Nutrient and virtual water flows in traded agricultural commodities

Globalization and increasing population pressure on food demand and land and water resources have stimulated interest in nutrient and virtual water flows at the international level. West Asia/North Africa (WANA), Southeast Asia, and sub-Saharan Africa are net importers not only of nitrogen, phosphorus, and potassium (NPK) but also of virtual water in agricultural commodities. Nevertheless, the widely recognized declines in soil fertility and problems related to water shortage continue to increase, especially in sub-Saharan Africa. The nutrients imported are commonly concentrated in the cities, creating waste disposal problems rather than alleviating deficiencies in rural soils. And also the water shortage problems continue to contribute to intensified desertification processes, which again lead to increased urbanization and thus water shortage problems in cities. Countries with a net loss of NPK and virtual water in agricultural commodities are the major food exporting countries-the USA, Australia, and some Latin American countries. Understanding the manifold factors determining the nutrient and water flows is essential. Only then can solutions be found which ensure a sustainable use of nutrients and water resources. The chapter ends by stressing the need for factoring environmental costs into the debate on nutrient and water management, and advocates more transdisciplinary research on these important problems.