is a relatively high extractable potassium content in the claypan due to the accumulation of cations. The high content of aluminium oxidates, and iron oxidates attract phosphorus to clay particles which increases the phosphorus content in the soil. Influences on plants The major negative influences of claypan on plants are root restriction, available water limitation and nutrient limitation. The dense structure of the claypan restricts root development. Plants with shallow roots, might not withstand the soil contraction forces due to the shrinkage of clay in the dry season. The low water infiltration rate and hydraulic conductivity may lead to a perched water table form on top of the claypan layer. Water in the perched water table evaporates instead of uptake by plants, especially in the dry season. In the wet season with high precipitation, water can penetrate throughout the soil. However, the low aeration in saturated soil may result in root rots that reduce the stability of plants. The acidic, clay-rich characteristics of the claypan lead to phosphorus (P) sorption to clay minerals. Even though the total P content in the claypan is relatively high, they are strongly attracted by the clay particles that are not available for plant use. Therefore, a high amount of P fertilizer is required to increase the available P for plant absorption. Different from P, the high content of potassium (K) in the claypan is available for plant use which reduces the application of potassium fertilizer. Risk of soil erosion Soil with a claypan layer is highly vulnerable to soil erosion. The low water infiltration rate and the perched water table form on top of the claypan layer largely increase the surface runoff during precipitation with a long duration or high intensity. The runoff water can remove the topsoil with mostly organic matter. It will further reduce the nutrient availability for plants. See also Gilgai Hardpan References Geomorphology Types of soil