Agricultural Systems 37 (1991) 451~,53
Plant and Crop Modelling--A Mathematical Approach to Plant and Crop Physiology. J. H. M. Thornley and I. R. Johnson. Clarendon Press, Oxford, 1990, 669 pp. Price 75 (hardback). ISBN 0 19 854160 0.
The authors of this exceptionally scholarly volume appear to have delib- erately avoided using 'models' in their title, perhaps to avoid deceiving anyone seeking a critique of computer models as frequently published in Agricultural Systems. These are sometimes referred to as simulation models, although 'to simulate' means 'to have or assume a false appear- ance of' (Chambers Dictionary)! Few if any of the models presented by Thornley and Johnson require the use of a computer as distinct from a good desk calculator and their treatment throughout is marked by the kind of mathematical rigour often absent from models of crops on farming systems.
The book opens with a useful review of different types of model (teleo- nomic, empirical and mechanistic all three well illustrated later) and with a discussion of the distinction between the use of models to generate knowledge or to stimulate new technology. The book is concerned exclu- sively with research models. The first seven chapters deal with a number of general topics whose choice closely matches the expertise of the authors. Part 2 ('Plant and Crop Physiology') has a similar bias but is more wide-ranging: photosynthesis, respiration, biochemical pathways, and water relations are dealt with in detail. Part 3 concerns models for branching and for phyllotaxis.
The book is intended for self-study by research and advisory workers, graduates and students in the plant sciences. The authors believe that 'As these methods (models) become standard equipment in the tool-kit of
Agricultural Systems (37) (1991)-- 1991 Elsevier Science Publishers Ltd, England. Printed in Great Britain
452 Book reviews
plant scientists, they constitute a springboard, both enabling and con- straining the next advances to be made'. Because they have so long been immersed in modelling themselves, they may not fully realise that most plant scientists will be fearful of jumping from the springboard into deep water beneath (even if they have taken the precaution of waterproofing their tool-kits!). However, it would be unfortunate if they put this book on one side simply because it contains more than 2000 equations. The authors have striven to present clear step-by-step derivations of these and have included worked examples at the end of every chapter.
Even if many of the equations set out by Thornley and Johnson never appear elsewhere, they will have served their purpose if they stimulate the next generation of plant and crop scientists to think quantitatively, rigorously, and imaginatively when planning experiments and when interpreting and analysing their observations. However, the authors would have encouraged the next generation more effectively if they had used far more illustrations from the laboratory and the field. Although there are nearly 200 graphs, hardly any demonstrate how measurements and models can be matched. All the rest constitute outputs from models and those who are using the book for self-study will find it hard to assess their realism. Measurements could also have been introduced through the examples, many of which are mathematical exercises in which plant crop responses play little or no part.
In a book concerned with plant and crop physiology, it is strange to find so few references to models developed in the Netherlands, the United States and Australia. Many of these deal with the behaviour of stomata which are barely mentioned in this text (no entry in the index) despite their central role in photosynthesis and water relations.
These criticisms do not dim my admiration for the logical and system- atic way in which the authors have assembled a mass of mathematical material and for its elegant layout in the best traditions of the publishers.
United Kingdom Register of Agricultural Models (1990). Edited by G. R. Squire and P. J. C. Hamer. AFRC Engineering, Wrest Park, Silsoe, Bed- ford MK45 4HS, UK. 12.00 (paperback), 92 pp,
This is '... the first edition of a register of mathematical models used in agricultural research and extension in UK'. Details of some 167 models are included, arranged into sections defined by subject and purpose. Part l consists of a summary and description of the register, where the