In recent years, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) has brought attention to the broad range of potential benefits from nature under the category of nature's contributions to people (NCP) [1]. NCP was suggested as an alternative framing to 'ecosystem services,' in part to engage a wider range of scholarship from the social sciences and humanities and a larger discussion of values around ecosystems, and 18 broad categories of NCP have been proposed [2]. This paper for the special issue on 'The role of soils in delivering NCP' reviews literature on three different but related NCP categories: those of NCP 15-Learning and Inspiration, NCP 16-Physical and Psychological Experiences, and NCP 17-Supporting Identities. For each case, while the use of the term 'NCP ' is not yet widespread in literature discussing soils, there are in fact numerous examples of how humans have imagined, understood and experienced soil that represent the types of benefits the term NCP tries to capture. Soils have inspired art, literature and film; contributed to mental and physical health benefits from a variety of recreational and livelihood activities; and shaped cultural identities and practices.
The three NCP reviewed here are unique. NCP have been broadly divided into regulating, material and non-material categories; the non-material NCP are also labelled elsewhere as 'cultural ecosystem services' [3]. These NCP share in common an attention to the non-consumptive, intangible and immaterial benefits that people receive from nature. Table 1 presents how these NCP categories have been defined by IPBES, along with related examples from the Common International Classification of Ecosystem Services (CICES). The Table 1. Explanation of and examples relating to the soil.
type of NCP definitions of NCP [4] related class and examples from CICES [5] examples found related to soil NCP 15 [10]. However, there is a long history of interdisciplinary work on human interactions with soil that fits with the idea of 'nature's contributions', ranging from humanities scholarship on art and soil to social science on the role of soil in shaping identities and the social and psychological benefits from nature [11], all of which are explored in § §3-5 below. More recent scholarship on relational values and human contributions to soil materiality (discussed in §6) also fits well within NCP framings.
On the second question of the usefulness of the NCP concept, unlike other authors who have used soil 'ecosystem services' concepts to explore what benefits soil can provide to humans [12,13], this review presents NCP as a way to provide a different approach to soil/society relations. Several authors have stressed that NCP do not exist a priori to be supplied by nature but are co-produced by interactions of humans with ecosystems [14]. An NCP approach can thus emphasize how reciprocal relations with nature can be both created by and manifested in soil [15], a framing that has implications for reconfiguring soil management practices and policies. Yet despite the wide-ranging contributions of soils to human well-being, the literature is uneven, as noted throughout the paper in answering the third question, and much more remains to be understood about how values can shape and be shaped by soil. The paper concludes with an examination of how NCP as a framing device can help expand the diversity of approaches to human engagement with soil, including through attention to soil ethics and care and to the soil as a biosocial entity.
Using keywords associated with each of the three NCP under review (table 1), Google Scholar and Web of Science were searched for scholarship on soil, focusing on exemplars and most cited works, particularly those explicitly dealing with soil, rather than studies that briefly mentioned soil amid a range of other NCP or ecosystem services. Rather than a systemic review, specific examples that illustrated a range of benefits and values have been highlighted, with an eye to incorporating literature from varied parts of the world and dealing with different types of ecosystems and soil properties. The focus remained on indicative approaches that particularly fit an NCP framing, not on being exhaustive with regard to the extensive history of literature on soils. The review also zeroed in directly on the soil itself, not indirect associations, such as the outcomes of poor soil management (e.g. famine) that might affect NCP, or NCP that derive indirectly from things that grow in soil (e.g. from forests or food). This review should therefore be seen as suggestive of the directions and emphasis of the historical and current literature on soil that coincide with 'intangible' NCP categories, requiring a broad-brush approach rather than a systematic examination of this wide field.
NCP 15 concerns how elements of nature have set the conditions for learning and other creative endeavours, including art, technology and other 'inspirational' benefits.
Learning about soil has a long history, given that it has been an object of study since at least the ancient Greeks, who often combined observations of physical properties with reflections on the relational value of soils to humans [16]. The formal discipline of soil science emerged in the nineteenth century, centred on such key figures as Russian Vasily Vasil'evich Dokuchaev and German Justus von Liebig, who worked in fields and laboratories, respectively, to determine the composition and histories of soil formation, and whose 'technocratic' approaches came to dominate the field to the exclusion of more relational approaches [16]. However, soil science as a discipline has in the past two decades centred on new interests in planetary change [17], reframing the field towards a conjoining of both technical and more socially oriented research foci.
