4.1. The Emergence of Soil Concepts
Many soil concepts have emerged at different times over the years. The soil fertility concept appeared to be the earliest of all of the soil concepts examined in both all journals (1908) and soil science journals (1917) (
Table 4 and
Table 5). Viets (1977) argued that much of the research that contributed to progress in soil fertility research was conducted even before the establishment of a formalized soil science [
21]. McNeill and Winiwarter (2004) supported this idea and asserted that the oldest writing on the topic—the book
Yugong, which described the characteristics of soil fertility in Northern China—appeared in around 500 B.C.E. [
22].
The soil fertility concept has a strong association with measurements of soil nutrients for crop production [
23]. Patzel (2004) found the historical linkage between human fertility and soil fertility in the writing—
Mother Earth [
24,
25]. The linkage has been developed across diverse cultures as farmers developed a general agronomic theory in the late 18
th century [
26]. Social and technological development and understanding have also impacted the development of soil concepts. Food supply shortages during and after the World Wars led questions of soil fertility to be central [
22] at a time when urgent demand for farm products and high prices confronted U.S. farmers [
27]. Many countries in Europe also recognized the need to increase agricultural production, especially after World War II [
28]. Justus von Liebig and John Lawes were early scientists in Europe who contributed to the initial development of organic chemistry for soils and mineral fertilizer production, which revolutionized agricultural production. A German chemist, Fritz Haber, later synthesized and industrialized nitrogen fertilizers, which coincided with trends to industrialize and corporatize agriculture and forest industries (e.g., machinery- and technology-derived agricultural revolutions). Land reform after World War II, enforced by U.S. occupation forces, also played an essential role in consolidating fragmented agricultural land in Japan [
29]. Other countries in South Asia have increased external inputs to enhance agricultural production by diversifying biophysical and chemical conditions. Soil fertility currently emphasizes the biological, chemical, and physical soil attributes important for provisioning crop nutrients and water [
30,
31]. The measurements and analysis of such soil properties have been explored as well in context of soil fertility studies, e.g., [
32,
33].
The concepts of soil conservation and soil productivity appeared in soil science journals at almost the same time in the late 1940s (
Table 4). The first author found in the search process for all journals in the Web of Science was Lipman (1926), who argued that soil conservation should deal with both plant-food ingredients and the ability of the soil to attain maximum crop production capability under all environmental conditions [
34]. The change point for the soil conservation concept came about 20 years later with Hopp and Slater’s (1948) article, published in SS [
35]. Hornbeck (2012) reported that many U.S. Plains areas had cumulatively lost more than 75% of their original topsoil due to deep plowing and drought, which was notably visible by the 1940s [
36]. Bennett (1974), argued that the origin of the U.S. national soil conservation program occurred much earlier than the U.S. Dust Bowl era of the 1930s [
37]. The author stated that an article he wrote, which was published by the Department of Agriculture in the 1920s, was the first comprehensive appraisal of the erosion issue in the U.S. Many regional erosion stations were built and thousands of soil and water measurements were performed to comply with the Buchanan Amendment to the Agricultural Appropriations Bill for 1930. Bennett argued that the commitment of scientists to prevent nutrient runoff and soil erosion was undertaken at the national level using a top-down approach. According to Ice [
38], the Soil Conservation Act of 1935, which sought to develop practical methods of managing lands, was the origin of the best management practices (BMPs) of today. Agricultural BMPs were designed to address and minimize agricultural non-point-source pollutions by the applications of excessive fertilizers and pesticides in the U.S. in the 1960s [
39]. This movement seems to correspond to the time when R. Carson published the famous book,
Silent Spring, in 1962. As public concerns for environmental degradations and pollutions had spread, soil conservation also experienced the change point in 1967 (
Table 6). From the mid-1960s onward, an increasing number of publications about soil conservation reflected the gradual accumulations of public understanding and awareness.
The enhancement of soil quality was regarded as a goal of improving soil fertility and agricultural productivity through soil conservation [
40]. The term “soil quality” appeared in a German soil science journal shortly after articles on soil conservation were published in a non-soil-science journal (
Table 4). Wolff (1939) used the term to explain the effect of land use changes on soil characteristics and, in particular, from soil profiling perspectives [
41]. The article was published in a German journal that focused on natural sciences [
42]. The journal was founded in 1913, and the article was published in Nazi Germany (1933–1941). The vision was to be self-sufficient in producing food for Germans toward World War II that demanded soil assessment (Reichs-Bodenschätzung). This approach to soil assessment could be considered a predecessor to more modern forms of digital soil mapping that emerged in the 1980s [
43]. Hans Jenny developed a conceptual model based on the soil-forming factors that were rooted in Vasily V. Dokuchaev’s work, and the model became a standard feature of U.S. survey reports in the 1940s and 1950s [
44].
