Comprehensive account of some of the most popular models of large watershed hydrology ~~ of interest to all hydrologic modelers and model users and a welcome and timely edition to any modeling library

This book contains articles from a workshop on the modeling of water and nutrient dynamics in crop-soil systems. Data sets from lysimeters and experimental fields of multiyear crop rotations were provided for modelers. A unique data set is provided of a 100-year, long-term field experiment into crop yield and organic carbon development under different management systems. The book includes a detailed description of data sets which can be used by modelers and the papers describe the applications of 18 different modeling approaches.

The first premise of this book is that farmers need access to options for improving their situation. In agricultural terms, these options might be manage ment alternatives or different crops to grow, that can stabilize or increase household income, that reduce soil degradation and dependence on off-farm inputs, or that exploit local market opportunities. Farmers need a facilitating environment, in which affordable credit is available if needed, in which policies are conducive to judicious management of natural resources, and in which costs and prices of production are stable. Another key ingredient of this facilitating environment is information: an understanding of which options are viable, how these operate at the farm level, and what their impact may be on the things that farmers perceive as being important. The second premise is that systems analysis and simulation have an impor tant role to play in fostering this understanding of options, traditional field experimentation being time-consuming and costly. This book summarizes the activities of the International Benchmark Sites Network for Agrotechnology Transfer (IBSNAT) project, an international initiative funded by the United States Agency for International Development (USAID). IBSNAT was an attempt to demonstrate the effectiveness of understanding options through systems analysis and simulation for the ultimate benefit of farm households in the tropics and subtropics. The idea for the book was first suggested at one of the last IBSNAT group meetings held at the University of Hawaii in 1993.

Systems approaches for agricultural development are needed to determine rational strategies for the role of agriculture in national development. Mathematical models and computer simulation provide objective tools for applying science to determine and evaluate options for resource management at field, farm and regional scales. However, these tools would not be fully utilizable without incorporating social and economic dimensions into their application. The second international symposium, Systems Approaches for Agricultural Development (SAAD), held in Los Baños, 6-8 December 1995, fostered this link between the biophysical sciences and the social sciences in the selection of keynote papers and oral presentations, a selection of which are included in these books. The contents further reflect how systems approaches have definitely moved beyond the research mode into the application mode. The large number and high quality of interdisciplinary research projects reported from different parts of the globe, to determine land use options that will meet multiple goals and yet sustain natural resource bases, is a key indicator of this `coming of age'. At the farm level, where trade-off decisions between processes and products (commodities) feature strongly, much progress is also evident in the development of systems-based tools for decision making. At the field level optimization of resource use and minimizing environmental effects has become of major concern for which systems approaches are indispensable. The books, of which Volume I deals with regional and farm studies level and Volume II with field level studies, will be of particular interest to all agricultural scientists and planners, as well as students interested in multidisciplinary and holistic approaches to agricultural development.