Knowledge base
Soil Health
The properties and processes that determine how soils function — structure, pH, salinity, organic matter, cation exchange, biology, and testing.
29 entries · every entry is sourced and dated
These entries cover soil properties and processes. For individual soil types and textures, see the Soils section.
- Soil physical property
Available Water Capacity
Available water capacity is the portion of soil water that plants can actually use, defined as the water held between field capacity and the permanent wilting point. It sets how much of a soil water store is useful to crops and how often irrigation or rainfall is needed.
- Soil chemical property
Base Saturation
Base saturation is the proportion of a soil cation exchange capacity occupied by base cations such as calcium, magnesium, potassium, and sodium, rather than by acidic cations. It is closely tied to soil pH and indicates the reserve of these nutrient cations.
- Soil physical property
Bulk Density
Bulk density is the dry mass of soil per unit of total volume, including pore space. It is a simple, widely used indicator of compaction and pore space, with higher values signalling denser soil that can restrict roots, water, and air.
- Soil chemical property
Cation Exchange Capacity
Cation exchange capacity (CEC) is a soil’s capacity to hold and exchange positively charged nutrient ions on the surfaces of clay and organic matter. It underpins how well a soil retains and buffers the supply of nutrients such as potassium, calcium, and magnesium.
- Soil physical property
Field Capacity
Field capacity is the amount of water a soil holds after it has been saturated and free drainage has largely stopped. It represents the practical upper limit of water the soil can store for crops and is a key reference point in irrigation scheduling.
- Soil chemical process
Nitrogen Cycle
The nitrogen cycle is the set of biological and chemical transformations that move nitrogen between the atmosphere, soil organic matter, and mineral forms plants take up. Understanding it is central to supplying nitrogen efficiently while limiting losses to water and air.
- Soil physical property
Soil Aeration
Soil aeration is the exchange of oxygen and carbon dioxide between the soil and the atmosphere through pore space, essential for root respiration and aerobic microbial activity, and strongly reduced by compaction or waterlogging.
- Soil management practice
Soil Amendments
Soil amendments are materials added to soil primarily to improve its physical or chemical properties, such as pH, structure, or salinity, rather than materials applied mainly as a concentrated nutrient source in the way conventional fertilizers are.
- Soil biological property
Soil Biology
Soil biology encompasses the full community of organisms living in soil — from bacteria and fungi to earthworms and arthropods — and the processes they drive, including decomposition, nutrient cycling, structure formation, and disease suppression.
- Soil survey and management
Soil Classification
Soil classification groups soils into named units based on measurable, observable properties such as horizons, texture, colour, and chemistry, so that knowledge and management guidance can be transferred between similar soils and mapped across the landscape.
- Soil physical property
Soil Compaction
Soil compaction is the compression of soil particles into a denser mass with less pore space, usually caused by mechanical pressure from machinery or livestock traffic. It restricts root growth, water infiltration, and aeration.
- Soil physical process
Soil Crusting
Soil crusting is the formation of a thin, dense layer at the soil surface, typically caused by raindrop impact breaking down unprotected aggregates, which can impede seedling emergence, reduce water infiltration, and increase runoff.
- Soil physical property
Soil Drainage
Soil drainage describes the rate and pattern at which water moves through and out of the soil profile. It shapes aeration, disease risk, workability, and which crops a soil can reliably support.
- Soil physical process
Soil Erosion
Soil erosion is the detachment and removal of topsoil by water or wind, a process accelerated by cultivation, sparse cover, and slope, that progressively reduces topsoil depth, organic matter, and long-term productivity.
- Soil management concept
Soil Fertility
Soil fertility describes a soil’s capacity to supply essential nutrients in adequate amounts and balance to support plant growth, shaped jointly by chemical nutrient status, physical structure, and biological activity rather than by nutrient content alone.
- Soil biological property
Soil Microorganisms
Soil microorganisms — bacteria, fungi, archaea, and protozoa — are the most numerous and diverse living component of soil. They drive decomposition and nutrient cycling, form key symbioses with plant roots, and help suppress some soil-borne pathogens.
- Soil chemical property
Soil Organic Carbon
Soil organic carbon is the carbon-based fraction of soil organic matter. It is a key soil-health indicator and a central quantity in discussions of soil carbon sequestration and climate mitigation.
- Soil property
Soil Organic Matter
Soil organic matter is the fraction of soil made up of plant and animal residues in various stages of decomposition, living soil organisms, and humus. Though usually a minor share of soil mass, it strongly influences structure, water retention, nutrient cycling, and biological activity.
- Soil chemical property
Soil pH
Soil pH is a measure of hydrogen-ion activity in the soil solution, expressed on a 0–14 scale. It strongly influences which nutrients are chemically available to plants and which minerals may reach toxic concentrations.
- Soil physical property
Soil Porosity
Soil porosity is the fraction of the soil volume made up of pores between and within particles. The amount, size distribution, and connectivity of pores govern how the soil stores and transmits water and air.
- Soil physical property
Soil Profile
A soil profile is the vertical sequence of horizons exposed from the surface down to parent material, recording how a soil formed and controlling how roots, water, air, and nutrients move through it.
- Soil chemical property
Soil Salinity
Soil salinity refers to the concentration of soluble salts in the soil, which can impair plant water uptake and, in severe cases, cause direct ion toxicity. It is a distinct but related concern to sodicity, where excess exchangeable sodium degrades soil structure.
- Soil chemical property
Soil Sodicity
Sodicity is the condition in which a high proportion of a soil exchange sites are occupied by sodium. Excess exchangeable sodium disperses clay, destroying structure and causing poor infiltration, waterlogging, crusting, and hard-setting that impair root growth.
- Soil physical property
Soil Structure
Soil structure is the arrangement of sand, silt, clay, and organic matter into aggregates and the pore spaces between them. It governs how water infiltrates, how easily roots grow, and how well a soil resists erosion and compaction.
- Soil physical property
Soil Temperature
Soil temperature governs seed germination, root growth, microbial activity, and nutrient release rates, varying with air temperature, solar radiation, soil moisture, colour, and cover, and differing meaningfully between the surface and deeper layers.
- Soil management practice
Soil Testing
Soil testing is the systematic sampling and laboratory or field analysis of soil properties — such as pH, nutrient levels, organic matter, and salinity — used to guide fertilizer, lime, and other management decisions.
- Soil physical property
Soil Water Retention
Soil water retention describes how much water a soil holds against gravity, and how much of that water is available for plant roots to extract. It depends on pore-size distribution, texture, and organic matter, and underpins irrigation and drought planning.
- Soil physical property
Water Infiltration
Water infiltration is the process by which water at the surface enters the soil. The infiltration rate determines how much rainfall or irrigation soaks in versus running off, and depends strongly on structure, texture, surface condition, and how wet the soil already is.
- Soil physical condition
Waterlogging
Waterlogging is the saturation of soil pore space with water for a period long enough to displace air and restrict root and microbial oxygen supply, arising from poor drainage, heavy rainfall, over-irrigation, or a shallow water table.