Learning about soil has also long existed outside of formal science settings as well, such as through work in community gardens, remediation sites, farms and events like the UN World Soil Day, providing opportunities for co-production of knowledge between experts and laypeople. For example, the French Observatory of Living Soils has promoted joint scientist-farmer work to map soil microbiology across a network of farms [18], contributing to the idea that humans help facilitate 'living' soil. Research on indigenous knowledge systems has also shown that learning about soil can be a source of ethical guidance on how human beings should behave within and towards nature in many cultures [19]. In particular, ethnopedology as a field has focused on identifying and understanding these soil knowledge systems unique to different cultural groups and often reflecting relational values within them [20].
Inspiration from soil can be seen in the ways in which artists have used soil, both as a spark for creativity and as a medium itself [21]. The first surviving pictorial art was made using soils and charcoals, then pigments like red and yellow ochre made from iron oxides, while the clay was first used to produce both functional and artistic pottery [22]. Soils have also been subjects of art, with many modern artists like Cézanne, Gauguin and Dubuffet drawing attention to the diversity and beauty of earth [23]. The later Land Art practitioners of the 1960s (including Robert Smithson, Ana Mendieta and Walter de Maria) emerged in an era of rising environmental awareness and used monumental components royalsocietypublishing.org/journal/rstb Phil. Trans. R. Soc. B 376: 20200184 of the natural environment (including soil) as a way of rejecting formal art galleries [24].
The ways in which soil as an artistic medium often reflects social or relational values can also be seen in contemporary artists engaging with soil (figure 1). These include Claire Pentecost, whose work shapes soils into ingots, representing soil's considerable value, while Yusuke Asai paints 'earth murals' (figure 1a) from local soils where he is exhibiting to demonstrate the contextual rootedness of soil. Truong Cong Tung has used soil to dye fabric and to fill galleries with the smell, representing conflicts over the environmental change in Vietnam (figure 1b), while Dineo Seshee Bopape, a South African artist, represents gender and language within her earth installations (figure 1c). These and other artists have been featured in a recent book on soil and art, with the literature in this field substantial and growing [25], and this soilattentive art has in turn raised awareness of threats to soil health [26].
Soil has also been an inspiration for literature, such as Frank Herbert's sci-fi book Dune [27] and its sequels and film, which were inspired by his working on a soil conservation and dune stabilization project in the 1950s in Oregon [28]. Other soilrelated novels include John Steinbeck's The Grapes of Wrath [29], in which mismanagement of topsoil in Dust Bowl Oklahoma drives mass migration that in turn shapes the future history of California [30], while Emile Zola's The Earth [31] and Pearl Buck's The Good Earth [32] take soil as either a key metaphor for their protagonists or the situations in which they find themselves. There has even been an entire poetry school focused on soil and earth, the 'geological school' associated with the Leningrad Mining Institute, again demonstrating the potential links between inspiring both science and art through soil [33].
Unlike in art, there has been comparatively less attention to soil and ideas of 'inspiration' in other fields, such as technology or design. Soil processes themselves are often imitated in human actions, such as composting, and many popular agro-ecological practices to improve soils, such as no-till or cover crops, are essentially a form of biomimicry [34]. Scientists have also used inspiration from Anthrosols, soils created by humans (such as the high carbon Amazonian dark earths known as terra preta and terra mulata), to guide research and application on new technologies such as biochar [35]. Other examples of using soil to both inspire design and provide a physical medium include housing styles using rammed earth walls, adobe, and compressed earth bricks, which often confer adaptive benefits like cooling or passive solar generation [36].
NCP 16 relates to obtaining physical and psychological benefits from being in or around nature. While the literature on physical benefits from nature is extensive, the soil is usually only the ground from which these benefits emerge, and there is little research specific to soil itself. Research on green spaces has noted that physical experiences of being in nature often result in more exercise and mobility, reduced weight, reduced stress and blood pressure, and improved diet [37]. The overall literature does not, however, make much distinction regarding the interactions with soils leading to such improved health outcomes.
