms, air slaking, and hydraulic conductivity changes. The book also discusses litter decomposition and matter transport, the characterization of pore organization, monitoring via a neutron activated tracer, various influences on growth and phosphorus supply of plants and on water uptake by plants, the effects of acidification, and much more. Improved procedures for measuring and calculating the unsaturated hydraulic conductivity of structured soils are also given.

The AAAS Selected Symposia Series was begun in 1977 to provide a means of more permanently recording and more widely disseminating some of the valuable material which is discussed at the AAAS Annual National Meetings. The volumes in the Series are based on symposia held at theMeetings which address topics of current and continuing significance, both within and among the sciences, and in the areas in which science and technology have an impact on public policy. The Series format is designed to provide for rapid dissemination of information, so the papers are reproduced directly from camera-ready copy. The papers are organized and edited by the symposium arrangers who then become the editors of the various volumes. Most papers published in the Series are original contributions which have not been previously published, although in some cases additional papers from other sources have been added by an editor to provide a more comprehensive view of a particular topic. Symposia may be reports of new research or reviews of established work, particularly work of an interdisciplinary nature, since the AAAS Annual Meetings typically embrace the full range of the sciences and their societal implications.

The Working Group M.O. (Interactions of soil minerals with organic components and microorganisms) (WGMO) of the International Soil Science Society (ISSS) was founded in 1990 at the 14th World Congress of Soil Science (Kyoto, Japan), with Professor P.M. Huang being the Chairman. Since then, the Working Group M.O. has served as a forum to bring together soil chemists, soil mineralogists, soil microbiologists, soil biochemists, soil physi cists and environmental, ecological, and health scientists. The objective of the Working Group M.O. is to promote research, teaching, and also the exchange of technology concerning the knowledge and the impact of the interactions between minerals-organics and microorganisms on environmental quality, agricultural sustainability, and ecosystem "health". This group is first a scientific group as defined just previously, but it also intends to develop exchange and transfer between scientists and engineers. The first International Meeting organized by Professor P. M. Huang, was held in Edmonton, Canada, in August 1992, where 87 papers were presented by scientists from 20 countries. Following this meeting, a two volume book was edited by P. M. Huang, J. Berthelin, J.-M. Bollag, W. B. McGill, and A. L. Page, entitled "Environmental impact of soil component interaction" : Volume I "Natural and anthropogenic organic-volume II "Metals, other inorganic and microbial activities", and published by c.R.C. Lewis Pub lishers (1995).

An authoritative reference on soil physics, Soil Physics Companion is lavishly illustrated with graphs, charts, line drawings, and equations. The book provides a valuable source of material and reference for most contemporary topics of soil physics and the vadose zone - arguably the most comprehensive volume available. In addition to being a reliab