Soil Science: Physical Properties, Texture, Structure, Density, and Porosity

Comprehensive vocabulary flashcards covering section 1 (Introduction to Soil) and section 2 (Soil Physical Properties: Colour, Texture, Structure, Density, and Porosity) based on lecture notes.

Physical Soil Properties

Soil characteristics including colour, texture, structure, density, and porosity that help formulate proper soil management practices.

Chemical Soil Properties

Soil properties including cation exchange capacity (CEC), fertility, pH, and salinity.

Biological Soil Properties

Soil properties involving organic matter, respiration, and microorganisms.

Soil Colour

The most easily determined and obvious soil characteristic, determined using a Munsell Colour Chart, which serves as a key indicator of organic matter content, humification degree, drainage, salinity, and weathering.

Munsell Colour System

A standardized color chart system used to evaluate and name soil color based on three dimensions: Hue, Value, and Chroma.

Gleyed Soil

Soil characterized by a uniformly bluish-green or bluish-grey colour due to waterlogged, anaerobic conditions that convert iron to its reduced form ($\text{Fe}^{2+}$).

Mottles

Splotches of rust-coloured material in soil created by oxidation of iron due to a fluctuating water table.

Ae Horizon

An eluvial horizon characterized by a white or light colour that is typically underlain by dark or reddish horizons.

Soil Texture

The relative proportions of sand, silt, and clay in the fine earth fraction ($\le 2.00\,\text{mm}$ in diameter) of a soil.

Sand

Soil mineral particles ranging from $0.05\,\text{mm}$ to $2.00\,\text{mm}$ in diameter, visible to the human eye.

Silt

Soil mineral particles ranging from $0.002\,\text{mm}$ to $0.05\,\text{mm}$ in diameter, visible under a microscope.

Clay

Soil mineral particles smaller than $0.002\,\text{mm}$ in diameter, which possess an extremely large specific surface area and exert the strongest influence on soil physical and chemical reactivity.

Gravel

Mineral particles greater than $2.00\,\text{mm}$ in diameter, which are excluded from the fine earth fraction classification.

Coarse-Textured Soils

Soil textural classes dominated by sand particles, specifically Sand (S), Loamy Sand (LS), and Sandy Loam (SL).

Medium-Textured Soils

Soil textural classes including Loam (L), Silt (Si), Silt Loam (SiL), and Sandy Clay Loam (SCL).

Fine-Textured Soils

Heavy soil textural classes containing high proportions of clay, including Silty Clay (SiC), Clay (C), Heavy Clay (HvC), Sandy Clay (SC), Clay Loam (CL), and Silty Clay Loam (SiCL).

Soil Structure

The arrangement of primary soil particles (sand, silt, clay) into larger secondary compound particles (peds) separated by natural lines of weakness.

Structureless Soil

Soil lacking observable aggregation or natural lines of weakness, occurring either as single grain (loose sand) or massive/amorphous (coherent clods in heavy clay).

Ped

A unit of soil structure, such as an aggregate, crumb, prism, block, or granule, formed by natural processes.

Clod

An artificial mass or lump of soil created by human disturbance, such as tillage, as distinguished from a naturally formed ped.

Structural Grade

A rating of strong, moderate, or weak that expresses the distinctness and clarity of individual peds in a soil profile.

Structural Class

A classification of soil peds based on physical size, categorized into fine, medium, coarse, and very coarse.

Structural Kind

A classification of soil structure based on shape and degree of roundness of peds, such as granular, blocky, platy, prismatic, or columnar.

Granular Structure

Spheroidal peds characterized by rounded vertices, commonly found in topsoil (A horizons) and desirable for agriculture.

Platy Structure

Horizontal, plate-like soil peds that restrict water percolation and root growth, considered an undesirable structural form.

Angular Blocky Structure

Block-like peds bounded by flat surfaces with rectangular faces and sharply angular vertices.

Subangular Blocky Structure

Block-like peds with subrectangular faces and mostly oblique or subrounded vertices.

Prismatic Structure

Vertically oriented column-like peds with well-defined sharp edges and flat tops.

Columnar Structure

Vertically oriented peds with non-sharp vertical edges and flat-topped, round-topped, or irregular tops, frequently found in Solonetzic B horizons.

Flocculation

The aggregation of individual colloidal clay particles into flocs or clusters, facilitated by divalent cations such as $\text{Ca}^{2+}$.

Microaggregate

A small soil aggregate approximately $0.3\,\text{mm}$ in size, held together by root hairs, fungal hyphae, and polysaccharides.

Bulk Density ($\rho_b$)

The dry mass of soil per unit total volume (solids plus pore space), determined after drying at $105^\circ\text{C}$ for 24 hours.

Particle Density ($\rho_s$)

The mass per unit volume of solid soil particles alone, standardly taken as $2.65\,\text{g/cm}^3$ for mineral soils.

Soil Porosity

The percentage of total soil volume occupied by voids (pores) that hold air or water, calculated as $\left(100 - \frac{\text{B.D.}}{\text{P.D.}} \times 100\right)\%$.

Macropores

Large pore spaces with diameters $\Phi > 0.06\,\text{mm}$ responsible for soil aeration, rapid water infiltration, and drainage.

Micropores

Small pore spaces with diameters $\Phi < 0.01\,\text{mm}$ responsible for retaining and storing water in soil.

Interaggregate Pores

Pore spaces existing between individual peds or aggregates in soil.

Intra-Aggregate Pores

Microscopic pore spaces existing inside individual soil peds or aggregates.

Soil

The unconsolidated mineral or organic material on the immediate surface of the Earth that serves as a natural medium for the growth of land plants.

Hans Jenny Soil Equation

The equation $S = f(\text{cl}, \text{o}, \text{r}, \text{p}, \text{t})$, defining soil as a function of climate (cl), organisms (o), relief (r), parent material (p), and time (t).

Soil Profile

A vertical section of the soil extending from the ground surface down to the parent material, displaying horizontal layers known as horizons.

Soil Horizon

A distinct layer parallel to the soil surface possessing unique physical, chemical, and biological properties, designated as O, A, B, or C.

Pedon

A three-dimensional body of soil with lateral dimensions sufficiently large to evaluate horizon properties, shapes, and relationships.

Newdale Clay Loam

The official provincial soil of Manitoba, named after the village of Newdale.