Soil health monitoring requires multiple indicators and continuous measurements

Moss and mushrooms.

This post was originally published on Luke website.

A major new law on soil health in Europe is being prepared in the European Union, and scientists report that one of the proposed indicators is not fit for purpose.

Operational monitoring of soil carbon is vital to improve soil-based ecosystem services, as stated in the Paris Climate Agreement and other national commitments. As a significant proportion of Europe’s soils are unhealthy, new regulation is needed. The European Union is committed to improving soil health and is currently developing a new Soil Monitoring Law that will establish monitoring a set of different soil health indicators.

HoliSoils and Benchmarks researchers are actively contributing to the ongoing process on this European Soil Monitoring Law by testing one of the proposed indicators. A recent publication shows that the ratio of soil organic carbon to clay (SOC:Clay), proposed as part of the new law to measure soil carbon loss, is not a reliable indicator for soil health.

Single indicator and its threshold value does not adequately reflect the diversity of European soils

The joint publication by EU funded HoliSoils and Benchmarks projects assessed the feasibility of the SOC:Clay indicator by evaluating its performance using data from the pan-European 2009 LUCAS soil survey. The results were also compared with changes in soil carbon stocks reported by countries to the UNFCCC.

Based on these findings, the researchers concluded that the SOC:Clay indicator proposed by the European Commission in the Soil Monitoring Law does not adequately monitor soil carbon status. They demonstrated that the use of this single indicator and its proposed threshold value of 1:13 for all soils under different land cover, management practices and climatic conditions, cannot account for the diversity of European soils, management practices, and climatic conditions.

The results also show that the SOC:Clay indicator provides an inconsistent conclusion on the proportions of non-healthy soils identified by using the SOC:Clay indicator when compared to changes in soil carbon stocks reported by national greenhouse gas (GHG) inventories. GHG inventories estimate changes in soil carbon stocks through repeated measurements or modelling. However, the proposed indicator, which would be based on the sampling and analysis of soil samples taken at a single point in time, may have therefore temporal limitations.

Soil monitoring indicators and tools need further development

The proposal for the Soil Monitoring Law has been discussed and voted on by the EU Parliament, after which it will be subject to further trilogue negotiations which will remain the responsibility of the next Parliament after the EU elections in June. Trilogue brings together the representatives of the European Parliament, the Council of the European Union and the European Commission and aims to reach a provisional agreement on the legislative proposal.

“The sustainable production of ecosystem services relies on healthy soils. To achieve this across Europe, as outlined in the Soil Monitoring Law, various actions must be taken in different regions. In addition to the indicators to be determined at the EU level, national tools are also necessary to monitor soil status and maintain soil health that meet the needs of different actors” says Raisa Mäkipää, Research Professor at Luke, HoliSoils project coordinator.

HoliSoils and Benchmarks researchers are committed to providing scientific input to the ongoing process of developing the new Soil Monitoring Law that best supports Europe’s important promise of healthy soils.

HoliSoils partners preparing numerous products in project’s penultimate year 

The HoliSoils project annual meeting gave consortium partners and stakeholder representatives the chance to discuss HoliSoils’ results and potential products in detail. 

HoliSoils is already in its penultimate year, and this year’s gathering brought into focus the depth of work being carried out in the project, from soil and forest management strategies, biophysical research linked to disturbance and to microbiological processes, to modelling, data and monitoring frameworks for greenhouse gas emissions (GHG).  

A detailed session focused on the various maps being developed through the project, and how the wealth of information will be accessible to potential end users. 

Two poster sessions allowed participants to dive more deeply into the research being carried out in the project. Many of the project’s post docs shared their work on specific research questions, and there was a second session focussing on experimental studies being carried out at the project’s test sites around Europe, as well as at the one from Uruguay. 

The HoliSoils Stakeholder and End-user Advisory Board (SEAB) has been instrumental in helping partners consider how different stakeholder groups in the project might use their findings and results. Their active engagement has made a real difference and in the dedicated panel session at this year’s meeting, the ten members who participated (nine in person and one online!) did not disappoint, sharing useful insights, critical questions and offering valuable advice in a fruitful conversation with the consortium. 


The consortium and SEAB members were also treated to two extremely interesting field excursions, the first to witness experiments being carried out on a peatland GHG site, the second to visit Kranzberg drought experiments in planted forests of spruce and beech, where one of the HoliSoils test sites is located. 

The fruits of all this labour will become available as results are published, via publications, web portals, updated modelling tools and recommendations for policy and practice. The challenge now and until the end of the project is to make sure that HoliSoils products reach as many people as possible so that all its stakeholders can benefit. 

Stay up to date with HoliSoils products as they become available: the HoliSoils toolkit is continuously updated and our repository in Zenodo already has many papers, with more added as they come out! 


