01-08-2025
Time of Sampling May Affect Eu Soil Health Monitoring Study
An organisation that is building a comprehensive map of European soils and their condition is warning that the EU's Soil Monitoring Law may be omitting a vital factor in assessing soil health in the bloc.
The EU plans to record and map the various soil types and soil health throughout the bloc, as envisaged through its proposed Soil Monitoring Law.
The law will make the monitoring of soil health mandatory, as part of efforts to have all soils in a healthy condition by 2050, in line with the EU Zero Pollution ambition.
Article 31 of the draft law states: "It is therefore appropriate to lay down criteria for sampling points that are representative of the soil condition under different soil types, climatic conditions, and land use."
The three variables mentioned will play a vital role in deciding where soils should be sampled in the vast area that the EU covers.
However, evidence is now emerging that a fourth variable should also be included and that is the time of sampling, which could significantly affect the results and render the overall picture inaccurate if not included.
The warning comes from an article published by AI 4 Soil Health, an organisation which is building a comprehensive map of European soils and their condition.
Soil sampling is the only way to really get to know a soil. Image: Petrol Post Driver
The author, Dr. Peter Lehmann of ETH University Zurich, makes reference to a study carried out in Switzerland which notes how water-absorbing capabilities of soils can very throughout the year, depending on weather patterns.
Although the research was carried out in natural forest, the findings indicate that all soils - wherever their location and use - will be subject to similar influences.
If these factors are not included in the final analysis for monitoring soil health, then the AI $ Soil Health map will likely fail to be within the 5% margin of error required by the EU.
The research demonstrated that the health of the soil can change significantly during dry summer months.
A water repellent layer can form at the surface as the organic chemistry of this zone changes in response to prolonged drought.
Soil can appear less healthy when dry
Those tending the land are well aware of this affect, as a summer shower will often not be absorbed by the soil, it takes a good soak for the soil to start absorbing the water.
It is the top 2cm that are responsible for this, which can give healthy, well-structured soil a water-resistant cap that adversely affects essential soil functions further on down the soil profile.
A further aspect of the soil function studied was the action of two extracellular soil enzymes that play an important role in the decomposition of organic carbon compounds and how they might be affected by soil conditions.
The study showed that one enzyme was more affected by the soil moisture while the other responded more to soil temperature,.
This reinforced the notion that weather patterns can distort our present assessments of soil health, and may have been doing so for some time.
The depth and type of cultivation may alter the soil's response to drought and so effect its apparent health
Dr. Lehmann concluded that the timing of measurements is crucial and depends on which specific soil functions are being assessed.
He also notes that another key lesson is the importance of where measurements are taken.
"The top surface layer plays a critical role in determining whether a soil can provide essential services like water storage and support for plant growth, or whether it should be considered unhealthy." he notes.
Just on this last point, the sun wheel-type implements that are sold as mechanical weeders here in Ireland are marketed as crust-breaking tools on the continent and said to work well as such when used in dry periods.
Sun wheel implements will keep the layer of soil open for rain to penetrate.
It is perhaps the disturbance of this water-repellent top layer of soil that is the secret to their success in drier areas of the EU, making them generally superfluous here in damper conditions.
