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A
- Acid Sulphate Soils
- Soils containing iron sulfides that, when exposed to air (eg through drainage), produce sulfuric acid, which can severely degrade soil and water quality.
- Aggregate Stability
- The ability of soil aggregates (clumps) to resist disintegration when subjected to forces such as water or tillage, which helps prevent erosion and maintain soil structure.
- Alfisols
- A soil order characterised by clay accumulation in the subsoil and moderate fertility, commonly found in temperate regions.
- Alluvial Soil
- Soil deposited by rivers or floods, often found in valleys and known for being fertile and ideal for agriculture.
- Alluvium
- Soil or sediment deposited by rivers or floodwaters, typically found in river valleys, which is often fertile due to its high nutrient content.
- Anaerobic Soil
- Soil that lacks sufficient oxygen, often due to waterlogging, which can lead to reduced microbial activity and plant root respiration.
- Andisols
- Soils formed from volcanic ash and characterised by high water-holding capacity and fertility.
- Anthropogenic Soil
- Soil that has been modified or created by human activities, such as through agriculture, urbanisation, or industry.
- Aridisols
- Soils found in arid regions, characterised by low organic matter and often containing salts.
B
- Bulk Density
- The mass of dry soil per unit volume, including the air space, which affects root penetration, water movement, and soil compaction.
C
- Capillary Action
- The ability of water to move through the tiny spaces in soil (or other porous material) against gravity due to surface tension and cohesion between water molecules.
- Cation Exchange Capacity (CEC)
- A measure of the soil’s ability to hold and exchange positively charged ions (cations), such as calcium, magnesium, and potassium, which are vital for plant nutrition.
- Chelation
- The process by which organic molecules bind to metal ions (like iron or manganese), making them more available for plant uptake or helping prevent nutrient toxicity.
- Claypan
- A dense, compact layer of clay in the soil profile that restricts water infiltration and root growth, often found in subsoils.
- Colloidal Clay
- Extremely fine particles in the soil that remain suspended in water and contribute to the soil’s ability to retain nutrients and water.
- Compaction
- The process by which soil particles are pressed together, reducing pore space and limiting air and water movement, which can inhibit root growth and decrease soil health.
D
- Denitrification
- A microbial process that converts nitrates in the soil to nitrogen gas, which is lost to the atmosphere, reducing soil nitrogen content.
- Desertification
- The process by which fertile land becomes desert-like, typically due to drought, deforestation, or inappropriate agricultural practices, resulting in loss of productivity.
E
- Eluviation
- The removal of soil materials, such as clay, iron, or organic compounds, from an upper horizon by water movement.
- Entisols
- Soils with little to no profile development, often found in areas with recent or ongoing deposition.
- Erosion
- The process by which soil is removed from the land surface by wind, water, or human activity, leading to loss of topsoil and reduced agricultural productivity.
- Evaporation
- The process of water turning from liquid to vapour and escaping from the soil surface into the atmosphere.
- Evapotranspiration
- The combined process of water evaporation from the soil surface and transpiration from plants, which affects soil moisture levels and plant water use.
F
- Field Capacity
- The amount of soil moisture or water content held in the soil after excess water has drained and the rate of downward movement has decreased. It is an indication of the water quantity available for plants and is important for determining irrigation needs. Also called Soil Water Holding Capacity.
- Flocculation
- The process by which individual soil particles aggregate into clumps or clusters due to the attraction of opposite charges, important for improving soil structure and water infiltration.
G
- Gleying
- A soil condition caused by poor drainage and water saturation, resulting in a characteristic bluish-grey colour due to anaerobic conditions and the reduction of iron compounds.
- Gleysols
- Wet soils with poor drainage characterised by greyish colours due to prolonged water saturation.
- Green Manure
- Crops grown specifically to be turned into the soil to improve soil fertility and organic matter content, often used as part of sustainable farming practices.
- Gypsum
- A soil amendment used to improve soil structure by reducing compaction, increasing aeration, and alleviating sodicity (high sodium levels).
H
- Hardpan
- A dense, compacted layer of soil, often found below the surface, that restricts water movement and root growth.
- Histosols
- Organic soils formed in waterlogged conditions, composed mostly of peat and muck.
