Glossary

There are several technical terms that are described in the digital soil map, the soil analysis and the Tea Bag Index. A glossary of some common terms that are used can be found here. For further details please refer to the resources page or feel free to contact us.

Organic

The term “organic” refers to something that is composed of carbon-based compounds and is usually derived from living things.

Microbes

Microbes or microorganisms describe tiny living organisms that cannot be viewed with the naked eye. Microbes in soil can include bacteria, fungi, viruses, protozoa and nematodes.

Microbial community

A microbial community refers to a group of microorganisms that are living in the same environment. These microbes interact with each other and the population can vary based on a range of environmental and internal factors.

Decomposition rate (k)

The decomposition rate is a measure of turnover of carbon in plant material and describes the initial breakdown which is important to release organic nutrients and carbon. A “healthy” soil is predicted to have a lower k indicating that the microbes decomposing the organic materials are more efficient in using the carbon, enabling greater carbon storage.

Factors that increase the decomposition rate include temperature and moisture.

Stabilisation factor (S)

Stabilisation factor describes a measure for stabilisation of organic carbon in plant material. A high stabilisation factor indicates a greater carbon storage capacity. Like the decomposition rate, the stabilisation factor is influenced by temperature and moisture. S values decrease as temperature and moisture increase.

Tea Bag Index (TBI)

The Tea Bag Index is a measure of decomposition and stabilisation of organic matter in soil. The index consists of two parameters – decomposition rate and stabilisation factor.

pH

Soil pH is an estimation of soil acidity or alkalinity. It varies along a scale between 0 and 14 with neutral soil being at pH 7. In nature, soil pH can range from pH 3 to 10. Soil pH affects the fertility of soil as it affects the microbial activity with most of the activity estimated to occur at pH levels between 5 and 7. Soil pH also affects the availability of nutrients, with nutrients like phosphorus becoming less available at a low pH.

Inorganic carbon

Inorganic carbon refers to inorganic compounds that contain carbon atoms that are not directly bonded to hydrogen atoms. In the soil, inorganic carbon is found mostly in the form of carbonates.

Organic carbon

Organic carbon in the soil can be derived from organic materials such as plant materials and microbial biomass (living and dead).

Total carbon

Total carbon describes all the carbon in the soil including organic and inorganic forms. Soil carbon can tell us about the fertility of the soil – particularly organic carbon. Total carbon can vary based on a number of factors including soil texture and the extent of human interaction with a site.

Electrical Conductivity

Electrical Conductivity (EC) is a measurement of the amount of salt in the soil, this is also known as soil salinity. It is an important indicator of soil health as it can affect nutrient availability, microbial activity and soil-water balance. As the EC increases, the activity of the microorganisms decreases.

Soil texture

Soil texture describes a physical property of the soil which is dependent on the percentage of different particle sizes in the soil. These particles can be arranged by size. Clay is the smallest (<0.002mm) followed by silt (0.002mm-0.05mm) and sand (0.05mm-2mm). Different soil textures affect the way soil can be worked, its aeration and the movement of water through it. For example, sandy soils are well aerated but do not hold much water and are low in nutrients. In contrast, clayey soils are better at holding water and supplying nutrients.

Soil Slaking Index

Soil slaking is a measure of soil aggregate stability. Soil aggregates describe a group of soil particles that bind together. These aggregates are important because they create pore space that allows air and water to circulate allowing plant roots to grow.

Therefore, soil aggregate stability refers to the ability of the soil aggregates to resist external forces, mainly from water. Soil aggregate stability can be affected by the amount and type of soil organic matter and the type and size of the soil microbial community.