The soil quality concept appeared in a soil science journal for the first time 32 years after the term appeared in a non-soil-science journal (
Table 7). The article was available as an English translation after being published in the SSS-USSR by Taychinov (1971) [
45]. The author used the term to describe the fundamental physicochemical, biological, and hydrological properties of soils as those attributes relate to productivity for agriculture, economic benefits, profitability, and production costs. The definitions/scopes/aims of soil quality were revisited by various authors [
2,
46,
47,
48,
49]. According to Karlen et al. (2001), the concept of soil quality was introduced in the North American literature after the mid-1980s, which was immediately after the concept’s change point in the number of publications over time (
Table 7) [
50]. This may mean that the definition was initially overlooked or not used in North America. A review of soil quality by Bünemann et al. (2018) shows that the broader definition considered soil productivity for agriculture as well as the quality of the environment and animal and human health [
31]. The authors argued that the term “soil quality” was introduced by Mausel (1971) [
51]; however, some authors pointed to others, such as Warkentin and Fletcher (1977) [
52], as being among the first to introduce the concept [
47]. In our opinion, the author initially found in the article search, W. Wolff (1939), introduced the term “soil quality.”
The similarity/difference between soil quality and soil health is arguable [
31]. In defining the concept of soil quality, Parr et al. (1992) stated that soil quality indices could be used to assess the impact of management practices on human and animal health [
53]. Though the appearance of soil health in all journals and soil science journals, as well as the change point, occurred many years later than soil quality, the terms have been used interchangeably. For example, Haberern (1992), whose article appeared in the search result for soil science journals, advocated for a soil health index as a report card to document gains and losses in soil quality [
54]. Moebius-Clune et al. (2016) posited that soil quality and soil health could be considered synonymous [
55]. Bünemann et al. (2018) suggested that the preferred term depends on the stakeholders (i.e., soil quality for researchers and soil health for farmers), although apparently there are no scientific surveys to validate this argument [
56]. Stevens (2018) defined soil health as “a holistic measure of a soil’s productivity, resilience, and sustainability [
6]”. The concept is straightforward in the abstract, yet challenging to define in practice from various viewpoints such as farmers, soil scientists, economists, and policymakers.
Some prominent definitions of soil health and soil quality proposed over the past 20 years were summarized and compared by Mizuta et al. (2018) [
2]. For example, Doran and Safley (1997) defined it as the “continued capacity of soil to function as a vital living system, within ecosystem and land-use boundaries, to sustain biological productivity; promote the quality of air and water environments; and maintain plant, animal, and human health [
57]”. The U.S. Department of Agriculture—Natural Resources Conservation Service (USDA-NRCS) simplified the definition of soil health in relation to soil quality as “the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals, and humans” [
58]. Stewart et al. (2018) proposed measuring the dynamic variables that mainly fell within biological, environmental, and agronomic groups that are responsive to soil management, such as cover crop, based on a meta-analysis of 192 unique peer-reviewed papers [
59]. These variables include soil respiration, soil aggregate stability, mineralizable nitrogen (N), soil erosion, infiltration, runoff, nutrient leaching, weed control, diseases, soil fauna, microbial indicators, soil N
2O emissions, microbial biomass N, and other soil health indicators. These variables were measured for traditional soil surveys as indicators of soil quality. Instead, new aggregation methods of existing soil information into a comprehensive, sensible, and scientific-sounding index are the focal point of current discussions in the soil science community [
5,
60]. Thus, soil health must be reconsidered similar to other soil concepts with the purpose of overcoming some limitations of past soil survey efforts, such as inconsistent soil measurement protocols. Under a large umbrella, the concepts of soil quality and soil health share the common goals of multiple stakeholders by targeting sustainable soil resource management under natural and anthropogenic pressures.
