Soil Physics

Soil Formation

• Soil formation is influenced by parent material, topography, climate, organisms, and time.

Forming Factors

Parent Material

• Differing in mineralogy, chemistry, and grain sizes, impacts soil properties.
• Determines soil color, chemical properties, mineral content, and permeability.
• Granite leads to sandy soils high in quartz.
• Basalt results in clayey soils with magnesium and calcium but low sand content.
• Ultrabasic rocks produce soils with high ferromagnesian minerals and heavy metals.
• Gneiss produces sandy soils.
• Slate produces clay soils.
• Wind-deposited material forms well-sorted aeolian deposits of sand and silt.
• Soil scientists are interested in the genesis, chemical-mineralogical composition, weathering stability, and physico-chemical properties of parent materials to understand the soils derived from them. They distinguish between natural substrates, loose materials, hard-rock sediments, and artificial substrates.

Topography

• Location determines soil accumulation.

Climate

• Determines the rate of weathering.
• Temperature and precipitation affect chemical and physical processes.
• Increased temperature speeds up reactions, more water promotes translocation.
• Climate impacts soil horizon development, including the vegetation type.

Organisms

• All organisms determine the rate of humus formation.
• Plants affect soils through organic matter input, nutrient cycling, root activity, and erosion reduction.
• Organisms consume and decompose organic matter, affecting soil properties like aeration.
• Earthworms aerate and aggregate soils.
• Human activities, including cattle and agriculture, change soil formation.

Time

• The duration material is subjected to weathering determines the thickness of the soil profile
• If parent material is hard and resistant, soil development may be prolonged.

Horizons

• Soil horizons are distinct layers within a soil profile, each with unique characteristics.
• O horizon: Leaf litter
• A Horizon: Topsoil
• B horizon: Subsoil
• C horizon: Parent Material

Minerals

• Oxygen (46.5%), silicon (28%), and aluminum (8%) are the three main elements forming the earth's crust.

Soil Processes: Additions

• Additions refer to soil processes where substances are added to the soil.
• Precipitation
• Flooding leaves sediment behind.
• Deposition occurs from wind, water, glaciers, etc. and humans.
• Leaf accumulation adds organic matter.
• Landslides deposit material on top of existing soil.
• Fertilization
• A huge input of inorganic or organic material

Soil Processes: Losses

• Losses refer to the ways something is removed from the soil
• Wind, water, plants, or microorganisms erode, leach, or harvest soil particles or chemical compounds
• Leaching removes materials from the soil into groundwater.
• Erosion is from wind, water, or ice.
• Landslides remove materials down slopes.
• Flooding can remove materials downstream.

Soil Processes: Transformations

• Transformations change materials already in the soil.
• Chemical weathering of sand forms clay minerals, changing coarse organic matter into decay-resistant humus.
• Physical weathering and fragmentation via freeze-thaw cycles, drying-rewetting cycles, and fire.
• Chemical weathering facilitates the formation of secondary minerals from primary minerals.
• Organic matter decomposes through microbial processes.

Soil Processes: Translocation

• Translocation involves the movement of soil constituents, like minerals and organic matter.
• Occurs within the soil profile and/or between horizons.
• Animal Digging: Animals physically bring materials to the surface.
• Mixing: Humans disturb soil, as plants and burrowing animals do.
• Ploughing: Tillage moves soil around, often bringing subsurface soil to the top.

