Nitrogen (N) is potentially one of the most complex elements on the Earth. It is necessary for all biological activity, but creates negative impacts on water and air quality. There is a balancing act between deficiency and surplus and the forms of N available further complicate our understanding of the dynamics. Biological fixation provides some plants with N supply while others are totally dependent upon N being available in the soil profile for the roots to extract. Nevertheless, the demand for N will increase because the human population with its increasing growth requires more protein and thus more N. Understanding the global N cycle is imperative to meeting current and future nitrogen demands while decreasing environmental impacts. This book discusses availability, production, and recycling of N in air, water, plants, and soils. It features information on N impacts to soil and water quality, management of N in agroecosystems, and techniques to maximize the use efficiency while minimizing the risks of leakage of reactive N into the environment. This volume in the Advances in Soil Science series is specifically devoted to availability, production, and recycling of N with impact on climate change and water quality, and management of N in agroecosystems in the context of maximizing the use efficiency and minimizing the risks of leakage of reactive N (NO-3, N¬2O) into the environment.

This is the first volume to provide comprehensive coverage of the biology of water use efficiency at molecular, cellular, whole plant and community levels. While several works have included the phenomenon of water use efficiency, and others have concentrated on an agronomic framework, this book represents the first detailed treatment with a biological focus. The volume sets out the definitions applicable to water use efficiency, the fundamental physiology and biochemistry governing the efficiency of carbon vs water loss, the environmental regulation of this process and the detailed physiological basis by which the plant exerts control over such efficiency. It is aimed at researchers and professionals in plant physiology, biochemistry, molecular biology, developmental biology and agriculture. It will also inform those involved in formulating research and development policy in this topic around the world.

ICARDA has the serious and urgent responsibility for increasing the quantity and availability of food in the extensive North Africa-West Asia region, and therefore must give high priority to optimising the use of soil water and nitrogen which are considered to be among the main limiting factors to production. To obtain the knowledge to further this aim, and with the help of the United Nations Development Program (UNDP), ICARDA is developing a special project on 'Increasing the Fixation of Soil Nitrogen and the Efficiency of Soil Water Use in Rainfed Agricultural Systems in the Countries of North Africa and Western Asia'. In planning this project, ICARDA has called on the expertise of leading scientists in a number of countries who can give the benefit of their experience, and advise on methods and priorities on which this specific research can be soundly based and conducted. To provide a forum for the presentation and exchange of such information, ICARDA, with the help of UNDP, invited a number of these scientists to a week-lung workshop at Aleppo in January 1980. This workshop gave rise to valuable discussions which culminated in several recommendations by which the project will be guided. The organising committee comprised Drs. J. Begg (Aus tralia), P. Cooper and D. Gibbon (lCARDA), P. Dart (Australia), G. J. Koop man and J. McWilliam (ICARDA Board of Trustees), A. Kassam (England) and P. Vlek (U.S.A.).