ISO/TS 18721:2026

Technical
Specification
ISO/TS 18721
First edition
Ecological soil functions —
2026-02
Characteristics, indicators and
methods
Fonctions écologiques du sol — Caractéristiques, indicateurs et
méthodes
Reference number
© ISO 2026
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Indicators of ecological soil functions . 1
4.1 General .1
4.2 Methods for measuring general soil characteristics and indicators, sampling and soil
preparation .3
4.3 Methods for measuring specific soil characteristics and indicators .6
Bibliography .15

iii
Foreword
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iv
Introduction
In recent years, the concern for soil sustainability has considerably increased. Many countries are setting
targets to reduce soil artificialisation and reinforce ecosystem rehabilitation and biodiversity conservation.
In Europe, the recent proposal for a directive on soil monitoring and resilience will set foundations for
member states to consider.
[86][97][98]
In this context, concepts of soil health and soil quality are being discussed and ecological soil
[87][90]
functions are being proposed . However, although several promising propositions have been made to
define lists of indicators of soil health and soil quality in different contexts (e.g. Reference [94]), there is
presently no consensus.
Based on the definitions of soil health and soil quality presented in ISO/TS 18718, this document aims to
provide an overview of the existing indicators and characteristics that are linked to soil functions and the
available methods to assess them whether they are internationally standardized, nationally standardized or
exist as peer-reviewed work.
Figure 1 — Links between ISO/TS 18718 and this document (ISO/TS 18721) on the soil functions
and related ecosystem services

v
Technical Specification ISO/TS 18721:2026(en)
Ecological soil functions — Characteristics, indicators and
methods
1 Scope
This document provides a generic description of the methods available for measuring soil characteristics and
indicators of core ecological soil functions. No distinction of context is made, i.e. no differentiation of land
use and management (e.g agricultural, forest, urban, natural or contaminated lands). For each ecological soil
function, the document specifically lists biotic and abiotic characteristics that can be measured. It focuses
on characteristics and indicators that are either available as ISO documents or published in peer-reviewed
papers.
This document applies to ecological soil functions and is not applied to soil functions such as geotechnical
functions (foundation support for buildings, tunnels, etc.) or geothermal functions. Indeed, ecosystem
services do not address soils without a topsoil, or with a covered topsoil (buildings, infrastructure,
greenhouse farming, solar panel parks).
Methods and indicators for ecological soil functions can help in the assessment of soil-related ecosystem
services but the overall assessment of ecosystem services is not covered in this document.
Other methods based on proxy indicators (e.g. soil occupation, hydrography parameters) can also be used
for land planning at large scale. These indicators are not included in this document.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 11074, Soil quality — Vocabulary
ISO/TS 18718, Soil functions and related ecosystem services — Definitions, descriptions and conceptual
framework
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 11074 and ISO/TS 18718 apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Indicators of ecological soil functions
4.1 General
Soil functions are one or a combination of soil processes that drive the dynamics of the ecosystem structure
or composition (see Table 1). Each function can be divided into different sub-functions (see Table 1). Soil
processes are the interactions among physical, chemical and biological soil components underlying soil
functions.
Table 1 details soil functions and illustrates how these functions and sub-functions are influenced and
connected to either biological or physico-chemical processes or both. Further descriptions of each function
and sub-function are provided in ISO/TS 18718.