Soil Structure Formation Mechanisms:

• Flocculation/dispersion
• Swelling and shrinking processes
• Cementation
• Adhesion
• Soil tillage

Soil Phases

• Solid: Mineral and organic particles
• Liquid: Soil water and solutes
• Gas: Air
• The content and spatial distribution of the three phases are highly variable and influence soil characteristics.
• A soil with one phase missing is considered a 2-phase system and presents hostile conditions for specialized organisms.
• Gleye soils or other hydromorphic soils and desert soils are examples.
• Fully Saturated Soils: Only water and solid
• Dry Soils: Oven-fried; air and solid

Mass, Volume, and Density

• Phase fractions of these three components are important for soil characterization.
• Mass Fractions: Related to dry mass, for expressing analysis results
• Volume Fractions: Related to bulk volume, for expressing results as vol%
• Unit for mass is kilograms, for volume is meters cubed.
• Particle Density is the mass unit per volume of soil particles excluding pores.
• Particle density is a relatively constant parameter.
• Mineral soils generally have a particle density of 2.65 Mg/m3.
• Soils the high amount of organic matter have lower particle density

Particle Density (dP)

• Solid soil mass (SM) related to the solid volume (SV)
• dP [Mg * m-3] = SM / SV
• dP is mostly also considered as dry density (105° C)
• Depends on humus content, 2.4-2.7 Mg/m³.
• dP is normally not measured because it is time consuming.
• Soil science assumes 2.65 Mg/m³ (if quartz is the main mineral component)

Bulk Density

• Defined as the mass per unit bulk volume of soil that has been dried to a constant weight at 105°C, and it indicates soil compaction.
• Volume includes soil particles and the volume of pores among them
• Mass of dry soil / Volume of soil
• Bulk density (dB) is solid soil mass (SM) related to total soil volume (TSV)
• dB [Mg * m-3] = SM/TSV
• Dry bulk density (105° C) is mostly used; moist bulk density at natural water content. dB ranges in soils 0.3-1.8 Mg/m3
• Overcompaction is when horizontal stress is the highest and the vertical stress the lowest.
• It can only be repaired by turbation (Bioturbation, arboturbation, Cryoturbation, Peloturbation, Technoturbation)
• Soil compaction decreases soil porosity/coarse pores.
• This may be good for higher water holding capacity, but if the soil air content is below 10 vol% then it is not good.
• Factors that affect density include SOM, texture, and the density of soil minerals.
• Well-aggregated, porous, soils with high amounts of organic matter have lower bulk densities compared to sandy soils that have higher bulk densities due to less pore space.

Soil Texture

• Organic substances are generally destroyed in the lab to measure soil sizes as they are hard to classify them.
• Soil particles classified into sand, silt, and clay with limits commonly on a logarithmic scale.
• Further classified by dividing the scale sections in the middle of the logarithmic scale.
• Measure for determination of particle sizes in soil and sediments
• Comparison of particles is complex, because of their very different shapes.
• The "equivalent diameter" is an alternative value, indicating the size of a theoretical regular-shaped particle that behaves the same way as the real particle under investigation.
• This analysis makes it easier to analyze the particle size distribution
• If particle sizes are determined by mechanical sieving, the equivalent diameter refers to the diameter of a sphere that barely passes through a defined sieve pore.
• Common for the sand fractions
• Smaller particle sizes are often determined by sedimentation in aqueous medium
• The equivalent diameter refers to the diameter of a sphere with the same density and sedimentation velocity.
• For silt/clay fractions, Stoke's law is used to deduce particle size distribution
• Particles settle in water proportional to mass and size.
• Amount of suspended soil determines particle size fractions.
• Amount of soil in suspension is determined using a pipette or hydrometer.

Equivalent Diameter

• Needed to define: diameter of theoretical cylindrical capillar with equivalent water retention force or capillary rise. The equivalent diameter of a soil pore to a straight circular capillary rises.
• In nature, pores are shaped different.
• Capillarity law is the base for the calculation of pore size classes (only the radius is variable!)

The homogeneity factor U

• Expresses the sorting grade of soil particle sizes.
• Is important whether particle size is homogeneous (= badly sorted = all particles with similar size) or heterogeneous (= well sorted = many different sizes).
• The sizes are measured at two points of the texture curve (60% and 10% on the y-axis).
• U less than 100 is very homogeneous and U greater than 400 is heterogeneous.
• Detrital loam has a U-factor of 465 while sand has a U-factor of 4.