Time to get serious about forest soil

HoliSoils researcher at work.

Originally published in Publico.es in Spanish.

European legislation on forests and climate and the forthcoming legislation on soil quality place particular emphasis on the importance of the soils that support our forests. These soils store more carbon and biodiversity than the trees they feed and are full of water and nutrients that provide a myriad of services. The European Union warns that, in general, degraded soils reduce the provision of ecosystem services such as food, timber, nutrient cycling, carbon sequestration, pest control or water regulation – a loss that costs the EU billions of euros every year. After the degradation of urban, industrial and agricultural soils, forests can be a lifeline against impacts such as climate change.

In the forests of Gamiz, a council of the city of Vitoria (Álava) located in the foothills of the Vitoria Mountains, work is being carried out as part of what is considered “the largest research project in Europe on the central, though little understood, role of forest soils in the fight against climate change”. This is what is stated in HoliSoils, an acronym for Holistic management practices, modelling & monitoring for European forest soils, a project of the EU’s Horizon 2020 programme in which 20 European universities and research centres are participating, including four Spanish ones.

The work being carried out in Gamiz includes that done by Jorge Curiel, the principal researcher in Spain at HoliSoils, who also leads the working group dedicated to the vulnerability of soils to climate change. He stops for a moment to talk to us: “We have three plots with a common design where we test, on the one hand, how different types of wood extraction affect the soil, such as 50% thinning and clear-cutting – cutting down all the trees in a forest area – and, on the other, how we can accelerate soil recovery with two treatments: in one we leave the soil bare and in the other we use the remains of the cutting, which are broken up and spread to create a layer that protects it and accelerates its recovery”.

An important part of this work is to analyse the carbon sequestration achieved by forest management taking into account different soil treatments. Forest soils store more carbon than trees, thanks to the combined action of dead wood, litter and the innumerable associated fauna, flora, and fungal communities, including other important micro-organisms such as protists, bacteria, and archaea.

Forest soils: champions of carbon sequestration

Gonzalo Almendros, research professor at the Department of Biogeochemistry and Microbial Ecology of the National Museum of Natural Sciences (MNCN/CSIC), highlights this value in figures: “In general, soils contain 2,500 petagrams of carbon (one petagram is equivalent to one thousand trillion grams), that is, more than three times the amount of atmospheric carbon and four times the amount stored in the biomass of plants and animals. Therefore, the interest in forest soils lies in the fact that they constitute a reservoir of carbon in slowly biodegradable forms, which is not actively exchanged with CO2 in the atmosphere”.

But there is a risk that climate change will accelerate this loss of soil carbon, as Pablo García-Palacios, a scientist at the Consejo Superior de Investigaciones Científicas at the Instituto de Ciencias Agrarias (ICA-CSIC), pointed out in a study published in June 2021 in the journal Nature: “Until now, the size of the carbon pool has been balanced annually between carbon losses from soil respiration and gains from carbon fixation by plants. However, anthropogenic warming is disturbing this balance”.

HoliSoils, like other European projects working in the same direction (DrySom, Benchmark, Atlantis, etc.), seeks to halt the loss of valuable forest soil, which is why not only research centres are involved in it, but also associations of forest owners, the European Environment Agency, the United Nations Convention on Climate Change and the FSC forest certification seal. Dozens of forest plots in various countries with different climates, tree species and management are serving as test laboratories.

Undergrowth in Peñacaballera, Sierra de Béjar, Salamanca. Photo: Javier Rico.

Every soil is a world

Each soil is different depending on all these factors: climate, altitude, trees, type of management, slope… There is nothing like taking a look at some of the almost 2,900 entries on the blog Un universo bajo nuestros pies (A universe beneath our feet) to make sure of this. It is the work of Juan José Ibáñez, senior scientist at the Desertification Research Centre (CSIC-University of Valencia), who constantly repeats that “soil is a very fragile and non-renewable resource”. There are soils dominated by leaf litter, in others by the herbaceous stratum, in others by scrub, and in some there is more moss, or rocky and stony ground, or a bit of everything. Ibañez even claims the value of dead wood: “The fall of a tree is essential for the maintenance of the dynamics of forest ecosystems and their soils”.

In this variety of soils and their composition also lies the ability to adapt to impacts such as those induced by climate change. Ana Rey, MNCN/CSIC scientist and expert in forest ecology, says: “Preliminary results of a study we are carrying out in Mediterranean forests on different types of soils indicate that forests with soils that are in principle more unfavourable seem to be less susceptible to drought, because they have already developed an adaptation to extreme conditions. Therefore, although they grow less, they are more resilient”. According to Jorge Curiel, “in the Iberian Peninsula, the most fragile forests are on steeper slopes, with more erosion potential, which increases depending on the type of management they have”.