Table 1 — Soil functions and underling processes
Biological processes Physico-chemical processes
Soil function Sub-function
(examples) (examples)
Water retention by soil texture
Water retention Bioturbation, aggregation, fragmentation and organic matter (adsorption,
Water regulation,
retention)
retention and
release
Infiltration and Macropore formation, root foraging, bi-
Diffusion
percolation oturbation, aggregation
Biotic fragmentation, microbial grazing, Fragmentation linked to climate
Decomposition
microbial respiration, methanogenesis conditions
Organic matter
storage, Resource Aggregation, bioturbation, exudation, food
Leaching, adsorption
transformation reallocation web assimilation
and recycling
Biochemical Methanotrophy, nitrification, denitrifica-
Leaching, adsorption
transformation tion
Fragmentation of rocks
Fragmentation of litter, mineralization,
Nutrient (e.g. frost/thaw), physical and
nitrogen transformations, sulfur transfor-
transformation chemical weathering of rocks,
mation,biochemical weathering
precipitation, dissolution
Adsorption/desorption, atmos-
Nutrient cycling
Nutrient pheric deposition, precipitation/
Aggregation, bioturbation
reallocation dissolution, erosion/run-off,
leaching, N volatilization
Nutrient Food web assimilation, mycorrhizal acqui-
assimilation sition, nitrogen fixation, root uptake
Biosorption, bioassimilation, bioaccumu-
Retention Sorption, complexation, …
lation
Contaminant
retention, Photodegradation, oxido-reduc-
Transformation Biotransformation
transformation tion
and degradation
Photodegradation, oxido-reduc-
Degradation Biodegradation, mineralization
tion
Organismal activity (e.g. respiration, ni-
Emission trous oxide and methane Diffusion, exchange
Gas exchanges
production)
with atmosphere
Organismal activity (e.g. nitrogen fixation,
Captation Diffusion, exchange
methane consumption)
Abiotic conditions (e.g. moisture
Biotic foraging (e.g. plants,
and temperature, pH, organic
earthworms)
matter, porosity, …)
Abundance, diversity and activity of soil
biota
Habitat
Interactions/networks as antibiosis, com-
provision
petition and invasive
alien species, predation,
parasitism, microbial grazing
Resistance and defence, plant
metabolism enhancement
Abiotic aggregation (texture,
Inherent soil
Aggregation linked to biological activity stone and OM content, pH), ero-
stability
Physical
sion (water and wind), lixiviation
stability
Stability evolu-
Macropore formation, bioturbation, roots Freeze-thaw alternation
tion
Soil is a very complex ecosystem of which the functioning and thus ecosystem service provision relies on
interactions between the abiotic and biotic components. This document proposes to separate general soil
characteristics and indicators, which need to be measured as they influence soil processes, from specific
ones, which directly reflect soil processes. This organisation is presented in Figure 2.
Figure 2 — Differentiation between general soil characteristics and specific soil characteristics
Many methods have been developed to measure these characteristics and indicators. Among these
methods, some are normalized and applicable worldwide while others are based on normalized methods
but applicable only at a sub-worldwide scale. Finally, emerging approaches are available and used in the
scientific literature but are not yet normalized or do not yet dispose of an interpretation referential. These
two levels of standardization are considered here and are so after named:
— Level 1: Standardized methods applicable worldwide (ISO);
— Level 2: Standardized methods applicable or standardized at a sub-worldwide scale (proxies or
modelling) or emerging methods not yet standardized or without an interpretation reference (scientific
literature).
4.2 Methods for measuring general soil characteristics and indicators, sampling and soil
preparation
General soil characteristics reflect the physico-chemical composition of soils and give a first assessment
of a sample. Some are required to interpret specific soil characteristics and indicators. General soil
characteristics and indicators include texture, soil depth, soil density, pH (acidity), cation exchange capacity
(CEC), cations (Ca, K, Mg, Na), total carbon, nitrogen and phosphorus, the amount of coarse elements, calcium
carbonate (CaCO ,), and the presence of contaminants. The assessment of all or part of these characteristics
is a pre-requisite for assessing soil processes and should be carried out.
Moreover, assessing general soil characteristics or specific characteristics requires representative sampling
[1-7]
and soil preparation before analysis (see the ISO 18400 series ).
The existing methods for measuring general soil characteristics are presented in Table 2 according to their
level of standardization.
