dependent on moisture, topography, drainage, and activities of organisms). The
environmental factors also include the properties of soil constituents, because each
soil constituent interacts with other soil constituents and the reactivity of soil
constituents is highly variable. The abundance of some soil constituents (such as
allophane and imogolite) is related to the parent materials and the weathering
conditions. The formation of allophane and imogolite from volcanic ash is favored
by moist climate and good drainage conditions and impeded by dry climate and
submerged conditions (as also described in Chap. 4). The first half of this monograph
concisely describes the major inorganic soil constituents with visual aids. The latter
chapters describe the behaviors of inorganic constituents under various soil environmental conditions.
Chapter 2 focuses mainly on the primary minerals in soil, that is, minerals that
have not been chemically altered since their deposition and crystallization from
molten lava. Primary minerals are abundant in the silt-and-sand fraction (particlesize fraction with diameter > 2 μm) of soil. The primary minerals provide physical
strength to soil and contribute to soil formation through dissolution or weathering at
various speeds. The elements released by the weathering of primary minerals include
nutrients for organisms.
Chapter 3 introduces the secondary minerals, which are more active in soil than
the primary minerals. Exchangeable cations are a subset of secondary minerals with
changeable composition and soil-dependent characteristics. For example, acidic
soils contain exchangeable Al, whereas some alkaline soils include exchangeable
Na. The composition of exchangeable cations is easily affected by solute changes in
soil water, although it is not easily affected by simple dilution using pure water. The
composition of exchangeable cations also affects the physical properties of soil
(Baver 1928). The retention of nutrient cations contributes to plant production.
Types of these minerals can be identified by changes in the basal spacing with
exchangeable cations and accommodation of organic molecules at the interlayer site.
Chapter 4 discusses the non-crystalline soil constituents that characterize many
areas of volcanic activity. Under good drainage conditions, volcanic glasses alter to
non-crystalline materials such as allophane, imogolite, and Al–humus complexes.
All of these materials are highly reactive with phosphate, show variable charge
properties, and have characteristic physical properties. Phytoliths are another
non-crystalline silica material frequently found in humus-rich horizon soils.
Phytoliths are a possible source of Si for plants.
Reducing conditions result from submergence of soil and microbial activity. The
chemical forms of redox-sensitive elements, including many nutrient elements,
differ under reducing and oxidizing conditions. Redox-sensitive inorganic soil
constituents are discussed in Chap. 5.
Chapter 6 introduces three topics related to inorganic constituents in soil, namely,
tsunami-affected soils, Cs-affected soils, and phosphate reactions in the soil–plant
system. The huge tsunami that struck the Pacific coast of eastern Japan in March of
2011 inundated coastal areas with a large volume of seawater. Tsunamis affect soil
mainly by erosion, deposition, and by increasing the salt concentration in soil water
and the exchangeable Na. Although exchangeable cations are a part of silicate
4
1 Purpose and Scope
environmental factors also include the properties of soil constituents, because each
soil constituent interacts with other soil constituents and the reactivity of soil
constituents is highly variable. The abundance of some soil constituents (such as
allophane and imogolite) is related to the parent materials and the weathering
conditions. The formation of allophane and imogolite from volcanic ash is favored
by moist climate and good drainage conditions and impeded by dry climate and
submerged conditions (as also described in Chap. 4). The first half of this monograph
concisely describes the major inorganic soil constituents with visual aids. The latter
chapters describe the behaviors of inorganic constituents under various soil environmental conditions.
Chapter 2 focuses mainly on the primary minerals in soil, that is, minerals that
have not been chemically altered since their deposition and crystallization from
molten lava. Primary minerals are abundant in the silt-and-sand fraction (particlesize fraction with diameter > 2 μm) of soil. The primary minerals provide physical
strength to soil and contribute to soil formation through dissolution or weathering at
various speeds. The elements released by the weathering of primary minerals include
nutrients for organisms.
Chapter 3 introduces the secondary minerals, which are more active in soil than
the primary minerals. Exchangeable cations are a subset of secondary minerals with
changeable composition and soil-dependent characteristics. For example, acidic
soils contain exchangeable Al, whereas some alkaline soils include exchangeable
Na. The composition of exchangeable cations is easily affected by solute changes in
soil water, although it is not easily affected by simple dilution using pure water. The
composition of exchangeable cations also affects the physical properties of soil
(Baver 1928). The retention of nutrient cations contributes to plant production.
Types of these minerals can be identified by changes in the basal spacing with
exchangeable cations and accommodation of organic molecules at the interlayer site.
Chapter 4 discusses the non-crystalline soil constituents that characterize many
areas of volcanic activity. Under good drainage conditions, volcanic glasses alter to
non-crystalline materials such as allophane, imogolite, and Al–humus complexes.
All of these materials are highly reactive with phosphate, show variable charge
properties, and have characteristic physical properties. Phytoliths are another
non-crystalline silica material frequently found in humus-rich horizon soils.
Phytoliths are a possible source of Si for plants.
Reducing conditions result from submergence of soil and microbial activity. The
chemical forms of redox-sensitive elements, including many nutrient elements,
differ under reducing and oxidizing conditions. Redox-sensitive inorganic soil
constituents are discussed in Chap. 5.
Chapter 6 introduces three topics related to inorganic constituents in soil, namely,
tsunami-affected soils, Cs-affected soils, and phosphate reactions in the soil–plant
system. The huge tsunami that struck the Pacific coast of eastern Japan in March of
2011 inundated coastal areas with a large volume of seawater. Tsunamis affect soil
mainly by erosion, deposition, and by increasing the salt concentration in soil water
and the exchangeable Na. Although exchangeable cations are a part of silicate
4
1 Purpose and Scope