Atterberg Limits

• Test establishes the moisture amount in fine-grained clay and silt soils.
• Defines the transition between solid, semi-solid, plastic, and liquid states.
• The liquid limit is when soil changes from plastic to liquid with little disturbance.
• The plastic limit is the border between plastic and semisolid. Test rolling soil until it crumbles.
• Shrinkage is at the point where further waterloss does not reduce soil volume.
• The plasticity index indicates sensitivity to the water content
• Needed to find consistency for soil tillage at plastic limit
  • PI=%H2O (LL)-%H2O (PL)

Soil texture

• Soil texture is the relative proportions of sand, silt, or clay.
• The soil textural class is a grouping of soils based on these proportions
• Clay soils have the finest texture, while sands are the coarsest. A soil that has mixture of sand, silt, and clay is called a loam.
• Texture triangle helps determine the class.
• Understanding soil helps aggregate smaller units, predict properties, and apply research.
• Why classify soil types? Compress info into the soil type, predict things like hydrology, aggregate soil for different applications.
• Sandy soils have poor structure and lack cohesion compared to toloam and claysoils.
• Sandy soils are free-draining
• Sandy soils are not rich in nurtients which are washed down
• Sandy soils advantage: easy to cultivate, warm up quickly
• Sandy soils are difficult to manage
• Clay soil has the highest level of cohesion, is often sticky while wet and dry
• Clay soils Feels smooth, are hard to separate when formed into clods
• Clay consists of a lot of clay particles and Slow draining leading to water logging
• Loamy soils have greater cohesion than sandy, greater moisture retention while still well drained, soft and rich in touch
• Silty soils are slippery when wet and are the most fertile. High risk of erosion. Podsol sandy is a typical sandy soil, chernozem is a silty soil
• Temporal Changes
• Is usually a very stable soil property, but over time changes by Dissolution, Precipitation and Clay illuviation

Soil Organic Matter

What is SOM

• Organic matter component of soil, consisting of plant and animal matter, tissues, and substances.
• Non-humic substances vs. humic substances
• Non humic is material with plan or animal origins, not decomposed
• Humic is Strongly decomposed, usually dark, difficult to decomposes,
• Properties of humic substances: Chemically not clearly defined, made of carbon, hydrogen, and oxygen, negatively charged, large surface area, binds water
• Cation exchange capacity(CEC) higher than clay minerals! and very good on aggregate
• Classifying SOM: Easily degraded(labile), very hard degrades (stable). Labile is the easy degraded composts that serves as nutrients

Humus

• Formed by well integrated formation of organic matter, rich in CEC, composed of small humus. Good conditions for decomposition with many burrowing animals.
• SOM Analyses is determination of C by loss-on-ignition, Wet oxidation of organic, CO2 analyses and Characterization

Soil Colour

• Diagnostic properties provide clues to soil properties, you understand the level of nutrients, how old the soil is,
• Munsell color chart
• Hue is the dominant spectral colour , saturation etc
• Redoximorphic Features occur, when a soil's colors are formed by the repeated chemical/reduction of iron
• grey removal of Clay/iron/ magnesium oxides mean saturation

Specific Surface Area

• Area of soil particles per unit mass or volume of soil particles
• Surface increased when partials decrease, surface increased when Weathering increased . Especially imporant in solid liquid boundary
• The shape of particles is influences by particle size, porosity and reactive properties
• Helps you estimate if materilas were transports over longer distances

Soil Porosity

• Pore size distribution is classified by the following:
• Fine Pores, Medium Pores, Narrow Coarse,
• "Equivalent diameter” Needed to be defined as cylindrical with equivalent water retention force. In Nature, pores are very random. Pore size is affected by particles
• The function h depends on the arrangement of soil and retention curve. Based on CAPILLARY Law. h= Surface tension, D=dencity gravity