Curiel is also a research professor at one of the centres participating in HoliSoils, the BC3 (Basque Centre for Climate Change). He says that all the work carried out (types of felling, soil treatments, placement of sensors, analysis of carbon sequestration, inventory of organisms, measurement of soil health parameters) “serves, first, to generate evidence that what is being done so far is not correct and, second, to generate more responsible management practices focused on soil conservation”.

Time to get serious about forest soil

Raisa Mäkipää, coordinator of HoliSoils and research professor at the Natural Resources Institute of Finland, stresses: “Soils really matter, but they have not been studied enough, especially forest soils. By learning more about how they trap and release CO2, countries can help ensure that their forests can adapt to and mitigate climate change”.

In the meantime, the EU has also got down to work. On 5 July 2023, the European Commission (EC) presented the proposal for a Directive of the European Parliament and of the Council on soil monitoring and soil resilience. The main objective is to achieve a healthy state of EU soils by 2050. It recognises that soil degradation costs us tens of billions of euros per year by affecting basic ecosystem services that provide important economic benefits: food, timber, carbon sequestration, pest control, erosion control, etc.

The variety of soils and their composition also determines the capacity of forests to adapt to impacts such as those induced by climate change. Photo: Javier Rico.

Without departing from the economic line, the proposed directive mentions: “The availability of healthy and fertile soils and land is crucial for the transition to a sustainable bioeconomy and can therefore help to increase and preserve land values”. In an article in The Conversation, Jorge Curiel and four other BC3 researchers stress that “the bioeconomy should take into account forest soil conservation”, but he warns: “We cannot expect the bioeconomy to cover all the production and business niches that are currently covered by other materials such as concrete or petroleum derivatives because, like these, natural resources are not infinite”.

One of the mainstays of the forest bioeconomy is the extraction of biomass for energy production. The Spanish Biomass Association (Avebiom) they state: “The companies that carry out works of exploitation and extraction of this biomass must comply with the requirements imposed by the EU Renewable Energy Directive, and they are doing so, many of them with the help of the European certification system SURE (Sustainable Resources Verification Scheme)”. In addition, they consider that removing biomass from forests for energy recovery “contributes to increasing the resilience of our forests to increasingly dangerous forest fires and climate change. Keeping the destructive power of fires and forest stress at bay is also a way of caring for soils and biodiversity”.

No planting for planting’s sake

Ana Rey considers how we should deal with reforestation very important: “When we talk about reforestation, about planting trees, we must remember that a forest is not just trees, because sometimes we ignore the complexity of forests and the many ecosystem services they provide, including the great importance of the soil. We have to take into account the type of soil we plant in and the species we plant”. Almendros stresses: “Each situation has to be studied separately, taking into account climate, soil type and the quality of pre-existing organic matter.”

Much remains to be done. The EC itself, in its proposal for a directive on soil monitoring and resilience, estimates: “More than 60% of European soils are unhealthy and scientific evidence shows that they are being further degraded due to unsustainable land management, pollution and overexploitation, combined with the impact of climate change and extreme weather events”.

Become Luke’s new Principal Scientist in forest soil science

Mushroom in a forest

HoliSoils’ project coordinator Natural Resources Institute Finland (Luke) is looking for a Principal Scientist to strengthen soil research in the institute. The selected candidate will work to develop and lead Luke’s research on carbon and nutrient cycling processes in forest soils on mineral soil sites, and how these processes are controlled.

The research will focus on soil carbon and nutrient cycling processes, nutrient availability, and organic matter quality. The objective is to better understand the linkages between these factors, and their significance both for the biomass production of forest ecosystems and for the environmental and climate impacts. The main focus should be on the response of soil processes and properties to forest management in changing environment and climate.

The position of Principal Scientist is permanent. The tasks include planning and leading research projects and working in those, as well as developing both field and laboratory methods connected to the research topics. The Principal Scientist is expected to publish at international scientific level, acquire research funding and be active in both national and international collaboration networks.

The deadline for applications is 23 February 2024, 16:00 Finnish time.

Read all the details on this opportunity & discover how to apply!

Slovak media and forestry professionals discover more about HoliSoils’ progress

Photo: HoliSoils – Technical University of Zvolen

Stakeholders from the forestry sector in Slovakia were recently able to learn more about the preliminary results of the HoliSoils project as well as the national PROBIOFOR project (Trade-offs between biomass production and biodiversity in beech and spruce forests under changing environmental conditions) at a workshop and field visit organised by the Technical University of Zvolen. This event, which brought together more than 40 participants from the state and private forestry sector, was held on 12 October and was attended by, among others, the Administration of the Protected Landscape of the Poľana Mountains, the State Nature Protection of Slovakia, Pro Silva Slovakia, the National Forestry Centre and the Technical University of Zvolen and Slovak public media journalists.

