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Part 4 of Methods of Soil Analysis deals with physical methods. It is the update of the well-reputed Methods of Soil Analysis. Part 1. Physical and Mineralogical Methods. The update of mineralogical methods will be printed separately. Part 4 contains eight chapters
Constraints on the time of the reviewer limit this review to Chapters 1 and 3, together comprising 858 pages, or roughly half of the total of 1692 pages.
The chapter titles and the number of pages illustrate the massive breadth and scope of the book. The volume aspires to be the definitive reference of physical and experimental methods in soil analysis, and the portion of the book covered by this review generally lives up to that aspiration.
The chapters are subdivided at three levels. At the highest level, a chapter is partitioned into different soil properties (i.e., Water Content), or a broad cluster of methods (i.e., Geostatistics, Simultaneous Determination of Water Transmission, and Retention Properties). At the two lowest levels, the subdivision varies both within and between chapters. The subdivisions are hierarchical, leading to individual methods. In some cases, subdivisions within a method address different aspects of a method (e.g., Equipment, Procedures).
Using the discussions of the individual methods, readers can use the book to identify a suitable experimental method for their specific needs. In addition to these discussions, many subchapters (the highest level of subdivision) contain valuable overviews, often presented in an Introduction or General Information section at the beginning of a subchapter, or as Comments in later sections within a subchapter. Together with the discussion of the methods, these overviews contain sufficient information to be of considerable help in the planning stage of experiments. In either case, useful information may well be found in sections other than the one dealing with the method the user eventually decides upon. It is therefore worthwhile to examine closely the 21-page Table of Contents to locate this information.
Both chapters reviewed include sections devoted to developing methods for which no detailed procedures can be given. Nonetheless, these sections can be valuable if one seeks an alternative approach to obtain or analyze data, as they contain very useful introductions of the principles of these methods. A case in point is the excellent introduction to wavelet analysis in Subchapter 1.8.
Despite the impressive range of methods treated in the book, some methods remain underrepresented. Direct measurements in the field and in the laboratory of water and/or solute fluxes other than evapotranspiration are absent, and lysimetry is only briefly discussed as a method to measure water fluxes through the soil surface, leaving unexplored the increased use of lysimeters to determine solute fluxes in soils. Tracer methods receive only minimal attention, even though impressive progress has been made in tracer application techniques in the field and image analysis is creating possibilities for observations with unprecedented detail.
The book has very many authors, and unavoidable differences in style and detail emerge. Some sections provide a brief introduction to a given method and require additional references (in virtually all cases provided in the reference list) to be consulted, while others serve as stand-alone texts that can be used as a manual in the laboratory (e.g., the sections on piezometry [3.2.1] and tensiometry [3.2.2] are written in a very hands-on style). In one case, the same name ("Long Column" was given to different methods (3.3.2.5 and 3.6.6.1a). Often the authors of a section developed one of the methods discussed therein. The editors and authors should be commended for the fact that this has not resulted in biased texts. Space limitations allow only a few sections to be discussed here in the following paragraphs.
Subchapter 1.5 (Geostatistics) extensively introduces the key definitions and ideas of geostatistics in such a way that it is an excellent starting point for anyone with no prior knowledge of the field. It also includes a useful selection of geostatistical software.
Subchapter 1.7 (Parameter Observation and Nonlinear Fitting) addresses the general problem of fitting the parameters of some theoretical model to observations that the model is expected to describe. The subchapter provides a thorough introduction of the basic principles of the mathematical techniques to identify optimal parameter values. The subchapter warns against the difficulties most frequently encountered when parameter estimation is applied to unsaturated water flow and solute transport problems (nonuniqueness and ill-posedness). The subchapter gives background information for simple parameter fitting codes to estimate parameters by fitting a curve to data, but it also introduces inverse modeling, examples of which are presented in Chapter 3 (3.6.2). Unfortunately, references to books lack page numbers, as is the case in several other sections.
Subchapter 3.1 systematically treats 11 methods (of which gamma ray attenuation is discussed in a later chapter) to determine the soil water content, including active and passive microwave techniques that can help assess the soil moisture status of large areas through air- or spaceborne sensors. These fields are rapidly developing. The principles are well described, but the section on active microwaves contains no references younger than the mid 1990s. The information in the section on passive microwave is sometimes unclear; for example, a "French research organization" is mentioned without its name or location.
Section 3.6.1.2 describes the instantaneous profile method, the plane of zero flux method, and the constant vertical flux TDR method to measure the unsaturated hydraulic conductivity curve in the field. The discussions of these three methods are excellent, and the reader can readily evaluate the key differences among them. Sections like this make the book particularly valuable in that they allow the reader to weigh various alternatives and make a prudent selection of the method that best suits a given situation. The section on inverse methods (3.6.2) to determine soil hydraulic properties discusses how inverse modeling could be applied to many of the methods discussed elsewhere in the book. It would have been helpful if sections devoted to these methods would, in turn, refer to the inverse modeling section. Apart form this, the cross-referencing between related sections is adequate and will certainly help the reader find the appropriate pages.
Compared with Part 1 of the Methods series, less attention is given to highly complicated apparatus that is likely to be employed only in specialized university laboratories, in favor of less delicate, more user-friendly methods. Methods not yet invented or matured at the time of Part 1 now receive the attention they require (e.g., the very comprehensive and insightful treatments of time domain reflectometry and inverse methods). The general consensus was that Part 1 need a much-deserved update, and Part 4 delivers. The fact that Part 4 contains many references to Part 1 indicates that this position will probably be next to Part 1, not replacing it.
Wageningen University Dep. of Environmental Sciences Sub-dep. Water Resources Soil Physics, Agrohydrology and Groundwater Management Group Nieuwe Kanaal 11 6709 PA Wageningen The Netherlands
(ger.derooij{at}wur.nl)
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