ABSTRACT
Water entering the soil profile from rain or irrigation is essentially a dilute solution. Rainwater is pure when it condenses to form clouds; during descent it absorbs atmospheric gases (i.e., CO2, N2, products of sulfur and O2, etc.). When water flows on soil surface as overland flow and/or through the soil matrix, it also dissolves solutes (e.g., salts, fertilizers, pesticides). These solutes not only move with soil water but also within the soil matrix mainly due to the concentration gradients. Sometimes, solutes react among themselves and/or with soil material according to a range of physical and chemical processes.
