El podsol (podzol en inglés o espodosol según el Soil Taxonomy) es un tipo de suelo característico de climas fríos y húmedos (Canadá, Escandinavia y Rusia septentrional) o templado frío (vertiente atlántica de Europa), con abundantes precipitaciones, que se caracteriza por una alta lixiviación, que propicia que una gran cantidad de sustancias superficiales migren a niveles inferiores. El horizonte B se caracteriza por un alto depósito de óxidos, que confieren a esta capa unas tonalidades rojizas características. Su nombre significa en ruso ‘debajo de las cenizas’ (de под [pod], ‘debajo’, y зола [zola], ‘cenizas’). El frío provoca una descomposición lenta de la materia orgánica, principalmente de árboles resinosos y brezos, los que dan lugar a la formación de un humus ácido (pH superficial de 3,5 a 4,5) que, de ser filtrante la roca madre subyacente (como son los casos de la arena y de la arenisca) ataca a la arcilla y la degrada. Las aguas infiltradas lixivian ese suelo y hacen descender más o menos profundamente su hierro y su alúmina. La parte inferior del primer horizonte consta entonces esencialmente de finos granos de cuarzo y adquiere el aspecto y el color de la ceniza. El horizonte B, en el cual se acumula el hierro, puede ser cementado por éste hasta formar un estrato concrecionado. En un podsol se distinguen de arriba abajo las siguientes capas: \n* un horizonte superficial negro, fibroso, de materia orgánica parcialmente descompuesta, \n* una capa delgada de granos silíceos mezclados con humus, \n* un horizonte eluvial (o sea, lixiviado por las aguas), pulverulento como la ceniza y de su mismo color gris claro, \n* un horizonte de acumulación iluvial, subdividido en una delgada capa con hasta 10 % de humus, y \n* un estrato pardo rojizo, rico en hierro y alúmina. Existen variantes en las cuales puede faltar alguna de las capas reseñadas, salvo la gris característica del podsol.

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In soil science, podzols (known as spodosols in China and the United States of America and podosols in Australia) are the typical soils of coniferous, or boreal forests. They are also the typical soils of eucalypt forests and heathlands in southern Australia, while in Western Europe podzols develop on heathland, which is often a construct of human interference through grazing and burning. Many podzols in this region may have developed over the past 3000 years in response to vegetation and climatic changes. In some British moorlands with podzolic soils there are brown earths preserved under Bronze Age barrows (Dimbleby, 1962). Podzol means "under-ash", and is derived from the Russian под (pod) + зола́ (zola); the full form is "подзо́листая по́чва" (podzolistaya pochva, "under-ashed soil"). It likely refers to the common experience of Russian peasants of plowing up an apparent under-layer of ash (leached or E horizon) during first plowing of a virgin soil of this type. Podzols are able to occur on almost any parent material but generally derive from either quartz-rich sands and sandstones or sedimentary debris from magmatic rocks, provided there is high precipitation. Most podzols are poor soils for agriculture due to the sandy portion, resulting in a low level of moisture and nutrients. Some are sandy and excessively drained. Others have shallow rooting zones and poor drainage due to subsoil cementation. A low pH further compounds issues, along with phosphate deficiencies and aluminium toxicity. The best agricultural use of podzols is for grazing, although well-drained loamy types can be very productive for crops if lime and fertilizer are used. The E horizon, which is usually 4 to 8 centimetres (1.57 to 3.15 in) thick, is low in Fe and Al oxides and humus. It is formed under moist, cool and acidic conditions, especially where the parent material, such as granite or sandstone, is rich in quartz. It is found under a layer of organic material in the process of decomposition, which is usually 5 to 10 centimetres (1.97 to 3.94 in) thick. In the middle, there is often a thin layer of 0.5 to 1 centimetre (0.2 to 0.4 in). The bleached soil goes over into a red or redbrown horizon called rusty soil. The colour is strongest in the upper part, and change at a depth of 50 to 100 centimetres (19.7 to 39.4 in) progressively to the part of the soil that is mainly not affected by processes; that is the parent material. The soil profiles are designated by the letters A (topsoil), E (eluviated soil), B (subsoil) and C (parent material). In some podzols, the E horizon is absent—either masked by biological activity or obliterated by disturbance. Podzols with little or no E horizon development are often classified as brown podzolic soils, also called umbrisols or umbrepts.

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