Soils {soil, land} have types and properties {pedology}|. Soil comes from eroded rocks and decayed organic matter. Soil {mountain soil} derived from lava is rich in minerals. Iron oxides cause red, yellow, or brown soil color. Humus causes black or dark-brown soil color. Soil can be acid or alkaline. Soil has layers.
Soil can have varying calcium, sodium, potassium, phosphorus, nitrogen, iron, magnesium, and sulfur amounts {soil fertility} {fertility, soil}|.
Clay and shell mixtures {marl}| can be fertilizers.
Soil types {soil texture} depend on soil particle size {peds}|. Gravel has largest peds and coarse texture. Sand is next largest. Silt is third largest. Clay has smallest peds and fine texture.
Soil can have no soil profile {azonal soil profile}.
Soil can have unstable but layered soil profile {intrazonal soil profile}.
Soil can have stable soil profile {zonal soil profile}.
Hardened soil layers {pan layer} can be below topsoil.
Soil surface layers {topsoil} can be porous and 0 to 24 inches thick.
Sediment from rivers makes sandy soil {alluvial soil}|.
humus and sand {chernozem}.
decayed organic matter {humus}|.
clay, silt, and sand mixture {loam}|.
Dry soils have different types {chernozemic soil} {grunosolic soil} {decentic soil}.
Humid soils have different types {podzolic soil} {latosolic soil} {tundra soil}.
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Date Modified: 2022.0225