Pedo Memory

Most soils are organized, structured, natural entities whose pedogenic properties have recorded the main features of environments and ecosystems that existed during their formation and subsequent changes. Soil, therefore, is commonly a product and a memory of long-term interactions and functioning in nature. During the past two or three centuries, much of the pedosphere has also recorded many anthropotechnogenic impacts and those portions now have memories of complex biosphere-geosphere-anthroposphere interactions.

Soils have different capacities for recording past and present environments depending on the time required for processes to come into quasi-equilibrium with environmental conditions (characteristic times, CTs). General CTs are: for gaseous phase, CT — 10_1-101 years; liquid phase, CT - 10_1-102 years; micro- and macrobiota, CT - 10_1-103 years; and solid phase, CT - 101-106 years. These orders of magnitude are only indicative of the wide ranges involved. Although solid-phase features reflect environmental changes slower than the other phases, they retain the changes much longer and are the major recorders of prior environmental conditions.

Pedogenic solid-phase properties also have different characteristic memory retention times; the more quickly formed properties may record changes for years, decades, and even centuries. Litter leaching and decomposition, soil structure formation and degradation, salinization and desalinization, and reduction and oxidation are examples. The slower-formed properties may record changes for millennia to millions of years, for example, deep and strong weathering, transformation and translocation of clays, and alteration and accumulation of iron-rich

World soil resources

World soil resources

I Acriosols, Alisols, Plinthosols (AC) I Albeluvisols, Luvisols (AB) Andosols (AN) Anthrosols (AT) Arenosols (AR)

Calcisols, Cambisols, Luvisols (CL) 'I Calcisols, Regosols, Arenosols (CA) ■■ Cambisols (CM)

H Chemozems, Phaeozems (CH) Cryosols (CR) Durisols (DU) I Ferralsols, Acrisols, Nitisols (FR) I Fluvisols, Gleysols, Cambisols (FL) I Gleysols, Histosols, Fluvisols (GL) Gypsisols, Calcisols (GY) I I Histosols, Cryosols (HR)

H Histosols, Gleysols (HS) I Kastanozems, Solonetz (KS) Leptosols, Regosols (LP) Leptosols, Cryosols (LR) Lixisols (LX)

_I Luvisols, Cambisols (LV)

Nitisols (NT) Phaeozems (PH)

Planosols (PL) Plinthosols (PT) Podzols, Histosols (PZ) Regosols (RG) Solonchaks, Solonetz (SC) Umbrisols (UM) Vertisols (VR) Glaciers (gl)

Dominant soils

I Acriosols, Alisols, Plinthosols (AC) I Albeluvisols, Luvisols (AB) Andosols (AN) Anthrosols (AT) Arenosols (AR)

Calcisols, Cambisols, Luvisols (CL) 'I Calcisols, Regosols, Arenosols (CA) ■■ Cambisols (CM)

Waterbodies Steep lands f \/ Limit of aridity 'V'Country boundaries

H Chemozems, Phaeozems (CH) Cryosols (CR) Durisols (DU) I Ferralsols, Acrisols, Nitisols (FR) I Fluvisols, Gleysols, Cambisols (FL) I Gleysols, Histosols, Fluvisols (GL) Gypsisols, Calcisols (GY) I I Histosols, Cryosols (HR)

H Histosols, Gleysols (HS) I Kastanozems, Solonetz (KS) Leptosols, Regosols (LP) Leptosols, Cryosols (LR) Lixisols (LX)

_I Luvisols, Cambisols (LV)

Nitisols (NT) Phaeozems (PH)

Planosols (PL) Plinthosols (PT) Podzols, Histosols (PZ) Regosols (RG) Solonchaks, Solonetz (SC) Umbrisols (UM) Vertisols (VR) Glaciers (gl)

Projection Flat Polar Quartic © FAO/EC/ISRIC, 2003

Figure 5 Map of world soil resources using the World Reference Base for names of major soil groups. Map produced by FAO, EC, and ISRIC.

compounds. The age of soil memory depends on the duration and interactions of soil-forming and weathering processes that occurred at a specific place.

Soils of the existing pedosphere generally consist of complex combinations of inherited properties of pre-Pleistocene and Pleistocene weathering, landscape evolution, and pedogenesis, as well as more recent Holocene and Anthropocene impacts. Some features of pedogenic properties are partially erased by erosion and other degrading processes such as excessive leaching or acidity, and later processes of landscape and soil evolution overprint properties and memories (a palimpsest phenomena). Usually local knowledge of geomorphology, sedimentation, and hydrology provide a foundation on which to base pedogenic interpretations. The complicated records of the pedosphere are slowly being read by pedologists to provide more information about past environmental conditions. Understanding soil components as carriers of pedo-memory and the rates of change of solid-phase properties remains a challenge to understanding and predicting future changes of the pedosphere.

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