Sorption is a process that results in the association of a liquid or gas phase with a solid material. The solid particle that absorbs another material is called sorbent, while the absorbed material is called sorbate. When sorbate adheres to a two-dimensional surface, the process is called adsorption and occurs on the surface of minerals through van der Waals interactions, dipole-dipole interactions, and electrostatic charges (Hemond and Fechner-Levy, 2000) . Absorption occurs in a three-dimensional surface. For example, a non-polar chemical can be absorbed by organic particles such as humic substances by displacing water molecules weakly held in humus (Schwarzenbach, 1993). Absorbent particles have a high surface area due to their small size (<1 μm). diameter) and consequently, a greater proportion of their atoms being on their surface (Langmuir, 1997). The high specific surface area gives small particles unique surface properties compared to their larger counterparts with otherwise similar physical structure. Partly because of their small size, they possess a high number of unsatisfied surface charges, which allows them to act as absorbents for compounds dissolved in the soil solution. These small particles have higher solubilities. Colloidal-sized particles, for example, do not settle out of solution and are capable of transporting sorbed materials through soil solution or into surface waters (Langmuir, 1997). The distribution of chemicals between the solid and liquid phases is an important determinant of bioavailability. and the movement of nutrients in forest ecosystems. Structurally identical molecules will behave differently if they are associated with a solid surface instead of being dissolved in the middle of a ......terial paper (Baldock and Skjemstad, 2000). The organic matter discussed in these studies is relatively low in nitrogen, but they illustrate the important role of sorption reactions in increasing turnover rates of nutrients, including nitrogen, in the soil. Oxidation of NH4+ to NO3- can alter ongoing sorption reactions, particularly in soils without variable loads. As a cation, NH4+ is more likely to persist in the soil while NO3- is easily leached in soils with CEC. When soil becomes waterlogged, its pH increases. Changing pH could potentially alter the sorption capacity of the soil, especially in soils with pH-dependent loadings. Ammonia volatilization of urea is influenced by urease enzymes sorbed into soil colloids, accounting for 79–89% of urease activity relative to microbial urease ( Ardakani et al., 1975 Paulson and Kurtz; ;, 1969).