The workshop started with four introductory lectures explaining to the participants climate change and its effects on forest ecosystems, the adaptation potential of tree species and the carbon balance of forest ecosystems. The programme continued with an excursion to the old-growth forest of Dobroc (a national nature reserve since 1913), including a visit to the test area established for the HoliSoils project.

The preliminary results that were shared with the participants can be summarised as follows:

  • Norway spruce trees are more affected by extreme weather conditions than European beech and silver fir. Fir and beech trees even created a larger increment in 2022 than in 2021, which was vice versa for the spruce trees.
  • Norway spruce trees strongly suffered from the drought of 2022, which together with a mild winter condition lowered its ability to protect against bark beetle invasion, leading to a large-scale disturbance in 2023.

  • Soil water storage and its availability to trees was also heavily affected by the drought in 2022. As early as April, the soil water content had already dropped below 10%, touching 5%, on the test site in spruce monoculture, whereas it remained at a level of around 20–30% on the test site in the nearby mixed forest by the end of June.

  • Soil CO2 fluxes were larger in the mixed forest compared to the spruce monoculture, likely due to higher microbial diversity and activity in the soil. It was also shown that the largest differences between the spruce monoculture and the mixed forest were at higher temperatures during the summer. However, during the drought, the differences were almost negligible. Carbon increment in the above- and below-ground biomass was approximately between 3.5 and 4.5 t C ha-1 yr-1, whereas the C emission from the soil was found to be around 5 – 6 t C ha-1 yr-1 in the spruce and 7 – 8 in the mixed forest. During the field trip, it was stressed that soil carbon and fluxes have to be considered when discussing the potential of forest ecosystems to sequester carbon from the atmosphere.

Journalists from the main public Slovak radio and television stations took part in the workshop. The reportage was broadcast on the RTVS Regina show on 17 October 2023.

Photo: HoliSoils – Technical University of Zvolen

Benefits of the transition to continuous cover forestry on fertile and drained peatland forests in Finland

A clear cut in the foreground of the spruce study site and an unharvested control area behind.

This press release was originally posted on Luke website.

Recent studies from the SOMPA project – coordinated by the The Natural Resources Institute Finland (Luke) – assessed the amount of greenhouse gas (GHG) emissions in fertile drained peatland forests according to different silvicultural practices in Finland. Continuous cover forestry on fertile drained peatland produced significant climate benefits, because their selection harvesting result in much fewer emissions in comparison to even-aged forestry and clear-cutting. However, selection harvesting does not significantly reduce the amount of soil emissions in comparison to uncut forests, especially if the soil water level is not greatly raised.

A study published in the Scientific Reports journal assessed how the GHG emissions of forests in Finland would change if clear-cutting in fertile and drained peatland forests were replaced by selection harvesting but timber production would be maintained at the average 2016–2018 level of 73 million cubic metres. 

“The transfer to selection harvesting in drained peatlands would yield significant climate benefits, because this would allow avoiding significant soil emissions after clear-cutting and the carbon sink of the growing stock would recover more swiftly after selection harvesting than after clear-cutting,” summarises Aleksi Lehtonen, research professor at Luke, and co-coordinator of the HoliSoils project, which identifies and tests novel soil management practices aiming to mitigate climate change.

A scenario calculation for 2022–2035 that does not allow for the clear-cutting of fertile drained peatland forests produces a larger carbon sink of forests by approximately 1–1,2 million tonnes of carbon dioxide equivalents (Mt CO2 eq,) in comparison to the scenario corresponding to the current method, where clear-cutting is allowed. This emission reduction is equal to approximately 10 per cent of road traffic emissions of Finland.

In this scenario, the relation between the reduction in harvesting volume and in the increase in carbon sink depends on the selected forest management method. If harvesting is reduced by a million cubic metres by transforming in nutrient-rich spruce forests to selection harvesting, emissions would reduce by 2–3 Mt CO2 eq. The emission reduction in an equivalent reduction in felling volume is only 1,5–2 Mt CO2 eq if clear-cutting in fertile drained peatland forests and other current forest management methods are continued.

Based on this study, areas of development for GHG inventories and GHG scenario works can also be recognised. Harvesting related emissions in fertile drained peatland should be specified with additional monitoring. Tree growth models should also be developed so that they can predict growth in forests with that have variable structures.

Selection harvesting alone would only raise groundwater level minimally

A studies published in the Science of The Total Environment identified the mechanism of the soil GHG emissions and the impact of the groundwater level in both unthinned drained spruce forests and those subject to selection harvesting. 

