(Upload on June 13 2015) [ 日本語 | English ]

Soil formation process (土壌形成過程)

Mount Usu / Sarobetsu post-mined peatland
From left: Crater basin in 1986 and 2006. Cottongrass / Daylily

soil formation = soil evolution

Weathering (風化)

= rock weathering

  1. physical (mechanical) weathering
  2. chemical weatehring
  3. biological weathering
Four processes of soil formation

addition (添加) of material to the developing soil profile from outside sources, such as organic matter from leaves, dust from the atmosphere, or soluble salts from groundwater

loss (損失) of material from the soil profile by leaching to groundwater, erosion of surface material, or other forms of removal (often transformation and translocation result in the accumulation of material in a particular horizon)


translocation (移動) or transportation of inorganic and organic materials from one horizon to another, either up or down (material is primarily moved by water but may also be moved by soil organisms)

transformation (物質変化) of soil constituents from one form to another, such as through mineral weathering and organic matter breakdown

factors on soil formation (土壌形成要因)

rhizosphere (根圏): soil that is directly influenced by root secretions and associated microorganisms
≈ rhizosphere soil or rhizospheric soil (根圏土壌)

endorhizosphere (内根圏)
rhizoplane (根面)
exorhizosphere (外根圏)

mycorrhizosphere (菌根圏)
a region around mycorrhizal fungi in which nutrients released from the fungi increase the microbial populations and their activities

Fig. An illustration of the rhizosphere A=Amoeba consuming bacteria BL=Energy limited bacteria BU=Non-energy limited bacteria RC=Root derived carbon SR=Sloughed root hair cells F=Fungal hyphae N=Nematode worm

Soil formation process (土壌形成過程)

Stratification (層化)

Podzolization (ポドゾル化)
Leaching (洗脱)
Calcification (石灰集積)
Feralization (鉄アルミナ富化)
Salinization (塩類集積)
Solodization (アルカリ化) rock
Rocky layer

Humus (腐植)

The fraction of soil organic matter that is amorphous and without the cellular structure of plants → rich in nutrients in general
1982 established IHSS (International Humic Substances Society)
Humic acid (腐植酸)
dark colored, acidic, relatively high-molecular substances
1919 Oden: used absorption spectrum of humic acids for the quantifiation
1930-40 Simon: separated into A type, B type and decayed substance
Melanic index, K450/K520

Fig. Processes of soil formation (Buol 1973)

Argillation and clay (粘土化と粘土)

(Soil Survey Staff 1951)

Types of soil structure (土壌構造形状)
A: prismatic (角柱状), B: columnar (円柱状), C: angular blocky (塊状), D: subangular blocky (亜角塊状), E: platy (板状), F: granular (粒状). Scanning electron micrographs of kaolin clays. A. Coarse-fraction kaolin (MP clay). B, C. Medium size particle fraction taolin (English clay). Note ped fabric unit in (C) and marco pores. Pore characteristics between ped units are different from pore characteristics in ped unit itsself. D. Structure of a compound ped.

[water for plant use]

Soil physics (土壌物理学)

Three phase distribution (三相分布)

three phase
Fig. Three-phase distribution