While recreation has been one of the most important cultural ecosystem services identified, there is less attention to physical recreation and tourism specifically built around the soil. Although spectators may not see the direct connection, many sporting experiences rely heavily on well-managed soils, affecting everything from ball rebound on clay tennis courts and cricket pitches to drainage of football fields [38], demonstrating that soil is often a taken-for-granted background to many important and enjoyable human experiences. Beyond a few designated 'geoparks' that have unique soil types, such as bogs and peats in Scotland that are well-integrated into tourist visits and hikes [39], or the practice of 'mudlarking', exploring sedimented riverbanks or other places for traces of antiquities, there is little formal recreation around the soil. In fact, the physical benefits that people may receive from recreating as tourists can result in soil compaction and damage, as is reported in some heavily visited sites [40].
The mental health benefits from experiencing nature, ranging from urban green spaces to practices known as 'forest bathing', have been widely recognized [41,42]. Without soil such benefits would not be possible, but much of the literature is not direct in terms of explaining soil's specific relevance, indicating a potential gap in research. Ecopsychology as a field has also drawn attention to the approach of treating individuals with psychotherapy that encourages stronger ecological identities [43]; again, however, there is little specific reference to the soil in and of itself in this field.
Gardening is the outdoor practice that makes the most direct reference to working with soils to derive psychological benefits; for example, digging in soil may provide mental health benefits by relieving stress, a phenomenon noted in both older and younger populations. In one study of allotment gardeners in Tokyo, those actively gardening had better self-reported mental health than their non-gardening neighbours, in addition to higher levels of social interaction [44]. In a study of school children who participated in garden projects, parents reported less stress and higher self-esteem [45], yet how working with the soil itself generated mental health benefits remains a gap. Additionally, food can provide psychological comfort, and there are cultural practices of direct soil consumption associated with geophagy worldwide that are perceived by practitioners to potentially provide some mental or health benefits [46,47].
NCP 17 focuses on the ways in which religious, spiritual, symbolic and social identity and experiences can be derived from nature, and thus is a very broad category covering many potential interactions with soil.
Soil has been metaphorically and linguistically linked to human identity from the earliest times; for example, the name Adam from the Biblical creation story derives from the Hebrew word adama, meaning earth, while our species name of homo comes from a related word for humus in Latin [48]. Other major world philosophies have echoed these ideas of earth as giving life to humans or as forming the basis for existence; for example, the five elements of wuyung philosophy in the I Ching refer to earth (tu ˘), which was associated with balance and harmony [49]. There are numerous ways in which metaphors around soil have formed the basis of cultural and national identities. The phrase 'native soil' often describes basic characteristics of a society; for example, the phrase xiangtu in Chinese combines the words for countryside and earth to present a metaphor for China's rural and agrarian roots [50]. The concept of 'blood and soil' originating in nineteenth-century Germany has much darker meanings, used to mythologize rural lives, racial purity and connections to homeland, a metaphor later adopted by other genocidal regimes [51]. Ethnic divisions and conflicts among self-described 'sons of the soil' and those perceived as outsiders have led to numerous atrocities in history [52].
The development of ethics surrounding soil is a far more positive way in which human identity has been linked to caring for the earth. For example, Aldo Leopold's land ethic described a type of reciprocal relationship with soil, in which care for the land is part of caring for people [53]. Studies have shown that relations with soil can be important in shaping many farmers' identities; for example, farmers' sense of place can influence how they address stewardship of their soils [54], while social cohesion can be shaped by judgements about how other farmers manage soil [55]. Attention to how values and identities shape relations to soil are particularly useful because they can impact whether farmers adopt soil conservation practices [56], help determine who might use soil data or benefit from extension services [57] and can move the discussion beyond the simple economic benefits of better soil management [58].
Gender is also another identity linked to and potentially shaped by soil relations, embodied by metaphors like 'Mother Earth'. Women can have unique soil knowledge, often resulting from specific cultivation practices, experiences resulting from gendered divisions of labour, or beliefs more focused on 'caring' [59,60]. There is also some evidence that women's soil use practices may be more sustainable than men's; in one study, men's labour was associated with excess fertilizer use and soil compaction in Hungary [61], while in another example, rich anthropogenic African 'dark earths' were traced to women's practices of mixing cooking residues (e.g. charcoals or palm oils) with soil [62]. Given that gender affects soil management through various channels, ranging from land tenure, choice of crops, access to marketing and other realms, this argues for more attention to gender in soil science and farmer extension, particularly because women tend to be underrepresented in soil education programs [63]. Further, when gender-blind interventions to improve soil properties have been introduced, this can affect women's land rights, access and use, leading to conflicts [64,65].