In the studies, thinning forests through selection harvesting only raised the water level by a bit and did not have a significant effect on carbon emissions. Neither did the soil easily change into a methane source. 

Reducing the carbon emissions produced by oxygen-rich peatlands would require a higher increase in groundwater levels. 

“In the studied peatland forests, draining was originally quite effective and a larger reduction in soil emissions would likely have required a partial damming of ditches in addition to selection harvesting,” says Mikko Peltoniemi, research professor at Luke.

The starting points for cutting emissions may vary between peatland forests. 
“Developing suitable water management solutions for various conditions would require further studies on the combined effects of thinning intensities and the partial blocking of ditches,” says Peltoniemi. 

Qian Li and Maija Kurki from the Natural Resources Institute Finland take peat samples in Ränskäläkorvi, Asikkala. The samples are used to determine the microbial diversity and the genes that regulate its function. Photo: Aleksi Lehtonen

Articles

The studies have been funded by the following projects

  • SOMPA (projects.luke.fi)– Novel soil management practices – key for sustainable bioeconomy and climate change mitigation, Suomen Akatemia, Strategic Research
  • BiBiFe – Biogeochemical and biophysical feedbacks from forest harvesting to climate change, Suomen Akatemia.
  • UNITE-lippulaiva (uniteflagship.fi), Suomen Akatemia.
  • TUIMA – CarbonNudges in Climate Wise Land Use in Agriculture and Forestry, Ministry of Agriculture and Forestry.

HoliSoils supports key stakeholders with science and tools for GHG reporting

Amanita mushrooms growing on ground among green herb

Experts from the Land Use, Land Use Change and Forestry (LULUCF) sector are one of HoliSoils’ main target stakeholders. The LULUCF group at the Joint Research Centre (JRC) Bioeconomy Unit provides science-based support to the European Commission’s services in understanding how forests mitigate and interact with climate change in the context of EU and international climate policies. Many of the results developed in HoliSoils are directly targeted to these experts and HoliSoils has established a good and regular dialogue with the group, not least through Anu Korosuo who represents JRC on the HoliSoils Stakeholder and End-User Advisory Board (SEAB).

Partners from the HoliSoils project were invited to present the project and its results so far at the 2023 JRC LULUCF workshop, held in May. The main purpose of these meetings is to provide understanding on how LULUCF regulation is interpreted and of the methods used by different member states for their GHG inventories. The May workshop focused on the needs and opportunities to enhance LULUCF reporting to support climate change mitigation targets for 2030 and beyond.

Aleksi Lehtonen (Luke) presented the HoliSoils project while Mart-Jan Schelhaas (WUR) presented on EFISCEN-Space, the high-resolution forest resource model being updated as part of the project. Hans Verkerk (EFI), also a partner in HoliSoils, presented the ForestPaths project, of which he is coordinator. HoliSoils is working with ForestPaths and other relevant EU-funded projects to ensure synergies between activities and avoid duplicating efforts.

The LULUCF workshop combined overview sessions on the state-of-art of the GHG inventories and the revised LULUCF regulation. Specific sessions focused on moving to higher Tiers in reporting, and on the use of geographically-explicit data and new advances in remote sensing in GHG inventories.

Interesting for HoliSoils is that countries will need to improve their GHG inventory methods in the near future. While many countries do well with forest biomass reporting, there is room for improvement: most countries use Tier 1 but will need to move to Tier 2 by 2028. HoliSoils is providing tools to support such a transition, with a model ensemble tool currently in a beta phase and soon to be launched. Also of interest is the HoliSoils peat map (and other maps) under development, which will support spatially explicit reporting and improve land-use change estimates by providing soil data, contributing to the reporting needed for biodiversity and emission hot-spots.

Presentations from the workshop are available from JRC’s LULUCF pages.

Early career research life in HoliSoils

Soil sampling

I am Qian Li, now working in the Natural Resources Institute Finland (Luke) in the HoliSoils project. I graduated with a PhD in 2021, then joined Luke as a post-doctoral researcher. My background is on peatland green-house gases (GHG) emissions and carbon (C) cycle under the effect of climate warming. Now in the HoliSoils project, my research focuses on how forest management and natural disturbances affect the GHG emissions and soil processes of peatland forests.

My research in HoliSoils

I mainly work in Ränskälänkorpi, a drained peatland forest located in the Southern Finland. This site has three different forest management practices: clearcutting, selection harvesting, and non-harvested control.

We measure total respiration (CO2 emissions) and other greenhouse gases (CH4 and N2O) exchange by putting a manual chamber on top of soil and linking it with a gas concentration analyzer. Then the concentration change of gas emit/uptake by soil is analyzed by the analyzer linked with the chamber. We do it to discover which forest management practices can help mitigate climate change through reducing greenhouse gas emissions. This information can also help policy makers when they consider how to manage forests to achieve the climate targets.

