ABSTRACT
The Natural Resources Conservation Service (NRCS) developed a technique (Elrashidi et al., 2003, 2004, 2005a, 2005b, 2007a, 2007b, 2008, 2009, 2010) to estimate element loss by runoff for agricultural watersheds. The NRCS technique applies the USDA runoff curve number model (USDA/SCS, 1991) to estimate loss of runoff water from soils by rainfall. The technique assumes that dissolved inorganic chemicals are lost from a specic depth of surface soil that interacts with runoff and leaching water. These chemicals may include any essential plant nutrients (i.e., nitrogen, phosphorus, copper, zinc, etc.), and environmentally toxic elements such as lead, cadmium, nickel, and arsenic. Geographical Information Systems (GIS) (ESRI, 2006) are used to present data spatially in watershed maps.
