Soil Water Measurement

A Practical Handbook

J. David Cooper

• Publisher: Wiley-Blackwell
• Year: 2016
• ISBN:
  9781119106029
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Geology & Earth Sciences

This book is written for all those involved in measurement of soil water phenomena, whether they be environmental scientists, field technicians, agronomists, meteorologists, hydrogeologists, foresters, physical geographers, civil or water engineers or students in these subjects. It contains a comprehensive description of all the major methods used for measurement of soil water content and potential, solute concentration, transport and balance of water and solutes, including recharge to groundwater aquifers. The emphasis is firmly on techniques which can be applied in the field or on samples obtained from the field. The theory and practice of the workings of the main instruments and methods available is described, along with practical tips on surmounting some of the main difficulties and explanations of many commonly encountered jargon words.

Part I
Introduction

1
Soil Water in Context

The interactions between water and soil are, arguably, the most fundamental relationships in the terrestrial environment. They control, in combination with other agents, such as the weather and plants, the fate of water after it falls as rain. This, in turn, determines aquifer recharge, river flow, water availability to crops and pasture for animals and the transport of nutrients and pollutants. These are critical in determining water resources, flooding, food production, the potability of water, ecology and public health. In view of these important roles, there has been and continues to be a great deal of scientific effort expended in understanding soil–water relationships. Nevertheless, many soil water specialists feel that the value of this work is not fully recognised and is underfunded by comparison with many other environmental topics. The reasons for this may include the fact that several aspects of the subject run counter to most people’s intuition, that work in the field is physically hard and frequently messy, that little spectacular equipment or results are involved and that the subject rarely offers good photo opportunities.

The applications of soil physics are principally in the fields of agriculture, environmental protection and water resources. Some of the more common uses are:

• Measuring or estimating the soil bearing capacity to support agricultural operations
• Characterising the soil water status at various stages of crop growth
• Estimating irrigation requirements
• Optimising the quantity and timing of fertiliser or pesticide applications
• Estimating the water consumption of crops and other land covers
• Estimating the recharge of water to aquifers
• Estimating the rate at which pollutants travel through the unsaturated zone to groundwater bodies or watercourses
• Forecasting and mitigating the hazards of floods

Serious study of the physics involved in the relations between water and soil started in the early 20th century in the United States, driven by the need to increase food production for a rapidly expanding population. Later, important centres of research developed in the Netherlands, Australia, Israel and the United Kingdom. The motivation was usually to increase agricultural yields, focussed either on irrigation in arid areas or land drainage in humid and low-lying ones. From the 1970s, environmental concerns have accounted for an increasing proportion of the research effort, focussing on flood generation, pollution of rivers and aquifers from both natural and artificial sources, water resources assessment and effects on biodiversity. This has taken the subject into the area between what would normally be regarded as ‘soil’ and the zone of saturated rock, which is the province of hydrogeologists. This is often referred to as the vadose zone, particularly in America, although many hydrologists prefer to define the unsaturated zone as a composite of the soil and vadose zone. In this book, the term unsaturated zone will be used, recognising that there is, in reality, no neat subdivision between the soil, the underlying porous material of weathered or unweathered rock and, indeed, the saturated zone.

The amount of work on soil physics has produced a steady stream of books on the subject (e.g. Marshall et al., 1996; Warrick, 2002, 2003; Hillel, 2004; Jury & Horton, 2004; Lal & Shukla, 2004; Rose, 2004). Some of these are highly mathematical and theoretical, while others attempt to explain the principles in relatively simple language. Few of them contain much detail explaining how it is actually done. There are also several books dealing with measurement methods and principles. Pride of place should probably go to the encyclopaedic work of Dane and Topp (2002), one of a series of books on all aspects of soil measurement. Over some 300 pages, it explains the principles behind most methods of soil water measurement, as well as having sections on all manner of other physical measurements in the soil. In similar mode is Mullins and Smith’s (2001) book, focussed more specifically on soil water. While giving comprehensive coverage of the principles of measurement, both books tend to lack information on the practicalities of making measurements in frequently imperfect conditions. The book closest in spirit to the present one is that of Dirksen (1999). This book is intended to update and extend the contents of Dirksen (1999); to explain without descent into hand-waving argument, but using no more mathematics than necessary, the principles of operation of the most common instruments and methods of water measurement in the unsatur...

Table of contents

• Cover
• Title Page
• Table of Contents
• Preface
• Part I: Introduction
• Part II: Water Content
• Part III: Water Potential
• Part IV: Water Content – Potential Relations
• Part V: Hydraulic Conductivity
• Part VI: Solute Measurement
• Part VII: Water and Solute Movement
• Part VIII: Conclusion
• References
• Index
• End User License Agreement