Nitrogen constitutes about 79 percent of the earth's atmosphere, yet, in an agricultural plant production system, it is still common for soils to be deficient in the nitrogen needed for maximum plant growth. Nitrogen fertilizers, however, despite being essential for the economically driven production of food and fiber, are recognized as polluters of natural waters, and it has become increasingly apparent that manufactured and naturally occurring nitrogen resources must be better managed. This book addresses the problem by describing how such factors as types of soils and crops, irrigation methods, climate, and the nitrogen cycle itself affect levels of nitrogen in agricultural plant production systems. The book also provides a practical guide to the use of different fertilizers with regard to environment, type of plant, and method of farming. This book will help to achieve effective nitrogen management in agriculture and will be of interest to workers in local, state, and federal agricultural extension services, consulting firms, environmental regulators, and students and researchers in soil chemistry.