Third, my co‐authors and I recognize and acknowledge soil health assessment is not an exact science, but there are a few principles that are non‐negotiable. First, to qualify as a meaningful, comprehensive assessment, soil biological, chemical, and physical properties and processes must all be included. Failure to do so, does not invalidate the assessment, but rather limits it to an assessment of “soil biological health”, “soil physical health”, “soil chemical health”, or some combination thereof. Furthermore, although some redundancy may occur, at least two different indicator measurements should be used for each indicator group (i.e., biological, chemical, or physical). To aid indicator selection, many statistical tools are being developed and evaluated to help identify the best combination of potential measurements for assessing each critical soil function associated with the land use for which an evaluation is being made.
There is also no question that any soil health indicator must be fundamentally sound from all biological, chemical, physical and/or biochemical analytical perspectives. Indicators must have the potential to be calibrated and provide meaningful information across many different types of soil. This requires sensitivity to not only dynamic, management‐induced forces, but also inherent soil properties and processes reflecting subtle differences in sand, silt, and clay size particles derived from rocks, sediments, volcanic ash, or any other source of parent material. Soil health assessments must accurately reflect interactions among the solid mineral particles, water, air, and organic matter contained within every soil. This includes detecting subtle changes affecting runoff, infiltration, and the soil’s ability to hold water through capillarity– to act like a sponge; to facilitate gas exchange so that with the help of CO2, soil water can slowly dissolve mineral particles and release essential plant nutrients– through chemical weathering; to provide water and dissolved nutrients through the soil solution to plants, and to support exchange between oxygen from air above the surface and excess CO2 from respiring roots.
Some, perhaps many, will disagree with the choice of indicators that are included in these books. Right or wrong, our collective passion is to start somewhere and strive for improvement, readily accepting and admitting our errors, and always being willing to update and change. We firmly believe that starting with something good is much better than getting bogged down seeking the prefect. This does not mean we are discounting any fundamental chemical, physical, thermodynamic, or biological property or process that may be a critical driver influencing soil health. Rather through iterative and ongoing efforts, our sole desire is to keep learning until soil health and its implications are fully understood and our assessment methods are correct. Meanwhile, never hesitate to hold our feet to the refining fire, as long as collectively we are striving to protect and enhance the unique material we call soil that truly protects humanity from starvation and other, perhaps unknown calamities, sometimes self‐induced through ignorance or failing to listen to what our predecessors have told us.
Douglas L. Karlen (Co‐Editor)
References
1 Alexander, M. (1971). Agriculture’s responsibility in establishing soil quality criteria In: Environmental improvement– Agriculture’s challenge in the Seventies. Washington, DC: National Academy of Sciences. p. 66–71.
2 Bouma, J. (2019). Soil security in sustainable development. Soil Systems. 3:5. doi:10.3390/soilsystems3010005
3 Donahue, R. L., J. C. Shickluna, and L. S. Robertson. 1971). Soils: An introduction to soils and plant growth. Englewood Cliffs, N.J.: Prentice Hall, Inc.
4 Doran, J.W., Coleman, D.C., Bezdicek, D.F., and Stewart, B.A., editors. (1994). Defining soil quality for a sustainable environment. Soil Science Society of America (SSSA) Special Publication No. 35. Madison, WI: SSSA Inc.
5 Doran, J.W., and Parkin, T.B. (1994). Defining and assessing soil quality. In: J.W. Doran, D.C. Coleman, D.F. Bezdicek, and B.A. Stewart, editors, Defining soil quality for a sustainable environment. SSSA Special Publication No. 35. Madison, WI: SSSA. p. 3–21. doi:10.2136/sssaspecpub35
6 Doran, J.W., and Jones, A.J. (eds.). (1996). Methods for assessing soil quality. Soil Science Society of America (SSSA) Special Publication No. 49. Madison, WI: SSSA Inc.
7 Hartemink, A. E. and Anderson, S.H. (2020). 100 years of soil science society in the U.S. CSA News 65(6), 26–27. doi:10.1002/csann.20144
8 Hillel, D. (1991). Out of the earth: Civilization and the life of the soil. Oakland, CA: University of California Press.
1 Soil Health: An Overview and Goals for These Volumes
Douglas L. Karlen*, Diane E. Stott, Maysoon M. Mikha, and Bianca N. Moebius‐Clune
Synopsis of Two‐Volume Book
Farmers and ranchers, private sector businesses, non‐governmental organizations (NGOs), academic‐, state‐, and federal‐research projects, as well as state and federal soil conservation, water quality and other environmental programs have begun to adopt soil health as a unifying goal and promote it through workshops, books, and public awareness meetings and campaigns. The driver is an increased awareness that soil resources are crucial for not only meeting global demand for high‐quality food, feed, and fiber but also to help mitigate more extreme weather events and to protect water and air quality, wildlife habitat, and biodiversity.
Volume 1 briefly reviews selected “Approaches to Soil Health Analysis” including a brief history of the concept, challenges and opportunities, meta‐data and assessment, applications to forestry and urban land reclamation, and future soil health monitoring and evaluation approaches.
Volume 2 focuses on “Laboratory Methods for Soil Health Analysis” including an overview and suggested analytical approaches intended to provide meaningful, comparable data so that soil health can be used to guide restoration and protection of our global soil resources.
Introduction
Soil health research, books, workshops, websites, press releases, and other forms of technology transfer materials have made rural and urban producers and consumers of all ages more aware of soil resources and the services they provide. Innovative farmers and ranchers, the private sector, non‐governmental organizations (NGOs), academic, state, and federal researchers, and policymakers around the world are becoming more aware of how properly functioning soils more effectively respond to: (1) changing climate patterns and more extreme weather events (Paustian et al., 2016); (2) increasing demands for abundant, high‐quality food, feed, and fiber to meet needs of an increasing global population (Doran, 2002), and (3) the need to protect water, air, wildlife, plant, and microbial biodiversity (Andrén & Balandreau, 1999; Havlicek & Mitchell, 2014).
Enhancing global soil health will improve humankind’s capacity to maintain or increase crop yield, achieve better yield stability, reduce purchased input costs, and enhance critical ecosystem services (Boehm & Burton, 1997). Striving for improved soil health is not only important for croplands, but also for pastures, native rangelands, orchards, and forests (Herrick et al., 2012; Chendev et al., 2015; Gelaw et al., 2015; Vitro et al., 2015). Yet, there is still a lot of confusion and uncertainty regarding soil health in the U.S. and around the world. One reason is that soils are complex and perform many different functions that respond to changes in the same properties and processes in different and sometimes conflicting ways. For example, what may be considered good soil health characteristics for crop productivity (e.g., well aggregated, porous with good water infiltration, efficient nutrient cycling) may not be optimum for water quality if high infiltration rates and/or macropores result in rapid transport of contaminants to surface or subsurface water resources. Similarly, no‐tillage as a single practice may improve soil health by increasing soil organic carbon (SOC), but improper management decisions