SOIL CONSERVATION

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Soil Conservation, Assessing the National Resources Inventory. Volume 2. National Academy Press, 1986, distributed by John Wiley, Chichester, soft- cover, price £23.75,314 pp., ISBN: 0-309-03676-5.

The Committee on Conservation, Needs and Opportunities, Board on Agri- culture, National Research Council and National Academy of Sciences, Wash- ington, DC, assembled the papers in this book. Thir ty scientists contributed to the papers that assess several aspects of soil erosion, including applications of the United States' 1982 National Resource Inventory (NRI) . Three major aspects of the NRI are addressed: analytical results and methods; specific applications; resource policy and decision making.

Overall, the papers are well prepared. In some sections, however, insufficient attention was given to the complexity of soil erosion and its effects. For exam- ple, in the section on erosion assessment, the '5 tons /ac re /year soil loss tol- erance' level was used in the taxonomy of cropland erodibility without any explanation on the limitations of this 5-ton value. Firstly, using this soil tol- erance level implies sustainability and that soil is formed at a rate of 5 tons/ acre/year. This is true only if the topsoil depth is 0.5 inch, but soils of 0.5 inch have little or no practical value for crop production. With topsoils of about 10 inches, the soil formation rate is 0.5 tons/acre/year or one-tenth the 5 tons /acre/year soil tolerance value presented in this section. Shouldn' t our goal be sustainability in the NRI?

In the section dealing with 'assessing soil erosion productivity damage', the focus is primarily on the reduced soil depth that results from erosion. Soil erosion effects on reduced soil depth are cumulative and, therefore, are impor- tant. However, measuring soil-erosion productivity damage using only reduced soil depth is much too simplified and accounts for only about 5% of the pro- ductivity damage from erosion for the growing season. The other 95% of pro- ductivity damage during the growing season associated with erosion is the loss of water via rapid water runoff, reduced water-holding capacity, reduced soil nutrients and decrease in soil organic matter.

When the role of vegetative cover in soil conservation was analyzed, the authors concluded that conservation tillage and the maintenance of good plant cover is probably 'more effective in controlling erosion than previously consid- ered'. This helpful analysis emphasizes that the effects and control of soil ero- sion are far more complex than previously reported.

In another section of the book, the nature of off-site environmental effects of erosion is assessed. The conclusion reached was that off-site impacts are diverse and extremely complex. Documented information about sediment deposits in reservoirs, channel siltation, eutrophication and sediment and chemical effects on fish and other wildlife is extremely helpful.

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Overall, the book presents a detailed assessment of the extremely complex subject of soil conservation and soil erosion. Scientists and others interested in land degradation and associated environmental problems will find that this volume will enhance their understanding. The subjects analyzed are well doc- umented, and thus especially valuable for those interested in pursuing in detail certain aspects of the complex soil erosion question. The information gathered in this volume will also be a major asset to policy makers in the U.S. Govern- ment since it provides reliable data upon which to build future programs and policies dealing with soil erosion.

DAVID PIMENTEL Department o[ Entomology

CorneU University Comstock Hall

Ithaca, N Y 14853 U.S.A.

SOIL PHYSICS WITH BASIC

Transport Models for Soil-Plant Systems by G.S. Campbell. Soil Physics with Basic series, Elsevier Science Publishers, P.O. Box 330, 1000 AH Amster- dam, The Netherlands, 1986, xvi+ 150 pp., US$41.50/Dfl. 120.00, Diskette, US$31.00/Dfl. 90.00, ISBN: 0-444-42557-8.

The aim of this book is for the reader to get familiar with the quantitative approach to transport processes in the soil. To this end, the differential equa- tions that describe these processes are solved numerically. The processes dealt with are: gas diffusion; soil temperature and heat flow; infiltration and redis- tribution of water; t ransport of solutes; water uptake by plant roots; evapo- transpiration. The different chapters start with a theoretical view of the main soil physical processes as in most of the handbooks on soil physics. Secondly, quantitative aspects are treated, and finally a simulation model of the process is described.

To solve the differential equations numerically, the 'network analysis approach' (as resistance-capacitors network in electronics) and a number of other numerical techniques are adapted by the author. It is stated that this approach makes the physics of the systems very apparent. The explicit finite difference method which the author also mentions is in fact simpler, and makes the physics of the system even more apparent. Probably the choice of BASIC as a programming language, and implementation of the programs on micro- computers, led him to his approach. Indeed, the numerical solution of fast