Essay About Red Soil Properties
Mosaic of different soil colours across Queensland landscapes.
The colour of the soil is usually the first thing people notice.
Mostly this is just the topsoil but it does not reflect the entire soil. The topsoil is usually darker than lower layers (or horizons) because this is where organic matter accumulates.
Soil colour is usually due to 3 main pigments:
Colour can be a useful indicator of some of the general properties of a soil, as well as some of the chemical processes that are occurring beneath the surface.
Soil types and characteristics
Typical management implications
These soils are often associated with high levels of organic matter (peats).
Vertosols (cracking clay soils)
These soils are often referred to as bleached or 'washed out'. The iron and manganese particles have been leached out due to high amounts of rainfall or drainage.
This colour indicates good drainage. Iron found within the soil is oxidised more readily due to the higher oxygen content. This causes the soil to develop a 'rusty' colour. The colour can be darker due to organic matter.
Yellow to yellow-brown
These soils often have poorer drainage than red soils. The iron compounds in these soils are in a hydrated form and therefore do not produce the 'rusty' colour.
Soils associated with moderate organic matter level and iron oxides.
These soils are associated with very poor drainage or waterlogging. The lack of air in these soils provides conditions for iron and manganese to form compounds that give these soils their colour.
Source: Adapted from Soil Constraints and Management Package
The particles that make up soil are categorized into three groups by size – sand, silt, and clay. Sand particles are the largest and clay particles the smallest. Most soils are a combination of the three. The relative percentages of sand, silt, and clay are what give soil its texture. A clay loam texture soil, for example, has nearly equal parts of sand, slit, and clay. These textural seperates result from the weathering process.
This is an image comparing the sizes of sand, silt, and clay together. Sand is the largest. Clay is the smallest.
There are 12 soil textural classes represented on the soil texture triangle. This triangle is used so that terms like “clay” or “loam” always have the same meaning. Each texture corresponds to specific percentages of sand, silt, or clay. Knowing the texture helps us manage the soil.
Soil structure is the arrangement of soil particles into small clumps, called peds or aggregates. Soil particles (sand, silt, clay and even organic matter) bind together to form peds. Depending on the composition and on the conditions in which the peds formed (getting wet and drying out, or freezing and thawing, foot traffic, farming, etc.), the ped has a specific shape. They could be granular (like gardening soil), blocky, columnar, platy, massive (like modeling clay) or single-grained (like beach sand). Structure correlates to the pore space in the soil which influences root growth and air and water movement.
Read more and download our Soil Texture information sheet.
The color of soil is measured by its hue (actual color), value (how light and dark it is), and chroma (intensity).
Soil color is influenced primarily by soil mineralogy – telling us what is in a specific soil. Soils high in iron are deep orange-brown to yellowish-brown. Those soils that are high in organic matter are dark brown or black. Color can also tell us how a soil “behaves” – a soil that drains well is brightly colored and one that is often wet and soggy will have a mottled pattern of grays, reds, and yellows.
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