Introduction to Soils

What are the translocations in the soils processes?

- Clay, organic matter, and sesquioxides in leachates - Nutrients circulated by plants - Soluble salts in water - Mass movement by soil animals

What are soil profiles?

- Complete vertical succession of soil horizons - Continue down to: -parent material -other consolidated substrate material -a selected depth (~2 m) in unconsolidated materials

What does soil consist of?

- Equal parts of solid matter and holes -Equal proportions of air and water are best for plant growth -Fluctuations in water and air contents occur as the soil dries or moistens -Organic matter provides most of the naturally-occurring plant nutrients

What are soil horizons?

- Layers approximately parallel with the earth's surface. - Interrelated by processes of formation and degradation.

What are the transformations in the soils processes?

- Reduced particle size by physical weathering - Mineral decomposition - Structure development - Clay and organic matter changes - Humus from organic matter

What are the losses in the soils processes?

- Soil by erosion - Water by transpiration - N2 by denitrification - Carbon from organic matter - Water, nutrients, and elements by leaching

How to observe soil changes with depth?

- Soil pits are a cheap and effective means of exposing the changes in the horizons down a soil profile. - A hand-auger may be used routinely to describe and collect samples from soil profiles where no exposures occur.

What are the additions in the soils processes?

- Water as precipitation and runoff - Organic matter - Deposited sediments - O2 and CO2 from the atmosphere - N2 from legumes - Salts in groundwater

What are the main soil-forming processes?

- Water infiltration: rain or irrigation waters - Addition of organic matter at the soil surface - Weathering and transformations of rock-forming minerals in the soil parent material - Movement of clays, oxides, and carbonates and their accumulation lower in the soil profile - Leaching and loss of soluble salts from the soil profile

How are inert geological materials turned into soil profiles?

- Weathering: transformations and translocations of mineral matter - Accumulation of organic matter: plant and animal materials in the soil _ Live organisms: in the soil converting biotic residues into plant nutrients.

What is "Apedal"?

-"Apedal" materials lack peds and are either "massive" (coherent, brick-like) or "single grain" (loose, like beach sand). -This soil displays a massive topsoil, and a strongly structured (coarse prismatic, 15 x 5 x 4 cm) subsoil.

How is soil structure describe?

-"Soil structure" relates to the arrangement of primary soil particles into natural aggregates called 'peds'. -Soil structure is described in terms of the shape (type), size, and grade (distinctness, degree of development) of the peds.

What is soil structure?

-A soil with strongly developed, fine, granular structure (left) compared with a poorly structured soil lacking aggregates (right). -Plant rootlets, soil organisms, and soil organic matter (humus) play major roles in developing structure in soil horizons.

What are the properties of each soil horizon?

-Horizon colour: using Munsell Soil Colour Charts -Field texture: determined by manipulation of moist soil -Coarse fragments: gravels, nodules, etc -Structure: sizes and shapes of peds (natural aggregates) -Consistence: resistance of aggregates to deformation Field pH: acidity or alkalinity

What is bad about subsoils?

-Impermeable, strongly acidic, or strongly alkaline subsoil layers can inhibit root growth -Poor drainage in the subsoil can result in waterlogged topsoils and plant root zones -Swell -shrink properties of the subsoil can result in poor plant growth and damaged constructions

What is the most important of all soil properties?

-Living tissues and dead remains of plants and animals in various stages of growth and decomposition: roots, leaves, feathers, logs, beetles, wombats, humans, etc. -Living soil microbes (e.g. bacteria, fungi, actinomycetes) and their residues: 1,000 million to 3,000 million individuals per gram of good soil; 7,000 million (the number of humans on the Earth) in seven fingernail loadings of soil -Organic substances, such as "humus": dark coloured, amorphous, very fine organic material, made from the decomposition products of dead organisms (plants, animals, and microbes)

What are the main ped types?

-Main ped types are: granular, lenticular, platy, angular and subangular blocky, polyhedral, prismatic, columnar.

How do you manage our finite soil resources?

-Many site and soil management practices overlook the inherent fragility of the soil and the enormous time it takes to form a soil profile. Because of the vast time periods required, eroded soils cannot "re-form" within human or historical time spans.

What are the soil moisture indicators?

-Red soils: contain hematite [Fe2O3], an oxidised iron oxide -good drainage and aeration Yellow soils: contain goethite [FeO(OH)], a hydrated iron oxyhydroxide - generally poorly drained -Grey soils: iron leached out of the soil matrix, may be deposited as ironstone gravel in the soil - very poor drainage and/or seasonal waterlogging -Mottles: strong iron redistribution - prolonged waterlogging -Bleached A2 horizons: impeded drainage in subsoil

What is soil organic carbon (SOC)?

