The word order of the title is an important clue to the focus and main strength of Kirkham's book, which is its exploration of water movement in the soil and how it is measured. Plant water relations take a back seat, accounting for approximately one-third of the 27 chapters. Unlike the title, the book's cover image of a savannah-like tree is somewhat misleading, for the examples, methods and instrumentation discussed in the text are chiefly agronomic, with an emphasis on corn (maize) and wheat. The book's preface describes the intended audience as graduate students, upper-level undergraduates, and scientists in ‘agronomy, biology, horticulture, forestry and recreational resources, biochemistry, and biological and agricultural engineering’. Agronomists, horticulturalists and agricultural engineers are likely to find the book most useful; foresters and biochemists are less likely to do so. Kirkham's approach is decidedly biophysical and is most successful when dealing with the many aspects of plants and soil that can be treated in terms of mechanical or electrical models. The preface goes on to state that the book will deal with first principles, which it does admirably with respect to soil, and with instrumentation, which is done a bit more unevenly. One further comment in the preface deserves note: that ‘no knowledge of calculus is required’. It may not be required, but it helps.
Somewhat surprisingly, the book goes into great detail about several pieces of equipment that are commercially available, giving not only brand names but occasionally model numbers and technical specifications. The discussions of the theory behind most of these instruments are often fascinating and more in keeping with the book's goal of elucidating first principles. For example, Kirkham presents what amounts to a treatise on the tensiometer so comprehensive that it gets its own chapter, as do the penetrometer, tension infiltrometer, thermocouple psychrometer, pressure chamber, and infrared thermometer as used to measure plant stress. Of these chapters, only that dealing with the infiltrometer seems unnecessarily detailed and lengthy; the other chapters should be helpful and occasionally amusing to anyone using such instruments in the lab or field.
An unusual element in such a book is the biographical sketches of noted scientists appended to each chapter. Kirkham's stated goal in including the sketches is to humanize the science presented earlier in the chapter. Most of the men (no women are included) are or were mathematicians, physicists, soil scientists or physiologists, and the sketches are straightforward and factual. A story of greater human interest arises incidentally from the author's frequent citation of personal communications with her father, a noted soil scientist and physicist, as well as from several references to events in his laboratory, her own, or those of her colleagues. For example, she describes her father and his students carrying a water-filled hose 10.3 m up the back stairs before the water column collapsed. She gives a similarly vivid description of her father's predecessor cutting a hole in the ceiling to accommodate the water-filled ascending tube of an early tensiometer. Kirkham's accounts of how she and her colleagues modify, calibrate and use various instruments are highlights of the book, not only as practical advice but also as glimpses into the human nature of science.
Because of the symmetry in titles between this book and Water relations in plants and soils by Paul J. Kramer and John S. Boyer (1995, Academic Press), a comparison of the two seems warranted. As the different word order in the titles suggests, Kramer and Boyer devote much more attention to water within the plant than does Kirkham. On that basis, the two books can be seen as complementary. By itself, Kirkham's book does not do a particularly good job of following what happens to water once it enters the root. For example, root water uptake is described mathematically in terms of Poiseuille's law, which is customarily applied to axial transport in the xylem. Despite the statement that the ‘main barriers to water transport are the cell membranes’, the book does not mention the radial path for water from the surface of the root to the root xylem. For the reader who is a plant biologist, it is troubling to come across phrases such as ‘For plants that have leaves that do not wilt, like cacti … ’ and ‘Lower plants such as fungi … ’ Even more bothersome is that some newer yet widely used methods of measuring water transport in plants, such as the heat-pulse or heat-balance methods, are not mentioned despite their utility in plants of agronomic or horticultural importance.
On balance, then, does Principles of soil and plant water relations belong on the shelf next to Kramer and Boyer? Yes, although the reader is advised to skim the chapters dealing chiefly with plants and focus instead on those that deal with the theory and practice of determining the fate of water in soils. As a final example of the book's scope and charm when it deals with measuring soil properties, here is a quote from chapter 9: ‘The earliest soil penetrometers were fists, thumbs, fingernails, pointed sticks, and metal rods’. Throughout the book, Kirkham manages to convey an appreciation for such early tools as she patiently lays out the theories and challenges of the more sophisticated devices that have replaced them.