Table 2 — Existing methods to measure general soil characteristics and indicators
General soil
characteristics and Level 1 Level 2
indicators
a) Soil texture (particle ISO 11277, Soil quality — Determination of particle size distribu- Adaptation of ISO 13320, Particle size analysis — Laser diffraction
[9]
size distribution) tion in mineral soil material — Method by sieving and sedimenta- methods for the measurement of soil texture (REFS)
[8]
tion
[10] [96]
b) Bulk density ISO 11272, Soil quality — Determination of dry bulk density Pedotransfer functions (Reference )
NF X 31-501, Soil quality - Physical methods - Measuring of the bulk
[11]
density of an undisturbed soil sample - Cylinder method
ISO 10390, Soil, treated biowaste and sludge — Determination of
c) pH (acidity)
[12]
pH
d) Cation exchange ISO 23470, Soil quality — Determination of effective cation ex-
capacity (CEC) change capacity (CEC) and exchangeable cations using a hexammi-
[13]
necobalt(III)chloride solution
ISO 11260, Soil quality — Determination of effective cation ex-
change capacity and base saturation level using barium chloride
[14]
solution
[93]
e) Soil structure and ISO 10930, Soil quality — Measurement of the stability of soil ag- Spade-test: Visual evaluation of soil structure (Reference )
[15]
[105]
stability gregates subjected to the action of water
Mini 3D soil profile (Tomis et al. 2019)
[92]
Slake test (Reference )
[95]
Aggregate stability (Reference )
[101]
Visual Soil Assessment (Reference )
[85]
Profil cultural (Reference )
f) Exchangeable cations ISO 23470, Soil quality — Determination of effective cation ex-
+ + + +
(Ca , K , Mg , Na ) change capacity (CEC) and exchangeable cations using a hexammi-
[13]
necobalt(III)chloride solution
ISO 11260, Soil quality — Determination of effective cation ex-
change capacity and base saturation level using barium chloride
[14]
solution
g) Organic carbon ISO 10694, Soil quality — Determination of organic and total car- Rock-Eval pyrolysis combined with PartySOC model (Reference [89])
[16]
(organic matter) bon after dry combustion (elementary analysis) for assessing stable and active fractions of total organic carbon in
temperate ecosystems
ISO 17184, Soil quality - Determination of carbon and nitrogen by
[17]
near-infrared spectrometry (NIRS) NF X 31-516, Soil Quality - Granulo-densimetric fractionation of soil
[18]
organic particulate material in water
h) Carbonates ISO 10693, Soil quality — Determination of carbonate content —
[19]
Volumetric method
Table 2 (continued)
General soil
characteristics and Level 1 Level 2
indicators
[100]
i) Contaminants ISO 54321, Soil, treated biowaste, sludge and waste — Digestion of Pesticide Multi-residue method (Reference )
[20]
(depending on the aqua regia soluble fractions of elements
context)
ISO 11504, Soil quality — Assessment of impact from soil contami-
[21]
nated with petroleum hydrocarbons
ISO 21268-1, Soil quality — Leaching procedures for subsequent
chemical and ecotoxicological testing of soil and soil-like materi-
als — Part 1: Batch test using a liquid to solid ratio of 2 l/kg dry
[22]
matter
ISO 21268-2, Soil quality — Leaching procedures for subsequent
chemical and ecotoxicological testing of soil and soil-like materi-
als — Part 2: Batch test using a liquid to solid ratio of 10 l/kg dry
[23]
matter
ISO 21268-3, Soil quality — Leaching procedures for subsequent
chemical and ecotoxicological testing of soil and soil-like materi-
[24]
als — Part 3: Up-flow percolation test
ISO 21268-4, Soil quality — Leaching procedures for subsequent
chemical and ecotoxicological testing of soil and soil-like materi-
als — Part 4: Influence of pH on leaching with initial acid/base
[25]
addition
ISO 17402, Soil quality — Requirements and guidance for the selec-
tion and application of methods for the assessment of bioavailability
[26]
of contaminants in soil and soil materials
ISO 16198, Soil quality — Plant-based test to assess the environ-
[27]
mental bioavailability of trace elements to plants
j) Dry matter ISO 11465, Sludge and solid environmental matrices — Determina-
tion of dry residue or water content and calculation of the dry matter
[28]
fraction on a mass basis
Required for the physico-chemical analysis, it allows calculation of
element concentration in the dry matter
k) Total N ISO 13878, Soil quality — Determination of total nitrogen content
[29]
by dry combustion (“elemental analysis”)
l) Total P ISO 11263, Soil quality — Determination of phosphorus — Spec-
trometric determination of phosphorus soluble in sodium hydrogen
[30]
carbonate solution
4.3 Methods for measuring specific soil characteristics and indicators
Soil processes are linked to soil sub-functions and functions as described in ISO/TS 18718. To assess soil
processes, many methods exist to measure specific soil characteristics and indicators. As for general soil
characteristics, these are standardised at different levels.