The earliest publication on soil sustainability was found in a soil science journal in 1992; one year later, a soil resilience paper appeared. These concepts were the only ones found first in soil science journals (
Table 4 and
Table 5). Considering that the two concepts appeared at almost the same time, they would likely share similar content, target, audiences, and semantic definitions, because they may be used interchangeably. However, A. J. Friend (1992), the author of the first soil sustainability publication available in the Web of Science, claimed differently [
61]. The author first defined soil sustainability as the “susceptibility of soil to change under natural or anthropogenic perturbations,” while soil resilience was defined as “soil’s ability to recover to the antecedent state following degradative perturbation or change in land use.” Soil degradation would be the manifestation of a loss of soil sustainability and resilience. The author also argued that soil sustainability was characterized by three aspects, soil stability, soil resilience, and soil quality, all of which can be influenced by soil surface management (e.g., tillage) to a large degree. This view of soil stability and resilience seems to be consistent with other publications as well. For example, Vogel et al. (2018) argued that the stability and resilience of soil are produced by the complex interactions of functional soil attributes. The important question of how to integrate fragmented knowledge on soil processes from various perspectives was addressed in the article [
62].
The roots of the resilience concept can be found in ecology [
63]. C. S. Holling, whose work was published in 1973, is considered to be the founder of modern ecological resilience by distinguishing ecological and engineering resilience [
64]. However, Olsson et al. (2015) argued that the prevalent theory was not integrated with sociology as socio-ecological resilience [
65]. This integral development has altered the earlier definition of the ecological resilience by a different view. Specifically, that resilience expresses the achievement of a new state or equilibrium after perturbations.
Ludwig (2018) considered sustainability from a biodiversity perspective and asserted that potential maximum ecological performance (MEP) is the measurable part of soil characteristics for sustainable management [
66]. Three ecological stages were delineated in the framework: resistance, resilience, and regime. The threshold between the first two responses to a disturbance of the ecosystem is expressed by effective MEP, while the threshold between the last two is characterized by potential MEP. However, the sustainability framework is often rather holistic. Wu and Wu (2012) organized various indicator frameworks based on social, environmental, economic, and institutional dimensions [
67]. The authors introduced hundreds of various indicators that would be aggregated into indices as measures of sustainable development. The measures of soil sustainability and resilience are still open for discussion. New techniques to quantify the functions or capabilities of soils through integration of existing information with communal consensus seem valuable in advancing the monitoring of soil resources for sustainable use.
The soil care concept does not seem to be used often in scientific journal publications. The concept itself has not been discussed deeply, in terms of definitions, conceptual framing, and practical applications. Review papers were not identified in the database. However, the soil care concept may play a role as a foundation of various soil management strategies based on top-down and bottom-up approaches. Yaalon (1996) defined the concept as “the activity of selecting and implementing, locally and regionally, a system of soil and land use management suitable for maintaining and improving soil usefulness and quality for any selected purpose [
8].” Yaalon also argued that knowledge on the topic also needs to be discussed deeply, quantified, and organized, similar to other soil concepts such as soil sustainability. However, Krzywoszynska (2019) addressed the act of care beyond ethical and practical commitments of securing matters by introducing attentiveness [
7]. Attentiveness was described as a focal point to relational ethics as “attending to the non-human other, of becoming response-able to them” (p. 4). According to the author, this practice of attentiveness fosters ethical expansions and transformations through encounters between humans and non-humans. Forming care networks of interconnected entities whose existence enables the well-being of the primary object of care, soil is necessary. Grunwald (2021) proposed a novel Pluralistic Integral Soil Ethics (PISE) framework of which one of the pillars is soil care [
68]. The ethics of soil care (relational ethics) is rooted in cognitive empathy, which is what a person thinks and understands about soils and the environment, and emotional empathy, which is what a person viscerally feels in relation to soils. Purely cognitive empathy provides factual understanding about soils, while emotional empathy is an embodied experience. They both rely on each other to support action, but empathic concern is a necessity to bring forth compassionate actions (e.g., conservation management). In essence, soil care arises from a compassionate lived emotive relationship between carer (person/community) and cared-for (soil/land/nature). It follows that if somebody (or a community) does not care for soil, and attributes less (or no) value to soil compared to other things, soil degradation and loss in soil quality are tolerated. This conception of soil care stands in contrast to earlier definitions by Yaloon and Wallace that are system-oriented and only involve cognitive empathy.