- Horizon
- A distinct layer of soil, each with different characteristics such as colour, texture, structure, and composition. Major horizons include O (organic), A (topsoil), B (subsoil), and C (parent material).
- Humus
- The stable decomposed plant and animal organic matter in soil that improves its structure, water retention, and nutrient availability, and plays a key role in soil fertility.
I
- Illuviation
- The accumulation of soil particles, organic matter, and minerals in a particular horizon (usually the subsoil) as a result of their downward movement from upper layers.
- Inceptisols
- Soils with minimal horizon development, often found in transitional areas between Entisols and more developed soils.
- Infiltration
- The process by which water on the ground surface enters the soil. It influences the rate at which water is absorbed and affects erosion and runoff.
- Infiltration Rate
- The speed at which water enters and moves through the soil profile, which can vary based on soil texture, structure, and moisture content.
J
K
L
- Laterisation
- A soil-forming process in tropical regions where intense weathering causes the leaching of silica and accumulation of iron and aluminum oxides, often resulting in nutrient-poor soils.
- Leaching
- The process by which water removes dissolved nutrients or chemicals from the soil, carrying them deeper into the soil profile or out of reach of plant roots. Common in places with high rainfall and potentially causes nutrient loss and groundwater pollution. Also called Nutrient Leaching.
- Lime Requirement
- The amount of lime needed to raise the soil pH to a desired level for optimal plant growth, commonly used to treat acidic soils.
- Loam
- A soil type that contains a balanced mix of sand, silt, and clay, considered ideal for most agricultural crops due to its ability to retain moisture and nutrients while providing good drainage.
M
- Macronutrients
- Nutrients required by plants in larger quantities, including nitrogen (N), phosphorus (P), and potassium (K), which are key for growth, reproduction, and disease resistance.
- Macropores and Micropores
- Macropores are larger soil pores that allow the movement of water and air, while micropores are smaller and help retain water within the soil.
- Matric Potential
- The potential energy of water in soil due to capillary forces and adhesion to soil particles, affecting how water is retained in the soil.
- Micronutrient Deficiency
- A lack of essential trace elements such as zinc, copper, iron, or boron in the soil, which can lead to poor plant health and reduced crop yields.
- Micronutrients
- Essential nutrients needed by plants in small amounts, such as iron (Fe), zinc (Zn), manganese (Mn), copper (Cu), and boron (B), which play vital roles in plant health and growth.
- Mollisols
- Fertile soils typically found in grassland ecosystems, known for their high organic matter content and excellent agricultural potential.
- Mulching
- The practice of covering the soil surface with organic or inorganic materials to reduce evaporation, prevent erosion, suppress weeds, and maintain soil temperature.
- Mycorrhizae
- Symbiotic associations between fungi and plant roots that enhance nutrient uptake, especially phosphorus, in plants.
N
- Nutrient Cycling
- The movement and transformation of nutrients like nitrogen, phosphorus, and potassium through the soil, plants, and organisms, critical for maintaining soil fertility.
O
- Oxisols
- A soil order characterised by highly weathered, nutrient-poor soils found in tropical and subtropical regions, rich in iron and aluminum oxides.
P
- Parent Material
- The underlying geological material (rock or sediment) from which soil is formed, influencing its properties like mineral content, composition, fertility, and texture.
- Peat Soil
- Soil composed primarily of organic material (partially decomposed plant matter) found in waterlogged conditions, often used in horticulture.
- Pedogenesis
- The process of soil formation, influenced by factors such as parent material, climate, organisms, topography, and time.
- Pedon
- The smallest unit or volume of soil that represents all of the characteristics of a particular soil type, typically used in soil classification and mapping.
- Peds
- Naturally occurring clumps of soil that form through the processes of wetting, drying, freezing, thawing, and the action of roots and organisms.
- Percolation
- The downward movement of water through the soil profile, which is critical for groundwater recharge and soil water management.
- Permanent Wilting Point
- The moisture level at which plants can no longer extract water from the soil, leading to wilting and eventual death if conditions persist. Also called wilting point.
- Permeability
- The ability of soil to transmit water and air, determined by the size of soil pores. Sandy soils tend to have high permeability while clay soils have low permeability.
- Phytoremediation
- The use of plants to remove, degrade, or contain harmful contaminants in soil or water, a practice used in soil remediation.