Soil has also been fundamental to many religious and cultural worldviews. Humans have long worshipped deities representing soil fertility and productivity, from Gaia and Demeter in royalsocietypublishing.org/journal/rstb Phil. Trans. R. Soc. B 376: 20200184 ancient Greece, the Celtic god Danu and Ma ¯ori beliefs regarding Papa-tu ¯-a ¯-nuku, the earth mother [66]. The Japanese and Chinese words for 'earth' are derived from ideas of land spirits that resided in soil, and the symbol for the word 'earth' is itself represented as a horizon of soil (土) [67]. There are significant religious buildings dedicated to soils and earth, including temples devoted to Shintoism in Japan and the Altar of the Earth and Heavens in Beijing [66]. Christianity also has many Biblical references to soil or dust as being the composite material of which man is made. Other diverse religious and cultural practices and rituals worldwide have been shaped by soil, from mound building by early inhabitants of North America and continued rituals by their descendants [68] to the many significant burial practices and rituals involving soil [69]. Such religious practices have often focused on themes of stewardship, care and reciprocity with nature [47].
Soils have an important role to play in symbolic discussions of social and environmental justice as well, as racism and disempowerment have left many communities facing soil degradation. For example, the numerous benefits of community gardening noted previously have been tempered by the realization that many urban soils are contaminated, often because of environmental injustices around siting of polluting industries [70]. Injustices in soil science, such as the national soil survey process in the early twentieth century that excluded non-white farmers in the USA [71], have also been documented. Concerns about the inequitable consequences of the commodification of agriculture, soils and other resources have influenced the work of activists like Vandana Shiva, whose well-known tract Soil Not Oil [72] highlights the pitfalls of industrialized agriculture, while the ways in which soil has been used to further the development of capitalism and widening economic divides have been the subject of another recent book [73]. The potential injustices of soil carbon markets that could marginalize communities through 'green grabs' have also been a recent topic of concern [74]. Much of this attention to the social consequences of inequal access to the benefits of soil emerges from the field of political ecology, which traces the ways in which structural forces shape environmental change [75], and the growth of the field is often traced to Piers Blaikie's ground-breaking book on land degradation [76]. Subsequent work has continued to show the ways in which marginalized peoples are often blamed for soil erosion, rather than the practices of the powerful [77,78].
The literature on the 'social' NCP and their non-material benefits has revealed a wide variety of practices, ideas, imaginaries and identities linked to the soil around the world. The literature also reveals useful linkages to some of the NCP explored in the rest of this special issue; for example, artists featuring soil have brought attention to biophysical soil health and the need for restoration practices [79]. Yet despite the prominence given in religions, philosophies and art, intangible NCP linked to soil are often overlooked in research. Unlike forests or wildlife, for which extensive studies of non-material benefits have emerged [80,81], soil all too often remains in the background, only the substrate from which other benefits arise or as the material underfoot in human activities, like recreation. Such gaps argue in favour of extending NCP-focused studies to ensure that cultural and intangible benefits, and the ways in which values shape soil management, receive further attention. Two areas where an NCP framing can help draw attention to soil-human interactions and expand research in useful directions are outlined below, which reflect recent relevant scholarship on relational values, knowledge production and soil materiality.
(a) Reframing soil relations through culture and care
Recent studies have proposed ways to draw more attention to soil's enormous role in planetary health, from serving as a repository for carbon to harbouring rich biodiversity [57], and one suggestion has been to reframe attention to the soil through a security lens in particular [82]. Yet such studies of 'soil security' have neglected some of the NCP dimensions reviewed here. Similarly, improving the monetary valuation of soil ecosystem services, as some have proposed, is likely to miss the values embedded in the intangible NCP that are potentially of importance [83]. Instead, a reframing around the holistic concept of NCP might assist in recognizing that soil has been fundamental to human spiritual and intellectual flourishing. Improved understanding of the cultural elements of soil interactions, including the concept of 'care', appear useful in this regard, and can help make the case for attention to the multiple benefits and plural values of soil.
