ABSTRACT
This chapter summarizes nitrogen transformation, and transport and fate processes in the subsurface environment; factors influencing nitrogen leaching from fertilizers; and the use of laboratory studies for examination of both the transformation processes and leaching. The transport and fate of nitrogen in the subsurface environment depends upon the form of entering nitrogen and various biochemical and physicochemical processes involved in transforming one form of nitrogen to another form. Nitrogen can enter the subsurface environment in either organic or inorganic forms, depending upon the source. Ammonification is the first step in the mineralization of organic nitrogen. Ammonification is defined as the biological conversion of organic nitrogen to ammonium-nitrogen. Diffusion of ammonium-nitrogen and nitrate in the subsurface environment plays a role in subsurface transport along with abiotic processes such as adsorption and ion exchange. Nitrate is typically more mobile in the subsurface environment than ammonium-nitrogen.
