Soil Physics Measurements

Soil Physics deals with the analysis and quantification ofthe physical properties and processes in the upper layer of the earth's crust, with major emphasis and activity on transport and accumulation of water and solutes in the (water) unsaturated zone. There is a relative abundance of textbooks dealing with the theory and application of Soil Physics, but there are very few books that give detailed descriptions of soil physics measurements and step by step instructions for exercises that are suitable for teaching. This book is intended to help fill this gap for measurements related to water transport in unsaturated soil. It is impossible to cover all the soil water measurements that are presently in use. This volume gives a representative cross section of the available types of methods. As such, it reflects the present status of the practical "Soil Physics Measurements" (SPM) that was initiated at Wageningen University about fifteen years ago. This advanced practical is required for undergraduates in the Soil, Water and Atmosphere study program, but is also taken regularly by undergraduates in related disciplines and graduate students from abroad. Through the years, new measuring methods and techniques have been incorporated. A prime example is soil water content measurements. Whereas in the past gamma ray attenuation and neutron thermalisation have been used, presently water contents are measured, beside the standard gravimetrical method, mainly by time domain reflectometry. The contents of the SPM practical is covered in chapters on soil water content, tensiometry, steady hydraulic conductivity measurements, instantaneous profile method, and sorptivity and diffusivity measurements. The final chapter presents a frame work for evaluating direct and indirect methods for determining soil hydraulic conductivity functions. More elementary experimental operations such as retrieving "undisturbed" core samples, gravimetric determination of soil water content, volume fractions, bulk density, and soil water retention characteristic, as well as measurements of hydraulic conductivity, infiltration, capillary rise, and sorptivity under saturated conditions are taught in an introductory practical. To make this book complete in itself, a review of the basic concepts of Soil Physics and detailed descriptions of these elementary experimental operations are presented in the second chapter. An introductory chapter briefly describes the hydrology and hydraulic properties of the unsaturated zone and summarizes the contents of each of the chapters. It also offers organizational details ofthe SPM practical for teachers who may want to set up a similar practical. The general pattern of the chapters consists of theory, review of available methods, selection of one or more methods, practical aspects, evaluation, and step by step instructions for exercises. They are written from the experimentalist's point of view. Only the easily understood head equivalents of soil water potentials are used and the mathematics is kept to a minimum. Students and professionals in soil science, hydrology, and other earth sciences with little knowledge of calculus should be able to understand the subject matter and carry out the exercises. Students participating in the practical are expected to have mastered the subject matter treated in the book "Elements of Soil Physics" (Koorevaar et al., 1983), but only parts of the third and fifth chapter of this book are really needed.