- Plow Pan
- A compacted soil layer that forms just below the depth of tillage, often created by repeated ploughing, which can restrict root growth and water movement. Also known as hard pans.
- Podzolisation
- A soil-forming process, typically in colder climates, that leads to the leaching of iron, aluminum, and organic matter from the upper layers to form distinct horizons.
- Podzols
- Acidic soils with a leached, bleached horizon above a dense, iron-rich subsoil, common in cool, humid regions.
- Pore Water Pressure
- The pressure exerted by water within the soil pores, influencing soil stability and plant water availability.
- Porosity
- The volume of open spaces (pores) in soil, affecting its ability to retain water and air.
Q
R
- Rhizosphere
- The narrow region of soil directly influenced by root secretions and associated soil microorganisms. This area is critical for nutrient uptake and soil health.
S
- Saline Soil
- Soil that contains high concentrations of soluble salts, which can inhibit plant growth and reduce soil fertility. Salinisation often occurs in arid and semi-arid regions.
- Salinisation
- The accumulation of soluble salts in soil, often as a result of improper irrigation practices, which can reduce soil fertility and crop yields.
- Salinity
- The concentration of soluble salts in the soil, which can affect plant growth, often resulting from poor irrigation practices or natural soil conditions.
- Saturation
- The condition in which soil pores are completely filled with water, preventing air from occupying the pore spaces, often leading to anaerobic conditions.
- Saturation Point
- The condition where all the pores in the soil are filled with water, with no air remaining, often occurring after heavy rainfall or irrigation.
- Sequestration
- The process of capturing and storing carbon in soils or vegetation, which is essential for mitigating climate change.
- Siltation
- The accumulation of silt (fine soil particles) in rivers, lakes, and other water bodies, often caused by soil erosion, which can reduce water quality and aquatic life.
- Sodic Soil
- A type of soil with a high concentration of sodium ions, leading to poor soil structure, reduced infiltration, and drainage problems.
- Soil Acidification
- The process by which soils become more acidic over time due to factors like acid rain, excessive fertiliser use, or natural leaching.
- Soil Acidity
- The level of hydrogen ion concentration in soil, which influences nutrient availability and can result in toxic conditions for plants if extreme.
- Soil Aeration
- The process by which air in soil is exchanged with air from the atmosphere, essential for root respiration and microbial activity.
- Soil Aggregate
- A cluster of soil particles that bind together more strongly than to surrounding particles, creating a stable structure that improves water infiltration and reduces erosion.
- Soil Aggregate Stability
- The ability of soil aggregates (clusters of soil particles) to resist disintegration when exposed to external forces like water. Important for erosion prevention and root health.
- Soil Aggregation
- The clumping together of soil particles into larger masses, which improves soil structure and enhances water retention and root penetration.
- Soil Amendment
- Materials added to soil to improve its physical or chemical properties, such as compost, lime, or gypsum, used to enhance fertility, structure, or pH balance.
- Soil Biogeochemistry
- The study of chemical, physical, biological, and geological processes that influence the composition and function of soils.
- Soil Bioremediation
- The use of living organisms such as plants or microbes to clean contaminated soils, particularly in areas affected by heavy metals, pesticides, or oil spills.
- Soil Biota
- The community of organisms living in the soil, including bacteria, fungi, earthworms, and insects, which play essential roles in nutrient cycling, soil structure, organic matter decomposition, and soil health.
- Soil Buffering Capacity
- The soil’s ability to resist changes in pH or nutrient levels, important for maintaining soil health and fertility.
- Soil Bulk Density
- The mass of soil per unit volume, which indicates soil compaction and porosity.
- Soil Capillarity
- The ability of soil to draw water upward from a wet source due to the soil’s pore structure.
- Soil Carbon Dynamics
- The processes governing the storage, release, and transformation of carbon in soil, which affects soil fertility and climate change.
- Soil Colloids
- Extremely small particles in the soil, primarily composed of clay and organic matter, which have a large surface area relative to their size and play a key role in nutrient and water retention.
- Soil Colour
- The colour of soil, which can provide clues about soil composition and drainage. Colour is often described using the Munsell Soil Colour Chart.