Manual chamber measurement. Photo: Qian Li

To understand the production, consumption and transportation of gases inside soil layers, we also measure the gas concentration in the soil profile by taking gas samples through the silicon tubes buried underground.

We are also interested in knowing about the drivers of soil processes. So, we also take soil samples from surface to 1 meter deep to analyze microbial community structure and soil chemistry.

Uprooting
Uprooting. Photo: Qian Li

In this site, we also study how natural disturbances i.e. storms or windthrows impact soil C and N cycle. In addition to causing breakdown of tree stands, such disturbances can also destroy the upper soil layer by uprooting, or adding woody debris to soil surface, which all impact the soil processes. Especially extreme events are expected to be more frequent due to climate change, so it’s now urgent to know the consequences of such disturbances on ecosystems.

Photo: Qian Li

My feeling to be a member of HoliSoils family

HoliSoils is an EU project in which there are partners from several different European countries as well as from Uruguay and Japan. After joining this project and communicating with them, I have extended my knowledge scale of what kind of research topics they are focusing on and what novel techniques or analysis they are using in their research.

As a researcher who mainly focuses on experiments and field monitoring, I now have a deeper understanding of how models can use our experimental data and help us predict. As my first job after PhD, I am so happy to join Luke and HoliSoils project. This work experience not only brings me the knowledge and skills in science but also extends my network, which could help me to build my future career.

Is it feasible to increase soil carbon stocks by 4 per 1000 per year?

Soil with seedling

Extreme heatwaves, wildfires, floods, droughts… The effects of climate change are no longer predictions: they are happening right now. And, according to the experts of the Intergovernmental Panel on Climate Change (IPCC), they will continue to happen and become more and more intense in the future.

So, what can we do to stop them?

Most importantly, we need to reduce the emissions of greenhouse gases (GHG), such as carbon dioxide (CO2) from fossil fuel burning and deforestation, and nitrous oxide (N2O) and methane (CH4) from agriculture. But this is still not enough. In order to achieve carbon neutrality (that is, a net zero difference between what we emit and what we put back in the soil) we will need additional efforts to sequester CO2 from the atmosphere and store it in the soil.

This can be done, for example, by avoiding deforestation and improving the management of agricultural soils.

Soil

Soils play a crucial role for C sequestration:

  • They store the largest amount of C compared to all other terrestrial ecosystems.
  • They also store twice to three times more C than the atmosphere and – because the soil and the atmosphere interchange C – this means that even small changes in the soil C stocks can have a huge impact on the concentration of CO2 in the atmosphere.
  • C improves the fertility and other functions of the soils, so having soils rich in C is beneficial for food production.

Basically, storing more C in the soil can help to mitigate climate change and feed the world!

How can we restore carbon in the soil?

Carbon is naturally brought to the soil through plant photosynthesis and organic matter deposition. It leaves the soil once microbes and other organisms decompose it and respire it back to the atmosphere. Hence, storing additional soil organic C (SOC) can be done in two ways:

  • By increasing the amount of C entering the soil (e.g., the amount of CO2 fixed by the plants, or the amount of organic material added to the soil)
  • By decreasing the C output from the soil (e.g., decreasing the rate of microbial decomposition)

Researchers have found that the most efficient way to store C is to increase the C input to the soil.

Figure 1 Global carbon cycle between the land and the atmosphere. The values were taken from Ciais et al. (2013). Uncertainty in the atmospheric CO2 growth rate is ± 0.02 Gt C yr-1. Figure adapted from Le Quéré et al. (2018). Icons from www.flaticon.com.

How much should we increase the C input?

Assuming that we aim to increase the SOC stocks by a certain fixed target, we estimated the additional C input required to reach this target, and assessed whether this amount is realistic with current land use management practices. Following the 4 per 1000 initiative, we set the target to an annual 4‰ increase of the SOC stocks.

In order to address these questions, we used mathematical models that simulate the processes that influence the accumulation of C in the soil and estimated the additional C input required to reach a 4‰ objective in Europe.

The methods used

We used data from 16 long-term agricultural experiments where agricultural practices with organic matter addition were carried out for several years under controlled conditions. At these experiments, pedo-climatic conditions were monitored over time in order to see the effect of organic matter addition on the system.

Mathematical models are largely used by soil scientists and policy makers to predict the evolution of SOC stocks with time, following changes in land management practices and climate. They help to better understand the behavior of the system, and to predict its future responses to external changes. However, they are still highly uncertain. This is mainly due to the uncertainty of:

  • The processes described in the models, which are still largely unknown;
  • The data used to run them, such as climate and soil variables;
  • The parameters that are included in the model equations, which are usually considered constant although they actually vary in space and time, and which values are not always related to measurable physical processes.