Some of the methods are direct measurements of a function or sub-function whereas others are indirect. For
example, microbial biomass is an indirect indicator of organic matter mineralisation potential whereas soil
respiration is a direct measurement.
Tables 3, 4 and 5 are organised as follows: in Table 3, soil functions and sub-functions are linked to soil
characteristics and indicators reflecting soil processes. Tables 4 and 5 further link the soil functions with
the characteristics and indicators at level 1 and level 2, respectively, and provide references.

Table 3 — Specific soil characteristics and indicators reflecting soil processes associated to soil functions and sub-functions
Specific soil characteristics and indicators Specific soil characteristics and indicators
Functions Sub-functions
a b
associated to level 1 methods associated to level 2 methods
L1-C1. Total organic carbon content
SF1-Water retention
F1 - Water
L1-C2. Water retention
regulation,
L2-C1. Soil structure assessment via X-ray computed
retention and
tomography
SF2-Infiltration and percolation L1-C3. Permeability
release
L2-C10. Permeability
L1-C4. Microbial soil biomass L2-C2. Organic matter mineralisation in soil
SF3-Decomposition
L1-C5. Feeding activity L2-C3. Litter bag
F2 - Organic matter
SF4-Resource reallocation L1-C1. Total organic carbon content
storage,
L2-C4. Carbon quality – active and stable organic
transformation
L1-C1. Total organic carbon content
carbon
and recycling
SF5-Biochemical transformation
L1-C6. Microbial respiration (carbon mineraliza-
L2-C5. Functional diversity: Genes coding analysis
tion)
L2-C6. Microbial catabolic activities
L1-C4. Microbial soil biomass
L1-C7. Enzymatic activities
SF6-Nutrient transformation L2-C6. Microbial catabolic activities
L1-C8. Total nitrogen content
L1-C9. Assimilable phosphorus content
F3 - Nutrient cycling
L1-C10. CEC and exchangeable cations
SF7-Nutrient reallocation L2-C11. CEC and exchangeable cations
L1-C7. Enzymatic activities
L2-C7. Microbial activities (denitrification)
SF8-Nutrient assimilation L1-C11. Available NO and NO
2 3
L2-C5. Functional diversity: Genes coding analysis
L1-C12. Bioavailability of metal contaminants.
SF9-Retention
L1-C13. Total and extractable metal trace element
F4 - Contaminants
SF10-Transformation L2-C6. Microbial catabolic activities
retention,
transformation
L1-C7. Enzymatic activities
a
and degradation
SF11-Degradation L1-C14. Soil microbial diversity L2-C6. Microbial catabolic activities
L1-C15. Degradation of organic chemicals
SF12-Emission L2-C6. Microbial catabolic activities
F5 - Gas exchanges
L2-C4. Carbon quality – active and stable organic
with the atmosphere
SF13-Captation
carbon
Table 3 (continued)
Specific soil characteristics and indicators Specific soil characteristics and indicators
Functions Sub-functions
a b
associated to level 1 methods associated to level 2 methods
L1-C1. Total organic carbon content
L2-C4. Carbon quality – active and stable organic
L1-C4. Microbial soil biomass carbon
‒
L1-C16. Ecotoxicological quality L2-C1. Soil structure assessment via X-ray computed
F6 - Habitat
tomography
L1-C17. Effect of chemicals on macrofauna
provision
L1-C14. Soil microbial diversity
L2-C8. Taxonomic diversity (bacteria and fungi)
‒
L1-C18. Abundance and diversity of soil inverte-
L2-C9. Fungal, bacterial ratio
brates
L2-C1. Soil structure assessment via X-ray computed
SF14-Inherent soil stability
tomography
F7 - Physical
Salinisation requires:
L2-C1. Soil structure assessment via X-ray computed
stability
tomography
SF15-Stability evolution L1-C16. Electrical conductivity
L2-C11. CEC and exchangeable cations
L1-C10. CEC and exchangeable cations
a
Level 1 methods are provided in Table 4.