- Soil Compaction
- The increase in soil density caused by pressure from machinery or heavy foot traffic, which can impede root growth and water infiltration.
- Soil Compaction Layer
- A dense layer within the soil profile that restricts root growth and water movement, often caused by heavy machinery. Also called plough pan.
- Soil Conservation
- Practices aimed at protecting soil from erosion and depletion, often involving contour ploughing, crop rotation, terracing, and reforestation.
- Soil Contamination
- The presence of harmful substances in soil, which can affect plant growth and human health. Examples of harmful substances are heavy metals like Mercury and Lead.
- Soil Crusting
- The formation of a hard surface layer often after heavy rains or irrigation, which can hinder seedling emergence and water infiltration.
- Soil Degradation
- The decline in soil quality and productivity due to factors like erosion, pollution, compaction, salinisation, nutrient depletion or overuse.
- Soil Drainage
- The ability of soil to allow water to pass through it, which influences plant growth and susceptibility to waterlogging.
- Soil Drainage Class
- A classification based on how well soil drains water, ranging from well-drained to poorly drained.
- Soil Erosion Control Measures
- Practices and techniques implemented to reduce soil erosion, such as planting cover crops and building terraces.
- Soil Family
- A category within a soil great group that describes soil texture, mineral composition, and other characteristics that affect soil behaviour.
- Soil Fertility
- The ability of soil to provide essential nutrients to plants in adequate amounts for growth, often influenced by organic matter, nutrient content, and pH.
- Soil Fertility Index
- A numerical or qualitative measure of soil fertility based on various factors like nutrient content and organic matter.
- Soil Fertility Restoration
- Methods used to restore soil fertility, including the application of organic amendments and balanced fertilisation.
- Soil Great Group
- A classification within a soil suborder that specifies more detailed properties and soil formation conditions.
- Soil Health Index
- A composite measure that evaluates soil health based on various indicators like organic matter, microbial activity, and nutrient availability.
- Soil Horizons
- Distinct layers of soil that differ in colour, texture, structure, and chemical composition, typically classified as O (organic), A (topsoil), B (subsoil), and C (parent material).
- Soil Macronutrients
- Essential nutrients required by plants in large quantities, including nitrogen (N), phosphorus (P), and potassium (K), often referred to as NPK.
- Soil Management Practices
- Techniques and strategies used to maintain or improve soil health, such as crop rotation, cover cropping, and reduced tillage.
- Soil Mapping
- The process of classifying and documenting different types of soil in an area based on factors like texture, structure, and composition to aid land-use planning.
- Soil Microbial Activity
- The level of activity of soil microorganisms, which influences nutrient cycling and soil health.
- Soil Microbial Biomass
- The total mass of microorganisms in the soil, which plays a key role in nutrient cycling and soil health.
- Soil Microbial Diversity Index
- A measure of the variety and abundance of microbial species in the soil, important for ecosystem functions.
- Soil Microflora
- The community of microscopic organisms, including bacteria, fungi, and algae, that live in the soil and contribute to nutrient cycling and organic matter decomposition.
- Soil Microorganisms
- Bacteria, fungi, protozoa, and other microscopic organisms that live in soil, playing vital roles in decomposing organic matter and nutrient cycling.
- Soil Mineralogy
- The study of the minerals in the soil, which influence soil properties such as fertility, structure, and water retention.
- Soil Moisture
- The amount of water present in the soil, which can be in three states: hygroscopic (bound tightly to particles), capillary (held between soil particles), or gravitational (free-moving water). The water contained in the soil, important for plant growth. Soil moisture levels are influenced by precipitation, evaporation, and soil properties.
- Soil Moisture Deficit Index
- A quantitative measure of the gap between the soil’s water holding capacity and the actual moisture available for plants.
- Soil Moisture Profile
- A representation of soil moisture content at different depths within the soil profile.
- Soil Moisture Regime
- The pattern of soil moisture availability throughout the year, affecting soil classification and land use. Examples include arid, humid, and subhumid.
- Soil Moisture Tension
- The force required for plants to extract water from soil, influencing irrigation practices and plant water availability.
- Soil Moisture Variability
- The differences in soil moisture levels across a field or region, affecting crop growth and water management.