In order to estimate some of this uncertainty, instead of running one single model we ran a multi-model ensemble, which allowed to consider different ways of representing soil processes.

We also calibrated model parameters in order to correctly reproduce the evolution of measured SOC stocks. This means that we adjusted the values of model parameters to reproduce the conditions of the sites that we studied.

Feasibility of the 4 per 100

On average across the models and across the sites, we found that the C input had to increase by 119% compared to the initial conditions. That is, an additional 1.5 ± 1.2 Mg C ha-1 would need to be annually input to the soil in order to increase the SOC stocks by 4‰ each year.

To give an order of magnitude, we estimated from Zhang et al. (2017) that the annual C input applied to European croplands, derived only from livestock manure, is around 0.3 to 0.9 Mg C ha-1. But this is already applied! Meaning that, if we wanted to provide additional 1.5 ± 1.2 Mg C ha-1, that would need to come from different sources of organic material. Doubling the C input where mineral and organic fertilizers are already applied is unlikely without the implementation of other agricultural practices, such as agroforestry systems, cover cropping, improved crop rotations, and crops with a high belowground biomass. This is the case for Europe, for example, where croplands are usually minerally fertilized and where organic fertilizers are already widely applied.

Figure 2 Annual SOC stock increase (%) for different levels of additional C input in agricultural experiments (black spots) and additional C input required to reach the 4‰ SOC increase according to the 1) non-calibrated multi-model median (MMM) (blue cross) and the 2) calibrated MMM (orange cross). Errors are shown as confidence intervals (CI) The regression line between additional C input and SOC stock increase in the EOM treatments is indicated in the figure (y=m (±〖SD〗_m)∙ x + b ± 〖(SD〗_b)).

Model uncertainties

Concerning the model simulations, we found large uncertainties across models, even when they were calibrated to reproduce the observed SOC stocks of the experiments. In particular, we found that the uncertainty across models was mainly due to the way the models represented (or not) water related variables, such as precipitations and potential evapotranspiration. This indicates that the choice of the hydrological processes included in the models and their representation affect model predictions, and it suggests that major efforts should be made to better represent these processes and reduce their associated uncertainties.

Figure 3 Required additional C input (± standard deviation, SD) relative to the unfertilized control, to reach a mean annual 4‰ SOC stock increase for 30 years across the 16 sites. The bars represent the different models and multi-model median (MMM). The non-calibrated and calibrated configurations are in blue and orange, respectively. For the MMM, the SD bar represents the median SD across models.
Figure 4 Heatmap of the simulated additional C input to reach the 4‰, for each calibrated model and each site. Darker cells show lower C input and lighter cells represent higher C input. Dendrograms above the heatmap represent the relationship of similarity among groups of models, calculated as the minimal correlation distance.

Conclusions and perspectives

Despite uncertainties in model simulations, there is compelling evidence that a radical change in agricultural management will be required to cope with climate change and food security in the near future. In a recent report from the Mission Board for Soil Health and Food, the European Commission was suggested to set ambitious targets to increase SOC stocks and improve the health of European soils. Yet, we are far from being optimistic. The last fifty years of international agreements on the response of world nations to climate change have proven that, no matter how compelling evidence the scientific community provides, indicators of adverse change are still on a rise (Glavovic et al., 2021). Governments need to take action before it is too late.

Diversity in science

In the last decades, thousands of works have been published on the effects of land management, land-use change and climate change on SOC. However, studies are narrowed to a selected number of specific drivers and geographical regions. In fact, studies on agricultural management practices have mostly focused on mineral fertilization, organic amendments, and tillage, while drivers of SOC changes have only occasionally been studied in North and Central Africa, and in the Middle East and Central Asia (Beillouin et al., 2022).

Future research should focus on more local and diversified knowledge on how to preserve and restore SOC stocks, while covering understudied geographical regions.

Besides, increased knowledge on the effects of diversified practices on SOC stock changes, under different pedo-climatic conditions, will help to improve model simulations and provide reliable SOC stock projections under future climate change.

Read more about this in the open access paper published in the European Journal of Soil Science: Multi-modelling predictions show high uncertainty of required carbon input changes to reach a 4‰ target

References and related articles

Beillouin, Damien, Rémi Cardinael, David Berre, Annie Boyer, Marc Corbeels, Abigail Fallot, Frédéric Feder, and Julien Demenois. “A Global Overview of Studies about Land Management, Land‐use Change, and Climate Change Effects on Soil Organic Carbon.” Global Change Biology 28, no. 4 (February 2022): 1690–1702. https://doi.org/10.1111/gcb.15998.

