Claypan is a dense, compact, slowly permeable layer in the subsoil. It has a much higher clay content than the overlying material, from which it is separated by a sharply defined boundary. The dense structure restricts root growth and water infiltration. Therefore, a perched water table might form on top of the claypan. In the Canadian classification system, claypan is defined as a clay-enriched illuvial B (Bt) horizon. Location Claypan is present in a wide area of the central United States (about 4 million ha) across multiple states such as Kansas, Oklahoma, and Illinois. It can also be found in Australia throughout the south-west Queensland. Formation Claypan is formed in different parent materials depending on geological locations, such as floodplains. The formation of the claypan relates to a lack of vegetation coverage, soil particle size distribution, and high rainfall. The lack of vegetation coverage makes soil become more susceptible to raindrop attacks. When the raindrops hit on bare soil with high energy, the fine sand, silt, and clay particles are re-arranged to plug all the pore spaces. When all the pores are filled, a packed layer is formed to limit the water infiltration. Characteristics The dominant material is the montmorillonite clay material which has a high swell and shrinks characteristics depending on the soil water content. In the dry season, evaporation moves water from the deep horizon toward the soil surface through capillary action. The water removal results in shrinkage of clay, and the soil becomes dry and hard. In the wet season, high precipitation leads to a swell of clay to absorb water. The high moisture content results in wet and sticky clay texture. When the clay swells, the low saturated hydraulic conductivity prevents the vertical water infiltration to the deeper soil horizon. It leads to water perches above the claypan layer. The water permeability is restricted in the claypan layer resulting in low soil aeration. The water-holding capability of the claypan is high. However, most of the stored water is not available for the plant since water evaporates frequently and soil pore size is tiny. Since the claypan is acidic and clay-rich, there is high sorption of Al, K and Fe oxides to clay minerals. Therefore, the claypan contains a cations-dominated zone that leads to a relatively high cation exchange capacity (CEC) to absorb and retain nutrients. The concentration of extractable potassium positively relates to clay content. There