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However, while the principles of soil-water movement are clearly explained, it is a pi ty the authors ignore hysteretic effects in their introduction to flow in unsaturated soils, although such effects are discussed when soil-water re- distribution is considered. Thus they incorrectly state in their opening para- graph in the section, that "in an unsaturated soil any gradient of the matric potential of necessity implies that the water content of the soil changes along that gradient"; this may not be the case in hysteretic conditions. Even in elementary textbooks , simplification wi thout qualification is unwise and may lead to wrong useage of theory; for example, soil-water diffusivity may be "measured" and used by some workers in hysteretic conditions if it is not pointed ou t that that concept can only be defined for non-hysteretic condi- tions. Also it would have been prudent for the authors to have mentioned that in non-steady state soil-water f low it is an approximation to ignore the movement of air. This is particularly the case when the authors give in detail the outf low method of measuring soil-water diffusivity, a method prone to difficulties on account of the air phase. Indeed, soil physicists may wonder why the authors chose to discuss this method so fully, while omitting other more established methods. However, the presentation of theory without men- tioning these complications must make it easier for non-specialists to acquire an understanding of fundamental soil physics.

While soil physics is dominated by soil water and the physical processes involved in its movement , a book entitled "Soil Physics" may be expected to encompass other physical aspects of soils. The present book is a little disap- pointing in that the coverage of these other aspects o f the subject, such as thermal properties, soil particle movement, gaseous diffusion and ionic move- ment in soils, is not done in greater detail. These matters are not dealt with in separate chapters, but are included in the last three chapters on the more applied aspects of soil physics. Although a comprehensive treatment of all fundamental aspects o f soil physics would indeed have been useful, neverthe- less, the book provides a clearly writ ten account of many aspects of the sub- ject, particularly those connected with the retention and movement of soil water. It is a valuable addition to the literature for the scientist working in en- vironmental sciences.

E.G. Y O U N G S (Harpenden, Great Britain)

IRRIGATION

Quality of Irrigation Water. I. Shainberg and J.D. Oster. IIIC Publication No. 2, Volcani Center, P.O.Box 49, Bet Dagan, Israel, 1978, 65 pp. ISBN 92-9019-002-9.

This publication presents a useful discussion of the effects of salinity and sodicity on soil properties and crop product ion under irrigation. The title

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implies a somewhat more restricted t reatment than one finds in the volume. After a brief introduction, Chapter II, Properties of Irrigation Water, de~

scribes common units o f measurement and their interrelations, and discusses derived parameters such as SAR, RSC, and SARadj with their relation to ex- changeable sodium. It also calls at tention to minor element toxicities and lists recommended tolerance levels. The composit ions of the waters in four rivers are given as examples, calculated with the derived parameters.

The next chapter, Soil Properties Affecting Water Quality, outlines some basic principles of clay mineralogy and the diffuse double layer. It then pro- ceeds to describe the effects of single and mixed salt systems on swelling and dispersion and on hydraulic conductivity. Ion exchange equilibria are intro- duced to complete the description.

In Crop Growth and Salinity, the authors briefly describe the effect of sa- linity on plant growth, emphasizing the osmotic effect. A table of salt toler- ance for various crops is included, as are tables of tolerance levels for Na and C1.

The final chapter, Irrigation Management for Salt Control, deals with man- agement principles. Salt balance and the leaching requirement are explained and related to crop salt tolerance. Processes of salt precipitation in and dis- solution from the soil are illustrated, and sodicity hazard is discussed. After a brief discussion of irrigation methods in relation to salinity, the book con- cludes with a section on reclamation.

In general, the authors have effectively highlighted the essential features of the subject matter, mixing in an appropriate way the fundamental principles and practical recommendations. In the process, they make some important, if sometimes controversial, points; they pass over some issues too lightly, or use outdated information.

They state in the introduction, for example, that salinity may reduce crop yield, while sodicity may cause deterioration of soil properties. Later, they state that calcium and magnesium deficiencies are likely to develop on non- saline sodic soils; thus again, albeit indirectly, they relate a sodicity hazard to soils and not to plants. Yet further on, a table is included on Na tolerance levels of various crops. This reviewer would have preferred to see the concept carried through consistently that sodicity affects soils, but that alleged Na toxici ty generally is a misnomer for Ca deficiency.

The boron tolerance table, taken from Wilcox, no doub t is too conservative. The authors probably did not have access to this reassessment of old and pub- lished data. The routine conversion of 640 ppm for 1 mmho/cm has caused substantial confusion over the years; a paragraph of explanation would have helped.

The development of leaching requirement and its relation to the crop salt tolerance data was very sketchy and, frankly, not at all clear. Considering both the importance of this concept and its common misuse, it would have been desirable to have had this section developed more carefully.

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These examples indicate that the publication is not without limitations. Just the same, it presents a reasonably comprehensive introduction to an important subject and should meet with an appreciative audience.

JAN VAN SCHILFGAARDE (Riverside, CA, U.S.A. )

Announcement

THIRD INTERNATIONAL SYMPOSIUM ON WATER SUPPLY AND IRRIGATION IN THE OPEN AND UNDER PROTECTED CULTIVATION

Organized under patronage of the International Society for Horticultural Science

Dates: 1--7 March 1981 Place: Wageningen, The Netherlands Information and registration: J. Drijver (administrative secretary),

International Agricultural Centre, P.O. Box 88, 6700 AB WAGENINGEN, The Netherlands.