Martix Potential

• Matrix Potential Is the potential energy of soil water due to the attractive forces (adhesion and cohesion) between water and the soil matrix.
• Matrix Potentialis expressed as energy per unit volume and equals the product of the height of rise in a capillary tube, the water density, and the gravitational constant.
• Matric head is expressed as energy per weight and is equal to the height of rise in a capillary tube.
• A measure for amount of water being adhered to Cohesion, and Water amount and Matrix are equal, as increase in water is an increase is height matrix, and higher matrix are gravitationally constant.
• Define the gravity potential: The work, which is necessary to rise a unit water from a free water surface (ground water table) to a certain height in a soil pore (capillary) against the force of gravity!
• If this height lies above the Gravity potential, the water acquires a position energy from which a certain amount of work could be produced if it flows downwards (positive sign). If this level lies under the gravity potential, then the gravity potential has a negative sign.
• pF-curve In soils a particular soil water potential ψis related to the soil water content 0. The potential is also expressed as pressure head h. The functional relationship h(0) is typical for a given soil having its particular status of geometrical arrangement of particles (e.g. soil particle distribution).
• The function h(0) is called a soil water retention curve or soil moisture characteristic curve.Because h extends over three or four orders of magnitude, it is frequently plotted in logarithmic scale(pF-curve). It is possible to compute the available water for a plant with the pF-curve.
• Soil Matrix, air water, Soil= 40/80mm, and 50/80
• The hydraulic potential gradient follows direction and amount of water move,
• when soil has high water potential it it is high: describes the direction and magnitude of water movement in soils.
• Negative Gradient: Water moves upward or against gravity, typically due to capillary rise or strong suction forces in dry soils.
• Occurs in unsaturated soils when matric suction dominates or during evaporation.
• Positive Gradient: water moves downward. Common in saturated soils after rainfall or irrigation.
• Gravity potentia: the work, which is necessary to rise a unit water from a free water surface (ground water table) to a -certain height in a soil pore (capillary) against the force of gravity,

Soil Structure

• Structure is a spatial arrangement of particles to complex units, and aggregation pores.
• Soil particles come together to form units "“peds"
• Large scale structure in observing profiles of Soil
• Attraction in soil are affect by the elements of soil

Important Soil Structure Properties

• This helps determine the Amount of water, porosity, run off, affects the microorganisms.
• It helps you estimate if materials were transports over longer distances by looking at roundness, and clay is water transported
• Three dimensional phase is matrix water and air
• Morphologically are are: The view point, point of view
• Soil particle are influences by Gravity,
• Structuraless VS, Angular Soil, Primislike

Formation

• Soil clay are dispersed unattached. So the are many components in the clusers of san, silt, cal.

Capillarity

• Governs movements of water based surface tension and Law
• Smaller capillaries means less space which higher capillirization and pressure. Soil has less capillarity, with a more coarse texture.
• Capillary increase is due to the amount negative pressure the soil has, and fine grain soils have higher water retention.
• At Low moisture content ( around zero) its called "saturation"
• Capillary is governed by the amount of water in unsatured state and it a plot of the PF scale and soil
• Soil Texture/High capilarty happens when the soil is super fine
• Saturation Levels: Is when everything is at 0 and the soil is super wet.
• The mixing of soil material by soil organisms and plants. Deep turbations occur in continental steppe regions (Weinviertel, Pannon) through digging soil animals and earthworms. •Earth worm activity: Earth worms form very stable dejection aggregates, with high content of organic matter, they further form stable channels (coarse pores) •Influence of plants: Plants influence the soil formation especially on top soil, where their root system is highly developed, roots penetrate axially and radially. If the radial growth encounters different resistances on the bottom, the needed space is obtained through elevation of the soil surface.
• Formula for capillary is h = 2ycos0/pgr .

Shearing depends on Content, structure. Specific heat determines charatistic of soil:

Here's an outline incorporating your updates:

Quiz de soil physics (Soil Science Refresher, Lectures on soil, Soil Physics & Chemistry)