Soil security also experienced its change point almost immediately after soil science journals published articles. This indicates that publishing research on soil concepts in soil science journals may be a key step in enhancing awareness of newly proposed soil concepts, though the soil science community might not acknowledge the value of new ideas for many years. Interestingly, the definition of soil security found in the first article published in a non-soil-science journal differed from the one first published in a soil science journal. Tadanier and Ingles (1985) used the term to refer to a physical feature of soil (i.e., water retention ability) [
69], while Bouma and McBratney (2013) used the term to frame soils as a broader term to address environmental issues, defining soil security as the “maintenance or improvement of the world’s soil resource so it can provide sufficient food and fiber, fresh water, contribute to energy sustainability and climate stability, maintain biodiversity and overall environmental protection and ecosystem services” [
70]. Most of the results for the soil security concept used the holistic definition. The sources of publications for soil security can be found in
Global Soil Security [
71], though the Web of Science did not recognize the book in the database. The first book chapter conceptualized soil security similarly to food and water security, though soil security was not perceived as a global existential challenge by the public as much as the other security concepts were [
72]. Bouma and McBratney (2013) proposed the five C dimensions that define soil security: capability, condition, capita, connectivity, and codification [
70]. Grunwald et al. (2017) proposed another C, cognizance, as the fundamental factor that binds the other five dimensions [
73]. This feature was characterized as ecological awareness that motivates actions that value, care for, and secure limited natural resources. Although all aforementioned soil concepts aim to protect and preserve soils, their underlying motivations and justifications differ widely [
68]. Soil quality, soil health, and soil fertility (and possibly soil productivity as well) have a tight linkage to agricultural production systems, in which the values of the concepts are found in optimized management so that they meet the needs of people and, potentially, other organisms. An anthropocentric stance undergirds soil conservation, suggesting that humans control soil/land/nature to provide benefits for people and the environment. Soil sustainability is associated with “good” stewardship for future generations, while the security of soils refers to being free from the risk of losing functionality and goods and services of sustainable environment [
10].
4.2. Factors for Propagating New Ideas in Soil Science
Overall, many soil concepts appeared in soil science journals 20 years or more after they appeared in non-soil-science journals for the first time. This reflects the soil science community’s slow adaptation to new concepts. However, the earlier a soil concept appeared in the first article in the category ‘all journal’, the earlier the change points occurred in general, except for soil quality and soil health (A and C-A in
Table 7). This phenomenon is possibly due to the more recent rapid increase in the number of articles on newer soil concepts (
Figure 1). Publishing new soil concepts in soil science journals is essential for the soil science community to recognize and build communal understanding and values though that would not be a sufficient factor. Sharing a new concept with a large general readership would also help the propagation of soil concepts.
Older concepts were generally cited more over time (
Table 3,
Figure 1). The minimum number of citations necessary to experience a statistical change point of the publications or a citation inflation in soil science journals was 57 (
Table 3), while the number for all journals was 119 (
Table 3). The readership of journal subscribers/attention/citations has varied by journal over time, though each journal has fixed scopes/aims/definitions and specific readers. Publishing soil concept articles in a journal with a large readership would be the best strategy, or creating a journal based on a given soil concept is another strategy. For instance, the change point for a number of publications on soil conservation occurred the same year that the JSWC published the first articles (
Table 7). Out of 798 and 49 journals in all journals and soil science journals, the journal published the most articles on soil conservation.
To enhance attention from soil science communities and beyond, other important factors must be considered. Rogers (2010) proposed the diffusion of innovation theory to explain how and at what rate a new idea or technology spreads in an organization or community [
74]. The diffusion approach has been used to evaluate the impact of development programs in agriculture, family planning, public health, and other fields. According to Rogers, there are five elements of a new concept/idea/innovation that will each partly determine whether the adoption or diffusion of a new one will occur: relative advantage, compatibility, complexity, trialability, and observability. These elements are designed to answer some of the same questions raised in this study (e.g., Why do certain innovative ideas spread more quickly than others, and why do others fail?). Relative advantage is the degree to which a new concept is perceived as better or more useful for particular stakeholders. Compatibility is the degree to which a new concept is consistent with or relevant to existing experiences, values, and the needs of stakeholders. Complexity evaluates how easily a new concept is comprehended—that is, the easier the concept is to understand, the more rapidly it can spread. Trialability indicates whether a new idea can be tested repeatedly. The last criterion, observability, ensures that a new concept will produce visible results.
