Editorial for special issue on “understanding soil functions – from ped to planet”

Soil functions are fundamental for solving the societal challenges of food security, climate action, biodiversity protection and environmental integrity. Yet, soils have suffered from the “Cinderella syndrome” for decades when it comes to the public perception of the relevance of natural resources for human well-being. Blum (1993) eventually “passed the golden shoe” with the introduction of the soil functions concept, which triggered public understanding of the potential of soils to store carbon, to host biodiversity, to transform matter into plant-available nutrients, to retain and purify water, and to contribute to plant growth. The soil function concept was further elaborated as a link between ecological processes and human well-being to support the science–policy interface (Bouma, 2010; Helming et al., 2018) the science–practice interface (Schulte et al., 2014) and a systemic approach to science-based decision support (Vogel et al., 2018). Still, at the European level, a soil policy framework failed to be implemented following multi-annual negotiations in the first decade of the 21st Century. In policy regulations and strategies, such as climate strategies, biodiversity strategies, bio-economy strategies, and the agri-environmental and greening measures of the European Union Common Agricultural Policy, soils are treated implicitly as co-objectives or supporting measures rather than explicitly (Glæsner, Helming, & de Vries, 2014). Most of these policies and strategies are not legally binding or treat soil protection as an optional rather than mandatory instrument. A further boost to soil protection, and in particular to the carbon storage function of soils, emerged in the frame of the Paris Agreement on climate action in 2015, when the French Ministry launched the so-called 4 per mille initiative (Ministère de l'Agriculture, de l'Agro-alimentaire et de la Forêt, Hiver, 2015/2016), proposing that with an annual increase of 4 ‰ of soil organic carbon (SOC) stocks the annual increase of carbon dioxide (CO2) in the atmosphere would be significantly reduced. However, the feasibility of the 4 per mille initiative under current conditions for agricultural management has been heavily challenged by some leading soil researchers (Baveye, Berthelin, Tessier, & Lemaire, 2018) and the Conference of the Parties (COP) to the United Nations Climate Change Conference (UNFCCC) in November 2017 had not taken the topic up (Rumpel, Lehmann, & Chabbi, 2018). Also as part of its climate protection efforts, the European Commission adopted the European New Green Deal in 2019, which aims to achieve carbon neutrality by the year 2050 through an ecological transformation of the economy. Therein, the Farm to Fork strategy lays the foundation for a sustainable food system, which considers soil functions not only as carbon reservoirs but also as key partners in the transition to agro-ecological economies with a strong reduction in pesticide use. With these strategies' efforts to return to a circular economy and to reduce the use of finite resources, the intrinsic potential of soils to deliver ecosystem services and to convert (solar) energy into plant biomass is ultimately regaining the fundamental importance it always had in pre-industrial times. Synergies, but also trade-offs and spill-over effects, in environmental and socioeconomic terms, might be associated with this endeavour (Fuchs, Brown, & Rounsevell, 2020), and have to be carefully revealed in scientific assessments. This special issue of the EJSS presents contributions from participants of the Wageningen Soil Conference in August 2019 (https://wageningensoilconference.eu/2019/), which was held for the fourth time since its establishment in 2011, with a focus on “understanding soil functions – from ped to planet”. The conference received over 250 participants and discussed a range of topics based around four key themes: 1. Soil functions for society 2. Innovative methods for measuring soil functions 3. Modelling and mapping of soil functions across scales 4. Can we understand synergies and trade-offs between soil functions?