- Soil Nutrient Cycle
- The natural process by which soil nutrients are recycled through biological and chemical processes.
- Soil Nutrient Deficiency
- A lack of essential nutrients in soil, leading to poor plant growth and reduced crop yields.
- Soil Order
- The broadest classification in soil taxonomy, representing major soil types based on their formation and properties. Examples include Mollisols, Oxisols, and Alfisols.
- Soil Organic Carbon (SOC)
- The carbon component of organic compounds in the soil, which is essential for soil fertility, structure, and moisture retention.
- Soil Organic Carbon Content
- The amount of carbon contained in soil organic matter, important for soil fertility and climate change mitigation.
- Soil Organic Matter (SOM)
- The organic fraction of soil, including plant and animal residues at various stages of decomposition, cells and tissues of soil organisms, and substances synthesised by the soil population. SOM helps maintain soil structure and fertility.
- Soil Organic Matter Decomposition Rate
- The speed at which organic matter breaks down in the soil, influencing nutrient availability and soil health.
- Soil Organic Matter Stabilisation
- The process by which organic matter is preserved and integrated into soil over time, affecting soil fertility and structure.
- Soil Permeability
- The ability of soil to transmit water and air through its pores, with sandy soils being highly permeable and clay soils having low permeability.
- Soil Plasticity
- The capacity of soil to be moulded or deformed under pressure, typically associated with clay-rich soils.
- Soil Porosity
- The measure of the volume of pores or spaces within soil, which affects its ability to hold water and air necessary for plant roots and microorganisms.
- Soil Profile
- A vertical section of soil from the ground surface downwards to where the soil meets the underlying rock, showing different layers called horizons. It provides insight into soil formation, composition, and history.
- Soil Profile Development
- The formation of distinct layers in the soil (horizons) due to long-term physical, chemical, and biological processes.
- Soil Respiration
- The process of microbial and plant root activity in the soil, releasing carbon dioxide (CO₂), which is an indicator of biological activity and organic matter decomposition.
- Soil Sampling
- The process of collecting soil specimens for analysis to determine its properties such as nutrient content, pH, and organic matter.
- Soil Series
- The most specific level of soil classification, representing soils with similar physical and chemical properties and formation processes.
- Soil Structure
- The arrangement of soil particles into aggregates or clumps, which affects water movement, root penetration, and air flow within the soil.
- Soil Structure Assessment
- The evaluation of soil arrangement into aggregates and layers, affecting aeration, drainage, and root penetration.
- Soil Structure Dynamics
- The changes in soil structure over time due to natural processes or human activities, influencing soil health.
- Soil Suborder
- A subdivision within a soil order that provides more detail about soil characteristics and formation processes.
- Soil Taxonomy
- A system for classifying soils based on their physical and chemical properties, used globally to understand soil management needs.
- Soil Texture
- Refers to the relative proportions of sand, silt, and clay particles in a soil sample, which affects water retention, drainage, and root growth.
- Soil Texture Triangle
- A graphical representation used to classify soil texture based on the relative proportions of sand, silt, and clay.
- Soil Tillage
- The mechanical manipulation of soil to prepare it for planting, often influencing soil structure, aeration, and moisture retention.
- Soil Tilth
- The condition of soil regarding its suitability for planting, influenced by factors like moisture, aeration, and structure, which determine ease of cultivation and root growth.
- Soil Water Availability
- The amount of water in the soil that is accessible to plants for growth.
- Soil Water Retention Curve
- A graph showing the relationship between the water content of soil and the matric potential (suction) that holds water in the soil, helping to assess water availability to plants.
- Soil pH
- A measure of the acidity or alkalinity of soil, which affects nutrient availability and microbial activity. Soils can be acidic (pH < 7), neutral (pH 7), or alkaline (pH > 7). Most crops grow best in soils with a pH between 6.0 and 7.5.
T
- Transpiration
- The process by which water is absorbed by plant roots, moves through the plant, and is released as water vapour from the plant’s leaves.
U
V
- Vertisols
- A soil order characterised by high clay content, which shrinks and swells significantly with moisture changes, leading to cracking and challenging agricultural management.
W
- Waterlogging
- A condition where the soil is saturated with water, leading to a lack of oxygen for plant roots and negatively impacting plant growth.
X
Y
Z