The first three elements of the diffusion theory are essential to improve the adaptability of new ideas for various stakeholders. For example, the choice of wording may draw different associations and intuitions that could track the attention of stakeholders. Puig de la Bellacasa (2015) stated that soil care is a widely used notion, though the publication result for this concept was relatively low [
75]. The term soil care has been associated with intimate relationships, nurturing motherly care (for something or somebody), qualitative values (e.g., long-term sustainability to secure our children’s future), and the feminine, which have been devalued in the sciences and overpowered in societies attuned to profitability (e.g., maximize crop production from soil), achievement (e.g., maximize soil carbon sequestration), power, and doing-orientation (e.g., manage and control soils, production agriculture, or “fix the soil degradation crisis”). More discussions on the soil care concept can be found in Grunwald (2021) [
68].
Earlier concepts of soil, on the other hand, seem to be limited to agricultural perspectives but were cited in many publications. Multiple factors explain the propagation of new ideas in a community, including needs (e.g., soil degradation); crises/problems (e.g., the Dust Bowl, global climate change); curiosity; psychological (e.g., spiritual or inner motivation to use specific soil concepts); and social (tribal patterns, e.g., scientists may feel inclined to study soil health because their colleagues study soil health).
Social and environmental changes, along with technological advancements and public awareness regarding the need for poverty reduction and sustainable management of natural resources, have impacted public or professional organizations and soil science. Trends in science can shift over time based on the interests of scientists and funding agencies [
76]. The prominence of conceptual studies in the literature reflects a given research emphasis and how it has sustained momentum over time.
Soil quality is a good example: it has a clear history of broadening its definition to address complex soil/environmental challenges [
31,
49]. These conceptual criteria can also be found in the assessments of various soil concept indices. For example, Karlen et al. (1997) asserted that the critical characteristics of a soil quality framework should be that it is (1) influential for the purpose of the assessment (i.e., relative advantage); (2) measurable (i.e., trialability/observability); and (3) sensitive to detect differences at the point scale in time and space (i.e., compatibility) [
46]. Doran (2002) proposed that the important criteria for soil quality/health indices are (1) utility and accessibility for agricultural specialists, producers, conservationists, and policymakers (relative advantage/complexity, trialability, and observability) and (2) sensitivity to management and climatic variations (compatibility) [
77].
Despite the conceptual criteria for the adoption or diffusion of a new concept, this study offers practical viewpoints for propagating awareness of soil concepts. The choice of journals in which to publish articles on a soil concept influences the citation trend of soil concepts. The large audience/readership outside of the soil science communities needs to be considered because 63% of the citations for the soil concepts selected for this study were from non-soil-science journals. The united efforts of professional organizations/institutes within a country are also valued. It is notable that publication sizes for authors in the Chinese Academy of Science (CAS) for many soil concepts were the largest, including soil conservation, fertility, productivity, quality, and sustainability. This observation may be linked to a large number of scientists from 114 institutions under the CAS, which is the world’s largest research organization recognized by Nature Index [
78]. However, one might claim that this is not a fair comparison because many countries, including the U.S., have not adopted the scheme that the Chinese have. Collaborations across nations or people who speak different native languages is another factor in determining scientific awareness as a part of cultural adaptability. The most prominent languages varied depending on the soil concept, but the least cited concepts—soil care and soil security—were only published in English. Efforts by a single organization (i.e., the University of Sydney) contributed the majority of publications on soil security in all journals (39.4%) and soil science journals (46.7%), which indicates the monopolization. However, opposite trends were found for other soil concepts that showed pronounced diversification in the form of English/non-English publications indicating cultural and social adaptability.
A cultural or typological aspect may play an important role in restricting citations. Lal (1993) referred to soil resilience as “soil’s ability to recover to the antecedent state following degradative perturbation or change in land use” [
20]. However, Olsson et al. (2015) argued that the use of the term “resilience” in the natural sciences may cause disciplinary tensions with the social sciences [
65]. The application of resilience theory may change the definition from coherent to internally contradictory, from precise to vague, from descriptive to normative to predictive, and from concise to comprehensive. Sojka et al. (2003) also warned that the vague quality of assessments requires deconstruction for interpretation [
9]. Expanding stakeholders by broadening soil concepts may succeed in considering diverse stakeholders and functions of soils, but it also seems to be a tradeoff with the possibility of losing the capability for scientific advancement. Furthermore, vagueness can confuse readers/users, and, as a result, divisions within soil science might be created. Soil quality and soil health are good examples because these are interchangeably used depending on the author.