Indigenous knowledge could be particularly helpful in understanding these interactions, given that these systems often see soil management as a way to engage in larger reciprocal relations with nature [84]. Examples include practices in West Africa around the incorporation of termites into soil management, rather than their eradication, recognizing their positive role as a 'partner' to the farmer in improving soil fertility [85]. Indigenous knowledge systems could provide resources to improve management and understanding elsewhere, ranging from soil erosion prevention to integrated agro-ecological management [86]; such intimate knowledge and attention often allow for pinpointing interventions needed for soil health, rather than reliance on science and technology alone [87].
Critical assessments of how knowledge around soils is produced have shown that researchers also play a large role in stabilizing the concept of what 'soil' is and what it does for humans [88], and the different ways scientists and farmers both engage and relate to soil often shape divergent outcomes in terms of priorities for management [89]. In other words, how we understand soil shapes how we design policies for it; this argues for additional explorations of the ways in which different types of soil knowledge can lead to practices that can help tackle the soil degradation crisis [90]. For example, identification of the multiple ways different communities think of soil can help shift attention away from a focus on yield and production alone in favour of attention to ethics and care [91,92], and the linkages between soil and human experiences and selves outlined in NCP 17 highlight how identities can shape these values [15,54,58]. Given the many threats to soil discussed elsewhere in this special issue, understanding the ways in which soil-conserving values can be fostered is a useful contribution of an NCP framing [93,94].
royalsocietypublishing.org/journal/rstb Phil. Trans. R. Soc. B 376: 20200184 (b) Soil as a co-constructed and biosocial entity Across all three examined NCP, one common theme was the ways in which soil can be seen as an encapsulation of nature and culture together, or as a co-constructed and 'biosocial entity'. Such approaches are in contrast with many current conceptualizations to soil; for example, the European Commission recognizes social benefits from soil including as a 'physical and cultural environment for humans and human activities' and an 'archive of geological and archaeological heritage', but these definitions reflect a one-way relationship of soils servicing human needs, rather than acknowledging the co-construction of soil from human actions and relationships [95].
One framing of a more biosocial relationship with soil is through the lens of 'relational materiality' [96]. Rather than simply rendering services to people, soil in this way of thinking is considered active matter that is shaping and being shaped by society [15]. Relational materiality stresses the agency of soils and the symmetry of relations: soils are both generated by human attention and in return generate their own reactions (i.e. politics, identities or ideas) [97]. As noted previously, concepts of relationality with soil are often deeply embedded in many indigenous ontologies, as well as material practices of soil creation or amendment [98]. Some authors have proposed that the current era of the Anthropocene calls for a new recognition of the anthro in soil studies (e.g. an anthropedology), which could focus not only on human impact on soils, but how new soils like 'Anthrosols' and 'Technisols' are being created through the impacts of a warming climate or the emergence of new microorganisms [99].
Thinking of soil as a biosocial entity could also lead to new conversations about how to treat soils as other than inert matter. As one example, helping farmers 'see' differently through heuristic and aesthetic strategies that emphasize the multispecies worlds embedded in soil could improve agricultural practices for both better soil and farmer health [94]. In another trend, recent conversations around the rights of nature have been extended to the idea of that there should be 'rights of soil', whereby threats to soil health and functionality should be approached not just from technical or financial interventions, but legal and cultural ones. Eminent soil scientist Rattan Lal has recently proposed that 'soil degradation, pollution, and depletion is a moral and ethical wrong that must be stopped' in recognition of the living components of soil and the right of those components to flourish [100].
Through this review, it is clear that soils provide a widespread range of non-material benefits; indeed, it is hard to see any aspect of human civilization that does not have some link to soils, whether in the ways we grow food, the scope of our imaginations, or the aesthetics of our creative worlds. At the same time, these cultural and relational values have clear ties to understanding and improving material properties of soil: identities of farmers may influence their farming practices, thereby expanding or shrinking soil carbon stocks, while art and aesthetics around soil can build support for restoration efforts that would improve soil health and supply of other NCP like water quality. Overall, the conceptual framing of 'nature's contributions' affords a broad examination of these issues and highlights the variety of ways that humans value and understand soil. Approaching soils from an NCP lens helps illuminate the fact that soils have played a large role in human creative endeavours, are the root of significant relationships to the environment, and can be conceptualized as a bridge linking culture and nature together. Continuing efforts are needed to expand on these foundations and push further attention to learning, inspiration, physical and psychological benefits, and social identities in relation to soil, particularly around the promising concepts of soil care and biosocial relations.
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