-SOC forms aggregates and stabilises water-movement pathways in soils -SOC may be up to 10 -12% by weight of "highly organic, peaty topsoils" -SOC should be at least 1.8%in a good soil (SOM> 3%) -SOC is commonly less than 0.9% in poorly managed soils -SOC content and composition defines the quality and health of a soil

How does soil organic matter decompose?

-Soil microbes break complex components of organic residues down, releasing carbon dioxide to the air -One year after incorporation into the soil, more than 2/3 of the carbon will be lost from the soil as carbon dioxide -Decomposition rates are very high in the tropics -More organic matter put into the soil means that even more carbon dioxide will be produced by the microbes

What does the soil structure describe?

-Soil structure describes the manner in which soil constituents are aggregated together into peds, and the nature of the system of pores and channels in the soil.

What is gravelly soil?

-The coarse fraction may be inherited from gravelly soil parent materials or formed by pedogenic processes in the soil (nodules and concretions). -Gravels occupy space that could be occupied by water and nutrients. -Gravelly soils have low soil profile water storage capacity: -Wet season: waterlogged soils. -Dry season: droughty soils.

How do you describe different soil profiles?

-The soil materials should be laid out systematically in 30 cm increments down the borehole. -The properties of each soil horizon should be described using standard terminology.

What are the properties of good arable soils?

-Topsoil depth: 100 -200 + mm -Soil profile depth: 1 -2 m -Plant nutrient supply: organic and mineral -Beneficial (non-toxic) soil chemical properties -Good surface soil structure -Large pores:water entry, transmission, and drainage -Fine pores: water retention and storage for plant use -Approximately equal amounts of sand, silt, and clay: loam texture -Little gravel: few particles larger than 2 mm

What is subsoil?

-Zone of accumulation of clay, iron, etc. -The horizons in the soil profile below the topsoil, and above the soil parent material (i.e. above rock or deposited sediments)

What is topsoil?

-Zone of maximum biological activity -The organically enriched surface horizon -Contain the bulk of the plant roots -Is the major entry point into the soil of air and water -Provides the chief nutrient reservoir in the soil

What are the different field texture?

-light textured soils are sandy -heavy textured soils are clayey -loamy soils: equal mix of sand, silt and clay -estimate of particle-size distribution -water entry and water-holding capacity -ease of cultivation -susceptibility to erosion

What are the soil colours used as an indicator for?

-soil moisture status -organic matter content (i.e. soil fertility) -oxidation state of iron (i.e. profile drainage) -seasonal waterlogging

What are the soil processes?

Additions, Looses, Transformations, Translocations

How long does it take for clay-rich subsoils to form?

At least 1,000 years, and possibly as much as 10,000 years

How long does it take for deep subsoil fratures to form?

At least 10,000 years, may be of the order of 100,000 years

How long does it take for organic matter-enriched topsoil horizons to form?

At least 100 to several thousands of years

How are soil differences marked?

By the differences in the nature and distribution of soil horizonsdown the soil profile

Define soil

Collection of natural bodies occupying parts of the earth's surface that support plant life and that have properties due to the integrated effect of climate and living matter acting upon parent material, as conditioned by relief, over periods of time

What is the size of soil particles?

Gravel: > 2 mm > 2000 micrometre Sand: 2 - 0.02 mm 2000 - 20 micrometre Basketballs / Tennis balls Silt: 0.020 - 0.002 mm 20 - 2 mircometre Marbles Clay: < 0.002 mm < 2 micrometre Talcum powder

What is good about subsoils?

Much of the water and some of the nutrients needed by plants are stored in the subsoil

How to calculate Soil Organic Matter (SOM)?

Soil organic carbon (SOC) x 1.72 = soil organic matter (SOM)

What are the properties of soil?

The properties of soils vary as a result of different combinations of five soil forming factors (climate, parent material, organisms, relief, time) occurring across the landscape.

What are the different soil materials?

The soil parent material, either in situ bedrock under hillslopes or transported sediments, weathers to form the overlying soil.

What is deep subsoil?

The weathered soil parent material

What are the 3 major soil horizons?

Topsoil, Subsoil and Deep subsoil

What causes impeded subsoil drainage?

Unfavourable physical and chemical properties of poorly structured, clayey, or impermeable subsoils inhibit deep root penetration.

Cumulic Stage

What stage is this?

Extended Subsolum Stage

What stage is this?

High Contrast Stage

What stage is this?

Low Contrast Stage

What stage is this?

Stratic Stage

What stage is this?

How is the Munsell colour system arranged?

hue: red, yellow, green, blue, purple, red value: dark to light chroma: colour intensity