Bruni, Elisa, Bertrand Guenet, Yuanyuan Huang, Hugues Clivot, Iñigo Virto, Roberta Farina, Thomas Kätterer, Philippe Ciais, Manuel Martin, and Claire Chenu. “Additional Carbon Inputs to Reach a 4 per 1000 Objective in Europe: Feasibility and Projected Impacts of Climate Change Based on Century Simulations of Long-Term Arable Experiments.” Biogeosciences 18, no. 13 (July 2, 2021): 3981–4004. https://doi.org/10.5194/bg-18-3981-2021.

Bruni, Elisa, Bertrand Guenet, Hugues Clivot, Thomas Kätterer, Manuel Martin, Iñigo Virto, and Claire Chenu. “Defining Quantitative Targets for Topsoil Organic Carbon Stock Increase in European Croplands: Case Studies With Exogenous Organic Matter Inputs.” Frontiers in Environmental Science 10 (February 14, 2022): 824724. https://doi.org/10.3389/fenvs.2022.824724.

Chenu, Claire, Denis A. Angers, Pierre Barré, Delphine Derrien, Dominique Arrouays, and Jérôme Balesdent. “Increasing Organic Stocks in Agricultural Soils: Knowledge Gaps and Potential Innovations.” Soil and Tillage Research 188 (May 2019): 41–52. https://doi.org/10.1016/j.still.2018.04.011.

Glavovic, Bruce C., Timothy F. Smith, and Iain White. “The Tragedy of Climate Change Science.” Climate and Development, December 24, 2021, 1–5. https://doi.org/10.1080/17565529.2021.2008855.

Martin, Manuel Pascal, Bassem Dimassi, Mercedes Ŕomàn Dobarco, Bertrand Guenet, Dominique Arrouays, Denis A. Angers, Fabrice Blache, Frédéric Huard, Jean‐François Soussana, and Sylvain Pellerin. “Feasibility of the 4 per 1000 Aspirational Target for Soil Carbon. A Case Study for France.” Global Change Biology, February 4, 2021, gcb.15547. https://doi.org/10.1111/gcb.15547.

Riggers, Catharina, Christopher Poeplau, Axel Don, Cathleen Frühauf, and René Dechow. “How Much Carbon Input Is Required to Preserve or Increase Projected Soil Organic Carbon Stocks in German Croplands under Climate Change?” Plant and Soil 460, no. 1–2 (March 2021): 417–33. https://doi.org/10.1007/s11104-020-04806-8.

Soussana, Jean-François, Suzanne Lutfalla, Fiona Ehrhardt, Todd Rosenstock, Christine Lamanna, Petr Havlík, Meryl Richards, et al. “Matching Policy and Science: Rationale for the ‘4 per 1000 – Soils for Food Security and Climate’ Initiative.” Soil and Tillage Research 188 (May 2019): 3–15. https://doi.org/10.1016/j.still.2017.12.002.

Zhang, Bowen, Hanqin Tian, Chaoqun Lu, Shree R. S. Dangal, Jia Yang, and Shufen Pan. “Global Manure Nitrogen Production and Application in Cropland during 1860–2014: A 5 Arcmin Gridded Global Dataset for Earth System Modeling.” Earth System Science Data 9, no. 2 (September 6, 2017): 667–78. https://doi.org/10.5194/essd-9-667-2017.

New publication on the impact of management on soil carbon sequestration

Mushrooms on forest soil

A new study, developed in the framework of the HoliSols project, was recently published on Forest Ecology and Management.

The publication synthesises information on forest management practices that can mitigate climate change by increasing soil carbon stocks and reducing greenhouse gas emissions. The study also identifies soil processes that affect soil greenhouse gas balance and discusses how models represent forest management effects on soil in greenhouse gas inventories and scenario analyses to address forest climate change mitigation potential.

Read the full article

Reference

Mäkipääa, R., Abramoff, R., Adamczyk, B., Baldy, V., Biryol, C., Bosela, M., Casals, P., Yuste, J.C., Dondini, M., Filipek, S., Garcia-Pausas, J., Gros, R., Gömöryová, E., Hashimoto, S., Hassegawa, M., Immonen, P., Laiho, R., Li, H., Li, Q., Luyssaert, S., Menival, C., Mori, T., Naudts, K., Santonja, M., Smolander, A., Toriyama, J., Tupek, B., Ubeda, X., Verkerk, P.J., Lehtonen, A. 2023. How does management affect soil C sequestration and greenhouse gas fluxes in boreal and temperate forests? – A review. Forest Ecology and Management, 529, 120637. https://doi.org/10.1016/j.foreco.2022.120637