Activities under this topic will help to progress towards the objectives of the Mission ‘A Soil Deal for Europe’^[1], in particular towards its specific objectives 2 “Conserve and increase soil organic carbon stocks” and 6 “Improve soil structure to enhance habitat quality for soil biota and crops”. Activities should also contribute to the EU Soil Strategy^[2] and to the Long-term vision for EU’s rural areas^[3], as the Mission is one of its flagship initiatives.

Project results should contribute to all of the following outcomes:

• Improved access for land managers and public authorities to data and knowledge on the spatial variations of the chemical, physical and biological conditions and dynamics in subsoils. This should support the development of sustainable soil management practices as well as financial and policy incentives.
• Accelerated deployment of sustainable management practices for protecting and restoring subsoils in agricultural, forest and other types of soils, and increasing relevant soil-dependent ecosystem services such as the provision of food and fibre or habitats for soil biodiversity.
• Improved understanding of the role of the subsoil in climate change adaptation and mitigation, e.g. regarding carbon and water storage.

The term “subsoil” refers to the horizons immediately below the topsoil^[4]. In the past, this layer has often been neglected as most land management practices (e.g. tillage, cover crops, forestry) are focused on the topsoil. Our understanding of subsoil issues (e.g. compaction and its persistence) in semi-natural environments (e.g. heathlands, peatlands, natural grassland) is even less developed than for agricultural and forestry subsoils. Spatial datasets on soils at both national and EU-scale have also mostly focused on topsoils.

The subsoil can have a large impact on soil's potential for productivity and the supply of ecosystem services. It is estimated, for example, that plants extract between 10 and 80% of their nutrient and water requirements from the subsoil. Carbon sequestered in subsoils generally contributes to more than half of the total stocks within a soil profile. In contrast to topsoil, organic matter stored in subsoil horizons is characterised by high mean residence times^[5]. Conversely, subsoil degradation (e.g. through compaction, pollution, salinization) may limit root penetration, reduce nutrient uptake and result in plants becoming increasingly susceptible to stress such as from pests and diseases or drought and floods. Reduced water infiltration in subsoils limits plant growth, while increasing surface water runoff and the risk of soil erosion. Timber-related activities in forests, for example, can also cause considerable soil compaction leading to a decrease in productivity of forests due to increased surface water runoff and erosion.

Activities under this topic should improve our understanding and knowledge of the links between the subsoil and ecosystem services, and they should promote practices that enhance the health status of subsoils in agriculture, forestry and urban areas, as well as in sites of nature conservation and sensitive landscapes.

Proposed activities should:

• Increase knowledge on the properties (e.g. soil structure) as well as chemical, physical and biological process dynamics and their relationships in subsoils, and how these contribute to overall soil health and the delivery of ecosystem services such as carbon storage and greenhouse gas (GHG) mitigation, water retention, nutrient provision, crop productivity, and habitat for soil biodiversity. Amongst others, activities should explore the potential of modelling to help capturing the complexity of processes and dynamics in subsoils.
• Identify pressures on the subsoil that impair a range of soil functions and ecosystem services, as well as drivers for subsoil degradation.
• Identify indicators to assess subsoil driven changes in soil ecosystem functioning.
• Identify the potential of subsoils to store and maintain carbon, and to contribute to mitigating other GHG (e.g. N₂O) emissions. Work should take into account potential barriers and the synergies and trade-offs between climate regulation and other ecosystem services, such as the support to biodiversity. Consideration should be given to existing and future land use options.
• Identify existing as well as develop and test sustainable management practices to improve the conditions and functions of subsoils (e.g. water retention, nutrient provision, habitat for soil biodiversity, carbon storage). Activities should be undertaken in close cooperation with land managers and allow for wide demonstration and dissemination of practices.
• Develop tools and methods for risk assessment as regards subsoil degradation, reflecting diverse soil uses. Demonstrate practical approaches for the use of these tools and methods by land managers and policy-decision makers.
• Establish robust methods to spatially assess and monitor the chemical, physical and biological characteristics of subsoils and to improve data collection and use. For this, sampling methods for subsoil should be harmonised in order to provide comparable and reliable data. The long-term storage and access to subsoil data should be done in close collaboration with the European Soil Observatory (EUSO).

In carrying out activities, proposals should consider various soil types and land uses and climatic/biogeographical regions in the EU and Associated Countries. With regard to agriculture, work should draw on sustainable practices, applied across a range of farming systems and benefit both conventional and organic farming. The proposals selected under this topic should dedicate the necessary resources to work closely together and maximise synergies.

Activities should be undertaken in close cooperation with the European Commission’s Joint Research Centre (JRC). The cooperation with the JRC is particularly relevant for further developing the LUCAS Soil survey and the Soil Health Dashboard under the European Soil Observatory (EUSO). Proposals should demonstrate a route towards open access, longevity, sustainability and interoperability of knowledge and outputs, amongst others through close collaboration with the EUSO. Potentially, the projects funded under this topic could also cooperate with living labs and lighthouses that will be created in this and future calls of the Mission ‘A Soil Deal for Europe’.

In this topic, the integration of the gender dimension (sex and gender analysis) in research and innovation content is not a mandatory requirement.

[1] https://ec.europa.eu/info/research-and-innovation/funding/funding-opportunities/funding-programmes-and-open-calls/horizon-europe/missions-horizon-europe/soil-health-and-food_en

[2] https://ec.europa.eu/environment/strategy/soil-strategy_en

[3] Long-term Vision for EU’s rural areas, https://ec.europa.eu/info/strategy/priorities-2019-2024/new-push-european-democracy/long-term-vision-rural-areas_en

[4] For the purpose of this topic topsoil is defined as the uppermost layer of natural soil. Typically, this means a layer of about 10-30 cm in thickness, although this can vary according to soil type. Generally, it contains most plant roots, nutrients and biological activity, and it is affected by agricultural activities.

[5] Rumpel, C., Chabbi, A., Marschner, B. (2012). Carbon Storage and Sequestration in Subsoil Horizons: Knowledge, Gaps and Potentials. In: Lal, R., Lorenz, K., Hüttl, R., Schneider, B., von Braun, J. (eds) Recarbonization of the Biosphere. Springer, Dordrecht. https://doi.org/10.1007/978-94-007-4159-1_20