Agriculture transforms the environment. The simplification of agroecosystems structure increases the hazards of leaching, wind and water erosion, and volatilization of chemicals from soil. Soil nitrogen is of interest as a major crop nutrient, but also as a potential environmental pollutant. Knowledge about the behavior of soil nitrogen is desirable in order to optimize plant growth and crop yield and to minimize environmental side effects. This book also gives information about the function of biogeochemical barriers in the form of shelterbelts, which efficiently decrease the concentrations of various forms of nitrogen in ground water.