Different methods across Europe: New project aims to harmonise soil measurements and data
SoilHarmony has begun its mission to harmonise soil monitoring across the EU – building the transfer functions that will let Member States keep their national systems and still speak one common language under the new Soil Monitoring Law.
Healthy soil is the foundation of food production, biodiversity, clean water and climate regulation. Yet 60–70 % of European soils are today considered degraded. In response, the EU has adopted a new directive – the Soil Monitoring Law (SML) – to ensure coherent and standardised monitoring of soil health across every Member State. The directive sets out reference methods for a long list of descriptors – from soil organic carbon and pH to bulk density, phosphorus, electrical conductivity and heavy metals – so that the condition of European soils can finally be compared across borders and used as a trustworthy basis for climate, biodiversity and carbon farming policies.
The reality on the ground is more complicated. Each Member State has built its own national soil monitoring system over decades, with very different sampling depths, field protocols, laboratory methods and data models. As a result, soil data across Europe is neither comparable, interoperable, nor fully in line with the FAIR principles. A figure as simple as “the share of organic carbon in the topsoil” can mean different things depending on which country the sample came from.
Enter SoilHarmony
SoilHarmony brings together more than 27 research institutions to develop and validate the translation key that lets national monitoring systems continue – with all their long-term data series intact – while still delivering harmonised data to the EU. The work is built on five guiding principles: co-creation with Member States, optimal use of existing resources, minimisation of variability, built-in interoperability, and systematic integration of results across the project.
Central to this effort are two types of mathematical conversion tools. Transfer functions convert the same soil property measured with different methods. Pedotransfer functions go a step further, estimating soil properties that are difficult or expensive to measure directly using more readily available data. Both are indispensable for turning the SML’s ambitions into operational reality.v
| TRANSFER FUNCTIONS AND PEDOTRANSFER FUNCTIONS |
|---|
A transfer function (TF) is a mathematical formula that converts the same soil property measured using two different methods – for example, pH measured in water converted to pH measured in KCl solution. Same property, different protocol. A pedotransfer function (PTF) instead estimates one soil property from other, more easily measured ones. For example, a soil’s capacity to conduct water can be calculated from its sand, clay and carbon content – parameters that are already measured routinely – avoiding costly and time-consuming direct measurements. SoilHarmony develops and validates both types. The challenge is that existing functions are often calibrated on limited geographical areas, lack uncertainty estimates and do not cover the full range of soil types, land uses and climate zones found across the EU. Those are precisely the gaps the project will fill. |
A common reference across 21 countries
SoilHarmony will build on existing national monitoring systems and as a shared reference will also use the EU’s LUCAS Soil Programme – the only truly pan-European soil survey and the source on which the SML is largely based. In addition, existing transfer functions are scattered across the literature, rarely validated, and far from covering all SML descriptors and pedoclimatic zones in Europe. SoilHarmony addresses this directly by validating functions at scale: at least 4,000 new soil samples collected and analysed across 21+ Member States and 80 % of the EU’s land surface, calibrated against archived LUCAS and national locations.
A statistical toolbox – an open R package and a user-friendly web application – will make the functions accessible to authorities, advisors and researchers without programming skills, and a FAIR-by-design database and open metadata catalogue will keep the results alive long after the project ends, in close collaboration with the JRC’s EU Soil Observatory and the SoilWise project.
| LUCAS SOIL |
|---|
LUCAS (Land Use/Cover Area frame statistical Survey) is a large, EU-wide survey that Eurostat and the Joint Research Centre (JRC) have conducted since 2006. The soil component, LUCAS Soil, collects soil samples from tens of thousands of locations across the EU using a single shared protocol and analyses them in a central laboratory. It is the only truly standardised, pan-European soil data source – which is why the EU’s new Soil Monitoring Law has adopted the LUCAS protocol as its common reference. In SoilHarmony, LUCAS Soil serves as the shared pivot point to which all national methods are translated. |
From ambition to practice
The ambition, in short, is a common key for European soil monitoring: an open, validated and transparent infrastructure that ties together the diverse measurement methods of the Member States into one coherent, trustworthy picture of Europe’s soil health – and turns the Soil Monitoring Law from ambition into practice.
SoilHarmony is funded under Horizon Europe (HORIZON-MISS-2025-05-SOIL-04). Aarhus University’s contribution is carried out by DCA – the Danish Centre for Food and Agriculture and the Department of Agroecology.