b
Level 2 methods are provided in Table 5.

Table 4 — References and description of level 1 specific soil characteristics and indicators
Specific soil
Related
characteristics Description and references
functions
and indicators
[31]
ISO 23400, Guidelines for the determination of organic carbon and nitrogen stocks and their variations in mineral soils at field scale
L1-C1. Total F1-SF1;
[16]
organic carbon F2-SF5; ISO 10694, Soil quality — Determination of organic and total carbon after dry combustion (elementary analysis)
[17]
content F5-SF11
ISO 17184, Soil quality — Determination of carbon and nitrogen by near-infrared spectrometry (NIRS)
L1-C2. Water
[32]
F1-SF1 ISO 11274, Soil quality — Determination of the water-retention characteristic — Laboratory methods
retention
[33]
L1-C3. Permeability F1-SF2 ISO 17892-11, Geotechnical investigation and testing — Laboratory testing of soil — Part 11: Permeability tests
[34]
ISO 14240-1, Soil quality — Determination of soil microbial biomass — Part 1: Substrate-induced respiration method
[35]
ISO 14240-2, Soil quality — Determination of soil microbial biomass — Part 2: Fumigation-extraction method
[36]
ISO 16072, Soil quality — Laboratory methods for determination of microbial soil respiration
[37]
ISO 17155, Soil quality — Determination of abundance and activity of soil microflora using respiration curves
[38]
F2-SF3;
ISO 11063, Soil quality — Direct extraction of soil DNA
L1-C4. Microbial
F3-SF6;
ISO 17601, Soil quality — Estimation of abundance of selected microbial gene sequences by quantitative polymerase chain reaction
soil biomass
F6
[39]
(qPCR) from DNA directly extracted from soil
ISO/TS 29843-1, Soil quality — Determination of soil microbial diversity - Part 1: Method by phospholipid fatty acid analysis (PLFA)
[40]
and phospholipid ether lipids (PLEL) analysis
ISO/TS 29843-2, Soil quality — Determination of soil microbial diversity — Part 2: Method by phospholipid fatty acid analysis (PLFA)
[41]
using the simple PLFA extraction method
L1 – C5. Feeding ISO 18311, Soil quality — Method for testing effects of soil contaminants on the feeding activity of soil dwelling organisms — Bait-lam-
F2-SF3
[42]
activity ina test
L1-C6. Microbial
[36]
ISO 16072, Soil quality — Laboratory methods for determination of microbial soil respiration
respiration (carbon F2-SF5
[43]
ISO 23265, Soil quality — Test for estimating organic matter decomposition in contaminated soil
mineralization)
ISO 20130, Soil quality — Measurement of enzyme activity patterns in soil samples using colorimetric substrates in micro-well
[44]
plates
ISO 23753-1, Soil quality — Determination of dehydrogenases activity in soils — Part 1: Method using triphenyltetrazolium chloride
F3-SF6;
[45]
(TTC)
L1-C7. Enzymatic
F3-SF7;
activities
ISO 23753-2, Soil quality — Determination of dehydrogenases activity in soils — Part 2: Method using iodotetrazolium chloride (INT)
F4-SF11
[46]
ISO/TS 22939, Soil quality — Measurement of enzyme activity p
...