P. Smithson
International Centre for Research in Agroforestry PO Box 30677 Nairobi, Kenya
0308-521X/00/$ - see front matter#2000 Published by Elsevier Science Ltd. All rights reserved. P I I : S 0 3 0 8 - 5 2 1 X ( 0 0 ) 0 0 0 1 1 - 1
Soil Erosion at Multiple Scales. Principles and Methods for Assessing Causes and Impacts F.W.T. Penning de Vries, F. Agus, J. Kerr (Eds.); CABI Publishing, Wallingford, Oxon, UK. in association with the International Board of Soil Research and Man-agement (IBSRAM), 1998, 390 pages, hardbound, ISBN 0 85199 290 0, $60.00
This book consists of 22 chapters based on papers presented at a workshop held in November 1997 in Bogor, Indonesia, as well as the reports of six working groups, which discussed various aspects of soil erosion during the two ®nal days of the workshop. The objective of the workshop was to draw together the latest advances in soil erosion research, especially those related to dierences in scale, recognizing that much of the research conducted on small plots cannot easily be extrapolated to the level of farms, micro-catchments and catchments, and up to regional and national scales. Moreover, with new developments in computer technology and geographic information systems (GIS), and the concomitant development of simu-lation models, it is now possible to analyse complex processes of soil erosion and predict the eect of rainfall, topographical features, land use and management on runo, soil loss and nutrient losses, as well as o-site eects of sediment deposition in the landscape, in irrigation systems and reservoirs. With the increasing demand for sucient and high-quality water in the dry season and the need to prevent ¯oods in the rainy season, there is an increasing interest in looking beyond the direct eect of erosion on soil productivity at the farm level to the wider eects of soil erosion in the catchment and at the regional level. This book attempts to bring together the experiences of agronomists and soil scientists, who traditionally have worked at the plot and farm scale, with those of social scientists, economists and modellers who tend to work at larger scales, and to try to integrate both approaches. Such a workshop was clearly necessary to help promote a more ecient and integrative approach to resource management in uplands, especially in the Asian context.
The book starts with a description by Enders of a general framework for conducting a cost-bene®t analysis for assessing soil erosion as compared with soil conservation practices. Many authors mention that numerous plot experiments have identi®ed eective measures to control erosion, such as mulching, minimum tillage, contour hedgerows of grasses and leguminous shrub species, but that few of these practices have been adopted by farmers. Using cost-bene®t analyses, economists clearly show that the costs of these practices, especially establishment and maintenance costs of hedgerows, far outweigh the bene®ts for the individual farmer, at least in the short term (5±10 years). While most upland farmers are poor and have a relatively short
time-horizon, they show little interest or are unable to invest in soil conservation practices. Governments may thus have to devise policies, such as providing secure land tenure, improving rural infrastructure, developing markets for farm products or providing direct subsidies, that help to improve the welfare and ®nancial security of farmers, in order to enhance their ability to pay for soil conservation measures.
In Chapter 5, Garrity and others describe the use of natural vegetative (weedy) strips, which are quite eective in reducing erosion. Because of the low establish-ment and maintenance costs, this practice is being spontaneously adopted by farm-ers in the Philippines. Othfarm-ers concur that the most ``useful'' soil conservation practices are not necessarily those that are most eective in controlling erosion, but those that farmers will adopt, because they have low cost, will bring some immediate bene®ts, and ®t well in the existing farming systems. An alternative approach is described by Turkelboom and Trebuil, using ``erosion surveys'' to relate erosion processes with crops and cropping systems at the farm level, and to landscape and rural infrastructure at the catchment level, in order to pinpoint when and where erosion occurs and the farmer typologies most likely to experience severe erosion. The latter are the most appropriate target groups for participatory soil and water conservation projects.
Van Noordwijk and others in Chapter 15 challenge the conventional wisdom that soil erosion causes soil, water and nutrient losses, and point out that much of the ``lost soil'' is merely redistributed, as it is deposited elsewhere on the farm or in surrounding areas, and that farmers can take advantage of the increased fertility in those areas. They also point out that vegetation strips along the contour, along ®eld borders and along creeks and rivers are quite eective in ®ltering out sediments, thus reducing substantially the amount of soil lost from the catchment area.
In Chapter 13 Zech and others describe the use of the paired micro-catchment methodology to study the eect of changing land use in one catchment on the out-¯ow of soil, nutrients and biocides, in comparison with the unmodi®ed catchment. The method tries to quantify the eect of land-use management on a catchment scale by the use of measuring devices installed at each catchment's outlet. The methodology is rather costly, however, and questions remain as to whether the two catchments are truly comparable and representative of surrounding areas.
Chapters 17 to 21 describe various modelling approaches that try to quantify soil loss and overland ¯ow as well as the nutrient loss in bedload and suspended load, mainly to assess on-site eects in the uplands, while others use GIS-based models to take into account the spatial variation in topography and vegetation in the whole catchment, in order to estimate average soil and water losses from the system and the sediment delivery ratio at the catchment outlet. These models are still being improved, but the examples shown indicate that these are powerful new tools in estimating the eects of changing land use on erosion and water ¯ow rates in speci®c catchments, which allow planners and policy-makers to draw conclusions about the eectiveness of certain policy options designed to stem further land degradation.
how to describe and understand the complex processes involved in soil erosion and deposition. It also points out some failures in the past promotion of speci®c soil conservation practices, and highlights the importance of stakeholder participation in developing and disseminating more eective production practices that not only conserve the soil and water resources but also produce bene®ts to farmers.
R. Howeler
CIAT Regional Oce for Asia Department of Agriculture, Chatuchak, Bangkok 10900 Thailand E-mail address:ciat-bangkok@cgiar.org
Agrobiodiversity: Characterization, Utilization and Management
D. Wood and J.M. Lenne (Eds.); CABI Publishing, Wallingford, 1999, 490 pages, hard cover, ISBN 0-85199-337-0, £65 (US$120)
From the outset of this comprehensive book, a strong case is made for including agricultural biodiversity more convincingly in the international biodiversity debate. The schism between agriculturalists and environmentalists is explored, and the need to move toward the `middle ground' where increased food production and the pro-tection of the environment are jointly pursued is promoted. The main purpose of the book is described as the need to promote a more rational, technically sound and functional view of agrobiodiversity. Three major themes are covered: (1) the current status of the concept and usage of the word agrobiodiversity and its relation to biodiversity; (2) a review of the nature, role and function of various components of agrobiodiversity, how they impact on agricultural production, and how agrobiodi-versity can best be managed for sustained food production; and (3) whether the extensive knowledge of the management of agrobiodiversity can provide models and practices for the wider management and conservation of biodiversity.
The breadth of coverage of this book is vast and includes crops and domesticated animals (and a history of the domestication of each), soils, pathogens, insects, agri-cultural landscapes, traditional management of agrobiodiversity, plus the implica-tions for genetic diversity of plant breeding, pest management strategies, alternative tillage systems and seed management systems.
Chapter 8, which covers the determinants of agrobiodiversity in agricultural landscapes, gives two interesting examples of very dierent agroecosystems that are rich in species and shows how intensi®cation does not necessarily adversely aect the level of biodiversity. However, the authors make it clear that it takes a very long time for ecological communities to adjust to environmental change; thus it is the speed of recent and sometimes widespread land-use changes that makes intensi®ca-tion a threat to biodiversity in many areas. The following chapter on tradiintensi®ca-tional 0308-521X/00/$ - see front matter#2000 Published by Elsevier Science Ltd. All rights reserved. P I I : S 0 3 0 8 - 5 2 1 X ( 0 0 ) 0 0 0 1 2 - 3
